COMPARISON OF THE EFFECT OF ETOMIDATE AND DESFLURANE ON BRAIN-TISSUE GASES AND PH DURING PROLONGED MIDDLE CEREBRAL-ARTERY OCCLUSION

Background: The authors compared the effects of etomidate and desflura ne on brain tissue oxygen pressure (P-O2), carbon dioxide pressure (P- CO2), and pH in patients who had middle cerebral artery occlusion for >15 min. Methods: After a craniotomy, a probe that measures P-O2, P-CO 2, and pH was inserted into cortical tissue at risk for ischemia durin g middle cerebral artery occlusion. A burst suppression pattern of the electroencephalogram was induced with etomidate (n = 6) or 9% end-tid al desflurane (n = 6) started before middle cerebral artery occlusion. Mean blood pressure Was supported with phenylephrine to 90-95 mmHg. R esults: During baseline conditions, tissue P-O2, P-CO2, and pH were si milar between the two groups (P-O2 = 15 mmHg, P-CO2 = 60 mmHg, pH = 7. 1). During administration of etomidate before middle cerebral artery o cclusion, tissue P-O2 decreased in five of six patients without a chan ge in P-CO2 or pH. During administration of 9% desflurane, tissue P-O2 and pH increased before middle cerebral artery dipping. Middle cerebr al artery occlusion for an average of 33 min with etomidate and 37 min with desflurane produced a decrease in pH with etomidate (7.09 to 6.6 3, P < 0.05) but not With desflurane (7.12 to 7.15). Conclusion: These results suggest that tissue hypoxia and acidosis are often observed d uring etomidate treatment and middle cerebral artery occlusion. Treatm ent with desflurane significantly increases tissue P-O2 alone and atte nuates acidotic changes to prolonged middle cerebral artery occlusion.