Cerebral blood flow and metabolism during isoflurane-induced hypotension in patients subjected to surgery for cerebral aneurysms

Abstract

Cerebral blood flow and cerebral metabolic rate for oxygen were measured during isofluraneinduced hypotension in 10 patients subjected to craniotomy for clipping of a cerebral aneurysm. Flow and metabolism were measured 5-13 days after the subarachnoid haemorrhage by a modification of the classical Kety-Schmidt technique using xenon-133 i.v. Anaesthesia was maintained with an inspired isoflurane concentration of 0.75% (plus 67% nitrous oxide in oxygen), during which CBF and CMRO2 were 34.3±2.1 ml/100 g min-1 and 2.32 ± 0.16 ml/100 g min-1 at PaCO2 4.1 ±0.1 kPa (mean ± SEM). Controlled hypotension to an average MAP of 50-55 mm Hg was induced by increasing the dose of isoflurane, and maintained at an inspired concentration of 2.2 ±0.2%. This resulted in a significant decrease in CMRO2 (to 1.73±0.16 ml/100 g min -1), while CBF was unchanged. After the clipping of the aneurysm the isoflurane concentration was reduced to 0.75%. There was a significant increase in CBF, although CMRO2 was unchanged, compared with pre-hypotensive values. These changes might offer protection to brain tissue during periods of induced hypotension. © 1987 British Journal of Anaesthesia.