The Effect of Blood Pressure on Cerebral Perfusion During Vascular Surgery

Background: Induction of anesthesia reduces mean arterial pressure (MAP) and cerebral blood flow is normally considered to be maintained by cerebral autoregulation despite changes in MAP between 60 - 150 mmHg and standard of care during anesthesia is to maintain MAP above 60 mmHg. Vascular surgical patients are often elderly with hypertension and atherosclerotic manifestations that may impair cerebral autoregulation of importance for anesthesia-induced reduction in blood pressure.

Objective: To assess the effect of MAP for preservation of cerebral blood flow and oxygenation during vascular surgery.

Hypothesis: The primary hypothesis is that during general anesthesia in vascular surgical patients, cerebral blood flow velocity and oxygenation is higher with MAP maintained at 80-90 mmHg, compared with a MAP maintained at a minimum of 60 mmHg.

MAP is controlled in both groups using continuous infusion of phenylephrine. Phenylephrine is used as a tool in order to assess the effect of MAP on the cerebral circulation. In both groups, central blood volume is optimized by infusion of lactated Ringer´s solution using a goal directed fluid therapy following induction of anaesthesia and before commencement of phenylephrine infusion.

Trial size: The investigators will include 40 participants (2 x 20) in order to detect or reject a 20% difference in middle cerebral artery velocity with a type I error risk of 5% and a type II error risk of 20% (power at 80%). Interim analysis will be conducted after inclusion of 20 patients (2 x 10). Excluded patients will be replaced.