The Effect of Ambient Light Conditions on Quantitative Pupillometry

Machine learning approach for ambient-light-corrected parameters and the Pupil Reactivity (PuRe) score in smartphone-based pupillometry

Introduction

The pupillary light reflex (PLR) is the constriction of the pupil in response to light. The PLR in response to a pulse of light follows a complex waveform that can be characterized by several parameters. It is a sensitive marker of acute neurological deterioration, but is also sensitive to the background illumination in the environment in which it is measured. To detect a pathological change in the PLR, it is therefore necessary to separate the contributions of neuro-ophthalmic factors from ambient illumination. Illumination varies over several orders of magnitude and is difficult to control due to diurnal, seasonal, and location variations.

Methods and results

We assessed the sensitivity of seven PLR parameters to differences in ambient light, using a smartphone-based pupillometer (AI Pupillometer, Solvemed Inc.). Nine subjects underwent 345 measurements in ambient conditions ranging from complete darkness (<5 lx) to bright lighting (≲10,000 lx). Lighting most strongly affected the initial pupil size, constriction amplitude, and velocity. Nonlinear models were fitted to find the correction function that maximally stabilized PLR parameters across different ambient light levels. Next, we demonstrated that the lighting-corrected parameters still discriminated reactive from unreactive pupils. Ten patients underwent PLR testing in an ophthalmology outpatient clinic setting following the administration of tropicamide eye drops, which rendered the pupils unreactive. The parameters corrected for lighting were combined as predictors in a machine learning model to produce a scalar value, the Pupil Reactivity (PuRe) score, which quantifies Pupil Reactivity on a scale 0-5 (0, non-reactive pupil; 0-3, abnormal/"sluggish" response; 3-5, normal/brisk response). The score discriminated unreactive pupils with 100% accuracy and was stable under changes in ambient illumination across four orders of magnitude.

Discussion

This is the first time that a correction method has been proposed to effectively mitigate the confounding influence of ambient light on PLR measurements, which could improve the reliability of pupillometric parameters both in pre-hospital and inpatient care settings. In particular, the PuRe score offers a robust measure of Pupil Reactivity directly applicable to clinical practice. Importantly, the formulae behind the score are openly available for the benefit of the clinical research community.

Video versus ultrasound pupillometry for detecting increased pupillary diameters due to nociceptive stimuli: a prospective observational study

PURPOSE

Ultrasound pupillometry (UP) is a potential alternative to video pupillometry (VP) for assessing changes in patients' pupillary diameter (ΔPD) due to surgical nociception, but the reproducibility of UP and VP has been unclear. We evaluated the reproducibility of nociceptive ΔPD measured with both methods.

SUBJECTS AND METHODS

This prospective observational trial with 15 healthy volunteers aged ≥ 18 years was conducted at a Japanese teaching hospital. The ΔPD due to tetanic stimuli randomly applied at 10-60 mA was measured with VP and UP. The primary outcome was the correlation between the ΔPD measured with VP and that measured with UP. The secondary outcome was the agreement between the methods. We also evaluated ΔPD pattern changes due to the raised pain intensity in each method.

RESULTS

The noxious ΔPD values of UP were weakly but significantly correlated with those of VP (Spearman's ρ = 0.38, p < 0.001). A significant constant error was identified between the two measurements (Bland-Altman: mean of the difference in ΔPD (VP - UP), - 0.4 [95% CI: - 0.52 to - 0.28, p < 0.001], generalized estimating equation: a beta estimator of ΔPD: 0.41, [95% CI: 0.26-0.56, p < 0.001]). The ΔPD pattern changes due to the raised tetanic stimuli were almost the same in the two methods.

CONCLUSION

Due to the significant constant error, we consider the reproducibility of the measured ΔPD between UP and VP moderate. Trial registry number UMIN 000047145. Prior to the subjects' enrollment, the trial was registered with the University Hospital Medical Information Network (Principal investigator: Mao Konno, Date of registration: 3.11.2022). https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000053778 .

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.

The Role of Automated Infrared Pupillometry in Traumatic Brain Injury: A Narrative Review

Pupillometry, an integral component of neurological examination, serves to evaluate both pupil size and reactivity. The conventional manual assessment exhibits inherent limitations, thereby necessitating the development of portable automated infrared pupillometers (PAIPs). Leveraging infrared technology, these devices provide an objective assessment, proving valuable in the context of brain injury for the detection of neuro-worsening and the facilitation of patient monitoring. In cases of mild brain trauma particularly, traditional methods face constraints. Conversely, in severe brain trauma scenarios, PAIPs contribute to neuro-prognostication and non-invasive neuromonitoring. Parameters derived from PAIPs exhibit correlations with changes in intracranial pressure. It is important to acknowledge, however, that PAIPs cannot replace invasive intracranial pressure monitoring while their widespread adoption awaits robust support from clinical studies. Ongoing research endeavors delve into the role of PAIPs in managing critical neuro-worsening in brain trauma patients, underscoring the non-invasive monitoring advantages while emphasizing the imperative for further clinical validation. Future advancements in this domain encompass sophisticated pupillary assessment tools and the integration of smartphone applications, emblematic of a continually evolving landscape.

Prognosis of consciousness disorders in the intensive care unit

Assessments of consciousness are a critical part of prognostic algorithms for critically ill patients suffering from severe brain injuries. There have been significant advances in the field of coma science over the past two decades, providing clinicians with more advanced and precise tools for diagnosing and prognosticating disorders of consciousness (DoC). Advanced neuroimaging and electrophysiological techniques have vastly expanded our understanding of the biological mechanisms underlying consciousness, and have helped identify new states of consciousness. One of these, termed cognitive motor dissociation, can predict functional recovery at 1 year post brain injury, and is present in up to 15-20% of patients with DoC. In this chapter, we review several tools that are used to predict DoC, describing their strengths and limitations, from the neurological examination to advanced imaging and electrophysiologic techniques. We also describe multimodal assessment paradigms that can be used to identify covert consciousness and thus help recognize patients with the potential for future recovery and improve our prognostication practices.

Repetitive Low-level Blast Exposure and Neurocognitive Effects in Army Ranger Mortarmen

INTRODUCTION

Occupational exposure to repetitive, low-level blasts in military training and combat has been tied to subconcussive injury and poor health outcomes for service members. Most low-level blast studies to date have focused on explosive breaching and firing heavy weapon systems; however, there is limited research on the repetitive blast exposure and physiological effects that mortarmen experience when firing mortar weapon systems. Motivated by anecdotal symptoms of mortarmen, the purpose of this paper is to characterize this exposure and its resulting neurocognitive effects in order to provide preliminary findings and actionable recommendations to safeguard the health of mortarmen.

MATERIALS AND METHODS

In collaboration with the U.S. Army Rangers at Fort Benning, blast exposure, symptoms, and pupillary light reflex were measured during 3 days of firing 81 mm and 120 mm mortars in training. Blast exposure analysis included the examination of the blast overpressure (BOP) and cumulative exposure by mortarman position, as well as comparison to the 4 psi safety threshold. Pupillary light reflex responses were analyzed with linear mixed effects modeling. All neurocognitive results were compared between mortarmen (n = 11) and controls (n = 4) and cross-compared with blast exposure and blast history.

RESULTS

Nearly 500 rounds were fired during the study, resulting in a high cumulative blast exposure for all mortarmen. While two mortarmen had average BOPs exceeding the 4 psi safety limit (Fig. 2), there was a high prevalence of mTBI-like symptoms among all mortarmen, with over 70% experiencing headaches, ringing in the ears, forgetfulness/poor memory, and taking longer to think during the training week (n ≥ 8/11). Mortarmen also had smaller and slower pupillary light reflex responses relative to controls, with significantly slower dilation velocity (P < 0.05) and constriction velocity (P < 0.10).

CONCLUSION

Mortarmen experienced high cumulative blast exposure coinciding with altered neurocognition that is suggestive of blast-related subconcussive injury. These neurocognitive effects occurred even in mortarmen with average BOP below the 4 psi safety threshold. While this study was limited by a small sample size, its results demonstrate a concerning health risk for mortarmen that requires additional study and immediate action. Behavioral changes like ducking and standing farther from the mortar when firing can generally help reduce mortarmen BOP exposure, but we recommend the establishment of daily cumulative safety thresholds and daily firing limits in training to reduce cumulative blast exposure, and ultimately, improve mortarmen's quality of life and longevity in service.

Multimodal monitoring: practical recommendations (dos and don'ts) in challenging situations and uncertainty

With the advancements in modern medicine, new methods are being developed to monitor patients in the intensive care unit. Different modalities evaluate different aspects of the patient's physiology and clinical status. The complexity of these modalities often restricts their use to the realm of clinical research, thereby limiting their use in the real world. Understanding their salient features and their limitations can aid physicians in interpreting the concomitant information provided by multiple modalities to make informed decisions that may affect clinical care and outcomes. Here, we present a review of the commonly used methods in the neurological intensive care unit with practical recommendations for their use.

Pupil maximum constriction velocity predicts post-induction hypotension in patients with lower ASA status: a prospective observational study

Background

Individuals affected by autonomic dysfunction are at a higher risk of developing hypotension following anesthesia induction. Dynamic pupillometry has previously been employed as a means of assessing autonomic function. This prospective observational study was developed to determine whether pupillary light reflex (PLR) parameters can reliably predict post-induction hypotension (PIH).

Methods

This study enrolled patients with lower ASA status (I-II) undergoing elective surgery. PLR recordings for these patients prior to anesthesia induction were made with an infrared pupil camcorder, with a computer being used to assess Average Constriction Velocity (ACV), Maximum Constriction Velocity (MCV), and Constriction Ratio (CR). PIH was defined by a > 30% reduction in mean arterial pressure (MAP) or any MAP recording < 65 mmHg for at least 1 min from the time of induction until 10 minutes following intubation. Patients were stratified into PIH and non-PIH groups based on whether or not they developed hypotension.

Results

This study enrolled 61 total patients, of whom 31 (50.8%) exhibited one or more hypotensive episodes. Patients in the PIH group exhibited significantly smaller ACV (P = 0.003) and MCV values (P < 0.001), as well as a higher CR (P = 0.003). Following adjustment for certain factors (Model 2), MCV was identified as a protective factor for PIH (Odds Ratio: 0.369). Receiver operating characteristic (ROC) analyses revealed that relative to CR (AUC: 0.695, 95% CI: 0.563–0.806; P = 0.004), the reciprocal of MCV (1/MCV) offered greater value as a predictor of PIH (AUC: 0.803,95%CI: 0.681–0.894; P < 0.001).

Conclusion

These results indicate that pupil maximum constriction velocity is a reliable predictor of post-induction hypotension in individuals of ASA I-II status undergoing elective surgery.

Trial registration

This study was registered with the Chinese Clinical Trial Registry (registration number: ChiCTR2200057164, registration date: 01/03/2022).

Mobile Smartphone-Based Digital Pupillometry Curves in the Diagnosis of Traumatic Brain Injury

Objective

The pupillary light reflex (PLR) and the pupillary diameter over time (the PLR curve) is an important biomarker of neurological disease, especially in the diagnosis of traumatic brain injury (TBI). We investigated whether PLR curves generated by a novel smartphone pupillometer application could be easily and accurately interpreted to aid in the diagnosis of TBI.

Methods

A total of 120 PLR curves from 42 healthy subjects and six patients with TBI were generated by PupilScreen. Eleven clinician raters, including one group of physicians and one group of neurocritical care nurses, classified 48 randomly selected normal and abnormal PLR curves without prior training or instruction. Rater accuracy, sensitivity, specificity, and interrater reliability were calculated.

Results

Clinician raters demonstrated 93% accuracy, 94% sensitivity, 92% specificity, 92% positive predictive value, and 93% negative predictive value in identifying normal and abnormal PLR curves. There was high within-group reliability (k = 0.85) and high interrater reliability (K = 0.75).

Conclusion

The PupilScreen smartphone application-based pupillometer produced PLR curves for clinical provider interpretation that led to accurate classification of normal and abnormal PLR data. Interrater reliability was greater than previous studies of manual pupillometry. This technology may be a good alternative to the use of subjective manual penlight pupillometry or digital pupillometry.

Pupillometry in neurocritical care

Though pupillometer use is becoming more widespread, there is a lack of evidence on its use by nurses in the neurosurgical ICU. This article explores the use of the pupillometer among neurocritical care nurses to better understand their experience and the device's clinical utility.

The use of quantitative pupillometry in patients with pituitary tumors: a technical note

Background

Pituitary tumors may cause compression of the optic chiasm, resulting in decreased visual acuity. Therefore, decompression of the optic chiasm is a major goal of surgical treatment in such patients. Quantitative pupillometry has been used in various clinical settings for assessing the optic system but has not been applied in patients with pituitary tumors. This study aimed to evaluate the potential of this technique to improve treatment modalities in patients undergoing surgical resection of pituitary tumors.

Method

Pupillometry using the automated NPi 200® Pupillometer was performed in seven patients who underwent surgical resection of large pituitary tumors at the University of Heidelberg in 2018. The neurological pupil index (NPi) was assessed preoperatively and postoperatively, and correlations with visual acuity and magnetic resonance imaging (MRI) findings regarding optic chiasm compression were determined.

Results

All patients experienced visual disturbance due to a large pituitary tumor. The NPi was < 4.0 in all patients in at least one pupil. Intraoperative MRI demonstrated successful decompression of the optic chiasm in all cases. Postoperatively, the NPi values increased, and this increase was correlated with improved visual acuity.

Conclusions

We found that quantitative pupillometry can detect optic chiasm compression in patients with pituitary tumors. Furthermore, postoperative improvement of NPi values may indicate sufficient decompression of the optic chiasm. Further studies are warranted to substantiate the granularity of this technique to gain valuable information for patients with pituitary tumors who are indicated for surgery.

Can Quantitative Pupillometry be used to Screen for Elevated Intracranial Pressure? A Retrospective Cohort Study

Background

Elevated intracranial pressure (ICP) is a serious complication in brain injury. Because of the risks involved, ICP is not monitored in all patients at risk. Noninvasive screening tools to identify patients with elevated ICP are needed. Anisocoria, abnormal pupillary size, and abnormal pupillary light reflex are signs of high ICP, but manual pupillometry is arbitrary and subject to interrater variability. We have evaluated quantitative pupillometry as a screening tool for elevated ICP.

Methods

We performed a retrospective observational study of the association between Neurological Pupil index (NPi), measured with the Neuroptics NPi-200 pupillometer, and ICP in patients routinely monitored with invasive ICP measurement in the intensive care unit. We performed a nonparametric receiver operator curve analysis for ICP ≥ 20 mm Hg with NPi as a classification variable. We performed a Youden analysis for the optimal NPi cutoff value and recorded sensitivity and specificity for this cutoff value. We also performed a logistic regression with elevated ICP as the dependent variable and NPi as the independent variable.

Results

We included 65 patients with invasive ICP monitoring. A total of 2,705 measurements were analyzed. Using NPi as a screening tool for elevated ICP yielded an area under receiver operator curve of 0.72. The optimal mean NPi cutoff value to rule out elevated ICP was ≥ 3.9. The probability of elevated ICP decreased with increasing NPi, with an odds ratio of 0.55 (0.50, 0.61).

Conclusions

Screening with NPi may inform high stakes clinical decisions by ruling out elevated ICP with a high degree of certainty. It may also aid in estimating probabilities of elevated ICP. This can help to weigh the risks of initiating invasive ICP monitoring against the risks of not doing so. Because of its ease of use and excellent interrater reliability, we suggest further studies of NPi as a screening tool for elevated ICP.

Dexmedetomidine and Other Analgosedatives Alter Pupil Characteristics in Critically Ill Patients

In critically ill patients with neurologic disease, pupil examination abnormalities can signify evolving intracranial pathology. Analgesic and sedative medications (analgosedatives) target pupillary pathways, but it remains unknown how analgosedatives alter pupil findings in the clinical care setting. We assessed dexmedetomidine and other analgosedative associations with pupil reactivity and size in a heterogeneous cohort of critically ill patients with acute intracranial pathology.

DESIGN

Retrospective cohort study.

SETTING

Two neurologic ICUs between 2016 and 2018.

PATIENTS

Critically ill adult patients with pupil measurements within 60 minutes of analgosedative administration. Patients with a history of intrinsic retinal pathology, extracranial injury, inaccessible brain imaging, or no Glasgow Coma Scale (GCS) data were excluded.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We used mixed-effects linear regression accounting for intrapatient correlations and adjusting for sex, age, GCS score, radiographic mass effect, medication confounders, and ambient light. We tested the association between an initiation or increased IV infusion of dexmedetomidine and pupil reactivity (Neurologic Pupil Index [NPi]) and resting pupil size (mm) obtained using NeurOptics NPi-200 (NeurOptics, Irvine, CA) pupillometer. Of our 221 patients with 9,897 pupil observations (median age, 60 [interquartile range, 50-68]; 59% male), 37 patients (166 pupil observations) were exposed to dexmedetomidine. Dexmedetomidine was associated with higher average NPi (β = 0.18 per 1 unit increase in rank-normalized NPi ± 0.04; p < 0.001) and smaller pupil size (β = -0.25 ± 0.05; p < 0.001). Exploratory analyses revealed that acetaminophen was associated with higher average NPi (β = 0.04 ± 0.02; p = 0.02) and that most IV infusion analgosedatives including propofol, fentanyl, and midazolam were associated with smaller pupil size.

CONCLUSIONS

Dexmedetomidine is associated with higher pupil reactivity (high NPi) and smaller pupil size in a cohort of critically ill patients with neurologic injury. Familiarity with expected pupil changes following analgosedative administration is important for accurate interpretation of pupil examination findings, facilitating optimal management of patients with acute intracranial pathology.

Inter-device reliability of the NPi-200 and NPi-300 pupillometers

The pupillary evaluation is an essential part of the neurological examination. Research suggests that the traditional examination of the pupil with a handheld flashlight has limited interrater reliability. Automated pupillometers were developed to provide an objective scoring of various pupillary parameters. The NPi-200 pupillometer is used for quantitative pupillary examinations, the NPi-300 was launched in July 2021 with enhanced features. The purpose of this study is to compare results from the NPi-200 to the NPi-300 to ensure that data are translatable across both platforms. This study examines the inter-device reliability of the NPi-200 compared to the NPi-300 in two cohorts: 20 patients at risk for cerebral edema and 50 healthy controls. Paired assessments of the devices were made from all participants. Each assessment included bilateral PLR readings within a 5-minute interval. Data showed high agreement between the two devices for the Neurological Pupil Index (NPi) reading (k = 0.94; CI: 0.91-0.99) and for pupil diameter assessment (k = 0.91; CI: 0.87-0.96). There is a very high level of agreement between the NPi-200 and NPi-300 among healthy controls and critically ill patients. Clinicians and researchers can interpret the results from either device equally.

Use of Automated Infrared Pupillometry to Predict Delirium in the Intensive Care Unit: A Prospective Observational Study

Introduction

Delirium is an acute state of brain dysfunction prevalent among critically ill patients. Disturbances in the sympathetic neurons, including cholinergic neurons, have been reported to cause delirium by upsetting the balance of neurotransmitter synthesis, release, and inactivation. The cholinergic system mediates pupillary constriction as a response to light stimulation, and this reflex can be measured using automated infrared pupillometry (AIP). The relationship between delirium and AIP parameters has been examined. The Confusion Assessment Method for the Intensive Care Unit (CAM ICU) and the Intensive Care Unit Delirium Screening Checklist (ICDSC) are used for assessing delirium. However, that between the ICDSC score and AIP parameters remains unclear.

Objective

To examine the relationship between AIP parameters and the various categories of delirium as defined by the ICDSC score (delirium, subsyndromal delirium, no delirium).

Methods

This prospective observational study included patients aged ≥18 years admitted to the intensive care unit (ICU) from May 2018 to September 2018. ICU patients were classified into delirium, subsyndromal delirium, and no delirium groups according to the ICDSC score during ICU stay. The pupillary light reflex was assessed in both eyes immediately after admission using AIP with a portable infrared pupillometer. Logistic regression analyses were used to estimate the odds ratio to examine the relationship between the severity of delirium as assessed by the ICDSC score and the AIP parameters.

Results

In total 133 patients were included in the study. Based on the ICDSC scores, 41.4% of patients had no delirium, 40.6% had subsyndromal delirium, and 18% had delirium. Dilation velocity (DV) measured by AIP was significantly different among the delirium, subsyndromal delirium, and no delirium groups. Post-hoc comparisons showed that DV was significantly slower in the delirium group than in the no delirium group but was not significantly different between the subsyndromal delirium and no delirium groups. After adjusting for patients’ sex and age at enrollment, DV was shown to be independently associated with delirium.

Conclusion

This study suggests that the use of AIP at ICU admission may improve the identification of patients at a high risk of developing delirium.

Measurement Methods of Fatigue, Sleepiness, and Sleep Behaviour Aboard Ships: A Systematic Review

Since seafarers are known to be exposed to numerous job-related stress factors that can cause fatigue, sleepiness, and disturbed sleep behaviour, the aim of this review was to provide an overview of the subjective and objective measurement methods of these strains. Using a systematic review, 166 studies were identified within the period of January 2010 to December 2020 using the PubMed database. Of the 21 studies selected, 13 used both subjective and objective measurement methods. Six studies used only subjective and two studies only objective methods. For subjective assessment, 12 different questionnaires could be identified as well as activity and sleeping logs. Actigraphy and reaction time tests (RTT) were the most common objective methods. In single cases, electrooculography (EOG), pupillometry and ambulatory polysomnography (PSG) were used. Measurement-related limitations due to vessel-related impacts were less often reported than expected. No restrictions of daily routines on board were described, and only single-measurement disturbances due to ship movements were mentioned. The present literature review reveals that there are various routines to measure fatigue, sleepiness, and sleep behaviour on board. A combination of subjective and objective methods often appears to be beneficial. The frequent use of actigraphy and RTT on board suggests good feasibility and reliable measurements with these methods. The use of ambulatory PSG in maritime-like contexts suggests that this method would also be feasible on board.

Exploring the Relationship Between Objective Pupillometry Metrics and Midline Shift

ABSTRACT

BACKGROUND: Pupillary examinations provide early subtle signs of worsening intracranial pathology. Objective pupillomtery assessment, although not yet the standard of care, is considered best practice. However, inconsistent findings from objective pupillometry studies have caused a lack of consensus among clinicians; as such, no clinical guidelines are available to guide clinical use of objective pupillometer devices. To add to the body of evidence, the purpose of this project was to explore the relationship between objective pupillometry metrics and midline shift (MLS). METHODS: A retrospective chart review of pupillometer data was conducted. Midline shift was correlated with objective pupillometry metrics including Neurological Pupil Index (NPi), pupil size, and anisocoria. Midline shift was measured for the patient's initial neuroimaging and with any defined neurological change. Spearman ρ was used for statistical analysis of correlations between pupillometer metrics and MLS measured at both the septum pellucidum and pineal gland. RESULTS: A total of 41 patients were included in the analysis; most were White (58.5%) and male (58.5%), with a mean (SD) age of 58.49 (16.92) years. Spearman ρ revealed statistically significant positive correlations between right pupil NPi and anisocoria with MLS, and significant negative correlations between left pupil NPi and pupil size with MLS. CONCLUSIONS: Results from this project are consistent with previous studies. Objective pupillometry continues to be a valuable component of a comprehensive neurological examination, because it has the ability to discern early and subtle changes in a patient's neurological status, leading to lifesaving interventions.

Narrative Review of Neurologic Complications in Adults on ECMO: Prevalence, Risks, Outcomes, and Prevention Strategies

Extracorporeal membrane oxygenation (ECMO), a life-saving technique for patients with severe respiratory and cardiac diseases, is being increasingly utilized worldwide, particularly during the coronavirus disease 2019(COVID-19) pandemic, and there has been a sharp increase in the implementation of ECMO. However, due to the presence of various complications, the survival rate of patients undergoing ECMO remains low. Among the complications, the neurologic morbidity significantly associated with venoarterial and venovenous ECMO has received increasing attention. Generally, failure to recognize neurologic injury in time is reportedly associated with poor outcomes in patients on ECMO. Currently, multimodal monitoring is increasingly utilized in patients with devastating neurologic injuries and has been advocated as an important approach for early diagnosis. Here, we highlight the prevalence and outcomes, risk factors, current monitoring technologies, prevention, and treatment of neurologic complications in adult patients on ECMO. We believe that an improved understanding of neurologic complications presumably offers promising therapeutic solutions to prevent and treat neurologic morbidity.

Automated Pupillometry for Assessment of Treatment Success in Nonconvulsive Status Epilepticus

BACKGROUND

Altered pupillary function may reflect nonconvulsive status epilepticus (NCSE). Neurological pupil index (NPi) assessed by automated pupillometry is a surrogate marker of global pupillary function. We aimed to assess NPi changes in relation to NCSE treatment response.

METHODS

In this prospective observational study, serial automated pupillometry was performed in 68 NCSE episodes. In accordance with local standards, patients were treated with clonazepam (1-2 mg), levetiracetam (40 mg/kg), and lacosamide (5 mg/kg) in a stepwise approach under continuous electroencephalography monitoring until NCSE was terminated. Patients with refractory NCSE received individualized regimens. NPi was assessed bilaterally before and after each treatment step. For statistical analysis, the lower NPi of both sides (minNPi) was used. Nonparametric testing for matched samples and Cohen's d to estimate effect size were performed. Principal component analysis was applied to assess the contribution of baseline minNPi, age, sex, and NCSE duration to treatment outcome.

RESULTS

In 97.1% of 68 episodes, NCSE could be terminated; in 16.2%, NCSE was refractory. In 85.3% of episodes, an abnormal baseline minNPi ≤ 4.0 was obtained. After NCSE termination, minNPi increased significantly (p < 0.001). Cohen's d showed a strong effect size of 1.24 (95% confidence interval 0.88-1.61). Baseline minNPi was higher in clonazepam nonresponders vs. responders (p = 0.008), minNPi increased in responders (p < 0.001) but not in nonresponders. NCSE refractivity was associated with normal baseline minNPi (principal component analysis, component 1, 32.6% of variance, r = 0.78), male sex, and longer NCSE duration (component 2, 27.1% of variance, r = 0.62 and r = 0.78, respectively).

CONCLUSIONS

Automated pupillometry may be a helpful noninvasive neuromonitoring tool for the assessment of patients with NCSE and response to treatment.

Quantitative assessments of pupillary light reflexes in hospital-onset unresponsiveness

BACKGROUND

Patients who develop hospital-onset unresponsiveness should be promptly managed in order to avoid clinical deterioration. Pupillary examination through pupillary light reflex is the gold standard method in the initial evaluation of unresponsive patients. However, the current method of shining light and subjective description often shows poor reliability. The objective of this study is to explore whether a quantitative measurement of pupillary light reflexes is useful in detecting brain herniation syndrome and predicting neurological outcomes in patients who developed hospital-onset unresponsiveness after admission for non-neurological reasons.

METHODS

This was a registry-based observational study on patients who activated the neurological rapid response team at Asan Medical Center (Seoul, Korea). Hospital-onset unresponsiveness was defined as a newly developed unresponsive state as assessed by the ACDU (Alert, Confused, Drowsy, and Unresponsive) scale during the hospital stay. Demographics, comorbidities, pupillometry parameters including Neurological Pupil index, brain herniation syndrome, in-hospital mortality, and modified Rankin Scale at 3-months were analyzed.

RESULTS

In 214 consecutive patients with hospital-onset unresponsiveness, 37 (17%) had brain herniation syndrome. The optimal cut-off value of Neurological Pupil index for detecting brain herniation syndrome was < 1.6 (specificity, 91% [95% confidence interval (CI) = 86-95]; sensitivity, 49% [95% CI = 32-66]). The in-hospital mortality rate was 28% (59/214); the Neurological Pupil index was negatively associated with in-hospital mortality after adjustments for the presence of brain herniation syndrome (adjusted odds ratio = 0.77, 95% CI = 0.62-0.96). Poor neurological outcomes (modified Rankin Scale ≥4) at 3 months was observed in 76% (152/201) of the patients; the Neurological Pupil index was negatively associated with poor neurological outcomes after adjustments for clinical variables (adjusted odds ratio = 0.67, 95% CI = 0.49-0.90).

CONCLUSIONS

Quantitative measurements of pupillary light reflexes may be useful for early detection of potentially life-threatening neurological conditions in patients with hospital-onset unresponsiveness.

Pupillary light reflex as a diagnostic aid from computational viewpoint: A systematic literature review

This work presents a detailed and complete review of publications on pupillary light reflex (PLR) used to aid diagnoses. These are computational techniques used in the evaluation of pupillometry, as well as their application in computer-aided diagnoses (CAD) of pathologies or physiological conditions that can be studied by observing the movements of miosis and mydriasis of the human pupil. A careful survey was carried out of all studies published over the last 10 years which investigated, electronic devices, recording protocols, image treatment, computational algorithms and the pathologies related to PLR. We present the frontier of existing knowledge regarding methods and techniques used in this field of knowledge, which has been expanding due to the possibility of performing diagnoses with high precision, at a low cost and with a non-invasive method.

Quantitative Infrared Pupillometry in Nonconvulsive Status Epilepticus

BACKGROUND

Nonconvulsive status epilepticus (NCSE) is a frequent disorder in neurocritical care and diagnosing it can be challenging. NCSE patients often show altered pupil function, but nature and extent may vary. Infrared pupillometry allows detection of subtle changes of pupil function. The neurological pupil index (NPi) is considered a surrogate marker of global pupil function which is supposed to be independent of absolute parameters such as the pupil diameter.

OBJECTIVE

Cross-sectional observational study to assess whether NPi is altered in NCSE.

METHODS

128 consecutive adult emergency patients who had experienced a suspected seizure, have not reached their prior functional level regarding level of consciousness, mental status or focal deficits, had no obvious clinical signs of status epilepticus and had an EEG indication as determined by the treating clinician for exclusion of NCSE were examined by routine EEG and pupillometry. Exclusion criteria were ocular comorbidity (n = 21) and poor EEG quality (n = 4). Pupillometry was performed once directly before the beginning of EEG recording. NCSE diagnosis (no NCSE, possible NCSE and confirmed NCSE) was established according to Salzburg consensus criteria blinded to pupillometry results. Group comparison was performed for right NPi, left NPi, lowest NPi of both sides (minNPi) and the absolute difference of both sides (diffNPi) applying non-parametric testing. In post-hoc analysis, receiver operating characteristics (ROC) of NCSE diagnosis (combined confirmed NCSE and possible NCSE) were performed for minNPi and diffNPi.

RESULTS

From 103 patients included in the final analysis, 5 (4.9%) had confirmed NCSE, 7 (6.8%) had possible NCSE. Right NPi (p = 0.002), left NPi (p < 0.001) and minNPi (p < 0.001) were significantly lower in "confirmed NCSE" and "possible NCSE" compared to "no NCSE"; diffNPi was significantly higher in "confirmed NCSE" and "possible NCSE" compared to "no NCSE" (p < 0.001). There was no significant difference of minNPi and diffNPi between "confirmed NCSE" and "possible NCSE". ROC analysis showed an optimal cut-off of minNPi for NCSE diagnosis of 4.0 (AUC = 0.93, 95% CI 0.86-0.99). Optimal ROC analysis cut-off of diffNPi for NCSE diagnosis was 0.2 (AUC = 0.89, 95% CI 0.80-0.99).

CONCLUSIONS

NPi was significantly reduced and the difference between left and right NPi was significantly higher in confirmed NCSE. An NPi < 4.0 on either side as well as an NPi difference of both sides > 0.2 may be potential indicators of NCSE. Infrared pupillometry may be a helpful diagnostic tool in the assessment of NCSE and should be studied further in larger populations.

Computerized dynamic pupillometry as a screening tool for evaluation of autonomic activity

OBJECTIVES

Dynamic pupillometry is a simple screening tool for quantifying pupillary light reflex (PLR), to indicate autonomic nervous system (ANS) activity. Heart rate variability (HRV) is the gold standard method for assessing ANS effects on the heart. The present study aimed to compare ANS activity as measured using dynamic pupillometry (DP) with short term HRV in healthy volunteers.

METHODS

The study includes 200 participants aged between 20-60 years. PLR was measured using infrared videography and categorized into different quantitative parameters that reflect ANS activity. Simultaneously, Lead II ECG was recorded for 5 min to evaluate the short term HRV of time and frequency domain parameters. The data obtained from the two methods were compared with each other to provide the relationship between PLR and HRV.

RESULTS

Study participants' mean age was 36.95 ± 9.45 years. The different pupillary indices of PLR and all the HRV parameters were within the range of normative data. Several PLR indicators of the parasympathetic function include mean constriction velocity (MCV; r = 0.60, P < 0.001), absolute constriction amplitude (ACA; r = 0.57, P < 0.001) baseline pupil diameter (BPD; r = 0.44, p < 0.001), and minimum pupil diameter (MPD; r = -0.35, p < 0.001) were significantly correlated with high-frequency power (HF in normalized units) of HRV signal.

CONCLUSION

PLR variables showed a significant relationship to HRV indices. Dynamic pupillometry can be a complementary tool to HRV for evaluating ANS activity.

A Systematic Review Assessing the Current State of Automated Pupillometry in the NeuroICU

The aim of this study was to assess the current state of automated pupillometry technology and its application in the neurointensive care unit (neuroICU). We performed a literature search using the PubMed, MEDLINE, and EMBASE databases from database inception through a search end date of October 18, 2018, to identify studies reporting on the use of automated pupillometry in the care of critically ill patients with neurological impairment. Two independent reviewers reviewed all titles and abstracts in two filtering phases. Data were extracted independently. One hundred and forty-one articles/abstracts have been published on the use of automated pupillometry in critical care since inception of the PubMed, MEDLINE, and EMBASE databases. We selected and reviewed 22 full-text articles and 8 abstracts, of which 26 were prospective, 2 were retrospective, and 2 were larger case series. Automated pupillometry increased precision, reliability, and reproducibility compared with the manual pupillary examination; detected subtle and early pupillary changes; detected pupillary changes that indicate a rise, or impending rise, in intracranial pressure detected level of analgesia and depth of sedation; served as a prognostic indicator; estimated the clinical severity of aneurysmal subarachnoid hemorrhage; and served as a noninvasive monitor of response to osmotic therapy. At present, no consensus guidelines exist endorsing routine use of automated pupillometry in the neuroICU. However, an increasing quantity of research supports the usefulness of automated pupillometry in this setting. Further large-scale prospective studies are needed before updated consensus guidelines recommending widespread adoption of automated pupillometry are produced.

Neuromonitoring of delirium with quantitative pupillometry in sedated mechanically ventilated critically ill patients

BACKGROUND

Intensive care unit (ICU) delirium is a frequent secondary neurological complication in critically ill patients undergoing prolonged mechanical ventilation. Quantitative pupillometry is an emerging modality for the neuromonitoring of primary acute brain injury, but its potential utility in patients at risk of ICU delirium is unknown.

METHODS

This was an observational cohort study of medical-surgical ICU patients, without acute or known primary brain injury, who underwent sedation and mechanical ventilation for at least 48 h. Starting at day 3, automated infrared pupillometry-blinded to ICU caregivers-was used for repeated measurement of the pupillary function, including quantitative pupillary light reflex (q-PLR, expressed as % pupil constriction to a standardized light stimulus) and constriction velocity (CV, mm/s). The relationship between delirium, using the CAM-ICU score, and quantitative pupillary variables was examined.

RESULTS

A total of 59/100 patients had ICU delirium, diagnosed at a median 8 (5-13) days from admission. Compared to non-delirious patients, subjects with ICU delirium had lower values of q-PLR (25 [19-31] vs. 20 [15-28] %) and CV (2.5 [1.7-2.8] vs. 1.7 [1.4-2.4] mm/s) at day 3, and at all additional time-points tested (p < 0.05). After adjusting for the SOFA score and the cumulative dose of analgesia and sedation, lower q-PLR was associated with an increased risk of ICU delirium (OR 1.057 [1.007-1.113] at day 3; p = 0.03).

CONCLUSIONS

Sustained abnormalities of quantitative pupillary variables at the early ICU phase correlate with delirium and precede clinical diagnosis by a median 5 days. These findings suggest a potential utility of quantitative pupillometry in sedated mechanically ventilated ICU patients at high risk of delirium.

Interrater reliability in pupillary assessment among intensive care nurses

BACKGROUND

Pupillary abnormalities are a common and reliable finding of brain herniation, ischaemia, and acute brain injury in critically ill patients. Reliable pupil assessment is a vital evaluation in diagnostic and therapeutic procedures for neurocritical patients.

AIM

To evaluate inter-rater reliability of pupillary assessment among intensive care.

METHODS

In this prospective, blind observational study, intensive care nurses and two researchers evaluated the pupil size, reactivity and symmetry of 200 patients with neurosurgery or neurological diseases. A total of 200 pupillary measurement sets were completed independently and blindly.

RESULTS

Three observers -two researchers and the nurse- found fair-to-good and excellent agreements in initial pupil size evaluations of right and left pupils, respectively (ICC = 0.70, 95%; ICC = 0.75, 95%). In patients with pupil size ≥4 mm, the observers found fair-to-good agreements in both right and left pupil initial size measurements (ICC = 0.52; ICC = 0.65). Agreement in pupil symmetry was moderated (K = 0.58), and reactivity was near perfect (K = 0.89) between the three observers.

CONCLUSION

Although the two researchers found near perfect agreement in pupil size, symmetry and reactivity assessment, two researchers and the nurse found moderate agreement in pupil symmetry and fair-to-good agreement in pre- and post-light stimulation pupil size.

Neurological Pupil index for Early Prognostication After Venoarterial Extracorporeal Membrane Oxygenation

BACKGROUND

Venoarterial extracorporeal membrane oxygenation therapy (VA-ECMO) after refractory cardiogenic shock or cardiac arrest has significant morbidity and mortality. Early outcome prediction is crucial in this setting, but data on neuroprognostication are limited. We examined the prognostic value of clinical neurologic examination, using an automated device for the quantitative measurement of pupillary light reactivity.

METHODS

An observational cohort of sedated, mechanically ventilated VA-ECMO patients was analyzed during the early phase after ECMO insertion (first 72 h). Using the NPi-200 automated infrared pupillometer, pupillary light reactivity was assessed repeatedly (every 12 h) by calculating the Neurological Pupil index (NPi). Trends of NPi over time were correlated to 90-day mortality, and the prognostic performance of the NPi, alone and in combination with the 12-h PREDICT VA-ECMO score, was evaluated.

RESULTS

One hundred consecutive patients were studied (51 with refractory cardiogenic shock and 49 with refractory cardiac arrest; 12-h PREDICT VA-ECMO, 40%; observed 90-day survival, 43%). Nonsurvivors (n = 57) had significantly lower NPi than did survivors at all time points (all P < .01). Abnormal NPi (< 3, at any time from 24 to 72 h) was 100% specific for 90-day mortality, with 0% false positives. Adding the 12-h PREDICT VA-ECMO score to the NPi provided the best prognostic performance (specificity, 100% [95% CI, 92%-100%]; sensitivity, 60% [95% CI, 46%-72%]; area under the receiver operating characteristic curve, 0.82).

CONCLUSIONS

Quantitative NPi alone had excellent ability to predict a poor outcome from day 1 after VA-ECMO insertion, with no false positives. Combining NPi and 12-h PREDICT-VA ECMO score increased the sensitivity of outcome prediction, while maintaining 100% specificity.

Quantitative Pupillometry in the Intensive Care Unit

Quantitative pupillometry provides a noninvasive and objective assessment within the neurological examination. This review details the physiology of the pupillary light response, the clinical significance of changes in pupillary reactivity, and the variables that compose the Neurological Pupil index or NPi are discussed. This article reviews the most recent applications and advances in quantitative pupillometry for noninvasive intracranial pressure monitoring, postcardiac arrest prognostication, and subarachnoid hemorrhage. Also discussed are the limitations and confounders of quantitative pupillometry in the modern neurological intensive care unit.

Quantitative pupillometry for the monitoring of intracranial hypertension in patients with severe traumatic brain injury

Background

Elevated intracranial pressure (ICP) is frequent after traumatic brain injury (TBI) and may cause abnormal pupillary reactivity, which in turn is associated with a worse prognosis. Using automated infrared pupillometry, we examined the relationship between the Neurological Pupil index (NPi) and invasive ICP in patients with severe TBI.

Methods

This was an observational cohort of consecutive subjects with severe TBI (Glasgow Coma Scale [GCS] < 9 with abnormal lesions on head CT) who underwent parenchymal ICP monitoring and repeated NPi assessment with the NPi-200® pupillometer. We examined NPi trends over time (four consecutive measurements over intervals of 6 h) prior to sustained elevated ICP > 20 mmHg. We further analyzed the relationship of cumulative abnormal NPi burden (%NPi values < 3 during total ICP monitoring time) with intracranial hypertension (ICHT)—categorized as refractory (ICHT-r; requiring surgical decompression) vs. non-refractory (ICHT-nr; responsive to medical therapy)—and with the 6-month Glasgow Outcome Score (GOS).

Results

A total of 54 patients were studied (mean age 54 ± 21 years, 74% with focal injuries on CT), of whom 32 (59%) had ICHT. Among subjects with ICHT, episodes of sustained elevated ICP (n = 43, 172 matched ICP-NPi samples; baseline ICP [T_− 6 h] 14 ± 5 mmHg vs. ICPmax [T_0 h] 30 ± 9 mmHg) were associated with a concomitant decrease of the NPi (baseline 4.2 ± 0.5 vs. 2.8 ± 1.6, p < 0.0001 ANOVA for repeated measures). Abnormal NPi values were more frequent in patients with ICHT-r (n = 17; 38 [3–96]% of monitored time vs. 1 [0–9]% in patients with ICHT-nr [n = 15] and 0.5 [0–10]% in those without ICHT [n = 22]; p = 0.007) and were associated with an unfavorable 6-month outcome (15 [1–80]% in GOS 1–3 vs. 0 [0–7]% in GOS 4–5 patients; p = 0.002).

Conclusions

In a selected cohort of severe TBI patients with abnormal head CT lesions and predominantly focal cerebral injury, elevated ICP episodes correlated with a concomitant decrease of NPi. Sustained abnormal NPi was in turn associated with a more complicated ICP course and worse outcome.

Functional Near-Infrared Spectroscopy as a Measure of Listening Effort in Older Adults Who Use Hearing Aids

Listening effort may be reduced when hearing aids improve access to the acoustic signal. However, this possibility is difficult to evaluate because many neuroimaging methods used to measure listening effort are incompatible with hearing aid use. Functional near-infrared spectroscopy (fNIRS), which can be used to measure the concentration of oxygen in the prefrontal cortex (PFC), appears to be well-suited to this application. The first aim of this study was to establish whether fNIRS could measure cognitive effort during listening in older adults who use hearing aids. The second aim was to use fNIRS to determine if listening effort, a form of cognitive effort, differed depending on whether or not hearing aids were used when listening to sound presented at 35 dB SL (flat gain). Sixteen older adults who were experienced hearing aid users completed an auditory n-back task and a visual n-back task; both tasks were completed with and without hearing aids. We found that PFC oxygenation increased with n-back working memory demand in both modalities, supporting the use of fNIRS to measure cognitive effort during listening in this population. PFC oxygenation was weakly and nonsignificantly correlated with self-reported listening effort and reaction time, respectively, suggesting that PFC oxygenation assesses a dimension of listening effort that differs from these other measures. Furthermore, the extent to which hearing aids reduced PFC oxygenation in the left lateral PFC was positively correlated with age and pure-tone average thresholds. The implications of these findings as well as future directions are discussed.