Acousto-Optic Cerebral Blood Flow Monitoring During Induction of Anesthesia in Humans.

Abstract

Past transcranial Doppler (TCD) studies have documented the effects of the sequence of anesthesia induction followed by intubation on cerebral blood flow (CBF) velocity. The purpose of this study was to determine whether acousto-optic CBF monitoring would detect changes in CBF which are known to occur with propofol and subsequent endotracheal intubation. Seventy-two patients scheduled for elective non-intracranial surgery were evaluated. A Cerox 3215F (Ornim Medical) acousto-optic CBF monitor was used. The acousto-optic transducers were applied bifrontally prior to induction. Baseline cerebral flow index (CFI) values were obtained for at least 2min prior to induction, set to a unitless value of 100. Subsequent relative changes in CFI from baseline were determined at the lowest value over 3min after propofol injection but before laryngoscopy; and the highest value over 5min after the start of laryngoscopy. CFI data were evaluated using Friedman's test. The median dose of propofol [interquartile range] given was 200mg [160-250]. CFI decreased to 84% of baseline after propofol and increased to 147% of baseline after endotracheal intubation (both p<0.001); MAP decreased after intravenous induction of anesthesia from 103±15 to 86±15mmHg (p<0.001) and then returned following endotracheal intubation to 104±20mmHg. Our data are congruent with previous observations made with TCD under similar experimental conditions. Such observations support the notion that acousto-optic monitoring yields valid real-time measures of changes in CBF in humans. Further validation against other quantitative measures of CBF would be appropriate.