PERIOPERATIVE RISKS IN CEREBRAL ANEURYSM SURGERY

The perioperative complications associated with cerebral aneurysm surg ery require a specific anaesthetic management. Four major perioperativ e accidents are discussed in this review. The anaesthetic and surgical management in case of rebleeding subsequent to the re-rupture of the aneurysm is mainly prophylactic. It includes haemodynamic stability as surance, maintenance of mean arterial pressure (MAP) between 80-90 mmH g during stimulation of the patient such as endotracheal intubation, a pplication of the skull-pin head-holder, incision, and craniotomy. The aneurysmal transmural pressure should be adequately maintained by avo iding an aggressive decrease of intracranial pressure. Once the skull is open, the brain must be kept slack in order to decrease pressure un der the retractors and avoid the risks of stretching and tearing of th e adjacent vessels. If, despite these precautions, the aneurysm ruptur es again. MAP should be decreased to 60 mmHg and the brain rendered mo re slack, in order to allow direct clipping of the aneurysm, or tempor ary dipping of the adjacent vessels. The optimal agents in this situat ion are isoflurane (which decreases CMRO(2)), intravenous anaesthetic agents (inspite their negative inotropic effect, they may potentially protect the brain) and sodium nitroprusside. Vasospasm occurs usually between the 3rd and the 7th day after subarachnoid haemorrhage. it may be seen peroperatively. The optimal treatment, as well as prophylaxis , is moderate controlled hypertension (MAP > 100 mmHg), associated wit h hypervolaemia and haemodilution, the so-called triple H therapy, wit h strict control of the filling pressures. Other beneficial therapies are calcium antagonists (nimodipine and nicardipine), the removal of t he blood accumulated around the brain and in the cisternae, and possib ly local administration of papaverine. Abrupt MAP increases are contro lled in order to maintain adequate aneurysmal transmural pressure. Bet a-blockers, local anaesthetics administered locally or intravenously, a carefully titrated level of anaesthesia, a maintained volaemia play a protective role. Cerebral oedema is sometimes already present at the opening of the skull or may arise later, due to a high pressure under the retractors, to the surgical manipulations of the brain or to brai n ischaemia subsequent to temporary clipping. Its treatment is aggress ive, with intravenous agents, mannitol, deep hypocapnia and/or lumbar drainage. Prophylaxis, according to the ''brain homeostasis concept', is the preferred method to avoid these four peroperative accidents. It includes normal blood volume, normoglycaemia, moderate hypocapnia, no rmotension, soft manipulation of the brain and optimal brain relaxatio n.