Frontal lobe oxygenation is maintained during hypotension following propofol-fentanyl anesthesia

Near-infrared spectroscopy (NIRS) assesses cerebral oxygen saturation (Sco2) as a balance between cerebral oxygen delivery and consumption. In 71 patients, we evaluated whether marked reduction in mean arterial pressure (MAP) during propofol-fentanyl anesthesia induction affects frontal lobe Sco2. The NIRS-determined arm muscle oxygenation (Smo2), heart rate (HR), and cardiac output (CO) were monitored, endtidal carbon dioxide tension was controlled at 3.5 to 4.5 kPa, and central blood volume was maintained. Before anesthesia, the median (range) MAP, HR, and CO were 93 mm Hg (61-126 mm Hg), 76 beats/min (50-96 beats/min), and 5.3 L/min (2.4-9.0 L/min), respectively, but immediately following intravenous administration of fentanyl and propofol, MAP decreased to 63 mm Hg (37-109 mm Hg), HR to 63 beats/min (40-103 beats/min), and CO to 4.1 L/min (7.9-70 L/min) (P < .05). When blood pressure decreased, the median (range) NIRS-determined Smo2 also decreased (73% [54%-94%] to 71% [52%-87%]), whereas Sco2 increased from 67% (46%-93%) to 74% (48%-95%) (P < .05), independent of age and gender. After anesthesia induction, variables recovered and remained at preanesthetic levels during surgery. The findings implicate that even an approximately 30% drop in MAP at the induction of anesthesia does not typically affect cerebral oxygenation.