Sevoflurane-Nitrous Oxide Anesthesia Attenuates the Heart Rate Response to Intravenous Isoproterenol Infusion

抄録

We studied the effects of sevoflurane-N2O anesthesia on isoproterenol-induced heart rate (HR) changes. Twenty-six patients (ASA class I, 23-46 y) were assigned to two groups. The control group (n=13) received no sevoflurane and no N2O. Patients in the sevoflurane-N2O group (n=13) received 5% sevoflurane and 67% N2O in oxygen. After tracheal intubation with rocuronium, anes- thesia was maintained with an end-tidal sevoflurane concentration of 1.5%, together with 67% N2O in oxygen. Mechanical ventilation was performed to maintain EtCO2 at 35 mmHg. After 15 min, all patients in both groups received intravenous isopro- terenol at incremental infusion rates (2.5, 5, 7.5, 10, 12.5, 15, 17.5, and 20 ng/kg/min for 2 min at each infusion rate), until HR increased by more than 20 beats/min from baseline values. At the end of each infusion period, hemodynamic data were collected. Though there were no significant differences bet- ween the groups with respect to age and sex distri- bution, basal HR (before isoproterenol infusion) was significantly higher in the sevoflurane group than the control group. The HR responses to isoprote- renol at 2.5, 5.0, and 7.5 ng/kg/min were attenuated in the sevoflurane-N2O group as compared to the control group (0 ± 2 vs. 2 ± 3, 3 ± 4 vs. 9 ± 4, and 6 ± 5 vs. 14 ± 4 beats/min, respectively; mean ± SD, P<0.05 between groups). During isoproterenol infusion at 17.5 ng/kg/min, HR increased by more than 20 beats/min in all patients in the control group, but only in 7 (54%) patients in the sevoflurane group (P＜0.0001). These results suggest that a higher isoproterenol infusion rate may be required for the treatment of bradycardia or heart block in patients under sevoflurane-N2O anesthesia as compared to awake patients.