Assessment of surgical stress using heart rate and plethysmographic pulse wave amplitude variability

Abstract: Stress free anaesthesia can be providedwith timely and adequate administration of hypnotic and analgesic drugs. Our goal was to develop a measure for the surgical stress in a patient. 60 patients were anesthetized with propofol and remifentanil target controlled infusion with rocuronium paralysis. We recorded physiological parameter data and calculated off-line heart rate (RRI) and plethysmographic amplitude (PPGA) variability parameters. The beat-to-beat RRI and PPGA time series were investigated in different time scales. The original time series were normalized using histogram transformation, which reduces the inter-patient variability by adjusting the measured parameter values to the same fixed range and distribution in all patients. Sympathovagal ratio and estimates for the irregularity of the respiratory modulation were calculated synchronized to artificial ventilation. These parameters were regressed with the estimated severity of surgical stimulation, remifentanil effect site concentration, and their combination. The parameters were ranked according to the mean regression coefficient divided by the standard deviation over the patient dataset. The best performing parameters were the normalized RRI and PPGA, which are the promising candidates for a surgical stress index.