Background: Evaluation of the nociception-anti-nociception balance during anesthesia is still challenging and routinely based on clinical criteria such as movement or vegetative response. Recently, the Analgesia Nociception Index (ANI) derived from heart rate variability and the Surgical Pleth Index (SPI) derived from photoplethysmographic signal were introduced for quantification of the analgesic component of anesthesia.
Methods: After obtaining informed consent, we studied twenty-four patients (ASA I-II) scheduled for elective surgery during induction of anesthesia with sevoflurane and a stepwise increase of remifentanil effect site concentrations. Insertion of a laryngeal mask, tetanic stimulations as well as tracheal intubation were studied as nociceptive events.
Results: A total of 120 events were analysed. Both ANI and SPI enabled consistent detection of nociceptive events by significant changes (∆). Further, ∆ANI and ∆SPI significantly indicated patient's movement after tetanic stimulation with a prediction probability of 0.74 and 0.84.
Conclusion: Non-invasive monitoring of ANI and SPI reflected nociceptive stimulation during sevoflurane-remifentanil anesthesia and therefore may indicate the nociception - anti-nociception balance. Whether guidance of anesthesia by these variables will improve anesthesia care during surgery needs to be further evaluated.