Effect of isoflurane-induced hypotension on cerebral autoregulation in the anesthetized pig

The influence of isoflurane-induced hypotension on regional cerebral blood flow (rCBF) and cerebrovascular autoregulation was evaluated in 11 normocapnic pigs during anesthesia comprising fentanyl and nitrous oxide in oxygen. rCBF was determined as sagittal sinus outflow and recorded continuously by an electromagnetic technique. Regional cerebral metabolic rate for oxygen (rCMRO2) was calculated as rCBF multiplied by the arteriosagittal sinus oxygen content difference. Cerebral autoregulation was evaluated by two formal tests; blood pressure increase by infusion of angiotensin and blood pressure decrease by caval block. Light hypotension [mean arterial blood pressure (MABP) 94 +/- 3 mm Hg] and moderate hypotension (MABP 56 +/- 1 mm Hg) were achieved with the inspired concentrations of 1.7 +/- 0.2 and 2.7 +/- 0.2% isoflurane, respectively. rCBF was measured and the tests were performed before, during, and after isoflurane administration. Isoflurane produced no significant change in rCBF at either level of hypotension. At moderate hypotension the rCMRO2 was decreased by 40 +/- 6%. At both levels of hypotension, isoflurane produced a dose-dependent impairment of the auto-regulatory response to the angiotensin test as well as to the caval block. After hypotension, the autoregulatory response to increased blood pressure was restored within 15-25 min and to decreased blood pressures within 25-50 min.