AUTOREGULATION OF HUMAN INNER-EAR BLOOD-FLOW DURING MIDDLE-EAR SURGERY WITH PROPOFOL OR ISOFLURANE ANESTHESIA DURING CONTROLLED HYPOTENSION

We used controlled hypotension to obtain a bloodless cavity during mid dle ear surgery under an optical microscope. No previous study has ass essed the effect of controlled hypotension on inner ear blood flow (IE F) autoregulation in humans receiving propofol or isoflurane anesthesi a. In the present study, the IEF autoregulation was determined using l aser Doppler flowmetry in combination with transient evoked otoacousti c emissions (TEOAEs) during controlled hypotension with sodium nitropr usside in 20 patients randomly anesthetized with propofol or isofluran e. A coefficient of IEF autoregulation (G(a)) was determined during co ntrolled hypotension, with a G(a) value ranging between 0 (no autoregu lation) and 1 (perfect autoregulation). During controlled hypotension with propofol, IEF remained stable (1% +/- 6%; P > 0.05) but decreased by 25% +/- 8% with isoflurane (P < 0.05). The G(a) was higher during propofol anesthesia (0.62 +/- 0.03) than during isoflurane anesthesia (0.22 +/- 0.03; P < 0.0001). Under propofol anesthesia, there were ind ividual relationships between TEOAE amplitude and change in IEF in fou r patients. Such a correlation was not observed under isoflurane anest hesia. These results suggest that human IEF is autoregulated in respon se to decreased systemic pressure. Furthermore, isoflurane has a great er propensity to decrease cochlear autoregulation and function than pr opofol. Implications: The present study shows that inner ear blood flo w is autoregulated under propofol, but not isoflurane, anesthesia duri ng controlled hypotension in humans during middle ear surgery. Further studies are needed to explore the postoperative auditory functional c onsequences of the choice of the anesthetic drug used in middle ear su rgery.