40. POST ANAESTHETIC CARE UNIT COMPLICATIONS

The incidence of post anaesthetic/surgery complications varies but has been estimated to occur in approximately 5% of patients. The most common complications are nausea and vomiting, hypotension, hypertension, arrhythmias, altered conscious state and respiratory depression. All patients should be observed in a post anaesthetic care unit till they are well enough to return to the ward.

CARDIOVASCULAR COMPLICATIONS

Hypotension

The accuracy of the blood pressure should be checked. In all cases the patient’s airway must be assessed and oxygen administered. Check the patient’s pulse. Bradycardia and tachycardia can cause hypotension. Obtain an ECG. Bradycardia may need up to 3 mg of atropine in 0.5 mg doses.

Raising the patient’s legs will improve venous return.

Hypovolaemia is the most common cause of hypotension in the PACU. Intravenous fluid (250 to 1000 ml) should be given whilst the anaesthetist reviews the patient’s history, anaesthetic and surgical history and examines the patient. Remember to check drains and dressings for blood loss. If the hypotension is not corrected by adequate volume replacement the anaesthetist must look for other causes of hypotension.

Other causes of hypotension include decreased vascular tone, decreased venous return due to mechanical forces and decreased myocardial activity.

There are several causes of decreased vascular tone including anaesthetic agents, spinal/epidural anaesthesia, anaphylaxis and infection. These patients need fluid replacement and drug treatment with alpha-receptor agonists such as metaraminol, epinephine (adrenaline) or norepinephine (noradrenaline).

Decreasing the force of contraction of the heart (decreased inotropy) will cause hypotension. There are many causes of decreased inotropy including myocardial ischaemia, myocardial infarction, arrhythmias, cardiac failure, drugs, infection and hypothyroidism. The anaesthetist must examine the patient for signs and symptoms and treat any cause. A 12 lead ECG and basic laboratory investigations may help in the diagnosis.

Mechanical causes of decreased venous return are unusual and include pneumothorax and pericardial tamponade. These patients will have signs of hypovolaemia (hypotension, tachycardia, dry mucous membranes, thirst, decreased urine output, decreased conscious state) and signs of obstruction to venous return (jugular vein distention, elevated central venous pressure, decreased breath and heart sounds). They also need volume replacement. The cause of the mechanical obstruction must be treated.

Hypertension

When hypertension occurs it is often caused by pain, hypercapnia, hypoxia, full urinary bladder or excessive intravenous fluid administration. Hypertension may also occur in patients with pre-existing hypertension especially if they have not received their usual anti-hypertensive medications.

The anaesthetist must check the accuracy of the blood pressure reading, administer oxygen, assess the patient’s airway, review the patient’s medical and surgical history and examine the patient.

Management aims at treating the cause and the hypertension. There are many drugs that are suitable for treating hypertension in the PACU including beta-adrenergic blockers, calcium channel blockers, hydralazine and nitrates.

Dysrhythmias

The causes of dysrhythmias include hypoxia, hypercarbia, pain, electrolyte imbalance (especially hypokalaemia), drugs acid-base imbalance and myocardial ischaemia.

The anaesthetist must assess the patient’s airway, give oxygen and check the patient’s blood pressure. Patients who are hypotensive, hypoxic or have signs of myocardial ischaemia need immediate treatment.

The most common dysrhythmias in PACU are sinus tachycardia, sinus bradycardia, premature ventricular beats, ventricular tachycardia and supraventricular tachycardia.

Sinus tachycardia may be caused by pain, hypoxia, hypercarbia, hypovolaemia, infection, cardiac failure or pulmonary embolism. The anaesthetist must treat the cause of the sinus tachycardia.

Sinus tachycardia can occur from a high spinal block, drugs and vagal stimulation. The anaesthetist should administer oxygen and check the blood pressure. Patients with bradycardia and hypotension need immediate treatment with atropine or adrenaline and intravenous fluid replacement depending on the severity.

Supraventricular tachycardia (SVT) has many causes including hypoxia, hypercarbia, acid base disturbances, electrolyte abnormalities, hyperthyroidism and valvular heart disease. The supraventricular tachycardia may arise from the sino-atrial node, atrium or atrio-ventricular node. The anaesthetist must assess the patient’s airway, administer oxygen and check the blood pressure. If the patient is not hypotensive the anaesthetist should try to diagnose the SVT. Diagnosis is made easier by slowing the ventricular rate (carotid body massage, adenosine 3 to 6 mg intravenously). If hypotension is severe the anaesthetist should give a vasopressor and consider immediate cardioversion. Atrial flutter can be treated with esmolol 10 mg intravenously, digoxin 0.25 mg intravenously or cardioversion 10 to 25 J if necessary. Atrial fibrillation can be treated with digoxin 0.5mg intravenously, verapamil 2.5 to 5 mg intravenously, esmolol 10mg intravenously or cardioversion 100 to 200 J. Re-entry tachycardia (including Wolff-Parkinson-White syndrome) can be treated with adenosine 3 to 6 mg intravenously or verapamil 2.5 to 5 mg intravenously up to a total of 20 mg. Avoid using calcium channel blocking drugs and beta blocking drugs together as they can cause severe hypotension.

Ventricular tachycardia has many causes including hypoxia, myocardial ischaemia, acidosis and hypokalaemia. The anaesthetist must assess the patient’s airway, administer oxygen and check the blood pressure. If the patient is hypotensive they need immediate cardioversion. Stable ventricular tachycardia can be treated with lignocaine 1.5 mg/kg intravenously, followed by an infusion at 1 to 4 mg/min.

Myocardial Ischaemia

The anaesthetist must correct any imbalance between myocardial oxygen demand and myocardial oxygen supply. Common causes include hypoxaemia, anaemia, tachycardia, hypotension and hypertension and must be treated.

RESPIRATORY COMPLICATIONS

The anaesthetist must assess the patient’s airway and establish a clear upper airway. The patient may need a “jaw thust”, oropharyngeal/nasopharyngeal airway, assisted mask ventilation or endotracheal intubation. Oxygen must be given. The anaesthetist should also check and treat the patient’s blood pressure and heart rate.

Hypoxaemia

General anaesthesia has several physiological effects that continue in the postoperative period that can cause hypoventilation and hypoxaemia. General anaesthesia causes a reduction in the functional residual capacity, inhibits hypoxic pulmonary vasoconstriction, inhibits hypoxic and hypercarbic ventilatory drive and decreases respiratory muscle strength.

Causes of hypoxaemia include pneumothorax, aspiration of gastric contents, bronchospasm, laryngospasm, upper airway obstruction, hypoventilation, pulmonary oedema and diffusion hypoxia.

Hypoxia must be excluded before giving a sedative to calm a patient. Sedatives (e.g. benzodiazepines) are rarely needed in recovery.

Hypoventilation

Decreased ventilatory drive or weak respiratory muscles can cause hypoventilation. Hypoventilation will cause hypoxia, hypercarbia and eventually, apnoea and myocardial ischaemia. The anaesthetist must assess the patient’s airway breathing and circulation. The anaesthetic history, medical history and examination of the patient may diagnose the cause.

Decreased ventilatory drive can be caused by anaesthetic agents (inhalation agents, narcotics, benzodiazepines). Naloxone will reverse hypoventilation due to opioids. Doses of 100 micrograms will treat the hypoventilation in 1 to 2 minutes and last 30 to 60 minutes. Naloxone has several side-effects including tachycardia, hypertension, pulmonary oedema and pain. Doses of flumazenil, 0.2 mg will reverse the hypoventilation caused by benzodiazepines.

Weak respiratory muscles may be from pre-existing respiratory disease or inadequate reversal of neuromuscular blockade. In most cases neuromuscular blockers should be reversed (neostigmine 2.5 mg plus atropine 1.2 mg). Neuromuscular blockade should be monitored during the operation with a peripheral nerve stimulator if available.

Clinical signs of inadequate reversal include hypoxia, shallow breathing, generalised twitching and patient distress. If adequately recovered from neuromuscular blocking drugs, the patient should be able to lift their head off the pillow for 5 seconds.

Upper Airway Obstruction

The anaesthetist must immediately treat upper airway obstruction and give oxygen. Patients will show signs of inadequate respiration, intercostal and suprasternal retraction and abnormal chest and abdominal movement. Patients may require a nasopharyngeal/oropharyngeal airway, assisted manual ventilation or endotracheal intubation.

Upper airway obstruction can be caused by incomplete recovery from anaesthesia, laryngospasm, foreign body or airway oedema.

The most common cause of upper airway obstruction is pharyngeal obstruction from a sagging tongue in the unconscious patient. This is most effectively treated by tilting the patient’s head backwards and moving the jaw forwards or moving the patient to a lateral position.

CENTRAL NERVOUS SYSTEM COMPLICATIONS

Failure to Regain Consciousness

The anaesthetist must check that the patient has a clear airway, is breathing and has an adequate blood pressure and heart rate. Oxygen should be given.

The most frequent cause of delayed awaking is the persistent effect of anaesthesia. The anaesthetist must assess the patient and anaesthetic history. Drugs such as naloxone and flumazenil will reverse some of the sedative effects of anaesthesia.

Other causes include decreased cerebral perfusion, hypoxaemia, metabolic causes such as hypoglycaemia, sepsis, severe hypothermia, hyponatraemia and other electrolyte, and acid base disturbances. Cerebrovascular accidents and raised intracranial pressure are rare causes of delayed awakening.

Emergence Delirium

Delirium is more common in the elderly and patients with a history of alcohol abuse and dementia but there are several other causes including hypoxaemia, acidosis, hypoglycaemia, sepsis, raised intracranial pressure, hyponatraemia and severe pain.

Postoperative Nausea and Vomiting

Postoperative nausea and vomiting (PONV) is common after surgery. Untreated, at least one third of patients who undergo surgery will have postoperative nausea and vomiting. Numerous pathophysical mechanisms are known to cause nausea and vomiting. Nausea and vomiting may be caused by visceral stimulation though dopamine and serotonin, by vestibular and central nervous system stimulation though histamine and acetylcholine, and by chemoreceptor trigger zone stimulation though dopamine and serotonin.

Volatile anaesthetics, nitrous oxide and opioids increase the incidence of PONV. Using multi-modal analgesia can reduce opioid doses. Intra-operative intravenous fluids can reduce postoperative nausea and vomiting.

4 mg of ondansetron (or a similar serotonin antagonist), 4 mg of dexamethasone, 1.25 mg of droperidol and total intravenous anaesthesia all reduce the relative risk of PONV to a similar extent (approximately 26 percent). These interventions all act independently of one another. Metoclopramide is probably ineffective prophylactically. Dexamethasone should be given at the start of anaesthesia. Because the relative risk reduction is similar the anaesthetist should choose the least expensive and safest option first.

Prevention of PONV will provide the greatest absolute risk reduction in patients with the greatest risk of PONV. The most important risk factors are female, non-smoker and a history of motion sickness and PONV and the use of postoperative opioids. Patients at high risk (3 or 4 risk factors) may benefit from a combination of interventions. Patients at moderate risk (2 risk factors) may benefit from a single intervention. Prophylaxis is rarely indicated for patients at low risk.

An antiemetic that has not been used prophylactically should be chosen for the treatment of PONV.

Postoperative Hypothermia and Shivering

Hypothermia causes shivering and increases metabolic rate, cardiac output and oxygen requirements (up to 500%). Patients who shiver should receive oxygen and be warmed. 25 to 50 mg of intravenous pethidine is usually effective for non-hypothermic shivering.