RESPIRATORY SINUS ARRHYTHMIA - AN INDEX OF LIGHT ANESTHESIA

This study was designed to test if changes in the degree of respirator y sinus arrhythmia (RSA) can be used as an index of light anaesthesia. An on-line, real-time data logging system was used to record simultan eously the EEG and ECG waveforms from 10 patients undergoing routine s urgery using i.v. propofol (Diprivan) anaesthesia. The degree of RSA w as determined in real-time. The median frequency of the EEG was derive d off-line and correlated with the degree of RSA. Time series analysis was performed on the derived indices off-line. Significant changes in the degree of RSA occurred in response to changes in propofol infusio n in all patients; these changes corresponded also to changes in the m edian frequency of the EEG. Heart rate and ventilatory frequency are m easured routinely during surgery and it is suggested that on-line moni toring of RSA, derived from these standard signals, provides a more co nvenient and objective index of lightening anaesthesia than either EEG analysis or classical estimates of anaesthetic depth based on arteria l pressure or heart rate.