The comparative effects of sevoflurane vs. isoflurane on cerebrovascular carbon dioxide reactivity in patients with hypertension

Background:  Sevoflurane has been shown to have different effects on cerebrovascular CO2 reactivity in comparison with isoflurane. In this study, the comparative effects of sevoflurane vs. isoflurane on cerebrovascular CO2 reactivity were examined in patients with hypertension. Methods:  Fifty patients, 30 hypertensive and 20 normotensive, were included in this study. The 30 hypertensive patients were divided into two groups: sevoflurane and isoflurane. Patients with controlled hypertension (n= 9 in each of the two groups) were those with normal blood pressure levels (systolic blood pressure below 139 mmHg). Patients with uncontrolled hypertension (n= 6 in each of the two groups) were those with high blood pressure levels despite medication (systolic blood pressure above 160 mmHg). Anesthesia was maintained with either 1.0 minimum alveolar concentration (MAC) of sevoflurane or 1.0 MAC of isoflurane in 33% oxygen and 67% nitrous oxide. A 2.5-MHz pulsed transcranial Doppler probe was attached to the patient’s head at the right temporal window for continuous measurement of the mean blood flow velocity in the middle cerebral artery (Vmca). After establishing baseline values of Vmca and cardiovascular hemodynamics, the end-tidal CO2 was increased by decreasing the ventilatory frequency by 2–5 breaths per minute. Results:  Values of the absolute and relative CO2 reactivity in the sevoflurane groups were lower than those in the isoflurane groups. There were no significant intra-group differences in the absolute and relative CO2 reactivity within the sevoflurane and isoflurane groups. Conclusions:  Our findings suggest that, in hypertensive patients, the control of cerebral blood flow by altering the pressure of arterial CO2 (Paco2) can be more effectively achieved during isoflurane rather than sevoflurane anesthesia.