gms | German Medical Science

Objective: Testing of the pupillary light reflex is probably the most commonly used neurological test on intensive care units when assessing unconcious patients. Although of utmost clinical importance, testing of the pupillary reflex has always been susceptible to subjective judgement of the investigator and performed using non-standardized penlights. In our age of high-tech medicine means to quantify and objectify the pupillary reflex seem to be a logical development.

Method: We tested the portable infrared monocular pupillometer NPi™-100 by NeurOptics^® in 47 patients on our neurosurgical ICU. The pupillometer measures pupil size, constriction and dilation velocity, constriction latency of which it calculates the Neurological Pupil index (NPi). The NPi ranges between 0 and 5: Values between 4 and 5 indicate normal, values between 0 and 3 pathological pupillary function. Measurements where made taking consideration of brain impairment (assessed with radiological or electroencephalic data), intracerebral pressure (ICP), narcotics and conventional pupillary testing.

Results: In isochoruous patients the NPi-values were normal even with severe brain impairment. When anisocoria was present NPi-values in general were lower ranging between 3 and 0. We observed deterioration of NPi-values of patients with anisocoria concomittant to clinical worsening. Both false-positive and false-negative results for conventional testing of pupillary reactivity compared to the pupillometer could be observed. The pupillometer was able to detect a pupillary reaction in patients with pronounced myosis due to high-dose opioid sedation when conventional testing did not show any reactivity at all.

Conclusions: The portable infrared NPi^TM-100 pupilometer is a useful resource-friendly tool to objectify commonly aquired data on a neurosurgical ICU. However further and systematic investigations have to be performed in the future to correlate NPi-values to other clinical parameters like ICP or P_tiO₂ and to radiographic changes in pathology. Development of binocular measurement of direct and indirect pupil reactivity seems to be useful in neurosurgical patients to establish infrared pupillometry as a standard procedure.