Spectral analysis of heart rate variability during desflurane and isoflurane anaesthesia in patients undergoing arthroscopy

Background: We studied the effect of desflurane (DES) and isoflurane (ISO) on heart rate variability (HRV) using power spectral analysis (PSA) of PR-interval in 30 patients undergoing arthroscopy, prior to induction, during anaesthesia and up to 3 h of recovery. PSA can distinguish low-frequency (LF) component and respiratory sinus arrhythmia (RSA) that are known to reflect predominantly sympathetic and parasympathetic activity, respectively. Methods: After premedication with diclofenac and midazolam the anaesthesia was induced with propofol and maintained during spontaneous ventilation with either DES or ISO added to a mixture of nitrous oxide and oxygen. ECG and transthoracic impedance respirometer data were recorded. Power spectra were calculated with an autoregressive modelling method. Results: Total power (P-TOT) and individual power in two frequency bands of the HRV spectrum (P-LF, 0.05-0.15 Hz and P-RSA) decreased after induction of anaesthesia in both groups. At 60, 120 and 180 min of recovery the P-TOT was back to control-value in the DES group but remained reduced in the ISO group. Calculated as normalised units, the P-LF (nP(LF)) predominated over the P-RSA (nP(RSA)) during control situations and during recovery. The reverse was the case during maintenance of anaesthesia. Thirty minutes after induction and during surgical stress the ISO group showed higher heart rate compared to the DES group as well as compared to control. Conclusion: DES and ISO produced similar alterations in studied parameters during the maintenance of anaesthesia. The differences observed between the groups during recovery may indicate an early intact neural reflex control system among the subjects exposed to DES. These results suggest that DES and ISO reduce the total autonomic neural system activity and alter the balance between sympathetic and parasympathetic activities in a comparable way during maintenance of anaesthesia. A more rapid recovery phase among the subjects exposed to DES is linked to differences in pharmacokinetic properties of the inhalation agents.