Assessment of pupil size and reactivity helps inform critical decisions about the care of patients with head trauma, cerebrovascular events and coma, and at end of life. Measurements are typically made by visual estimate, but inter-rater reliability can be poor. Factors such as dark eye color and obstacles like tubing can further reduce reliability.
“The impact of accurate versus slightly inaccurate serial measurement can be profound,” said Eli Zimmerman, M.D., an assistant professor in the Department of Neurology at Vanderbilt University Medical Center. “Pupillometry may allow for more urgent medical or surgical intervention in some of our sickest patients, particularly those with rising intracranial pressures that can result in permanent damage, like brain herniation.”
“Using the pupillometer to measure the more subtle changes in NPi is extremely helpful, because the NPi can change before pupil size does.”
Vanderbilt recently purchased twelve NeurOptics® pupillometers to take the guesswork out of these neurologic assessments. Neurology fellows Jennifer Burba, M.D., and Dennis Cole, M.D., developed the standard operating procedures (SOPs) for the use of pupillometers in the neurology ICU, the first unit at Vanderbilt to adopt them.
“Without pupillometry, measurements are non-specific. Now, instead of saying ‘The pupils are asymmetric,’ or ‘This pupil is not as reactive,’ we can quantify or verify what we are seeing,” Burba said.
Advantages of Automated Pupillometry
Manual checks with a penlight are still the standard method for pupillary evaluation. Burba says these subjective measurements are particularly prone to inter-rater error during shift change or when intubation, intravenous lines or other obstacles prevent a clear sightline to the patient’s eyes.
“Pupillometry may allow for more urgent medical or surgical intervention in some of our sickest patients.”
In contrast, the handheld automated pupillometer provides accurate and objective measurements of pupillary size, shape, and light reactivity. Measurements are expressed as the Neurological Pupil index (NPi), which can be recorded and tracked through the EHR.
Automated pupillary assessment has demonstrated high inter-rater reliability and superiority to manual assessment of pupil size and reactivity. For example, quantitative pupillometry outperformed manual measurements in comatose cardiac arrest patients, with significantly higher positive predictive value and specificity for unfavorable outcomes.
Zimmerman says advantages of automated pupillometry are particularly marked in challenging clinical situations such as sedation and pharmacologic paralysis. “Patients with large strokes who might need decompressive hemicraniectomy are often sleepy or even comatose, so there are limited components of a routine neurological exam that we can carry out,” he said.
In addition, automated pupillometry successfully identifies early changes in neurologic function, intracranial pressure, and treatment response to osmotherapy. “Using the pupillometer to measure the more subtle changes in NPi is extremely helpful, because the NPi can change before pupil size does,” Zimmerman explained.
The NPi has also been shown to be an effective indicator of neurological worsening in large hemispheric strokes and for early prognostication after venoarterial extracorporeal membrane oxygenation.
Indications for Use
At Vanderbilt, pupillometers are not replacing manual pupil examination altogether. The new SOP dictates the use of pupillometers for patients with intracranial injury or illness if they meet certain Glasgow Coma Scale scores, have an intracranial pressure monitor, or experience neurologic decline.
“Our SOP identifies the thresholds – for pupil size, differences between right versus left, and reactivity – at which the attending physician should be notified,” Burba said. In addition, the SOP indicates use of pupillometers for patients with pupils that are difficult to visualize.
The Vanderbilt team anticipates that more units will soon adopt pupillometers. “We were an obvious first choice to use them, but I foresee this being standard of care in trauma, ICU, NICU, the ED – any unit that treats critically ill patients with neurologic diseases,” Zimmerman said.