Dose effect of sevoflurane and isoflurane anesthetics on cortical blood flow during controlled hypotension in the pig.

Background: The ability of the brain to preserve adequate cerebral blood flow (CBF) during alterations in systemic perfusion pressure is of fundamental importance. At increasing concentrations, isoflurane and sevoflurane have been known to alter CBF, which may be disadvantageous for patients with increased intracranial pressure. The aim was to examine the effects of isoflurane and sevoflurane at increasing minimum alveolar concentrations (MAC) on CBF, during controlled hypotension.

Methods: We studied eight pigs during variations in perfusion pressure induced by caval block (100, 60, 50, and 40 mmHg) under normocapnia. CBF was measured locally in a defined area (4 x 5 measurement points covering 1 cm(2)) of the motor cortex using laser Doppler perfusion imaging. Physiological variables, assessed by analysis of arterial O(2) and CO(2), hemoglobin and hematocrit, were controlled. CBF was measured during propofol (10 mg x kg(-1)x h(-1)) and fentanyl (0.002 mg x kg(-1)x h(-1)) anesthesia, and then during anesthesia with either isoflurane or sevoflurane (given in random order) at increasing MAC (0.3-1.2). After a washout period, the measurements were repeated with the other gas.

Results: CBF was significantly higher in the cortex during normotensive (control) settings, MAP approximately 100 mmHg, compared with during hypotension (MAP 40-60 mmHg). Neither different anesthetic nor MAC or local measurement sites were found to influence CBF at any perfusion pressure.

Conclusion: In this experimental model, the effect of hypotension on CBF was not altered by the anesthetics used [isoflurane, sevoflurane (MAC 0.3-1.2) or propofol (10 mg x kg(-1)x h(-1))]. In this aspect (cortical tissue perspective), these volatile agents appear as suitable as propofol for neurosurgical anesthesia for patients at risk.