Normalized Pulse Volume as a Superior Predictor of Respiration Recovery and Quantification of Nociception Anti-nociception Balance Compared to Opioid Effect Site Concentration: A Prospective, Observational Study

Abstract

Background Quantifying pain and the balance between nociception and anti-nociception (NANB) in sedated patients is challenging. Traditional opioid titration methods overlook individual differences, while existing indices like the Noxious Stimulation Response Index (NSRI) lack correlation with effect-site concentration (Ce). The Normalized Pulse Volume (NPV), used in polygraphs, has potential for pain quantification but is underexplored. This study aimed to assess NPV’s efficacy as a pain monitoring tool compared to Ce and to explore its potential in various clinical settings. Methods The study included 39 patients undergoing surgery under total intravenous anesthesia from July 2013 to May 2014. Selection criteria were an American Society of Anesthesiologists physical status classification system (ASA score) of 1 or 2 and surgeries with minimal fluid resuscitation or blood loss. Exclusion criteria were significant posture changes, massive hemorrhage, and high perfusion index variation. NPV and Ce were measured using the Masimo SET adult SpO2 sensor. Results Out of 39 patients, 9 were excluded. NPV at recovery of spontaneous respiration (RoR) was 2.62 (95% CI: 2.26–2.98) with a coefficient of variation (CoV) of 36.3%, while total Ce was 1.48 ng/ml (95% CI: 1.14–1.84) with a CoV of 62.4%. NPV showed a narrower CoV than Ce (p < 0.05, 1.93*10−5), indicating less variability. NPV outperformed Ce in predicting RoR, suggesting a more accurate reflection of NANB balance. Its superiority in stable measurement underlines its potential as a reliable pain indicator. The study’s limitations include temporal differences in NPV and Ce calculations, affecting comparative analysis. Conclusion NPV demonstrates promise as an objective, reliable indicator of pain or NANB, showing a strong correlation with Ce. Its application could improve pain assessments in clinical settings, optimizing patient care and analgesic administration. Future research should integrate NPV with other vital signs for a comprehensive pain monitoring system.