Changing practices in neuroanaesthesia

Control of carbon dioxide levels during neuroanaesthesia: current practice and an appraisal of our reliance upon capnography

With the widespread availability of capnography, many anaesthetists have swung away from formally verifying hypocapnia by intraoperative arterial blood gas analysis and, instead, have come to rely upon capnography as an acceptable and constant predictor of arterial CO2 tension (PaCO2) during neurosurgery. However, the nature of the arterial-end-tidal CO2 gradient is complex, and is frequently unexpectedly large, or even negative. The importance of close intraoperative CO2 control during neurosurgery--more specifically, routine hyperventilation, and our reliance upon capnography to guide intraoperative management--is reappraised. There is a growing appreciation of the adverse effects of hyperventilation and hypocarbia, especially upon abnormal or ischaemic brain, and it is clear that capnography alone cannot be used to confidently predict the true PaCO2 during neuroanaesthesia.

Cerebral arteriovenous malformations in children

The treatment of cerebral arteriovenous malformations (AVM) or vascular anomalies are challenging neurosurgical procedures for an anaesthetist. Large AVMs are uncommon in children. Only 18% of AVMs become symptomatic before the age of 15 yr. This series reviews the experience at this institution during the period of 1982 to 1992. The symptoms at the time of presentation are varied and include haemorrhage (50%), seizures and hydrocephalus (36%) or congestive cardiac failure (18%). Symptoms of congestive heart failure predominate in the newborn whilst neurological symptoms, such as stroke, seizures or hydrocephalus occur more commonly in infants and older children. Approximately one third of AVMs in childhood present acutely. Radiological investigations, e.g., CT scan, MRI and cerebral angiography are essential to identify the precise location of the lesion. Therapeutic intervention in the acute presentation may involve craniotomy for evacuation of haematoma and treatment of increased intracranial pressure (ICP). Control of seizures and congestive heart failure may take priority and allow time to plan the elective procedures of embolization and surgical excision of the AVM. Operative intervention is hazardous and peroperative complications can be expected in more than 50% of patients. The morbidity and mortality associated with cerebral AVM are high, especially in infants who present in the neonatal period with congestive cardiac failure. The overall mortality in this series was 20%. Children presenting with intracranial arteriovenous malformations require a multidisciplinary approach. The successful management of anaesthesia either for embolization or surgical resection necessitates an understanding of the disciplines of paediatric and neuroanaesthesia. Special care and specific attention to detail may contribute to reduce the high morbidity and mortality encountered in these compromised children.