Diagnostic Capability of Pupillary Dilation Reflex to Measure Pain In The Critical Analgosedated Patient

Abstract Background: Pain continues to be an underdiagnosed problem. Objective tools are needed for its assessment. The objective of this study was to determine the diagnostic performance, validity and reliability of the pupillary dilation reflex (PDR) against the Behavioural Pain Scale (BPS) to assess pain in patients under light-moderate sedation.Methods: A study of diagnostic tests using PDR versus BPS as a reference test was performed. The patients were recruited from the Intensive Care Units of the Araba University Hospital and were consecutively admitted. They were older than 18 years, under intravenous analgosedation, mechanically ventilated and had a BPS score of three and a Richmond Agitation and Sedation Scale (RASS) score between -1 and -4. The responses to a non-painful (NP) stimulus, 10 mA, 20 mA, 30 mA and 40 mA stimuli, and was assessed with the BPS and PDR. PDR measurements were performed with an Algican® pupilometer. Pain was considered to be present at BPS≥4. The receiver operating curve (ROC) was plotted, and the area under the curve (AUC) was calculated. We identified the cut-off points showing the highest sensitivity and specificity. Diagnostic performance was studied based on the Youden index, negative predictive value (NPV), positive predictive value (PPV), accuracy, positive likelihood ratio (PLR), and negative likelihood ratio (NPC) of each of them. They are presented with their 95% confidence intervals (CI). Results: Thirty-one patients were included and 183 measurements were performed. 49 (27%) measurements showed a painful response according to the BPS. We obtained an AUC of 0.885 (95% CI 0.830-0.940). The PDR value with the best diagnostic efficacy was 11.5%, which had a sensitivity of 89.8% (95% CI 78.2-95.6) and a specificity of 78.4% (95% CI 70.6-84.5) with an accuracy of 81.4 (75.2-86.4). The agreement between BPS and PDR had a kappa index of 0.6. Conclusions: Pupillometry could be a valid alternative for identifying pain in analgosedated critical patients. Trial registrationPhase 1 of the project PUPIPAIN ClinicalTrials.gov Identifier: NCT04078113