Clinical Utility of an Automated Pupillometer in Patients with Acute Brain Lesion

Abstract

Objective: The purpose of this study was to evaluate the clinical utility and validity of using a pupillometer to assess patients with acute brain lesions.

Methods: Pupillary examinations using an automated pupillometer (NeurOptics®NPi™-100 Pupillometer) were performed every 4 hours and were simultaneously assessed using the Glasgow Coma Scale (GCS) and for intracranial pressure (ICP), from admission to discharge or expire in neuro-intensive care unit (NICU). Manual pupillary examinations were also recorded for comparison. By comparing these data, we evaluated the validity of using automated pupillometers to predict clinical outcomes.

Results: The mean values of the Neurologic Pupillary index (NPi) were different in the groups examined manually. The GCS correlated well with NPi values, especially in severe brain injury patients (GCS below 9). However, the NPi values were weakly correlated with intracranial pressure (ICP) when the ICP was lower than 30 cm H2O. The NPi value was not affected by age or intensity of illumination. In patients with a "poor" prognosis who had a Glasgow Outcome Scale (GOS) of 1 or 2, the mean initial NPi score was 0.88±1.68, whereas the value was 3.89±0.97 in patients with a "favorable" prognosis who had a GOS greater than 2 (p<0.001). For predicting clinical outcomes, the initial NPi value of 3.4 had the highest sensitivity and specificity.

Conclusion: An automated pupillometer can serve as a simple and useful tool for the accurate measurement of pupillary reactivity in patients with acute brain lesions.

Keywords: Light reflex; Neurologic Pupillary Index; Pupillometer.

Fig. 1. A : The shape of portable pupillometer. B : The display of pupillometer. MAX means the maximum pupil diameter before constriction. MIN means the pupil diameter at the peak of constriction. %CH means the percent of the change (MAX-MIN)/MAX. LAT means the latency and it represents the time of the onset of the constriction. CV, MCV means the average and the maximum constriction velocity. DV means the dilation velocity. The graph below the table depicts change of size of pupil according to change of time.

Fig. 2. The graph presents the mean value of the Neurologic Pupillary index (NPi) in four groups divided according to the Glasgow Coma Scale (GCS). The NPi value tends to decrease as the GCS decreases, especially in the "poor" clinical group with a GCS of 3 to 5.

Fig. 3. There is no relationship between NPi and ICP when ICP is lower than 30 cm H2O. However, the NPi value significantly decreased when ICP was higher than 30 cm H2O. NPi : Neurologic Pupillary index, ICP : intracranial pressure.

Fig. 4. The closer the curve to the left upper angular point, the more reliable the test becomes. This ROC curve shows the AUC of 0.92, and both sensitivity and specificity are optimal when the NPi cut-off value is 3.4 (starred dot). ROC : receiver operating characteristic, AUC : area under the curve, NPi : Neurologic Pupillary index.