Pupillometry: A loupe to mirror intracranial status during recovery after neurosurgery

Dear Editor,

Pupillometry is a useful bedside monitoring adjunct in the neuroanesthesia armamentarium with a wide spectrum of clinical applications in the perioperative period.[1] The quantification of pupillary responses such as pupillary constriction to light stimulus and pupillary dilatation to nociceptive stimuli using this automated device has enabled the assessment of important patient-related outcomes in the perioperative period. In addition to the assessment of depth of hypnosis[1] and perioperative pain,[2] it noninvasively mirrors the intracranial pressure (ICP) status.[3] The utility of this portable device continues to be explored, with a recent study highlighting its role in outcome prediction among patients affected by stroke.[4] We report an unexpected turn of events at the end of an apparently uneventful neurosurgical procedure where pupillometry assessment was a clinically useful adjunct to the management algorithm.

Atypical manifestations of intracranial pathologies can confound the differential diagnosis and delay the institution of the restorative treatment. We report a clinical scenario where inconclusive clinical signs eventually guided us to an underlying complication in a neurosurgical patient. A 12-year-old male child presented to us with a holo-cranial headache of 3 months’ duration. On clinical examination, the Glasgow Coma Scale (GCS) score was 15, with no focal neurological deficits and bilaterally equal, normal sized, and reactive pupils to light stimulus. Following a radiological diagnosis of a third ventricular lesion with caudate extension [Figure 1a], he had an uneventful intraoperative course during the planned elective left frontal parasagittal craniotomy and lesion resection under general anesthesia using balanced anesthesia technique with controlled mechanical ventilation. The histopathological diagnosis was pilocytic astrocytoma of the World Health Organization grade 1. At the end of a 6-h surgery, there was delayed awakening from anesthesia. The adequacy of neuromuscular blockade reversal and washout of anesthetic agents were ensured before the clinical evaluation for neurological deterioration. The delay in awakening was amidst the resumption of spontaneous respiration that was cyclically rhythmic with an apneic pause after every paired breath mimicking the Cheyne stokes pattern [Figure 1b]. This was interestingly accompanied by intermittent waxing and waning of consciousness, cessation, and resumption of spontaneous respiratory efforts and inconsistent motor response of GCS score (fluctuating between obeying commands to localization of pressure stimulus). Each of the three episodes lasted 5–10 min, spanning over 15–20 min with interspersed phases of apparent normalcy. Ocular examination revealed bilateral upward outward divergent pupils [Figure 1c] with an abnormal bilateral quantitative pupillometry index (QPi) of 2, suggesting an abnormal pupillary reactivity [Figure 1d and 1e]. We performed the pupillometry assessments once each during the three episodes of clinical deterioration. The patient was rushed for emergent brain computed tomography (CT) imaging, which unveiled a right temporoparietal skull pin-site extradural hematoma (EDH) [Figure 1f], whose emergent evacuation restored normal neurological status and ocular gaze.

Figure 1.

(a) Magnetic resonance imaging of the brain with an arrowhead pointing to the third ventricular lesion; (b) Capnography trace with an arrow indicating the characteristic cyclical respiratory pattern; (c) Ocular examination showing bilateral upward outward divergent pupils; (d and e) Pupillometry showing bilateral abnormal pupillary reactivity; (f) Computed tomography image of the brain with an arrow indicating the right temperoparietal extradural hematoma

Space-occupying intra-ventricular lesions can obstruct cerebrospinal fluid drainage, leading to chronically elevated ICP. Surgical decompression can cause an abrupt drop in ICP, which, in addition to the direct pressure by skull pins can predispose to intermediary vascular disruption and hence an EDH.[5] The resulting increased ICP presented as abnormal eye movement, unresponsive pupils, and distinctive breathing patterns during the recovery from anesthesia.[6] Subsequent imaging revealed the underlying hemorrhage, which was swiftly treated. The presentation of exotropia as a sign of increased ICP is reported in children with idiopathic intracranial hypertension and is related to bilateral dysfunction of the oculomotor nerve.[7] In addition to the direct evaluation of the presence of the constriction response to light, pupillometry quantifies the latency and magnitude of response and computes a single index termed the QPi. The pupillary reactivity is considered normal when the QPi is between 3 and 5. Any value below this indicates abnormal reactivity. The quantitative pupillometry index (QPi) and neurological pupillary index are both quantitative indices of pupillary reactivity.[8] The device used here was the Neurolight device™ that computes this index as QPi. The thresholds for clinical interpretation are the same for both. Pupillary dilatation to pain is used as a surrogate measure for responsiveness and hence for prognostication.[9] Here, the QPi was attenuated reflecting obtundation of these responses, hence correlating with other clinical findings in indicating an underlying pathology. In addition to QPi, the constriction velocity (CV) was 1.48 mm/s and 0.99 mm/s in the right and left eyes, respectively. The significance of CV is to determine the briskness of response to light. The normal values of CV are above 1.5 mm/s indicating a sluggish response in our patient.[10] Futhermore, another parameter of interest is the latency of pupillary constriction with a normal value of around 200 ms.[10] A latency of 284 ms additionally indicates a sluggish pupillary response.

In our case, the early use of pupillometry provided an adjunct and important information about the deranged intracranial dynamics. Pupillometry can serve as a quick reckoner to evaluate the ocular signs of the underlying ICP status during patient recovery from neurosurgical procedures. While a comprehensive neurological evaluation with careful attention to recovery patterns during anesthetic emergence are essential, the use of automated quantitative pupillometry in dubious clinical signs following neurosurgery certainly play a significant role in clinical practice.

Author contributions

SRP: conception and design of the report, acquisition and analysis of data, drafting of the manuscript; RM, AS, SKM: acquisition and analysis of data, revision of the manuscript.

Ethical policy and institutional review board statement

No ethical statement was required, since no data was acquired prospectively with the aim to perform a study. We hereby confirm that this study was performed in accordance with the ethical standards detailed in the Declaration of Helsinki.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Data availability statement

Data sharing is not applicable to this article as no datasets were generated and/or analyzed during the current study.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.