Purpose

To provide guidelines for the use of automated pupillometer in critical care patients with intracranial injuries. This guideline incorporates recent literature defining threshold parameters of normal versus abnormal in order to clarify when nursing staff should contact the primary team for re-evaluation. These guidelines are not a substitute for clinical judgment, but rather an approved multidisciplinary approach to optimize this clinical tool to identify neurologic worsening early while avoiding unnecessary alarms for the primary team.

This guideline applies to all patients for whom there is an intracranial neurologic injury with risk of decompensation per primary team.

Background

The pupillary light reflex (PLR) has long been a clinical sign used to prognosticate and monitor brain injured patients. This neuronal circuit transverses the mid-brain and localizes to optic nerve, and oculomotor nerve and also receives blood supply from both anterior and posterior circulation1. Thus, there is interest in using this circuit to both monitor for early brainstem compression from mass lesions,2 and also to identify alterations in circulation from processes such as delayed cerebral ischemia post subarachnoid hemorrhage3 or increased intracranial pressure4,5. A basic neurologic examination includes evaluating the PLR and reporting size and reactivity, however these measurements are very subjective and suffer from poor inter-rater reliability6,7. With the advent of automated pupillometry, objective measures of the PLR can be reliably obtained with very high inter-rater and inter-device reliability8 in civilian9 and military10 populations.

Beyond pupil size and reactivity, multiple metrics (pupil minimum / maximum size, percentage change of pupil, latency, constriction velocity, maximum constriction velocity, dilatation velocity) can be gathered and compared to normative standards. A commonly employed device is the NPi-200 Pupillometer, manufactured by NeuroOptics (Laguna Hills, CA). This device, in addition to gathering the above data, compares the gathered data to established normal values to create a Neurologic Pupillary Index (NPi) score which ranges from 0-5. NPi values < 3.0 reflect an abnormal PLR5. The presence of a decreased constriction velocity (CV < 0.8 mm/s) is also strongly correlated (but independent) to an abnormal NPi as well as independently associated with elevated intracranial pressure11. Developing an understanding of NPi and CV may provide early insight to neurologic deterioration12.

Because of the rather large anatomic localization of the PLR and the ability to monitor the reactivity of this network reliably and accurately, it has been hypothesized that PLR can be used clinically to follow patients at risk for neurologic decline as a component to a regular neurologic examination. NPi values have been correlated with intracranial pressure as well as mass lesions with brainstem / cranial nerve compression2,11. However, more importantly, there is now evidence that changes in the NPi preempts clinical decline.

- In a case series of patients with transtentorial herniation, PLR changes preceded neurologic deterioration by more than 7 hours in half of the subjects13.
- In a cohort of 56 patients who were admitted to Neurologic Intensive Care Unit with subarachnoid hemorrhage, 7 of 12 patients who developed delayed cerebral ischemia had NPi changes with 71.4% of these changes occurring 8 hours prior to clinical deterioration3.
- In a cohort of 134 patients who had intracranial pressure monitoring and were evaluated with serial pupillometry, those subjects with abnormal NPi (< 3.0) had significantly higher peak ICPs (19.6 vs 30.5 mmHg). On average, the transition to an abnormal NPi occurred 15.9 hours prior to peak ICP5.

RECOMMENDATIONS

1. For all patients at risk for neurologic decline from progression of intracranial lesion (traumatic brain injury, intracranial hemorrhage, intracranial mass lesions, vasospasm, hydrocephalus, etc.) pupillometry should be included and recorded with scheduled nursing neurologic examination.
2. If patient’s pupillometry values meet any one of the below criteria, the neurosurgeon should be called to evaluate:
   - NPi drops from > 3 to < 3.
   - NPi decreases from previous exam > 1.0.
   - A new difference in NPi (left eye vs right eye) is >1.0.
3. If above thresholds met, then evaluation should include:
   - Review of vitals, inputs/outputs, current medications/drips
   - Repeat full neurologic examination (GCS, cranial nerves, language, visual fields, motor exam).
   - Contact Neurosurgeon on call.
   - If deemed appropriate by the Surgical Trauma Intensive Care Unit and Neurosurgery repeat CT head (discussion with Neurosurgery if CTA of head and/or neck also indicated).
   - Review and readdresses goals of neuroprotective measures (intracranial pressure, cerebral perfusion pressure, temperature, serum sodium, etc.).

REFERENCES

1. Cahill M, Bannigan J, Eustace P. Anatomy of the extraneural blood supply to the intracranial oculomotor nerve. Br J Ophthalmol, 1996. 80(2): p. 177-81.
2. Chen JW, Vakil-Gilani K, Williamson KL, Cecil S. Infrared pupillometry, the neurological pupil index and unilateral pupillary dilation after traumatic brain injury: implications for treatment paradigms. Springerplus, 2014. 3: p. 548.
3. Aoun SG, Stutzman SE, Vo PN, El Ahmadieh TY, et al. Detection of delayed cerebral ischemia using objective pupillometry in patients with aneurysmal subarachnoid hemorrhage. J Neurosurg, 2019: p. 1-6.
4. McNett M, Moran C, Grimm D, Gianakis A. Pupillometry trends in the setting of increased intracranial pressure. J Neurosci Nurs, 2018. 50(6): p. 357-361.
5. Chen JW, Gombart ZJ, Rogers S, Gardiner SK, Cecil S, Bullock RM. Pupillary reactivity as an early indicator of increased intracranial pressure: the introduction of the neurological pupil index. Surg Neurol Int, 2011. 2: p. 82.
6. Kerr RG, Bacon AM, Baker LL, Gehrke JS, Hahn KD, Lillegraven CL, Renner CH, Spilman SK. Underestimation of pupil size by critical care and neurosurgical nurses. Am J Crit Care, 2016. 25(3): p. 213-9.
7. Olson DM, Stutzman S, Saju C, Wilson M, Zhao W, Aiyagari V. Interrater reliability of pupillary assessments. Neurocritical care, 2016. 24(2): p. 251-257.
8. Zhao W, Stutzman S, DaiWai O, Saju C, Wilson M, Aiyagari V. Inter-device reliability of the NPi-100 pupillometer. J Clin Neurosci, 2016. 33: p. 79-82.
9. Lee MH, Mitra B, Pui JK, Fitzgerald M. The use and uptake of pupillometers in the intensive care unit. Aust Crit Care, 2018. 31(4): p. 199-203.
10. Mease, L., R. Sikka, R. Rhees. Pupillometer use: validation for use in military and occupational medical surveillance and response to organophosphate and chemical warfare agent exposure. Mil Med, 2018.
11. McNett M, Moran C, Janki C, Gianakis A. Correlations between hourly pupillometer readings and intracranial pressure values. J Neurosci Nurs, 2017. 49(4): p. 229-234.
12. Shoyombo I, Aiyagari V, Stutzman S, Atem F. Understanding the relationship between the neurologic pupil index and constriction velocity values. Scientific Reports, 2018. 8(1): p. 6992.
13. Papangelou A, Zink EK, Chang WW, et al. Automated pupillometry and detection of clinical transtentorial brain herniation: a case series. Mil Med, 2018. 183(1-2): p. e113-e121.