Comparison of Three Normalization Methods in Monitoring Analgesic Depth with Photoplethysmographic Diastolic Interval

The purpose of the present study was to investigate the ability of three different normalization methods, namely root mean square (RMS) value, mean value, and maximum which referred to pulse beat interval (PBI), based on photoplethysmographic diastolic interval (DI) in response to laryngeal mask airway (LMA) insertion under various remifentanil concentrations during general anesthesia. Sixty patients were randomly allocated to one of the four groups to receive a possible remifentanil effect-compartment target concentration (Ce_remi) of 0, 1, 3, or 5 ng/ml, and an effect-compartment target controlled infusion of propofol to maintain the state entropy (SE) at 40~60. Three normalized measures DI_RMS, DI_Mean, and DIPBI were compared with the DI values without normalization. Before LMA insertion, only DI showed a considerable correlation with remifentanil concentrations. DI_RMS and DI_Mean performed better than DI in discriminating 'insufficient' concentrations (0 and 1 ng/ml) from 'sufficient' concentrations (3 and 5 ng/ml). DIRMS was superior to all other variables in grading analgesic depth after nociceptive event occurred with PK value of 0.836. These results demonstrate that the normalization using RMS value, compared to using mean value and maximum, seems to provide a more effective approach for signal pre-processing.