Ketamine, not propofol, attenuates cerebrovascular response to carbon dioxide in humans with isoflurane anesthesia

Study Objectives: To investigate the effects of ketamine and propofol on the cerebrovascular response to carbon dioxide (CO2) in humans during isoflurane anesthesia. Design: Randomized clinical investigation. Settings: University hospital of a medical school. Patients: 30 ASA physical status I and II adult, elective surgical patients. Interventions and Measurements: With each patient given air/oxygen/isoflurane anesthesia, the flow velocity in the middle cerebral artel (Vmca) and pulsatitity index were measured using the transcranial Doppler method tinder hypocapnic [arterial CO2 tension (PaCO2) 28-32 mmHg], normocapnic (PaCO2 38-42 mmHg), and hypercapnic conditions (PaCO2 48-52 mmHg). PaCO2 was altered by supplementing the inspired gas with CO2 without changing the respiratory conditions. Patients were then randomly assigned to receive either ketamine 1 mg . kg(-1) or propofol (2 mg . kg(-1) followed by an infusion of 6-10 mg . kg(-1) . hr(-1)) (n = 15 for each drug), and the measurements were repeated. Main Results: Ketamine reduced both absolute and relative cerebrovascular reactivity to CO2 significantly [2.9 +/- 0.8 (control) vs. 2.6 +/- 1.0 (ketamine) cm . sec(-1) . mmHg(-1): p < 0.05; and 3.5 +/- 0.7 (control) vs. 2.8 +/- 0.9 (ketamine) % . mmHg(-1): p < 0.01, respectively]. However, ketamine did not reduce Vinca during hypercapnic conditions (117 +/- 29 cm . sec(-1)) compared with controls (120 +/- 28 cm . sec(-1)). Although propofol decreased Vmca during all conditions, it did not cause any change in either absolute or relative CO2 reactivity [2.5 +/- 0.8 (control) vs. 2.5 +/- 1.0 (propofol) cm . sec(-1) . mmHg(-1), and 3.3 +/- 1.3 (control) vs. 4.1 +/- 1.0 (propofol) % . mmHg(-1), respectively]. Conclusions: In humans given isoflurane anesthesia, a) ketamine reduced cerebrovascular response to CO2, but cerebral blood flow (CBF) during hypercapnic conditions was comparable with controls, and b) although propofol decreases CBF, it maintains the cerebrovascular response to CO2. (C) 2001 by Elsevier Science Inc.