Analgesia, Anaesthesia and Pregnancy. 4th Ed. Róisín Monteiro

Chapter 127. Convulsions

Convulsions occurring ante-, peri- or postpartum are uncommon but important causes of collapse on the labour ward; they may herald significant maternal disease or reflect a transient disturbance, but in either case management must be prompt and appropriate. Although petit mal (absence seizures) and focal seizures may occur, they are less common in the maternity suite than grand mal (tonic-clonic seizures).

Problems and special considerations

The diagnosis may be uncertain if the event is not witnessed by an experienced observer - for example, a simple faint may be labelled as a ‘fit’. A history of a tonic-clonic seizure may not always be obtained. Furthermore, collapse from non-neurological causes may itself lead to convulsions if severe hypotension or hypoxaemia occurs.

Physiological effects include increased cerebral and whole-body oxygen requirements, with increased carbon dioxide production. Together with hypoventilation arising from airway obstruction and chest wall rigidity, this may result in hypoxaemia, acidosis, hypercapnia and increased sympathetic activity. These effects may be exacerbated by the increased cardiac output and metabolic requirements of the pregnant woman compared with the non-pregnant one.

Convulsions in pregnancy may be more likely to lead to stroke than in the non-pregnant state. Aortocaval compression further exacerbates the situation before delivery. If inadequately treated, convulsions may merge into each other without breaks in between (status epilepticus).

As for collapse generally, the labour ward staff may be less familiar with emergency equipment and drugs than staff elsewhere. Although most of the possible causes of convulsions are the same as outside of the maternity suite (Table 127.1), the emphasis is different in this setting.

Management options

Initial management includes avoidance of aortocaval compression, protection of the airway (remembering the risk of aspiration) and support of ventilation and circulation.

The differential diagnosis (Table 127.1) is usually one of exclusion; the initial task is to distinguish between a primary convulsion and one resulting from hypoxaemia and/or cardiovascular collapse, hence the importance of a careful history from the patient and observer(s). Since eclampsia is such an important and relatively common cause in the peripartum period, it should be assumed until proven otherwise. Although ‘pre-eclampsia screening’ investigations are commonly performed, eclampsia may precede other evidence

Table 127.1 Causes of convulsions on the labour ward

Neurological disease

Pre-existing epilepsy

Stroke

Cerebral venous thrombosis

Infection

Migraine

Posterior reversible encephalopathy syndrome Reversible cerebral vasoconstriction syndrome Incidental disease, e.g. tumours

Hypoxaemia

Cardiovascular collapse, e.g. haemorrhage Pulmonary embolus

Obstetric

Eclampsia

Amniotic fluid embolism

Metabolic

Hypoglycaemia

Hypocalcaemia

Hyponatraemia a

Uraemia

Autoimmune

Thrombotic thrombocytopenia purpura

Drugs

Anaesthetic, e.g. local anaesthetics

Others, e.g. intoxication, overdoses, acute withdrawal (including alcohol)

Other

Psychogenic non-epileptic seizures

a Hyponatraemia is especially important in the delivery suite, where it may follow prolonged infusion of oxytocin diluted in dextrose solutions.

of pre-eclampsia. A thorough neurological examination should be performed and baseline laboratory investigations and a toxicology screen should be done. A computerised tomography (CT) or magnetic resonance imaging (MRI) scan of the head is generally advised unless a clear history of epilepsy is obtained or the picture is consistent with eclampsia in pregnancy. Blood gas analysis may be useful in guiding management but not in the differential diagnosis; it may reveal marked metabolic and respiratory acidosis resulting from the seizure itself, although this may also represent cardiorespiratory collapse preceding the convulsion. Hypoxaemia may be apparent if aspiration has occurred. Further investigations are guided by the results of preliminary testing and the clinical course.

Drug treatment is with standard anticonvulsant drugs (e.g. diazepam 5-10 mg boluses intravenously; phenytoin 10-15 mg/kg slowly intravenously, preferably with electrocardiographic monitoring), although magnesium sulfate has been shown to be more effective in preventing recurrent eclamptic seizures and should be the first choice unless eclampsia can be excluded. Thiopental, tracheal intubation and controlled ventilation may be required if convulsions are severe and continuous; however, this does prevent further neurological assessment.

Prolonged seizures may cause fetal hypoxia, and fetal monitoring should not be forgotten. Once control of the convulsion has been achieved and the mother is stabilised, delivery should be considered, depending on the aetiology of the convulsions, the gestation and the state of the mother and fetus. In eclampsia, delivery is usually expedited as soon as the stability of the mother allows.

Key points

• Convulsions on the labour ward should be considered as eclampsia until proven otherwise, although other causes should not be overlooked.

• Immediate management is with support of the airway, breathing and circulation, and avoidance of aortocaval compression; magnesium sulfate is the treatment of choice in eclampsia to prevent further convulsions.

• Continuous fetal monitoring is essential.

Further reading

Hart LA, Sibai BM. Seizures in pregnancy: epilepsy, eclampsia and stroke. Semin Perinatal 2013; 37: 207-24.



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