The pupillary dilation reflex to a nociceptive stimulus as a tool for analgesia management: A diagnostic study

More than 70% of patients demonstrate pain after endotracheal aspiration. Tools are needed to objectify the need for analgesia in non-communicative critically ill patients.

The objective of this study was to identify the lowest intensity electrical stimulus for detecting pain before daily care interventions.

Study of diagnostic tests to assess pupillometry to detect pain through the pupillary dilation response to noxious stimuli versus the Behavioural Pain Scale. Patients older than 18 years, under analgosedation, subjected to invasive ventilation, baseline Behavioural Pain Scale of 3, and Richmond Agitation-Sedation Scale between -1 and -4 were studied. We assessed the Behavioural Pain Scale and the pupillary dilation response to 10, 20, 30, and 40 mA stimuli. We studied the diagnostic performance based on sensitivity and specificity, negative predictive value, positive predictive value, and accuracy of the selected points after the different stimulations. AlgiScan® Pupillometer measured the pupillary dilation response. The presence of pain was considered as a Behavioural Pain Scale score of ≥4. Significance was defined as p <0.05.

Measurements were performed on 31 patients. In the 20 mA stimulus, we found an area under the curve of 0.85 (0.69-1.0). The cut-off point of pupillary dilation was 11.5%, with a sensitivity of 100% (34.2-100) and a specificity of 75.9% (57.9-87.8). This point had an accuracy of 77.4 (60.2-88.6) and a Youden's Index of 0.8.

Pupillary variation measurement during a 20 mA stimulus could help assess the need for analgesia before potentially painful interventions. Further studies are needed to confirm this.

Phase 1 of the project PUPIPAIN ClinicalTrials.gov Identifier: NCT04078113.