Measuring Pupillary Reflex Dilation in Critically Ill Pediatric Patients Using Infrared Pupillometry

Introduction: Assessing pain is difficult in critically ill, intubated, and sedated children. Clinical pain scoring scales are prone to subjectivity and interrater variability. Pupillary reflex dilation (PRD) is a sympathetically mediated reflex to pain and has been used to objectively assess pain, possibly avoiding these limitations. Our hypothesis was that PRD would correlate with pain in a longitudinal and practical fashion in a pediatric ICU (PICU).


Methods: This was a single-center, prospective observational study conducted in a tertiary PICU and pediatric cardiac ICU. Children 6 months-18 years of age who were orally intubated, mechanically ventilated, and continuously sedated with stable physiologic parameters were enrolled. Heart rate, blood pressure, clinical pain scoring using the rFLACC pain scale, and pupil measurements using a NeurOptics NPi-200 pupillometer (Irvine, CA) were obtained every 2 hours for up to 72 hours or until extubation. These measurements were repeated in between baseline measurements if a patient was in pain with a rFLACC score ≥ 4. The effect of pain on outcomes was evaluated using linear regression in a mixed model procedure with specification of AR(1) correlation structure for repeated measures.


Results: A total of 14 patients were enrolled from November 2022 – January 2023. Children with high pain scores (rFLACC ≥ 4) had statistically significant (p < 0.05) increased pupillary diameter (0.17 mm, 95% CI 0.01-0.33), neurologic pupil index (NPI) (0.14 points, 95% CI 0.05-0.24), dilation velocity after light stimulus (0.09 mm/s, 95% CI 0.02-0.17), heart rate (11.95 BPM, 95% CI 8.05-15.85), and blood pressure (11.24 mmHg, 95% CI 7.50-14.98) compared to their most recent baseline measurements. Average constriction velocity and maximal constriction velocity were not increased in patients with high pain scores.


Conclusions: This is the first study demonstrating PRD in a practical and longitudinal fashion in critically ill pediatric patients. NPI and dilation velocity after light stimulus were associated with high pain scores and may have applicability after future study to objectively assess pain in pediatric patients who are pharmacologically paralyzed.