Pupillometry in anesthesia and critical care

Pupil size reflects the balance between sympathetic and parasympathetic systems. Due to technological advances, accurate and repeated pupil size measurements are possible using infrared, video-recorded pupillometers. Two pupil size reflexes are assessed: the pupillary reflex dilation during noxious stimulation, and the pupil light reflex when the pupil is exposed to the light. The pupillary reflex dilation estimates the level of analgesia in response to a painful procedure or to a calibrated noxious stimulus, i.e., tetanic stimulus, in nonverbal patients. This might be of particular interest in optimizing the management of opioids in anaesthetized patients and in assessing pain levels in the intensive care unit. The pupil light reflex measurement is part of the routine monitoring for severely head-injured patients. The impact of pupillometry in this condition remains to be determined.