The Index For Monitoring Nociception Based On The Modality Of Photoplethysmogram

The monitoring nociception is important in general anaesthesia, Photoplethysmographic pulse wave (PPG) has been explored for monitoring nociception since several years ago. Several parameters has been extracted from PPG and normalized to develop monitoring indices for nociception, like Surgical Stress Index (SSI) and Response Index of Nociception (RN). However, these indices are mainly composed of parameters of PPG magnitude, which can be easily influenced by measuring conditions. The normalization method also has intrinsic drawbacks. On the other hand, modality of PPG is without these drawbacks.Therefore, the aim of this thesis was to extract parameters from the modality of PPG and develop an index named Surgical Pleth Modal Index (SPMI) for monitoring nociception. The following are innovation and main parts of the thesis.(1) Detection algorithm for critical points in PPG.A detection algorithm was proposed, which used a searching window and combined the first-order, second-order derivatives and rule-based logic. The estimation of the algorithm show that when detecting signal containing artifacts, both sensitivity and positive predictivity of the algorithm were above 95%. The result proved the validation of the algorithm.(2) The study on specificity and sensitivity of the PPG magnitude and modality.According to the theory of Windkessel model, Decay time constant of descending limb (QRC), area ratio of descending limb (ARD), area ratio of ascending limb (ARA), area ratio of a total period (ART) and pulse beat interval (PBI) were proposed as modal parameters. PPG magnitude (PPGA), a magnitude parameter, was also studied.In specificity study, relative variations of PPGA and ART were compared when blood perfusion, measuring position and body posture changed. Taking the two parameters as examples, the less variation of ART indicated that the modality of PPG was less influenced by measuring condition and more specific to nociception.In sensitivity study, nociception was induced by tracheal intubation, and its different levels were achieved by different anti-nociception concentrations of remifentanil. The prediction probability was adopted to compare the sensitivity of all the parameters. When predicting intubation, the order of sensitivity according to prediction probability was PBI>ART>PPGA>ARD>ARA>QRC. The differences of performance between magnitude parameter and modal parameters were not obvious. When predicting nociception of different levels, the order of sensitivity was PBI> ART>ARA>ARD>QRC>PPGA. The performances of all the modal parameters were better than the magnitude parameter.(3) The development of Surgical Pleth Modal IndexWith multi-parametric approaches and multiple linear regression, SPMI was developed as SPMI=30-43×PBI+45×ART. The Spearman coefficients between SPMI and the remifentanil concentration before and during intubation was-0.30 and-0.52, respectively. Both were higher than SSI (-0.21). The prediction probability of SPMI predicting CSSA was 0.819, higher than 0.78 of RN.In conclusion, this thesis dedicated to meet the utmost challenge of nociception monitoring. SPMI was proposed and based on the modality of PPG. The performance of SPMI was better than SSI and RN. SPMI would monitor nociception and guide anesthesia in a better way.