Changes in heart rate variability in sevoflurane and nitrous oxide anesthesia: effects of respiration and depth of anesthesia

Abstract

Study Objective: To quantify the effects of sevoflurane on autonomic nerve function by analyzing changes in heart rate (HR) variability in sevoflurane anesthesia; and to investigate the effects of anesthetic depth and apnea on HR variability. Design: Prospective study. Setting: Operating room (OR) of a university medical center. Patients: 7 ASA physical status I and II patients scheduled for elective surgery. Interventions: Patients were premedicated with ranitidine 150 mg. Anesthesia was induced with thiopental sodium 4 mg/kg intravenously (IV) and succinylcholine 1 mg/kg IV, and maintained with nitrous oxide (N 2 O) 67% and sevoflurane in oxygen. Patients were ventilated mechanically at a rate of 15 breaths/min. Measurements: R-R interval of electrocardiography (ECG), electroencephalogram (EEG), noninvasive arterial blood pressure (BP), and end-tidal sevoflurane concentration were recorded. Measurements were performed 1) after patients arrived at the OR and were placed in the supine position, 2) a stable period after inhalation of 2% sevoflurane, and 3) following the appearance of an isoelectric EEG at a higher concentration of sevoflurane. At times 2) and 3), data were recorded during mechanical ventilation and during apnea. Main Results: There were decreases in both the low-frequency (LF; 0.04 to 0.15 Hz) and high-frequency (HF; 0.15 to 0.4 Hz) components of HR variability during anesthesia compared with the awake state. HF decreased during apnea at 2% sevoflurane, but LF did not change. Neither LF nor HF changed in response to the absence or presence of respiration during isoelectric EEG. Conclusions: Autonomic nerve activity was attenuated by sevoflurane. Parasympathetic input to the heart by respiration was markedly suppressed following the appearance of isoelectric EEG.