Automated Pupillometry as an Assessment Tool for Intracranial Hemodynamics in Septic Patients

Evaluating the utility of quantitative pupillometry in a neuro-critical care setting for the monitoring of intracranial pressure: A prospective cohort study

INTRODUCTION

Assessment of the pupillary light reflex (PLR) is key in intensive care monitoring of neurosurgical patients, particularly for monitoring intracranial pressure (ICP). Quantitative pupillometry using a handheld pupillometer is a reliable method for PLR assessment. However, many variables are derived from such devices. We therefore aimed to assess the performance of these variables at monitoring ICP.

METHODS

Sedated patients admitted to neurocritical care in a tertiary neurosurgical centre with invasive ICP monitoring were included. Hourly measurement of ICP, subjective pupillometry (SP) using a pen torch device, and quantitative pupillometry (QP) using a handheld pupillometer were performed.

RESULTS

561 paired ICP, SP and QP pupillary observations from nine patients were obtained (1122 total pupillary observations). SP and QP had a moderate concordance for pupillary size (κ=0.62). SP performed poorly at detecting pupillary size changes (sensitivity=24%). In 40 (3.6%) observations, SP failed to detect a pupillary response whereas QP did. Moderate correlations with ICP were detected for maximum constriction velocity (MCV), dilation velocity (DV), and percentage change in pupillary diameter (%C). Discriminatory ability at an ICP threshold of >22 mmHg was moderate for MCV (AUC=0.631), DV (AUC=0.616), %C (AUC=0.602), and pupillary maximum size (AUC=0.625).

CONCLUSION

QP is superior to SP at monitoring pupillary reactivity and changes to pupillary size. Although effect sizes were moderate to weak across assessed variables, our data indicates MCV and %C as the most sensitive variables for monitoring ICP. Further study is required to validate these findings and to establish normal range cut-offs for clinical use.

Neuromonitoring of Pediatric and Adult Extracorporeal Membrane Oxygenation Patients: The Importance of Continuous Bedside Tools in Driving Neuroprotective Clinical Care

Extracorporeal membrane oxygenation (ECMO) is a form of temporary cardiopulmonary bypass for patients with acute respiratory or cardiac failure refractory to conventional therapy. Its usage has become increasingly widespread and while reported survival after ECMO has increased in the past 25 years, the incidence of neurological injury has not declined, leading to the pressing question of how to improve time-to-detection and diagnosis of neurological injury. The neurological status of patients on ECMO is clinically difficult to evaluate due to multiple factors including illness, sedation, and pharmacological paralysis. Thus, increasing attention has been focused on developing tools and techniques to measure and monitor the brain of ECMO patients to identify dynamic risk factors and monitor patients' neurophysiological state as a function in time. Such tools may guide neuroprotective interventions and thus prevent or mitigate brain injury. Current means to continuously monitor and prevent neurological injury in ECMO patients are rather limited; most techniques provide indirect or postinsult recognition of irreversible brain injury. This review will explore the indications, advantages, and disadvantages of standard-of-care, emerging, and investigational technologies for neurological monitoring on ECMO, focusing on bedside techniques that provide continuous assessment of neurological health.

Application of Pupillometry in Neurocritical Patients

Pupillary light reflex (PLR) assessment is a crucial examination for evaluating brainstem function, particularly in patients with acute brain injury and neurosurgical conditions. The PLR is controlled by neural pathways modulated by both the sympathetic and parasympathetic nervous systems. Altered PLR is a strong predictor of adverse outcomes after traumatic and ischemic brain injuries. However, the assessment of PLR needs to take many factors into account since it can be modulated by various medications, alcohol consumption, and neurodegenerative diseases. The development of devices capable of measuring pupil size and assessing PLR quantitatively has revolutionized the non-invasive neurological examination. Automated pupillometry, which is more accurate and precise, is widely used in diverse clinical situations. This review presents our current understanding of the anatomical and physiological basis of the PLR and the application of automated pupillometry in managing neurocritical patients. We also discuss new technologies that are being developed, such as smartphone-based pupillometry devices, which are particularly beneficial in low-resource settings.