The association between neurologic pupillary index (NPi) and functional outcomes in critically ill children

Automated pupillometry is a novel technology which can measure pupillary dynamics objectively at the bedside in critically ill patients. The Neurologic Pupil Index (NPi), a composite metric derived from pupillary reactivity parameters, has been proposed as a more objective measure of pupillary function and a potential prognostic tool in neurocritical illness. We hypothesized that the minimum NPi (NPimin) measured in critically ill children would correlate with functional outcome at hospital discharge. This was a single-center retrospective observational cohort study of patients admitted to the pediatric intensive care unit (PICU) with primary brain injury or risk of secondary brain injury. The NPimin reported during the PICU admission was compared with measures of outcome. Unfavorable outcome was defined by death or a change in functional status scale (FSS) score of ≥ 3 points from baseline to hospital discharge, whereas favorable outcome was alive and change in FSS score < 3). Automated pupillometry data were extracted from one-hundred and six patients, 77 (72.6%) of whom had a primary neurologic diagnosis and 25.5% of whom died. The NPimin was significantly lower in children who experienced an unfavorable outcome compared to those with a favorable outcome (0.8 vs. 3.7; p < 0.001). Prognostic performance of NPimin for unfavorable outcome was assessed using logistic regression which demonstrated an area under the receiver operative curve (AUROC) of 0.82 and optimal NPimin threshold of ≤ 2.1. When patients with an NPimin of 0 were excluded, NPimin best predicted unfavorable outcome at a higher NPi threshold of ≤ 3.5 with an AUROC of 0.72. Minimum NPi values were strongly associated with functional outcome at hospital discharge in a single-center cohort of critically ill children. Further research may reveal a role for NPi as an objective bedside biomarker that could enhance pediatric-specific prognostic models.