Early detection of Postoperative Delirium and the Neurological Pupil Index (NPI) in the Postanesthesia Care Unit: a pilot study

Abstract

Abstract Background: Postoperative delirium (POD) is a common and serious complication that occurs after surgery, particularly in older adults. It is associated with prolonged hospital stays, functional decline and increased mortality. Traditional delirium assessments rely on subjective clinical observations, leading to under-recognition. Quantitative pupillometry has emerged as a potential tool for delirium detection, particularly using pupillary light reflex (PLR) measurements and the Neurological Pupil Index (NPi). Objective: This study aimed to examine the association between PLR metrics and NPi and postoperative delirium. Methods: A prospective observational study was conducted in a tertiary hospital. Adult patients undergoing elective surgery were evaluated upon postoperative anesthesia care unit (PACU) admission. Delirium was assessed using the Nursing Delirium Screening Scale (NuDESC). Pupillary measurements included NPi, pupil basal diameter, contraction percentage, latency, and contraction velocity. Statistical analysis included t-tests and ROC curves. Results: Among 50 patients (median age: 63.5 years, 54% female), 6% (3 patients) developed POD. NPi values were significantly lower in delirium patients (mean NPi left eye: 3.60, right eye: 3.43) compared to non-delirious patients (left: 4.38, right: 4.31), both with p-values <0.001. ROC analysis demonstrated strong predictive accuracy (AUC: 0.978 left eye, 0.993 right eye). Analysis of other pupillary light reflex parameters indicated that the minimum pupil size (MinL, MinR) and latency (LatL) also differed significantly between groups, with lower pupil constriction observed in delirium patients (MinL: p=0.006, MinR: p=0.011, LatL: p=0.041). Conclusion: Lower NPi scores at PACU admission were strongly associated with POD, highlighting pupillometry as a promising, non-invasive tool for early delirium detection. Future studies should explore its integration into routine postoperative care.