Hypotension in anaesthetized patients during aneurysm clipping: not as bad as expected?

Background: Patients with aneurysmal subarachnoid haemorrhage (SAH) often have disturbed autoregulation of cerebral blood flow. A reduction in systemic blood pressure during surgery may therefore lead to delayed cerebral ischaemia (DCI). To assess the incidence and severity of intra-operative hypotension, we performed a retrospective cohort study in 164 patients with recent SAH and surgical clipping of the aneurysm. Methods: Intra-operative hypotension was defined in three levels of severity, as a decrease in mean arterial pressure (Delta MAP) of more than 30%, 40% or 50% compared with the pre-operative pressure. For each patient the total amount of time with intra-operative hypotension was retrieved. Logistic regression analysis was performed to study the relation between intra-operative hypotension and the occurrence of DCI and poor outcome. Results: A period with Delta MAP > 30% occurred in 128 patients (78%) with a median duration of this period of 105 min (25-75 parts per thousand 50-171 min). Delta MAP > 40% occurred in 88 patients (54%) and Delta MAP > 50% occurred in 22 patients (13%). In univariate analysis, Delta MAP > 50% was associated with poor outcome. After adjusting for age and World Federation of Neurological Surgeons grade, the association with poor outcome was no longer statistically significant [odds ratio (OR) 1.018; 95% CI 0.996-1.041]. Conclusion: Hypotension during surgical clipping of intracranial aneurysms occurred frequently. In our study population of patients mostly in good clinical condition, hypotension was not confirmed as an independent risk factor for DCI or poor outcome. Anaesthesia may have had a cerebral protective effect.