RESPIRATORY SINUS ARRHYTHMIA - COMPARISON WITH EEG INDEXES DURING ISOFLURANE ANESTHESIA AT 0.65 AND 1.2 MAC

Respiratory sinus arrhythmia (RSA) is a cyclical variation in heart ra te during breathing, where the heart rate increases during inspiration and decreases during expiration. RSA and the electroencephalogram (EE G) were monitored in 10 patients undergoing elective surgery with isof lurane and nitrous oxide in oxygen anaesthesia after induction with pr opofol. All patients were subject to controlled ventilation and recove ry from competitive neuromuscular block was facilitated by neostigmine and glycopyrronium (seven patients) or atropine (three patients). Med ian and spectral edge (95%) frequencies of the raw EEG were derived of f-line. RSA and EEG indices were obtained during preinduction (baselin e), induction, incision, 0.65 and 1.2 MAC of isoflurane maintenance du ring surgery and recovery. Significant decreases in the level of RSA, median and spectral edge frequencies were observed during induction an d significant increases in all indices were observed at recovery in al l patients. Significant decreases in the median and spectral edge EEG frequencies occurred in patients treated with atropine both to counter act bradycardia after propofol induction and at antagonism of neuromus cular block (n = 3), compared with patients treated with glycopyrroniu m (n = 7). in contrast, the level of RSA did not decrease significantl y with atropine. it is concluded that measurements of RSA could form t he basis of a useful index of anaesthetic depth during isoflurane anae sthesia, even during the use of pharmacologically appropriate doses of atropine. However, any effects of atropine on the raw EEG and on indi ces derived from the EEG, should be characterized further so that thes e effects are not confused with changes in anaesthetic depth.