Correlation between BIS and layered behavior of heart rate in children under general anesthesia

ABSTRACT

BACKGROUND: The bispectral index (BIS) is based on changes in the electroencephalogram, and is commonly used to monitor depth of anesthesia. The central nervous system (CNS) controls heart rate variability (HRV). The purpose of this study was to examine the relationship between heart rate variability and changes in BIS. METHODS: We recruited 33 patients, aged 2-12 years. On arrival at the operating room, electrocardiograph (ECG), SpO2, noninvasive blood pressure, and BIS were monitored. After induction and intubation, patients were ventilated with sevoflurane in 35% oxygen in air. At a tidal volume of 7 ml/kg, the respiratory rate was adjusted to maintain an end-tidal CO2 of 35-40 mmHg. Inspired and expired end-tidal sevoflurane concentrations were held constant at 1.0 or 2.5 vol% for more than 10 minutes, after which ECG and BIS data were obtained for 15 minutes. Low-frequency power (LFP), highfrequency power (HFP), approximate entropy (ApEn), maximum layered behavior indices (MaxLI), and mean layered behavior indices (MeanLI) were calculated from the ECG. The relationship between mean BIS and variability indices at the two sevoflurane concentrations was measured by Pearson's correlation coefficient. RESULTS: MaxLI and MeanLI were positively correlated to BIS; whereas LFP, HFP, and ApEn were not. CONCLUSIONS: BIS and ECG indices are correlated during sevoflurane anesthesia in children, and thus ECG-derived indices could be used to monitor depth of anesthesia.