34. PRE-ECLAMPSIA

Pre-eclampsia is hypertension (greater than 140/90 mmHg), proteinuria (greater than 0.3 g/l/day) and oedema occurring after 20 weeks of pregnancy and usually resolving within 48 hours of delivery. It occurs in 1 to 4% of pregnancies. There is a greater risk of developing pre eclampsia if the mother has chonic renal failure, twin pregnancy, is over 40 years old, is diabetic or has a family history of pre-eclampsia.

Pre-eclampsia rarely occurs before the 20th week of pregnancy and is usually associated with hydatidiform mole, with multiple pregnancy or with foetal triploidy.

Patients who develop pre-eclampsia early in pregnancy pose problems for foetal viability and tend to exhibit more maternal features of pre-eclampsia.

Patients with pre-eclampsia may have other symptoms including hyperreflexia and low platelet count. Up to one third of patients have thombocytopenia. Severe pre-eclampsia can cause disseminated intravascular coagulopathy, pulmonary oedema, cardiac failure, renal failure, hepatic and splenic infarcts, cerebral haemorrhage, convulsions(eclampsia), the HELLP syndrome (Haemolysis, Elevated Liver enzymes, Low Platelets) and death.

Severe pre-eclampsia is a systolic blood pressure greater than 160 mmHg, or diastolic blood pressure greater than 110 mmHg or urine output less than 500 ml/24 h, or urine protein greater than 5 g/24 h with or without headache, visual disturbances and epigastric pain.

Management of Pre-eclampsia

The management of pre-eclampsia is to deliver the baby and treat the symptoms. Mild pre-eclampsia can be treated with oral anti-hypertensives such as labetolol or alpha methyldopa and bed rest so that the pregnancy can progress until the foetus is more mature.

Severe pre-eclampsia needs to be treated definitively with delivery of the baby and placenta. The mother’s condition must be stabilised so that the anaesthetic can be performed safely. This will involve controlling the blood pressure, ensuring adequate intravascular filling, checking that the coagulation is normal, and prevention of eclampsia. The mother’s blood pressure, urine output, conscious state and tendon reflexes must be frequently checked. Ideally the anaesthetist would arrange blood tests for liver function test, full blood count, serum magnesium level and clotting.

Hypertension

Hypertension should be treated with an intravenous anti-hypertensive such as hydralazine or labetolol. The aim is to keep the mean arterial pressure between 100 and 140 mmHg. It is important to maintain placental perfusion. Hydralazine can be given as bolus injections of 5 to 10 mg every 15 minutes or as an infusion of 2 to 4 mg/h.

Fluid Resuscitation

Pre-eclampsia causes a reduced intravascular volume and the mother will need intravenous fluid replacement. The anaesthetist must assess the severity of dehydration (is the patient thirsty, is the urine output less than 30 ml/h, is the tongue dry, is the central venous pressure low?). Intravenous fluid replacement should be guided by monitoring of the central venous pressure and urine output (with a urinary catheter). The patient should have at least 1ml/kg of urine output each hour. The central venous pressure should be 2 to 4 cmH2O. It is important not to give too much intravenous fluid as the patient may develop pulmonary oedema due to leaky capillaries. Most patients will need 1 litre of intravenous fluid rapidly followed by 1 litre over the next hour. If the urine output is still less than 30 ml/h the patient may need another 500 ml over half an hour until urine output is normal or the central venous pressure is greater than 4 cmH2O. If the central venous pressure is greater than 4 cmH2O and the urine output is still low, then the patient may need a diuretic such as frusemide.

Coagulopathy

Ideally the patient’s coagulation and platelet concentration should be tested. Pre eclampsia can cause a rapid fall in platelet count. Spinal and epidural anaesthesia should not be performed if the platelet count is less than 100,000.

Convulsion control

The anaesthetist must assess the risk of the patient having a convulsion. Hyper-reflexia, headache, visual changes and high blood pressure all indicate that the patient may fit. Giving an anti-epileptic drug such as diazepam or phenytoin may prevent convulsions. Magnesium sulphate is the best drug. It will cause vasodilatation and also cause central nervous system depression. Magnesium sulphate is given as an intravenous bolus of 2 to 4 g over 15 minutes, then as an intravenous infusion of 1 to 3 g/h. Ideally magnesium blood levels should be monitored. An alternative regimen (described by Lucas, Leveno & Cunningham in 1995) is to give 10 g of magnesium sulphate intramuscularly followed by 5 g intramuscularly every 4 hours until 24 hours post delivery. The aim is to maintain magnesium levels at 4 to 8 mEq/l (2 to 4 mmol/l). (Deep tendon reflexes diminish at 10 mEq/l or 5 mmol/l and respiratory paralysis and heart block occur at 15 mEq/l or 7.5 mmol/l. If blood magnesium levels cannot be monitored then the patient must have frequent observation of their tendon reflexes, respiratory rate and heart rate. If depression of reflexes occurs, stop the infusion until the reflexes return). Magnesium will also increase the patient’s sensitivity to depolarising and non-depolarising muscle relaxants. The anaesthetist will need to reduce the dose of muscle relaxants (to 30% of the predicted dose) if the patient needs a general anaesthetic. Calcium gluconate is the antidote for magnesium sulphate.

Diazepam is still widely used but magnesium sulphate is the preferred agent.

The anaesthetist may be required to provide labour analgesia, provide anaesthesia for caesarean section or be involved in the medical management of the pre-eclamptic patient. They must ensure that patient has been optimally treated prior to an anaesthetic.

If coagulation is normal, an epidural will provide good labour analgesia and help control the blood pressure.

Choice of Anaesthetic

The choice of anaesthetic technique for caesarean section will depend on the health of the mother, health of the foetus and the technical ability of the anaesthetist. (It is safer to use a familiar technique). General anaesthesia may avoid the hypotension that can occur with spinal anaesthesia and is safer with thombocytopenia, but pre-eclamptic patients may be very difficult to intubate. There may be severe oedema of the airway. The anaesthetist must assess the pre-eclamptic patient’s airway with extreme care and always be prepared for a difficult or impossible intubation. The anaesthetist must also be aware that the pre-eclamptic patient may have exaggerated cardiovascular responses (hypertension, tachycardia) to intubation and extubation.

Spinal/epidural anaesthesia should only be performed if the patient’s coagulation is normal. The platelet count should ideally be above 100,000. Spinal anaesthesia should not cause a severe drop in blood pressure if the patient’s blood pressure is controlled and they have had adequate fluid resuscitation.

Post Delivery Care

The anaesthetist must be aware that the patient remains at risk from pre-eclampsia for up to 48 hours after delivery. More than 50% of convulsions and pulmonary complications occur in the post partum period.