Photoplethysmography parameters in monitoring nociception during general anesthesia.

Background: Validated monitoring methods for evaluating the balance of nociception and anti-nociception (BNAN) are needed in general anesthesia. This study assessed six photoplethysmography (PPG) parameters, computed from finger photoplethysmographic waveforms in patients undergoing gynecological surgery under general anesthesia.

Methods: A total of 20 participants were included, each undergoing general anesthesia with propofol and remifentanil. The same concentration of remifentanil was maintained throughout the experiment, four different intensities of electrical stimulation were administered, and the patient's fingertip PPG was meticulously recorded. PPG data were preprocessed to extract six PPG morphological parameters, and photoplethysmographic amplitude (PPGA), pulse beat interval (PBI), and surgical pleth index (SPI). Receiver operating characteristic (ROC) curves and the Area Under the Curve (AUC) were constructed and calculated to accurately measure its ability to reflect the nociceptive stimulus state. The consistency of different phase parameters at different stimulus intensities was evaluated by calculating the prediction probabilities. All results were compared with those obtained using SPI, PPGA, and PBI.

Results: After stimulation, all parameters and SPI showed significant changes compared with those before stimulation (p = 0.000). The catacrotic phase parameters (AC and MHC) showed higher discrimination in adequate analgesia and congruence with electrical stimulation intensity than the overall phase parameters, PPGA, and anacrotic phase parameters (AC: AUC = 0.851, Pk = 0.800; MHC: AUC = 0.837, Pk = 0.792).

Conclusions: In this study, six PPG morphological parameters were proposed and observed for the first time to effectively distinguish the occurrence of nociception. Compared with the overall phase parameters, PPGA, and anacrotic phase parameters, catacrotic phase parameters were more capable of characterizing noxious stimuli and more consistent with changes in electrical stimulation intensity.

Trial registration: ChiCTR2200062228; Registered at http://clinicaltrials.gov on July 30, 2022.