Heart rate is tightly controlled by brain. If activity of brain and electroencephalograph (EEG) are changed by anesthetics, electrocardiograph (ECG) might be changed. We investigated whether there is a correlation between EEG and ECG, ECG could replace EEG as a monitor for depth of anesthesia.

We recruited 50 patients, aged 2-8 years. Inspired and expired end-tidal sevoflurane concentrations were held constant at 1.0 or 2.5 vol%, after which ECG and EEG were obtained for 15 minutes. Total power (TP), low-frequency power (LFP), high-frequency power (HFP), approximate entropy (ApEn), and Hurst exponent (H) were calculated from the ECG. The relationship between EEG and ECG indices at the two sevoflurane concentrations was measured by Pearson's correlation coefficient.

As anesthesia deepened, ApEn, H of ECG and beta wave decreased and those of delta and theta increased in 4 channels. In FP2, changes of beta and theta wave were negatively correlated with ApEn and H of ECG (P < 0.05), and changes of delta wave was positively correlated with ApEn (P < 0.05) and H (P < 0.01). In F8, changes of beta and theta wave were negatively correlated with ApEn (P < 0.05) and only theta wave was negatively correlated with H (P < 0.05). In C4, change of delta wave was positively correlated with ApEn (P < 0.001) and H (P < 0.05).

EEG and ECG indices are correlated during sevoflurane anesthesia in children, and ECG-derived indices could possibly be used to monitor depth of anesthesia.