OBSTETRIC ANAESTHESIA
Final Objective:
On completion of this module you will be able to provide safe analgesia and anaesthesia for the obstetric patient.
Enabling Objective: To achieve this goal, you should know how to:
MATERNAL PHYSIOLOGY
Pregnancy results in physiologic changes in many organ systems. These changes begin in the first trimester and continue until after delivery. Labour presents its own unique physiologic fluctuations due to painful uterine contractions and the autotransfusion of blood following delivery. Many physiologic changes persist for days and some persist for a few weeks after delivery. These physiologic changes will have an impact on the provision of safe anaesthesia care of the mother.
Cardiovascular changes
Intravascular blood volume increases by 35%. The plasma volume increases relative to red cell volume so there is a relative anaemia. Normal vaginal delivery results in a blood loss of up to 500 ml. The pre-pregnancy intravascular volume is reached by 7-14 days post partum.
Cardiac output is increased by 40% at term due to systemic vasodilatation, increased contractility, myocardial hypertrophy and an increased stroke volume and heart rate. The systolic blood pressure is decreased due to a fall in systemic vascular resistance. It returns to normal towards the end of the second trimester. The uterus at term receives up to 20% of the maternal cardiac output. This has implications for rapid blood loss in an atonic uterus after delivery. Haemorrhage may be severe and rapid.
There are marked fluctuations in the cardiac output during labour. There is a 100% increase in cardiac output in labour. This can put significant stress on the heart if there is cardiac disease.
The supine hypotensive syndrome is a decrease in maternal blood pressure that occurs in about 10-15% of pregnant women near term when they lie supine. The gravid uterus obstructs the inferior vena cava and thereby reducing venous return to the heart. Supine hypotension can be avoided by maintaining the pregnant woman in the left lateral position or by using left uterine displacement. Because the aorta may also be compressed in the supine position, uterine blood flow may be compromised.
Respiratory changes
The upper airway of the pregnant woman becomes oedematous due to capillary engorgement and requires the placement of a smaller endotracheal tube if general anaesthesia is required. Due to nasal obstruction and oedema, the placement of a nasal tube is not recommended as this may lead to epistaxis.
The incidence of difficult intubation is increased in the pregnant woman due to airway oedema, weight gain and breast enlargement. Conditions that increase airway oedema such as pre-eclampsia will increase the difficulty with intubation.
Minute ventilation increases early in pregnancy and, by the end of the first trimester, minute ventilation is increased by about 50%. The resting arterial partial pressure of carbon dioxide (PaCO2) decreases to near 30mmHg.
Lung volumes change after the fifth month of gestation, probably due to the cephalad displacement of the diaphragm by the gravid uterus. Functional residual capacity decreases by 20%. This has implications for anaesthesia, as it reduces the potential oxygen stores. Because of the 20-40% increase in oxygen consumption and the reduction in FRC, there is a tendency to hypoxia during periods of apnoea.
Neuronal changes
Pregnancy decreases anaesthetic requirements. During pregnancy, the minimal alveolar concentration for volatile anaesthetics is reduced by 40% and the sensitivity to local anaesthetics increases. The doses administered for an epidural or spinal anaesthetic may be reduced by 30-50%.
Gastro-intestinal changes
The parturient is at increased risk of regurgitation of acidic gastric contents and therefore the development of acid aspiration syndrome. The enlarged uterus displaces the pylorus and symptomatic reflux in pregnancy is common. Regional anaesthesia is recommended to reduce the risk of aspiration.
The airway needs to be protected with a cuffed endotracheal tube during general anaesthesia in pregnancy after 18 – 20 weeks gestation and up to 18 hours after delivery. It is recommended that a histamine receptor antagonist (such as ranitidine 150 mg orally one hour before anaesthesia) and a non-particulate antacid (such as sodium citrate 0.3 M, 30 ml 15 minutes before anaesthesia) be given before general anaesthesia. Particulate antacids are associated with more severe pneumonitis should aspiration occur. Rapid sequence induction is recommended.
During labour, gastric emptying is delayed, especially if opioids have been given and the patient is obese. It is recommended that oral intake in active labour be limited to clear fluids. Routine prophylaxis with ranitidine every 6 hours should be considered in women with a risk of requiring general anaesthesia or surgery.
Renal changes
There is increased renal blood flow during pregnancy and an increase in glomerular filtration rate and creatinine clearance. The normal upper limits of the serum urea and creatinine levels are reduced by 50%. The renal calyces are dilated from the second trimester, which tends to lead to urinary stasis, putting the pregnant patient at risk for urinary tract infection.
Haematologic changes
There is an increase in red cell volume that does not match the increase in plasma volume resulting in a physiologic anaemia.
There is a tendency towards a hypercoagulable state as a result of increased fibrinogen, coagulation factors II, VII, VIII, IX, X, XII, reduction in plasminogen activator and increased number of platelets. The prothrombin time and activated partial thromboplastin time is decreased by 20%. The pregnant patient is at risk for deep venous thrombosis.
PLACENTAL PHYSIOLOGY
Maternal (basal plate) and foetal (chorionic) tissues form the placenta and they are separated by the intervillous space. Maternal blood enters the intervillous space and spreads over the foetal chorionic villi. Foetal blood leaves the foetus via the internal iliac arteries, which give rise to the umbilical arteries. Blood moves across the umbilical capillaries in the chorionic villi and maternal to foetal placental transfer occurs across the chorionic membrane. Oxygenated blood returns to the foetus via a single umbilical vein.
On the maternal side, uterine blood flow makes up 20% of the cardiac output at term. The blood is supplied via the uterine arteries that branch out to form the arcuate, radial and spiral arteries that extend into the placental tissue ending in the intervillous space. Uterine blood vessels are maximally dilated. Uterine blood flow is directly related to the mean maternal arterial blood pressure (average 80 mmHg) minus the uterine venous pressure (10 mmHg at rest) and inversely related to uterine vascular resistance. Uterine vascular resistance is low at rest but is affected by the tension in the myometrium and by vasoconstriction of the uterine, arcuate and radial arteries. The arteries respond to alpha-adrenergic stimulation.
The factors that influence uteroplacental perfusion are:
1. Aorto-caval compression
2. Hypotension (less than 100 mmHg systolic)
3. Increases in uterine vascular resistance (contractions, delivery, ketamine, oxytocin and placental abruption)
4. Maternal hypoxia, hypo and hypercarbia
5. Catecholamines (increase vascular resistance)
Placental transfer of substances occurs via simple diffusion, active transport, bulk flow, facilitated diffusion and breaks in the chorionic membrane.
Anaesthetic compounds cross the placenta by diffusion. The quantity of drug that is transferred is determined by molecular weight (small drugs cross easily), degree of ionisation (less ionised cross easily), lipid solubility (more lipid soluble cross easily), protein binding (less protein bound cross easily) and concentration gradient from maternal to foetal circulation. Most anaesthetic agents cross easily. Neuromuscular blockers are water soluble, ionised and have higher molecular weights, so do not cross the placenta readily.
FOETAL AND NEONATAL PHYSIOLOGY
Foetal blood returns from the placenta via the umbilical vein. 50% will enter the foetal portal circulation and the rest will enter the inferior vena cava. At the right atrium, the oxygenated blood from the inferior vena cava mixes with the poorly oxygenated blood from the superior vena cava (head and arms) and is shunted to the left atrium via the open foramen ovale. Blood then enters the left ventricle and out through the aorta. The most oxygenated blood is distributed to the head. The foetal lungs only receive a small amount of perfusion via the right ventricle and pulmonary outflow tract. The ductus arteriosus allows right ventricular blood flow to enter the aorta.
At birth, there is a removal of the placenta and the lungs expand (allowing pulmonary blood flow). The foramen ovale closes due to increased left atrial pressure and there is a functional closure of the ductus arteriosus with the decrease in prostaglandins and increasing oxygen tension. The shunts are not anatomically closed immediately after birth and a return to a foetal circulation can occur with resultant severe hypoxemia and circulatory collapse in response to major stresses such as hypoxia and acidosis, which increase pulmonary vascular resistance.
The normal foetal capillary pH is greater than or equal to 7.25. Foetal acidosis is defined as a pH less than 7.2. The normal values for blood gases at birth are pH 7.25, pCO2 40 mmHg, pO2 60 mmHg and by 30 minutes of life, the normal values are 7.33, 35 and 68 respectively.
PHYSIOLOGY OF LABOUR AND DELIVERY
Labour
During labour, painful contractions increase minute ventilation by up to 300%, which leads to hypocarbia and alkalemia. Hypocarbia may lead to uterine vasoconstriction and reduced placental perfusion. Between contractions, the patient may hypoventilate, which can lead to foetal and maternal hypoxemia.
Oxygen consumption tends to rise during labour, and it may increase by 100% during second stage.
During uterine contractions, there is an autotransfusion of blood from the uterus to the maternal circulation. This can increase central blood volume by 25%. The blood pressure tends to rise during contractions. The cardiac output increases by 60% after delivery due to the closure of virtual arterio-venous fistula that is the placental circulation and relief of aorto-caval compression.
Painful contractions will increase catecholamine levels and contribute to the rise in cardiac output as well as to vasoconstriction of the uterine circulation.
Delivery
Cardiac output rises immediately after birth due to an autotransfusion of 500-750 ml of blood from the sustained contraction on an empty uterus. The cardiac output returns to normal about four weeks post partum.
The functional residual capacity and residual volume return to normal rapidly. Alveolar ventilation returns to normal by 4 weeks post partum.
There is a post partum diuresis and the blood volume and hematocrit return to normal within 4 weeks.
ANALGESIA FOR LABOUR
Labour pain
Labour pain is mediated by the autonomic system and somatic system. The first stage of labour involves uterine contraction and cervical dilatation and effacement. This pain is transmitted to the spinal cord via the visceral afferents to the tenth thoracic to first lumbar spinal segments. It is autonomically mediated and poorly localized. It may be referred to the lower back and upper thighs, but is usually felt in the lower abdomen. Second stage of labour is the delivery of the foetus and involves stretching of the perineum. Pain is somatic and well localized to the perineum. The pudendal nerves transmit the pain to the second to fourth sacral spinal cord segments.
The options for labour analgesia include pharmacologic and non-pharmacologic methods.
Systemic analgesia
Systemic analgesia is used for labour when there is no epidural service or when there is a maternal contraindication to epidural analgesia. Opioids are used frequently in this situation and can be delivered by intermittent intramuscular or intravenous injection or via a patient controlled intravenous analgesia system. Unfortunately, opioid related maternal side effects such as sedation, nausea, itch and respiratory depression as well as incomplete analgesia, make systemic opioid administration troublesome.
Fentanyl is very lipid soluble and highly protein bound. It is 800 times as potent as pethidine and its time to peak effect is 3-4 minutes. Repeated dosing can cause an increase in its context sensitive half time, increasing its duration of action. It can be used in a patient controlled intravenous analgesia system in doses of 10 micrograms with a lockout of 12 minutes combined with a background infusion of 10 mcg per hour or it can be administered by the nurse with a loading dose of 50 mcg followed by 50-100 mcg every hour as required.
Epidural analgesia
Regional analgesia is the most effective and reliable way of relieving childbirth pain. Epidural analgesia involves the introduction of local anaesthetic and opioid agents into the epidural space. An epidural catheter is inserted using a sterile technique via a lumbar spinal interspace.
The local anaesthetic acts on spinal nerves and on the spinal cord to achieve a blockade of neural transmission. The aim is to provide analgesia by blocking the A delta and C fibres that transmit pain. With increasing doses of local anaesthetic it is inevitable that the larger sensory and motor fibres will also be blocked. Autonomic blockade is expected due to the small size of autonomic fibres.
Lipid-soluble opioids are used in conjunction with the local anaesthetic agents to allow a reduction in local anaesthetic doses. The opioids actwork on opioid receptors in the dorsal horn of the spinal cord.
Advantages of epidurals · Excellent analgesia
· Reduction of maternal catecholamine levels
· Reduction of maternal alkalosis from hyperventilation
· The ability to extend the epidural for operative and assisted delivery
Disadvantages of epidurals
· Hypotension occurs due to vasodilatation secondary to sympathetic blockade.
· Slowing of the progress of labour and need for assisted delivery. Regional analgesia is associated with increased duration of the second stage of labour and instrumental vaginal birth, but has no effect on the risk of a caesarean or immediate status of the neonate.
· Motor blockade is more frequent with higher concentrations of local anaesthetic. It means that the woman is not able to walk and dense motor block increases the need for instrumental (assisted) delivery.
· Impaired bladder function may require an indwelling urinary catheter.
Complications of epidurals
Intravenous access is secured and intravenous fluids are administered to reduce the incidence of hypotension (important for doses of greater than 25 mg of bupivacaine). Routine fluid loading is not required for low dose techniques.
Monitoring of the mother and foetus should be established prior to and during the performance of the block. Blood pressure, maternal and foetal heart rate, motor function and sensory level are monitored.
The patient is positioned in the flexed, sitting posture and the lower lumbar spaces are identified by palpation. The fifth, fourth or third lumbar spaces are commonly used for insertion. (The spinal cord terminates at the level of the second lumbar vertebra in most people, but can extend to the third vertebral level. Inadvertent intrathecal insertion of the needle may therefore injure the conus of the spinal cord if a higher lumbar level is used.) A loss of resistance to fluid technique is used to identify the epidural space using a sterile technique and a catheter is threaded into the space and secured with a sterile dressing.
A test dose is given via the epidural catheter once it is inserted to test for intrathecal (spinal) or intravenous placement.
A dose of dilute local anaesthetic (0.125% Bupivacaine) with or without fentanyl is administered incrementally until a sensory block to the tenth thoracic dermatome is achieved. The choice of local anaesthetic is usually based on the need for prolonged duration of action. The use of lignocaine is reserved for the need for rapid onset analgesia. Its duration of action is short and repeated doses may cause tachyphylaxis. There is no difference in analgesic effectiveness or adverse effects between ropivacaine and bupivacaine for labour epidural analgesia.
Ongoing analgesia can be achieved with intermittent top ups of local anaesthetic or with the use of an infusion of local anaesthetic with or without fentanyl.
Contraindications to epidural analgesia include coagulation disorders, sepsis at the intended insertion site, raised intracranial pressure, uncorrected hypovolemia and patient refusal.
Spinal analgesia for labour A single injection of intrathecal opioids provides comparable early analgesia to epidural local anaesthetics with less motor block. The combination of spinal opioids with local anaesthetics reduces dose requirements for either drug alone and may help to minimize motor block.
When resources are limited, it is possible to use single shot spinal injections of low doses of bupivacaine (2.5 mg) with fentanyl (15-25 mcg) to provide about 90-120 minutes of analgesia for labour. The time to onset of analgesia is five minutes with intrathecal fentanyl because it is very lipid soluble.
Multiple punctures are not recommended, as there is tachyphylaxis to opioid analgesia when used intrathecally.
Disadvantages of intrathecal injection for labour analgesia Unfortunately, it is not possible to extend the duration of action if delivery has not occurred within the duration of action of the fentanyl and bupivacaine.
Perineal pain may still occur if an episiotomy or forceps delivery is required because this technique does not produce a dense block.
Maternal hypotension is still possible, but less frequent than with larger doses of local anaesthetic (such as those used for caesarean section).
There is a risk of post dural puncture headache with the use of larger cutting needles, so a small pencil point needle should be used.
There is risk of meningitis, so a sterile technique is required.
Nausea and itch may be troublesome side effects. Respiratory depression is possible. Respiratory depression is more common with morphine (which is water soluble) and with the administration of systemic opioids along with the spinal opioids.
CAESAREAN SECTION
The World Health Organization (WHO) recommends an optimum caesarean section rate of 5-15% to ensure best outcome for the mother and neonate. The main maternal indications for caesarean section are obstructed labour, placental abruption, previous caesarean section, eclampsia, placenta praevia and malpresentation.
A four-tier classification of urgency of caesarean section has been broadly accepted.
1. Category one – Immediate threat to life of woman or foetus (recommended decision to delivery interval less than 30 minutes)
2. Category two – Maternal or foetal compromise, not immediately life threatening
3. Category three – Needing early delivery with no maternal or foetal compromise
4. Category four – At a time to suit the woman and staff
The choice of anaesthesia for caesarean section will depend on the urgency of the procedure, medical condition of the mother and on the experience of the anaesthetist.
Spinal analgesia
A regional technique is preferred for caesarean section in order to reduce the risk of airway complications associated with general anaesthesia in the pregnant patient. The most frequent technique for caesarean section is spinal anaesthesia, but epidural anaesthesia is used when there is an epidural catheter in situ from labour. Epidural anaesthesia is also used in the patient who needs to have a slow onset of anaesthesia to avoid hypotension.
The advantages of regional anaesthesia for caesarean section include, excellent operating conditions with a mother who is then awake to see the birth of her child, the avoidance of airway and pulmonary complications, good postoperative analgesia, avoidance of awareness under general anaesthesia, a reduction in the incidence of deep venous thrombosis, less neonatal depression, a reduction in blood loss and a quicker return of gastro-intestinal function.
The contraindications to regional anaesthesia are coagulation disorders, maternal refusal of the technique, infection at the site or systemic sepsis, uncorrected hypovolemia and raised intracranial pressure. Pre-existing neurologic conditions and stenotic cardiac valvular disease are relative contraindications and the benefits of regional anaesthesia must be weighed against the risks.
Hypotension is a frequent complication of neuraxial anaesthesia in obstetrics and may have detrimental effects such as a reduction in placental blood flow and reduced maternal cerebral flow. It is especially common during spinal anaesthesia and in non-labouring patients. Aorto-caval compression will occur when the patient is supine. Spinal or epidural anaesthesia will blunt compensatory reflexes, so hypotension becomes more likely in the supine position.
The definition of hypotension is a decrease in systolic BP to less than 80-100 mmHg or by 10-30% of baseline. In order to minimize the reduction in blood pressure, left uterine displacement is recommended after neuraxial block. Wrapping of the legs reduces the incidence of hypotension. Pre-hydration with crystalloids is not very efficacious for preventing hypotension, but normovolemia should be achieved in the dehydrated patient. Colloids are more efficacious but expensive and may produce adverse reactions. Vasopressors are useful but the choice of ephedrine over phenylephrine (or other alpha agonists) is controversial. A combination of intravenous co hydration and vasopressor infusion may be more effective than single therapies for preventing hypotension. All patients must be frequently monitored for hypotension and aggressively treated.
General anaesthesia for caesarean section
There is increased mortality and morbidity associated with general anaesthesia compared with regional anaesthesia. It is now only indicated if there is a contraindication to regional anaesthesia or when it is felt that there is not enough time to establish regional anaesthesiaa block.
Preparation for anaesthesia should include antacid prophylaxis, which includes ranitidine (50 mg intravenously or 150 mg oral 60 minutes before the procedure) and a non-particulate antacid such as sodium citrate 15 minutes before anaesthesia.
Pre oxygenation and a rapid sequence induction are recommended to protect the woman from aspiration of gastric contents. The induction agent of choice is thiopentone, in a dose of 4 mg/kg to prevent awareness, but still allow wakening if there is a failed intubation. Propofol is the alternative agent but may induce more hypotension. Ketamine can be used in the management of hypovolemic women requiring caesarean section. Suxamethonium is the relaxant of choice as it can rapidly produce good intubating conditions and will have a rapid offset if there is a failed intubation.
The main disadvantages of general anaesthesia are failed intubation, pulmonary aspiration and maternal awareness. Volatile anaesthetic agents are capable of uterine relaxation and can predispose to uterine atony and haemorrhage.
The typical blood loss for a caesarean section is 500 to 1000 ml, which does not require transfusion unless the haemoglobin drops below 7 g/dL. A blood group and screen should be performed before caesarean section.
Monitoring during caesarean section should include blood pressure, heart rate (ECG) and pulse oximetry with foetal heart rate monitoring before anaesthesia induction. End tidal capnographycraniography should be employed for general anaesthesia when it is available given that the most common causes of maternal complications arise from failure to intubate, ventilate and oxygenate. One The anaesthetist mustshould be prepared for a difficult airway and have a range of equipment available to manage a difficult airway and a plan for management of the failed intubation.
Before delivery of the foetus, a minimum inspired oxygen concentration of 50 % is used. A volatile agent is used throughout the procedure to minimize the risk of maternal awareness. Oxytocics and an opioid are given immediately after delivery. The induction to delivery interval should be kept to a minimum to avoid neonatal depression. Therefore anaesthesia is induced only once the patient and surgeon are ready for delivery (the skin is prepared and draped, urinary catheter is inserted). At the end of the procedure, the muscle relaxant is reversed with neostigmine and atropine and the mother is extubated when she is awake and able to maintain her own airway.
ANAESTHESIA FOR SURGERY DURING PREGNANCY
2% of pregnant patients will require surgery during their pregnancy. The procedures include surgery for trauma, ovarian cysts, appendicitis, cholecystectomy, breast biopsy and cervical cerclage.
Maternal physiology differs significantly from the pre-pregnant state. The important respiratory changes to consider for incidental surgery during pregnancy include increased oxygen consumption, reduced lung volumes, hypocapnia, increased mucosal vascularity, (so there is a propensity to epistaxis) and difficult intubation. The relevant cardiac changes include an increase in blood volume and cardiac output, dilutional anaemia and aorto-caval compression after 20 weeks gestation. The pregnant patient is at risk for pulmonary aspiration due to lower gastro-oesophageal sphincter tone and reflux and there is a reduction in anaesthetic dose requirements.
The main anaesthetic considerations are the maintenance of uterine perfusion, prevention of preterm labour and the potential for teratogenic and adverse effects of anaesthetic agents.
In general terms, there are minimal teratogenic effects of anaesthetic agents, but it is wise to delay surgery until after the first trimester (whenan organogenesis is complete). Elective operations should occur after the pregnancy, or if there is some urgency, surgery during the second trimester is the ideal time to avoid teratogenicity and preterm labour.
Aspiration prophylaxis should be considered, and premedication will alleviate anxiety and pain, both of which increase catecholamine levels and reduce uterine blood flow. Intraoperative positioning should minimize aorto-caval compression. There is no evidence that any technique is more superior provided that maternal oxygenation and perfusion are maintained. Continuous foetal monitoring is used once foetal viability is reached. Postoperative management includes the monitoring of foetal vital signs, uterine activity, and the treatment of preterm labour and thromboembolism prophylaxis.
In the case of trauma, foetal death occurs due to maternal death or placental abruption. Ultrasound is used to determine foetal viability and to diagnose abruption. Continuous foetal monitoring is recommended during trauma surgery. There are few indications for emergency caesarean section in this situation but they include: a stable mother with foetal distress on the cardio-tocograph, uterine rupture, a gravid uterus interfering with maternal abdominal surgery and a mother who cannot be saved with a viable foetus.
PRE-ECLAMPSIA
Pre-eclampsia is defined as the development of hypertension and proteinuria after 20 weeks gestation. The incidence is approximately 7% of all pregnancies. If seizures occur, the condition is known as eclampsia. Pre-eclampsia is a systemic disorder that is related to endothelial dysfunction. The major complications of pre-eclampsia are severe hypertension, which can lead to cerebral oedema and intracerebral haemorrhage, coagulation disorders (thrombocytopenia), pulmonary oedema, renal dysfunction, impaired liver function and seizures. Abnormalities of placental function can cause intra-uterine growth restriction. The condition is more commonly associated with multiple pregnancy, women with pre-existing hypertension and diabetes. The definitive management is delivery of the placenta, and it may take up to 48 hours before the symptoms resolve. This means that there is an ongoing risk of eclamptic seizures during this time.
The management until delivery is usually centred on the control of blood pressure and the prevention of seizures.
A combined anaesthetic and obstetric approach should be taken to enable the stabilization of the woman prior to delivery. The neonatal team should be made aware as many of these babies are at risk and may require resuscitation.
Magnesium sulphate
Magnesium sulphate is the first line treatment for seizures and recurrent seizures. It should be used for seizure prophylaxis in women with severe pre eclampsia and should be considered for seizure prophylaxis for women with mild pre-eclampsia.
Management of seizures includes, airway management (place the woman in the lateral position, use jaw thrust, and consider intubation if there is a prolonged fit or there is delayed recovery), ventilate with bag and mask to improve maternal oxygenation, and terminate the seizure with either a bolus of magnesium (4 gram over 5-10 minutes) or a benzodiazepine.
For seizure prophylaxis, an initial loading dose of 4 gram is given intravenously over 20 minutes, followed by an infusion of 1-2 gram per hour. If it is not possible to run an infusion of magnesium, regular intramuscular magnesium may be administered.
Overdose of magnesium may cause muscular weakness and respiratory depression. It is treated with the administration of calcium.
Blood pressure management
Severe hypertension (systolic greater than or equal to 160 mmHg or diastolic greater than or equal to 110 mmHg) should be treated. Elevated blood pressure should be lowered to levels of systolic 140-150 mmHg and diastolic 90-100 mmHg.
Antihypertensive drugs that can be used safely include labetolol, nifedipine and hydralazine. Drugs to be avoided as anti-hypertensives are diazoxide, ketanserin, nimodipine, magnesium sulphate (useful for seizure management but not for lowering blood pressure safely) and sodium nitroprusside.
Acute pulmonary oedema is a significant cause of morbidity and mortality and fluid management should be monitored very closely. Intravascular fluid depletion is common, in spite of peripheral oedema. This occurs due to increased capillary permeability. Fluid replacement with crystalloids is recommended to maintain renal and placental perfusion. Central venous pressure monitoring may be required if fluid boluses do not restore urine output, as it is also important to avoid fluid overload and pulmonary oedema.
Low platelet count below 75 is a contraindication to regional anaesthesia and analgesia. In the presence of normal coagulation, a count over 75 is safe.
Epidural analgesia is beneficial during labour as it limits the hypertensive response to pain and can be extended if a caesarean section is required. Regional anaesthesia is the technique of choice for caesarean section in order to avoid the hypertensive response to intubation with a general anaesthetic technique. If a general anaesthetic is required the major considerations are airway oedema (and the potential for difficult intubation) and the hypertensive response to intubation. Measures to blunt the hypertensive response to intubation are recommended. Magnesium will increase the action of non-depolarising muscle relaxants.
Oxytocic agents. Ergometrine should be avoided due to the risk of a hypertensive crisis. Oxytocin can be given slowly (5 units) for delivery of the placenta.
CARDIAC DISEASE IN PREGNANCY
Cardiac disease is major cause of maternal death. If a woman was symptomatic from her cardiac disease before her pregnancy, it is likely that she will develop severe symptoms as a result of the physiologic changes of pregnancy and delivery. The expected peak of cardiac output is at the end of the second trimester.
The principles of management during pregnancy are to treat anaemia (start on iron & folate supplements), give bacterial endocarditis prophylaxis (ampicillin or vancomycin and gentamicin) and consider anticoagulation in lesions that are at risk for thromboembolism. A team approach to management is required. Cardiology, obstetric, neonatal and anaesthetic teams should be involved in planning management.
During labour:
Caesarean delivery is performed for obstetric indications, but may be recommended for the patient in whom expulsive efforts would be detrimental. Regional anaesthesia is safe unless the patient is anticoagulated or has a fixed cardiac output state such as with left ventricular outflow obstruction. The sympathectomy that occurs with regional anaesthesia can lead to worsening hypoxemia in the presence of a right to left shunt. In most situations, a slow onset of regional block is useful. This may require the use of an epidural catheter rather than a spinal, which allows for the slower administration of local anaesthetic.
The blood pressure should be supported with the careful administration of vasoconstrictors and intravenous fluid. It is preferable to use alpha adrenoreceptor agonists to avoid a tachycardia in most situations.
General anaesthesia allows for controlled ventilation with 100% O2 (pulmonary vasodilatation), concomitant procedures (e.g. cardioversion) to be carried out, and less interference with anticoagulation therapy.
Cardiac stability is not guaranteed. Intravenous and volatile agents have negative ionotropic effects. Laryngoscopy will stimulate the sympathetic nervous system and blood loss is slightly greater with general anaesthesia.
There is no evidence to demonstrate superiority of one anaesthetic technique over another for caesarean delivery.
Mitral Stenosis is the most common lesion in pregnant rheumatic heart disease patients (90%). Symptoms develop when the valve area, which is normally 4-6 square centimetres, is below 2 square. centimetre. Severe mitral stenosis corresponds to a valve area less than one square centimetre. There is an increased maternal risk with severe disease and atrial fibrillation. The risk is further increased if pulmonary hypertension is present. The basic hemodynamic defect is obstruction to blood flow from the left atrium to the left ventricle to the left ventricle. Pregnancy results in increase in heart rate and blood volume. The increase in heart rate shortens diastole disproportionately reducing time for flow to occur resulting in a reduction in cardiac output and an increase in pulmonary capillary wedge pressure. With time, pulmonary hypertension develops leading to right ventricular hypertrophy and failure.
The management goals in mitral stenosis are to:
· Avoid rapid ventricular rates - treat atrial fibrillation
· Avoid large decrease in systemic vascular resistance and preload - lateral tilt
· Slowly titrated epidural analgesia / anaesthesia
· Avoid marked increases in blood volume – beware of autotransfusion with uterine contractions and at delivery
· Prevent increases in pulmonary artery pressure - oxygen supplementation.
HAEMORRHAGE
Maternal haemorrhage is a significant cause of maternal mortality worldwide. It may occur antepartum (APH), intrapartum or post partum (PPH). There is the potential for rapid massive blood loss that will require a swift response and rapid replacement of blood volume, as well as treatment of the cause.
Antepartum haemorrhage is most commonly due to placenta praevia or placental abruption. The incidence of low-lying placenta and placenta accreta is increased with previous caesarean section. Placental abruption is the premature separation of the placenta before birth. It is usually painful and there may not be any visible blood loss. Disseminated intravascular coagulation may occur, which will cause a coagulopathy. Regional anaesthesia can be considered for delivery after APH provided blood volume has been restored, there is good intravenous access and access to blood products and if haemorrhage is controlled and there is no coagulopathy.
Uterine rupture and vasa praevia are causes of intrapartum haemorrhage. Uterine rupture is more common if there has been a previous caesarean section or difficult delivery, or in the case of prolonged labour in association with excessive oxytocin stimulation. It presents with severe pain and maternal collapse and the foetal heartbeat may be lost. It has a high foetal and maternal mortality and early recognition is important to increase survival.
Postpartum haemorrhage occurs due to retained placenta, uterine atony, trauma to the birth canal and more rarely, uterine inversion. The retained placenta may be managed with manual exploration under a spinal or epidural block. It is important that blood volume be restored before the block is performed. General anaesthesia is performed in the unstable patient. A rapid sequence induction is performed to protect against maternal pulmonary aspiration.
Uterine atony may be treated with medications to stimulate uterine contraction such as oxytocin (given slowly to avoid severe hypotension), ergometrine and carbaprost (prostaglandin F2 alpha). Intrauterine balloons or arterial embolisation have been used to control PPH. If these measures fail, emergency hysterectomy or internal artery ligation may be required.
Management of major obstetric haemorrhage requires a co-ordinated response. The blood bank should be informed of the emergency, as large numbers of packed cells, and coagulation factors and platelets may be required. The general principles of management of massive blood loss should be applied. They include the maintenance of blood volume with crystalloids and colloids before blood is available, ensuring adequate oxygenation and ventilation, warming the patient, treatment of acidosis, monitoring of blood pressure, heart rate, saturation, ECG, temperature, urine output and measurement of blood loss. Regular assessment of laboratory investigations will be required, including full blood count, coagulation studies, electrolytes and acid base status.
NEWBORN RESUSCITATION
Approximately 5 to 10% of newborns require some degree of active resuscitation at delivery. More than 5 million neonatal deaths occur each year. 19% of these deaths are due to birth hypoxia. Effective neonatal resuscitation requires anticipation, preparation, evaluation and prompt initiation of appropriate techniques.
Personnel capable of initiating resuscitation should attend every delivery.
Evaluation of the neonate Assessment of the need for resuscitation should begin immediately after birth. All newborn need rapid assessment of their breathing, circulation, muscle tone, colour, and gestational age and for the presence of meconium in the amniotic fluid or on the skin.
Feeling the pulsations in the base of the umbilical cord or listening with a precordial stethoscope best assesses heart rate.
Normal newborn infants do not require suctioning. Suctioning of the baby, before delivery of the shoulders, makes no difference to the outcome of babies with meconium stained liquor. If the amniotic fluid contains thick meconium, and the infant has absent or depressed respirations, and decreased muscle tone, secretions obstructing the airway should be cleared immediately with wide bore suction under direct vision (laryngoscopy). Pharyngeal suction can cause laryngospasm, trauma to soft tissues, bradycardia and delay the onset of spontaneous respiration. Suction should be limited to no more than 5 seconds and no more than 5 cm from the lips in a term infant. The negative pressure should not exceed 100 mm Hg (13 kPa).
If meconium is seen in the amniotic fluid, the newborn’s mouth, nose and hypopharynx should be suctioned on delivery of the head. If the heart rate is less than 100 beats per minute or muscle tone is poor or respiration is absent or depressed, the trachea should be suctioned under direct laryngoscopy to remove meconium from the airway.
Resuscitation sequence
In the absence of meconium:
If the baby is breathing or crying and has good muscle tone, only routine care is required. This includes drying the baby, providing warmth, clearing the airway if required and assessing the breathing, colour and heart rate.
If the baby is not breathing or crying, or has poor muscle tone, dry and stimulate the baby, position the head and neck to open the airway and warm the baby, assess the breathing and heart rate. If the baby is breathing and the heart rate is over 100 beats per minute and beginning to look pink, provide routine care as outlined above and observe. If the heart rate is less than 100 beats per minute or there is inadequate breathing, give positive pressure ventilation until the heart rate is over 100 beats per minute and the infant is breathing.
If there is inadequate breathing and the heart rate is less than 60 beats per minute, assess the adequacy of ventilation and improve it if possible. If the heart rate does not increase, give chest compressions with positive pressure ventilation at a ratio of 3 compressions for every breath.
If the heart rate still does not increase over 60 beats per minute, reassess ventilation technique, give adrenaline and consider intravenous fluids.
Endotracheal intubation may be considered if breathing is inadequate or positive pressure ventilation with a facemask is not effective.
SELF-ASSESSMENT QUESTIONS
1. Outline the respiratory changes that occur with pregnancy and the significance to anaesthesia.
2. Why is a rapid sequence induction performed for a woman having a caesarean section under general anaesthesia?
3. What measures can be taken to reduce pulmonary aspiration for a woman in labour?
4. Discuss the physiology of labour pain.
5. What are the potential complications of spinal anaesthesia for caesarean section?
ASSIGNMENT
You are the director of anaesthesia in your obstetric hospital. Your colleagues and the obstetricians would like to provide regional analgesia for the women coming in for labour. What regional analgesia options are available to you? Discuss how you would develop a protocol for the monitoring of the mother and foetus during labour under regional anaesthesia. Discuss what you would like to monitor, how often, who will perform the monitoring and what parameters should be reported to the anaesthetist.
OBSTETRIC ANAESTHESIA CASE STUDIES
Case No 15.1. Pre eclampsia
Tungaa is having her first baby. She has a history of mild hypertension but is not on any medication for it. At her 34 week check t. The midwife has noticed that her blood pressure is 145/105 mmHg and Tungaa has been complaining of headache and peripheral oedema.
What are the diagnostic features of pre-eclampsia?
What are the options for blood pressure management and what blood pressure would be optimal?
Tungaa’s vision is becoming blurred. The obstetrician wants to commence magnesium sulphate. Describe how you would do this. What are the risks of magnesium administration? How should she be monitored?
What other management does Tungaa require?
The obstetrician decides that Tungaa will require caesarean delivery, as she is not suitable for induction of labour. Discuss how you should manage her pre eclampsia before delivery.
What anaesthetic would you choose for Tungaa? Justify your choice. Are there any special considerations with your choice of anaesthesia?
The next day, you are in the ward and are asked to attend Tungaa urgently as she appears to be having a seizure. What is your management?
Case No 15.2. Maternal haemorrhage
Enkhee has just delivered her 3rd baby and you are called to the obstetric ward to help manage a retained placenta. The midwife says there has been 700 ml of blood loss and that it is continuing. She needs an urgent manual removal of placenta.
Discuss how you will estimate blood loss and your immediate management of the situation.
What are the options for anaesthesia? Are there any advantages and disadvantages of each technique?
Enkhee continues to bleed after removal of the placenta. You have administered a spinal anaesthetic and she is now becoming restless. What is your immediate management?
After 15 minutes, Enkhee has lost a further 900 ml of blood. How will you manage the situation?
The surgeon has performed a hysterectomy, but says that there appears to be general ooze from the operative surfaces. How will you assess her and manage her apparent coagulopathy?
Case No 15.3. Labour analgesia
Ariuna is a 30-year-old primigravida who is seeking information about her options for pain relief in labour. She is currently 36 weeks pregnant and has no medical problems.
What are the options for labour analgesia for a healthy primigravida? Discuss the advantages and disadvantages of these techniques.
Ariuna is keen on regional analgesia. Are there any side effects and risks that you wish to discuss with Ariuna about regional analgesia for labour?
Outline how you would insert an epidural for analgesia for Ariuna?
Ariuna comes in to labour at 40 weeks at your hospital and you agree to insert an epidural for labour. Shortly after insertion of her epidural, she becomes unconscious. What are the potential causes? Outline your immediate management.
Case No 15.4. Neonatal resuscitation
You are in the labour ward when the midwife urgently requests your presence at the imminent delivery of a woman who is 42 weeks gestation. The midwife says she thinks the baby will require resuscitation and there is no neonatologist present.
What factors in the history and examination of athe woman would indicate that the neonate maywill require resuscitation?
What equipment do you consider you will need for newborn resuscitation?
The baby is delivered and is covered in meconium. He is floppy and not making any respiratory effort. What is your immediate response?
Case No15. 5. Anaesthesia for emergency caesarean section
Bayanaa is a 21 year old woman who has come in from the countryside in labour. She has had no antepartum care and her labour is obstructed. The obstetrician would like to perform a caesarean section.
How urgently should this caesarean section be performed? Are there any other factors that will make it more urgent?
What are the options for anaesthesia for Bayanaa? Outline the advantages and disadvantages of each?
You decide that you will perform a regional technique. Describe your technique.
What dermatome level will you aim for optimal anaesthesia for caesarean section?
What dose and type of local anaesthetic will you use? Are there any adjuncts you can add to improve the anaesthetic?
Bayanaa’s blood pressure has fallen to 90/50 mmHg and she is complaining of nausea shortly after you have performed the block. Discuss techniques of avoiding and managing hypotension secondary to spinal anaesthesia for caesarean section.
Final Objective:
On completion of this module you will be able to provide safe analgesia and anaesthesia for the obstetric patient.
Enabling Objective: To achieve this goal, you should know how to:
- Outline maternal, foetal and placental physiology.the physiology of the obstetric patient, placental and foetal physiology.
- Describe the process of labour and delivery and their physiologic implications.
- Conduct safe pain management for labour.
- Provide safe general and regional anaesthesia for delivery (vaginal and caesarean birth) and for surgery in the pregnant patient.
- Manage the common medical conditions associated with pregnancy such as pre-eclampsia and co-existing medical problems.
- Manage obstetric emergencies such as eclampsia and major haemorrhage.
- Resuscitate the newborn.
- Manage anaesthetic emergencies such as failed intubation, high spinal or epidural block, local anaesthetic toxicity and pulmonary aspiration.
- Developing Anaesthesia Chapters 29,30,31,32,33,36,38,43,44
- Obstetric anaesthesia seminar notes 2006
- Oxford Handbook of anaesthesia (2nd edition) Chapter 32
MATERNAL PHYSIOLOGY
Pregnancy results in physiologic changes in many organ systems. These changes begin in the first trimester and continue until after delivery. Labour presents its own unique physiologic fluctuations due to painful uterine contractions and the autotransfusion of blood following delivery. Many physiologic changes persist for days and some persist for a few weeks after delivery. These physiologic changes will have an impact on the provision of safe anaesthesia care of the mother.
Cardiovascular changes
Intravascular blood volume increases by 35%. The plasma volume increases relative to red cell volume so there is a relative anaemia. Normal vaginal delivery results in a blood loss of up to 500 ml. The pre-pregnancy intravascular volume is reached by 7-14 days post partum.
Cardiac output is increased by 40% at term due to systemic vasodilatation, increased contractility, myocardial hypertrophy and an increased stroke volume and heart rate. The systolic blood pressure is decreased due to a fall in systemic vascular resistance. It returns to normal towards the end of the second trimester. The uterus at term receives up to 20% of the maternal cardiac output. This has implications for rapid blood loss in an atonic uterus after delivery. Haemorrhage may be severe and rapid.
There are marked fluctuations in the cardiac output during labour. There is a 100% increase in cardiac output in labour. This can put significant stress on the heart if there is cardiac disease.
The supine hypotensive syndrome is a decrease in maternal blood pressure that occurs in about 10-15% of pregnant women near term when they lie supine. The gravid uterus obstructs the inferior vena cava and thereby reducing venous return to the heart. Supine hypotension can be avoided by maintaining the pregnant woman in the left lateral position or by using left uterine displacement. Because the aorta may also be compressed in the supine position, uterine blood flow may be compromised.
Respiratory changes
The upper airway of the pregnant woman becomes oedematous due to capillary engorgement and requires the placement of a smaller endotracheal tube if general anaesthesia is required. Due to nasal obstruction and oedema, the placement of a nasal tube is not recommended as this may lead to epistaxis.
The incidence of difficult intubation is increased in the pregnant woman due to airway oedema, weight gain and breast enlargement. Conditions that increase airway oedema such as pre-eclampsia will increase the difficulty with intubation.
Minute ventilation increases early in pregnancy and, by the end of the first trimester, minute ventilation is increased by about 50%. The resting arterial partial pressure of carbon dioxide (PaCO2) decreases to near 30mmHg.
Lung volumes change after the fifth month of gestation, probably due to the cephalad displacement of the diaphragm by the gravid uterus. Functional residual capacity decreases by 20%. This has implications for anaesthesia, as it reduces the potential oxygen stores. Because of the 20-40% increase in oxygen consumption and the reduction in FRC, there is a tendency to hypoxia during periods of apnoea.
Neuronal changes
Pregnancy decreases anaesthetic requirements. During pregnancy, the minimal alveolar concentration for volatile anaesthetics is reduced by 40% and the sensitivity to local anaesthetics increases. The doses administered for an epidural or spinal anaesthetic may be reduced by 30-50%.
Gastro-intestinal changes
The parturient is at increased risk of regurgitation of acidic gastric contents and therefore the development of acid aspiration syndrome. The enlarged uterus displaces the pylorus and symptomatic reflux in pregnancy is common. Regional anaesthesia is recommended to reduce the risk of aspiration.
The airway needs to be protected with a cuffed endotracheal tube during general anaesthesia in pregnancy after 18 – 20 weeks gestation and up to 18 hours after delivery. It is recommended that a histamine receptor antagonist (such as ranitidine 150 mg orally one hour before anaesthesia) and a non-particulate antacid (such as sodium citrate 0.3 M, 30 ml 15 minutes before anaesthesia) be given before general anaesthesia. Particulate antacids are associated with more severe pneumonitis should aspiration occur. Rapid sequence induction is recommended.
During labour, gastric emptying is delayed, especially if opioids have been given and the patient is obese. It is recommended that oral intake in active labour be limited to clear fluids. Routine prophylaxis with ranitidine every 6 hours should be considered in women with a risk of requiring general anaesthesia or surgery.
Renal changes
There is increased renal blood flow during pregnancy and an increase in glomerular filtration rate and creatinine clearance. The normal upper limits of the serum urea and creatinine levels are reduced by 50%. The renal calyces are dilated from the second trimester, which tends to lead to urinary stasis, putting the pregnant patient at risk for urinary tract infection.
Haematologic changes
There is an increase in red cell volume that does not match the increase in plasma volume resulting in a physiologic anaemia.
There is a tendency towards a hypercoagulable state as a result of increased fibrinogen, coagulation factors II, VII, VIII, IX, X, XII, reduction in plasminogen activator and increased number of platelets. The prothrombin time and activated partial thromboplastin time is decreased by 20%. The pregnant patient is at risk for deep venous thrombosis.
PLACENTAL PHYSIOLOGY
Maternal (basal plate) and foetal (chorionic) tissues form the placenta and they are separated by the intervillous space. Maternal blood enters the intervillous space and spreads over the foetal chorionic villi. Foetal blood leaves the foetus via the internal iliac arteries, which give rise to the umbilical arteries. Blood moves across the umbilical capillaries in the chorionic villi and maternal to foetal placental transfer occurs across the chorionic membrane. Oxygenated blood returns to the foetus via a single umbilical vein.
On the maternal side, uterine blood flow makes up 20% of the cardiac output at term. The blood is supplied via the uterine arteries that branch out to form the arcuate, radial and spiral arteries that extend into the placental tissue ending in the intervillous space. Uterine blood vessels are maximally dilated. Uterine blood flow is directly related to the mean maternal arterial blood pressure (average 80 mmHg) minus the uterine venous pressure (10 mmHg at rest) and inversely related to uterine vascular resistance. Uterine vascular resistance is low at rest but is affected by the tension in the myometrium and by vasoconstriction of the uterine, arcuate and radial arteries. The arteries respond to alpha-adrenergic stimulation.
The factors that influence uteroplacental perfusion are:
1. Aorto-caval compression
2. Hypotension (less than 100 mmHg systolic)
3. Increases in uterine vascular resistance (contractions, delivery, ketamine, oxytocin and placental abruption)
4. Maternal hypoxia, hypo and hypercarbia
5. Catecholamines (increase vascular resistance)
Placental transfer of substances occurs via simple diffusion, active transport, bulk flow, facilitated diffusion and breaks in the chorionic membrane.
Anaesthetic compounds cross the placenta by diffusion. The quantity of drug that is transferred is determined by molecular weight (small drugs cross easily), degree of ionisation (less ionised cross easily), lipid solubility (more lipid soluble cross easily), protein binding (less protein bound cross easily) and concentration gradient from maternal to foetal circulation. Most anaesthetic agents cross easily. Neuromuscular blockers are water soluble, ionised and have higher molecular weights, so do not cross the placenta readily.
FOETAL AND NEONATAL PHYSIOLOGY
Foetal blood returns from the placenta via the umbilical vein. 50% will enter the foetal portal circulation and the rest will enter the inferior vena cava. At the right atrium, the oxygenated blood from the inferior vena cava mixes with the poorly oxygenated blood from the superior vena cava (head and arms) and is shunted to the left atrium via the open foramen ovale. Blood then enters the left ventricle and out through the aorta. The most oxygenated blood is distributed to the head. The foetal lungs only receive a small amount of perfusion via the right ventricle and pulmonary outflow tract. The ductus arteriosus allows right ventricular blood flow to enter the aorta.
At birth, there is a removal of the placenta and the lungs expand (allowing pulmonary blood flow). The foramen ovale closes due to increased left atrial pressure and there is a functional closure of the ductus arteriosus with the decrease in prostaglandins and increasing oxygen tension. The shunts are not anatomically closed immediately after birth and a return to a foetal circulation can occur with resultant severe hypoxemia and circulatory collapse in response to major stresses such as hypoxia and acidosis, which increase pulmonary vascular resistance.
The normal foetal capillary pH is greater than or equal to 7.25. Foetal acidosis is defined as a pH less than 7.2. The normal values for blood gases at birth are pH 7.25, pCO2 40 mmHg, pO2 60 mmHg and by 30 minutes of life, the normal values are 7.33, 35 and 68 respectively.
PHYSIOLOGY OF LABOUR AND DELIVERY
Labour
During labour, painful contractions increase minute ventilation by up to 300%, which leads to hypocarbia and alkalemia. Hypocarbia may lead to uterine vasoconstriction and reduced placental perfusion. Between contractions, the patient may hypoventilate, which can lead to foetal and maternal hypoxemia.
Oxygen consumption tends to rise during labour, and it may increase by 100% during second stage.
During uterine contractions, there is an autotransfusion of blood from the uterus to the maternal circulation. This can increase central blood volume by 25%. The blood pressure tends to rise during contractions. The cardiac output increases by 60% after delivery due to the closure of virtual arterio-venous fistula that is the placental circulation and relief of aorto-caval compression.
Painful contractions will increase catecholamine levels and contribute to the rise in cardiac output as well as to vasoconstriction of the uterine circulation.
Delivery
Cardiac output rises immediately after birth due to an autotransfusion of 500-750 ml of blood from the sustained contraction on an empty uterus. The cardiac output returns to normal about four weeks post partum.
The functional residual capacity and residual volume return to normal rapidly. Alveolar ventilation returns to normal by 4 weeks post partum.
There is a post partum diuresis and the blood volume and hematocrit return to normal within 4 weeks.
ANALGESIA FOR LABOUR
Labour pain
Labour pain is mediated by the autonomic system and somatic system. The first stage of labour involves uterine contraction and cervical dilatation and effacement. This pain is transmitted to the spinal cord via the visceral afferents to the tenth thoracic to first lumbar spinal segments. It is autonomically mediated and poorly localized. It may be referred to the lower back and upper thighs, but is usually felt in the lower abdomen. Second stage of labour is the delivery of the foetus and involves stretching of the perineum. Pain is somatic and well localized to the perineum. The pudendal nerves transmit the pain to the second to fourth sacral spinal cord segments.
The options for labour analgesia include pharmacologic and non-pharmacologic methods.
Systemic analgesia
Systemic analgesia is used for labour when there is no epidural service or when there is a maternal contraindication to epidural analgesia. Opioids are used frequently in this situation and can be delivered by intermittent intramuscular or intravenous injection or via a patient controlled intravenous analgesia system. Unfortunately, opioid related maternal side effects such as sedation, nausea, itch and respiratory depression as well as incomplete analgesia, make systemic opioid administration troublesome.
Fentanyl is very lipid soluble and highly protein bound. It is 800 times as potent as pethidine and its time to peak effect is 3-4 minutes. Repeated dosing can cause an increase in its context sensitive half time, increasing its duration of action. It can be used in a patient controlled intravenous analgesia system in doses of 10 micrograms with a lockout of 12 minutes combined with a background infusion of 10 mcg per hour or it can be administered by the nurse with a loading dose of 50 mcg followed by 50-100 mcg every hour as required.
Epidural analgesia
Regional analgesia is the most effective and reliable way of relieving childbirth pain. Epidural analgesia involves the introduction of local anaesthetic and opioid agents into the epidural space. An epidural catheter is inserted using a sterile technique via a lumbar spinal interspace.
The local anaesthetic acts on spinal nerves and on the spinal cord to achieve a blockade of neural transmission. The aim is to provide analgesia by blocking the A delta and C fibres that transmit pain. With increasing doses of local anaesthetic it is inevitable that the larger sensory and motor fibres will also be blocked. Autonomic blockade is expected due to the small size of autonomic fibres.
Lipid-soluble opioids are used in conjunction with the local anaesthetic agents to allow a reduction in local anaesthetic doses. The opioids actwork on opioid receptors in the dorsal horn of the spinal cord.
Advantages of epidurals · Excellent analgesia
· Reduction of maternal catecholamine levels
· Reduction of maternal alkalosis from hyperventilation
· The ability to extend the epidural for operative and assisted delivery
Disadvantages of epidurals
· Hypotension occurs due to vasodilatation secondary to sympathetic blockade.
· Slowing of the progress of labour and need for assisted delivery. Regional analgesia is associated with increased duration of the second stage of labour and instrumental vaginal birth, but has no effect on the risk of a caesarean or immediate status of the neonate.
· Motor blockade is more frequent with higher concentrations of local anaesthetic. It means that the woman is not able to walk and dense motor block increases the need for instrumental (assisted) delivery.
· Impaired bladder function may require an indwelling urinary catheter.
Complications of epidurals
- Neurologic complications (such as spinal cord haematoma or epidural abscess, direct trauma to nerve roots or the spinal cord).
- Intravascular injection into epidural vessels of local anaesthetic will cause toxicity and may lead to seizures and cardiovascular collapse. Resuscitation may require immediate delivery of the foetus to relieve aorto-caval compression and improve cardiac output with external cardiac compressions. Bupivacaine may cause ventricular tachycardia and fibrillation that may be difficult to treat. Prolonged resuscitation may be required.
- Total spinal anaesthesia results from large doses of local anaesthetic injected in the subarachnoid space. This may occur if an unrecognised dural puncture has occurred. Management will include intubation, ventilation and treatment of hypotension with intravenous fluids and vasopressors.
- Post dural puncture headache occurs due to cerebrospinal fluid leak after inadvertent dural puncture with a large bore epidural needle. Initial management is simple analgesia and intravenous fluid hydration. An epidural blood patch may be required in severe cases and is very effective.
Intravenous access is secured and intravenous fluids are administered to reduce the incidence of hypotension (important for doses of greater than 25 mg of bupivacaine). Routine fluid loading is not required for low dose techniques.
Monitoring of the mother and foetus should be established prior to and during the performance of the block. Blood pressure, maternal and foetal heart rate, motor function and sensory level are monitored.
The patient is positioned in the flexed, sitting posture and the lower lumbar spaces are identified by palpation. The fifth, fourth or third lumbar spaces are commonly used for insertion. (The spinal cord terminates at the level of the second lumbar vertebra in most people, but can extend to the third vertebral level. Inadvertent intrathecal insertion of the needle may therefore injure the conus of the spinal cord if a higher lumbar level is used.) A loss of resistance to fluid technique is used to identify the epidural space using a sterile technique and a catheter is threaded into the space and secured with a sterile dressing.
A test dose is given via the epidural catheter once it is inserted to test for intrathecal (spinal) or intravenous placement.
A dose of dilute local anaesthetic (0.125% Bupivacaine) with or without fentanyl is administered incrementally until a sensory block to the tenth thoracic dermatome is achieved. The choice of local anaesthetic is usually based on the need for prolonged duration of action. The use of lignocaine is reserved for the need for rapid onset analgesia. Its duration of action is short and repeated doses may cause tachyphylaxis. There is no difference in analgesic effectiveness or adverse effects between ropivacaine and bupivacaine for labour epidural analgesia.
Ongoing analgesia can be achieved with intermittent top ups of local anaesthetic or with the use of an infusion of local anaesthetic with or without fentanyl.
Contraindications to epidural analgesia include coagulation disorders, sepsis at the intended insertion site, raised intracranial pressure, uncorrected hypovolemia and patient refusal.
Spinal analgesia for labour A single injection of intrathecal opioids provides comparable early analgesia to epidural local anaesthetics with less motor block. The combination of spinal opioids with local anaesthetics reduces dose requirements for either drug alone and may help to minimize motor block.
When resources are limited, it is possible to use single shot spinal injections of low doses of bupivacaine (2.5 mg) with fentanyl (15-25 mcg) to provide about 90-120 minutes of analgesia for labour. The time to onset of analgesia is five minutes with intrathecal fentanyl because it is very lipid soluble.
Multiple punctures are not recommended, as there is tachyphylaxis to opioid analgesia when used intrathecally.
Disadvantages of intrathecal injection for labour analgesia Unfortunately, it is not possible to extend the duration of action if delivery has not occurred within the duration of action of the fentanyl and bupivacaine.
Perineal pain may still occur if an episiotomy or forceps delivery is required because this technique does not produce a dense block.
Maternal hypotension is still possible, but less frequent than with larger doses of local anaesthetic (such as those used for caesarean section).
There is a risk of post dural puncture headache with the use of larger cutting needles, so a small pencil point needle should be used.
There is risk of meningitis, so a sterile technique is required.
Nausea and itch may be troublesome side effects. Respiratory depression is possible. Respiratory depression is more common with morphine (which is water soluble) and with the administration of systemic opioids along with the spinal opioids.
CAESAREAN SECTION
The World Health Organization (WHO) recommends an optimum caesarean section rate of 5-15% to ensure best outcome for the mother and neonate. The main maternal indications for caesarean section are obstructed labour, placental abruption, previous caesarean section, eclampsia, placenta praevia and malpresentation.
A four-tier classification of urgency of caesarean section has been broadly accepted.
1. Category one – Immediate threat to life of woman or foetus (recommended decision to delivery interval less than 30 minutes)
2. Category two – Maternal or foetal compromise, not immediately life threatening
3. Category three – Needing early delivery with no maternal or foetal compromise
4. Category four – At a time to suit the woman and staff
The choice of anaesthesia for caesarean section will depend on the urgency of the procedure, medical condition of the mother and on the experience of the anaesthetist.
Spinal analgesia
A regional technique is preferred for caesarean section in order to reduce the risk of airway complications associated with general anaesthesia in the pregnant patient. The most frequent technique for caesarean section is spinal anaesthesia, but epidural anaesthesia is used when there is an epidural catheter in situ from labour. Epidural anaesthesia is also used in the patient who needs to have a slow onset of anaesthesia to avoid hypotension.
The advantages of regional anaesthesia for caesarean section include, excellent operating conditions with a mother who is then awake to see the birth of her child, the avoidance of airway and pulmonary complications, good postoperative analgesia, avoidance of awareness under general anaesthesia, a reduction in the incidence of deep venous thrombosis, less neonatal depression, a reduction in blood loss and a quicker return of gastro-intestinal function.
The contraindications to regional anaesthesia are coagulation disorders, maternal refusal of the technique, infection at the site or systemic sepsis, uncorrected hypovolemia and raised intracranial pressure. Pre-existing neurologic conditions and stenotic cardiac valvular disease are relative contraindications and the benefits of regional anaesthesia must be weighed against the risks.
Hypotension is a frequent complication of neuraxial anaesthesia in obstetrics and may have detrimental effects such as a reduction in placental blood flow and reduced maternal cerebral flow. It is especially common during spinal anaesthesia and in non-labouring patients. Aorto-caval compression will occur when the patient is supine. Spinal or epidural anaesthesia will blunt compensatory reflexes, so hypotension becomes more likely in the supine position.
The definition of hypotension is a decrease in systolic BP to less than 80-100 mmHg or by 10-30% of baseline. In order to minimize the reduction in blood pressure, left uterine displacement is recommended after neuraxial block. Wrapping of the legs reduces the incidence of hypotension. Pre-hydration with crystalloids is not very efficacious for preventing hypotension, but normovolemia should be achieved in the dehydrated patient. Colloids are more efficacious but expensive and may produce adverse reactions. Vasopressors are useful but the choice of ephedrine over phenylephrine (or other alpha agonists) is controversial. A combination of intravenous co hydration and vasopressor infusion may be more effective than single therapies for preventing hypotension. All patients must be frequently monitored for hypotension and aggressively treated.
General anaesthesia for caesarean section
There is increased mortality and morbidity associated with general anaesthesia compared with regional anaesthesia. It is now only indicated if there is a contraindication to regional anaesthesia or when it is felt that there is not enough time to establish regional anaesthesiaa block.
Preparation for anaesthesia should include antacid prophylaxis, which includes ranitidine (50 mg intravenously or 150 mg oral 60 minutes before the procedure) and a non-particulate antacid such as sodium citrate 15 minutes before anaesthesia.
Pre oxygenation and a rapid sequence induction are recommended to protect the woman from aspiration of gastric contents. The induction agent of choice is thiopentone, in a dose of 4 mg/kg to prevent awareness, but still allow wakening if there is a failed intubation. Propofol is the alternative agent but may induce more hypotension. Ketamine can be used in the management of hypovolemic women requiring caesarean section. Suxamethonium is the relaxant of choice as it can rapidly produce good intubating conditions and will have a rapid offset if there is a failed intubation.
The main disadvantages of general anaesthesia are failed intubation, pulmonary aspiration and maternal awareness. Volatile anaesthetic agents are capable of uterine relaxation and can predispose to uterine atony and haemorrhage.
The typical blood loss for a caesarean section is 500 to 1000 ml, which does not require transfusion unless the haemoglobin drops below 7 g/dL. A blood group and screen should be performed before caesarean section.
Monitoring during caesarean section should include blood pressure, heart rate (ECG) and pulse oximetry with foetal heart rate monitoring before anaesthesia induction. End tidal capnographycraniography should be employed for general anaesthesia when it is available given that the most common causes of maternal complications arise from failure to intubate, ventilate and oxygenate. One The anaesthetist mustshould be prepared for a difficult airway and have a range of equipment available to manage a difficult airway and a plan for management of the failed intubation.
Before delivery of the foetus, a minimum inspired oxygen concentration of 50 % is used. A volatile agent is used throughout the procedure to minimize the risk of maternal awareness. Oxytocics and an opioid are given immediately after delivery. The induction to delivery interval should be kept to a minimum to avoid neonatal depression. Therefore anaesthesia is induced only once the patient and surgeon are ready for delivery (the skin is prepared and draped, urinary catheter is inserted). At the end of the procedure, the muscle relaxant is reversed with neostigmine and atropine and the mother is extubated when she is awake and able to maintain her own airway.
ANAESTHESIA FOR SURGERY DURING PREGNANCY
2% of pregnant patients will require surgery during their pregnancy. The procedures include surgery for trauma, ovarian cysts, appendicitis, cholecystectomy, breast biopsy and cervical cerclage.
Maternal physiology differs significantly from the pre-pregnant state. The important respiratory changes to consider for incidental surgery during pregnancy include increased oxygen consumption, reduced lung volumes, hypocapnia, increased mucosal vascularity, (so there is a propensity to epistaxis) and difficult intubation. The relevant cardiac changes include an increase in blood volume and cardiac output, dilutional anaemia and aorto-caval compression after 20 weeks gestation. The pregnant patient is at risk for pulmonary aspiration due to lower gastro-oesophageal sphincter tone and reflux and there is a reduction in anaesthetic dose requirements.
The main anaesthetic considerations are the maintenance of uterine perfusion, prevention of preterm labour and the potential for teratogenic and adverse effects of anaesthetic agents.
In general terms, there are minimal teratogenic effects of anaesthetic agents, but it is wise to delay surgery until after the first trimester (whenan organogenesis is complete). Elective operations should occur after the pregnancy, or if there is some urgency, surgery during the second trimester is the ideal time to avoid teratogenicity and preterm labour.
Aspiration prophylaxis should be considered, and premedication will alleviate anxiety and pain, both of which increase catecholamine levels and reduce uterine blood flow. Intraoperative positioning should minimize aorto-caval compression. There is no evidence that any technique is more superior provided that maternal oxygenation and perfusion are maintained. Continuous foetal monitoring is used once foetal viability is reached. Postoperative management includes the monitoring of foetal vital signs, uterine activity, and the treatment of preterm labour and thromboembolism prophylaxis.
In the case of trauma, foetal death occurs due to maternal death or placental abruption. Ultrasound is used to determine foetal viability and to diagnose abruption. Continuous foetal monitoring is recommended during trauma surgery. There are few indications for emergency caesarean section in this situation but they include: a stable mother with foetal distress on the cardio-tocograph, uterine rupture, a gravid uterus interfering with maternal abdominal surgery and a mother who cannot be saved with a viable foetus.
PRE-ECLAMPSIA
Pre-eclampsia is defined as the development of hypertension and proteinuria after 20 weeks gestation. The incidence is approximately 7% of all pregnancies. If seizures occur, the condition is known as eclampsia. Pre-eclampsia is a systemic disorder that is related to endothelial dysfunction. The major complications of pre-eclampsia are severe hypertension, which can lead to cerebral oedema and intracerebral haemorrhage, coagulation disorders (thrombocytopenia), pulmonary oedema, renal dysfunction, impaired liver function and seizures. Abnormalities of placental function can cause intra-uterine growth restriction. The condition is more commonly associated with multiple pregnancy, women with pre-existing hypertension and diabetes. The definitive management is delivery of the placenta, and it may take up to 48 hours before the symptoms resolve. This means that there is an ongoing risk of eclamptic seizures during this time.
The management until delivery is usually centred on the control of blood pressure and the prevention of seizures.
A combined anaesthetic and obstetric approach should be taken to enable the stabilization of the woman prior to delivery. The neonatal team should be made aware as many of these babies are at risk and may require resuscitation.
Magnesium sulphate
Magnesium sulphate is the first line treatment for seizures and recurrent seizures. It should be used for seizure prophylaxis in women with severe pre eclampsia and should be considered for seizure prophylaxis for women with mild pre-eclampsia.
Management of seizures includes, airway management (place the woman in the lateral position, use jaw thrust, and consider intubation if there is a prolonged fit or there is delayed recovery), ventilate with bag and mask to improve maternal oxygenation, and terminate the seizure with either a bolus of magnesium (4 gram over 5-10 minutes) or a benzodiazepine.
For seizure prophylaxis, an initial loading dose of 4 gram is given intravenously over 20 minutes, followed by an infusion of 1-2 gram per hour. If it is not possible to run an infusion of magnesium, regular intramuscular magnesium may be administered.
Overdose of magnesium may cause muscular weakness and respiratory depression. It is treated with the administration of calcium.
Blood pressure management
Severe hypertension (systolic greater than or equal to 160 mmHg or diastolic greater than or equal to 110 mmHg) should be treated. Elevated blood pressure should be lowered to levels of systolic 140-150 mmHg and diastolic 90-100 mmHg.
Antihypertensive drugs that can be used safely include labetolol, nifedipine and hydralazine. Drugs to be avoided as anti-hypertensives are diazoxide, ketanserin, nimodipine, magnesium sulphate (useful for seizure management but not for lowering blood pressure safely) and sodium nitroprusside.
Acute pulmonary oedema is a significant cause of morbidity and mortality and fluid management should be monitored very closely. Intravascular fluid depletion is common, in spite of peripheral oedema. This occurs due to increased capillary permeability. Fluid replacement with crystalloids is recommended to maintain renal and placental perfusion. Central venous pressure monitoring may be required if fluid boluses do not restore urine output, as it is also important to avoid fluid overload and pulmonary oedema.
Low platelet count below 75 is a contraindication to regional anaesthesia and analgesia. In the presence of normal coagulation, a count over 75 is safe.
Epidural analgesia is beneficial during labour as it limits the hypertensive response to pain and can be extended if a caesarean section is required. Regional anaesthesia is the technique of choice for caesarean section in order to avoid the hypertensive response to intubation with a general anaesthetic technique. If a general anaesthetic is required the major considerations are airway oedema (and the potential for difficult intubation) and the hypertensive response to intubation. Measures to blunt the hypertensive response to intubation are recommended. Magnesium will increase the action of non-depolarising muscle relaxants.
Oxytocic agents. Ergometrine should be avoided due to the risk of a hypertensive crisis. Oxytocin can be given slowly (5 units) for delivery of the placenta.
CARDIAC DISEASE IN PREGNANCY
Cardiac disease is major cause of maternal death. If a woman was symptomatic from her cardiac disease before her pregnancy, it is likely that she will develop severe symptoms as a result of the physiologic changes of pregnancy and delivery. The expected peak of cardiac output is at the end of the second trimester.
The principles of management during pregnancy are to treat anaemia (start on iron & folate supplements), give bacterial endocarditis prophylaxis (ampicillin or vancomycin and gentamicin) and consider anticoagulation in lesions that are at risk for thromboembolism. A team approach to management is required. Cardiology, obstetric, neonatal and anaesthetic teams should be involved in planning management.
During labour:
- Maintain adequate hydration, lateral tilt to preserve venous return
- Monitoring: ECG, SpO2, BP
- In practice, central pressure monitoring is rarely used
- Supplemental O2 if required
- Effective analgesia to avoid cardiac stress - epidural analgesia offers benefit by reducing catecholamine release, prevents tachycardia and the increased cardiac work associated with painful contractions. It is useful for maintaining perfusion of a potentially compromised placenta.
- Epidural analgesia (as opposed to anaesthesia) can be achieved with diluted concentrations of local anaesthetic; neuraxial opioid avoids sympathectomy
- Active pushing can cause significant hemodynamic instability, therefore should be limited in some women
- Caution with oxytocics for augmenting labour and management of 3rd stage – balancing risk of postpartum haemorrhage and cardiovascular effects of these agents.
- Ergot derivatives cause a more prolonged increase in both systemic & pulmonary vascular resistance.
- Non-pharmacological measures (e.g. rubbing up uterus, uterine sutures and intra-uterine balloon) to reduce bleeding should also be employed.
Caesarean delivery is performed for obstetric indications, but may be recommended for the patient in whom expulsive efforts would be detrimental. Regional anaesthesia is safe unless the patient is anticoagulated or has a fixed cardiac output state such as with left ventricular outflow obstruction. The sympathectomy that occurs with regional anaesthesia can lead to worsening hypoxemia in the presence of a right to left shunt. In most situations, a slow onset of regional block is useful. This may require the use of an epidural catheter rather than a spinal, which allows for the slower administration of local anaesthetic.
The blood pressure should be supported with the careful administration of vasoconstrictors and intravenous fluid. It is preferable to use alpha adrenoreceptor agonists to avoid a tachycardia in most situations.
General anaesthesia allows for controlled ventilation with 100% O2 (pulmonary vasodilatation), concomitant procedures (e.g. cardioversion) to be carried out, and less interference with anticoagulation therapy.
Cardiac stability is not guaranteed. Intravenous and volatile agents have negative ionotropic effects. Laryngoscopy will stimulate the sympathetic nervous system and blood loss is slightly greater with general anaesthesia.
There is no evidence to demonstrate superiority of one anaesthetic technique over another for caesarean delivery.
Mitral Stenosis is the most common lesion in pregnant rheumatic heart disease patients (90%). Symptoms develop when the valve area, which is normally 4-6 square centimetres, is below 2 square. centimetre. Severe mitral stenosis corresponds to a valve area less than one square centimetre. There is an increased maternal risk with severe disease and atrial fibrillation. The risk is further increased if pulmonary hypertension is present. The basic hemodynamic defect is obstruction to blood flow from the left atrium to the left ventricle to the left ventricle. Pregnancy results in increase in heart rate and blood volume. The increase in heart rate shortens diastole disproportionately reducing time for flow to occur resulting in a reduction in cardiac output and an increase in pulmonary capillary wedge pressure. With time, pulmonary hypertension develops leading to right ventricular hypertrophy and failure.
The management goals in mitral stenosis are to:
· Avoid rapid ventricular rates - treat atrial fibrillation
· Avoid large decrease in systemic vascular resistance and preload - lateral tilt
· Slowly titrated epidural analgesia / anaesthesia
· Avoid marked increases in blood volume – beware of autotransfusion with uterine contractions and at delivery
· Prevent increases in pulmonary artery pressure - oxygen supplementation.
HAEMORRHAGE
Maternal haemorrhage is a significant cause of maternal mortality worldwide. It may occur antepartum (APH), intrapartum or post partum (PPH). There is the potential for rapid massive blood loss that will require a swift response and rapid replacement of blood volume, as well as treatment of the cause.
Antepartum haemorrhage is most commonly due to placenta praevia or placental abruption. The incidence of low-lying placenta and placenta accreta is increased with previous caesarean section. Placental abruption is the premature separation of the placenta before birth. It is usually painful and there may not be any visible blood loss. Disseminated intravascular coagulation may occur, which will cause a coagulopathy. Regional anaesthesia can be considered for delivery after APH provided blood volume has been restored, there is good intravenous access and access to blood products and if haemorrhage is controlled and there is no coagulopathy.
Uterine rupture and vasa praevia are causes of intrapartum haemorrhage. Uterine rupture is more common if there has been a previous caesarean section or difficult delivery, or in the case of prolonged labour in association with excessive oxytocin stimulation. It presents with severe pain and maternal collapse and the foetal heartbeat may be lost. It has a high foetal and maternal mortality and early recognition is important to increase survival.
Postpartum haemorrhage occurs due to retained placenta, uterine atony, trauma to the birth canal and more rarely, uterine inversion. The retained placenta may be managed with manual exploration under a spinal or epidural block. It is important that blood volume be restored before the block is performed. General anaesthesia is performed in the unstable patient. A rapid sequence induction is performed to protect against maternal pulmonary aspiration.
Uterine atony may be treated with medications to stimulate uterine contraction such as oxytocin (given slowly to avoid severe hypotension), ergometrine and carbaprost (prostaglandin F2 alpha). Intrauterine balloons or arterial embolisation have been used to control PPH. If these measures fail, emergency hysterectomy or internal artery ligation may be required.
Management of major obstetric haemorrhage requires a co-ordinated response. The blood bank should be informed of the emergency, as large numbers of packed cells, and coagulation factors and platelets may be required. The general principles of management of massive blood loss should be applied. They include the maintenance of blood volume with crystalloids and colloids before blood is available, ensuring adequate oxygenation and ventilation, warming the patient, treatment of acidosis, monitoring of blood pressure, heart rate, saturation, ECG, temperature, urine output and measurement of blood loss. Regular assessment of laboratory investigations will be required, including full blood count, coagulation studies, electrolytes and acid base status.
NEWBORN RESUSCITATION
Approximately 5 to 10% of newborns require some degree of active resuscitation at delivery. More than 5 million neonatal deaths occur each year. 19% of these deaths are due to birth hypoxia. Effective neonatal resuscitation requires anticipation, preparation, evaluation and prompt initiation of appropriate techniques.
Personnel capable of initiating resuscitation should attend every delivery.
Evaluation of the neonate Assessment of the need for resuscitation should begin immediately after birth. All newborn need rapid assessment of their breathing, circulation, muscle tone, colour, and gestational age and for the presence of meconium in the amniotic fluid or on the skin.
Feeling the pulsations in the base of the umbilical cord or listening with a precordial stethoscope best assesses heart rate.
Normal newborn infants do not require suctioning. Suctioning of the baby, before delivery of the shoulders, makes no difference to the outcome of babies with meconium stained liquor. If the amniotic fluid contains thick meconium, and the infant has absent or depressed respirations, and decreased muscle tone, secretions obstructing the airway should be cleared immediately with wide bore suction under direct vision (laryngoscopy). Pharyngeal suction can cause laryngospasm, trauma to soft tissues, bradycardia and delay the onset of spontaneous respiration. Suction should be limited to no more than 5 seconds and no more than 5 cm from the lips in a term infant. The negative pressure should not exceed 100 mm Hg (13 kPa).
If meconium is seen in the amniotic fluid, the newborn’s mouth, nose and hypopharynx should be suctioned on delivery of the head. If the heart rate is less than 100 beats per minute or muscle tone is poor or respiration is absent or depressed, the trachea should be suctioned under direct laryngoscopy to remove meconium from the airway.
Resuscitation sequence
In the absence of meconium:
If the baby is breathing or crying and has good muscle tone, only routine care is required. This includes drying the baby, providing warmth, clearing the airway if required and assessing the breathing, colour and heart rate.
If the baby is not breathing or crying, or has poor muscle tone, dry and stimulate the baby, position the head and neck to open the airway and warm the baby, assess the breathing and heart rate. If the baby is breathing and the heart rate is over 100 beats per minute and beginning to look pink, provide routine care as outlined above and observe. If the heart rate is less than 100 beats per minute or there is inadequate breathing, give positive pressure ventilation until the heart rate is over 100 beats per minute and the infant is breathing.
If there is inadequate breathing and the heart rate is less than 60 beats per minute, assess the adequacy of ventilation and improve it if possible. If the heart rate does not increase, give chest compressions with positive pressure ventilation at a ratio of 3 compressions for every breath.
If the heart rate still does not increase over 60 beats per minute, reassess ventilation technique, give adrenaline and consider intravenous fluids.
Endotracheal intubation may be considered if breathing is inadequate or positive pressure ventilation with a facemask is not effective.
SELF-ASSESSMENT QUESTIONS
1. Outline the respiratory changes that occur with pregnancy and the significance to anaesthesia.
2. Why is a rapid sequence induction performed for a woman having a caesarean section under general anaesthesia?
3. What measures can be taken to reduce pulmonary aspiration for a woman in labour?
4. Discuss the physiology of labour pain.
5. What are the potential complications of spinal anaesthesia for caesarean section?
ASSIGNMENT
You are the director of anaesthesia in your obstetric hospital. Your colleagues and the obstetricians would like to provide regional analgesia for the women coming in for labour. What regional analgesia options are available to you? Discuss how you would develop a protocol for the monitoring of the mother and foetus during labour under regional anaesthesia. Discuss what you would like to monitor, how often, who will perform the monitoring and what parameters should be reported to the anaesthetist.
OBSTETRIC ANAESTHESIA CASE STUDIES
Case No 15.1. Pre eclampsia
Tungaa is having her first baby. She has a history of mild hypertension but is not on any medication for it. At her 34 week check t. The midwife has noticed that her blood pressure is 145/105 mmHg and Tungaa has been complaining of headache and peripheral oedema.
What are the diagnostic features of pre-eclampsia?
What are the options for blood pressure management and what blood pressure would be optimal?
Tungaa’s vision is becoming blurred. The obstetrician wants to commence magnesium sulphate. Describe how you would do this. What are the risks of magnesium administration? How should she be monitored?
What other management does Tungaa require?
The obstetrician decides that Tungaa will require caesarean delivery, as she is not suitable for induction of labour. Discuss how you should manage her pre eclampsia before delivery.
What anaesthetic would you choose for Tungaa? Justify your choice. Are there any special considerations with your choice of anaesthesia?
The next day, you are in the ward and are asked to attend Tungaa urgently as she appears to be having a seizure. What is your management?
Case No 15.2. Maternal haemorrhage
Enkhee has just delivered her 3rd baby and you are called to the obstetric ward to help manage a retained placenta. The midwife says there has been 700 ml of blood loss and that it is continuing. She needs an urgent manual removal of placenta.
Discuss how you will estimate blood loss and your immediate management of the situation.
What are the options for anaesthesia? Are there any advantages and disadvantages of each technique?
Enkhee continues to bleed after removal of the placenta. You have administered a spinal anaesthetic and she is now becoming restless. What is your immediate management?
After 15 minutes, Enkhee has lost a further 900 ml of blood. How will you manage the situation?
The surgeon has performed a hysterectomy, but says that there appears to be general ooze from the operative surfaces. How will you assess her and manage her apparent coagulopathy?
Case No 15.3. Labour analgesia
Ariuna is a 30-year-old primigravida who is seeking information about her options for pain relief in labour. She is currently 36 weeks pregnant and has no medical problems.
What are the options for labour analgesia for a healthy primigravida? Discuss the advantages and disadvantages of these techniques.
Ariuna is keen on regional analgesia. Are there any side effects and risks that you wish to discuss with Ariuna about regional analgesia for labour?
Outline how you would insert an epidural for analgesia for Ariuna?
Ariuna comes in to labour at 40 weeks at your hospital and you agree to insert an epidural for labour. Shortly after insertion of her epidural, she becomes unconscious. What are the potential causes? Outline your immediate management.
Case No 15.4. Neonatal resuscitation
You are in the labour ward when the midwife urgently requests your presence at the imminent delivery of a woman who is 42 weeks gestation. The midwife says she thinks the baby will require resuscitation and there is no neonatologist present.
What factors in the history and examination of athe woman would indicate that the neonate maywill require resuscitation?
What equipment do you consider you will need for newborn resuscitation?
The baby is delivered and is covered in meconium. He is floppy and not making any respiratory effort. What is your immediate response?
Case No15. 5. Anaesthesia for emergency caesarean section
Bayanaa is a 21 year old woman who has come in from the countryside in labour. She has had no antepartum care and her labour is obstructed. The obstetrician would like to perform a caesarean section.
How urgently should this caesarean section be performed? Are there any other factors that will make it more urgent?
What are the options for anaesthesia for Bayanaa? Outline the advantages and disadvantages of each?
You decide that you will perform a regional technique. Describe your technique.
What dermatome level will you aim for optimal anaesthesia for caesarean section?
What dose and type of local anaesthetic will you use? Are there any adjuncts you can add to improve the anaesthetic?
Bayanaa’s blood pressure has fallen to 90/50 mmHg and she is complaining of nausea shortly after you have performed the block. Discuss techniques of avoiding and managing hypotension secondary to spinal anaesthesia for caesarean section.