The effect of ketamine and nitrous oxide on the human pupillary light reflex during general anesthesia

Assessment of sedation by automated pupillometry in critically ill patients: a prospective observational study

BACKGROUND

Quantitative measurement of pupil change has not been assessed against the Richmond Agitation and Sedation Scale (RASS) and spectral edge frequency (SEF) during sedation. The aim of this study was to evaluate pupillometry against these measures in sedated critically ill adult patients.

METHODS

In ventilated and sedated patients, pupillary variables were measured by automated pupillometry at each RASS level from -5 to 0 after discontinuation of hypnotics, while processed electroencephalogram variables were displayed continuously and SEF was recorded at each RASS level. Correlations were made between percentage pupillary light reflex (%PLR) and RASS, and between %PLR and SEF. The ability of %PLR to differentiate light sedation (RASS ≥-2), moderate (RASS =-3), and deep sedation (RASS ≤-4) was assessed by areas under receiver operating characteristic (ROC) curves.

RESULTS

A total of 163 paired measurements were recorded in 38 patients. With decreasing sedation depth, median %PLR increased progressively from 20% (interquartile range 17-25%) to 36% (interquartile range 33-40%) (P<0.001). Strong correlations were found between %PLR and RASS (Rho=0.635) and between %PLR and SEF (R=0.641). Area under the curve (AUC) of 0.87 with a %PLR threshold of 28% differentiated moderate/light sedation from deep sedation with sensitivity of 83% and specificity of 83%. An AUC of 0.82 with a threshold of 31% distinguished light sedation from moderate/deep sedation with a sensitivity of 81% and a specificity of 75%.

CONCLUSIONS

Quantitative assessment of %PLR correlates with other indicators of sedation depth in critically ill patients.

Non-Invasive Objective Markers to Measure Pain: A Direction to Develop a Pain Device - A Narrative Review

Objective

To review the literature regarding non-invasive objective measurements of pain. Measuring pain is of uttermost importance, but it can be an inconvenient task, especially in terms of the interpretation of patient's information. Reiterating, there is no "standard" that provides the physician with a method to objectively quantify this problem of patient's pain. For assessing the pain, physician relies solely on unidimensional assessment tools or questionnaire-based pain assessment. Although pain is a subjective experience of the patient, but there is a need to measure pain sometimes in the individuals who cannot communicate their quality and severity of pain.

Material and Methods

The articles from PubMed and Google Scholar without any year and age limit were searched in the current narrative review. A total of 16 markers were searched and their relation to pain was studied.

Results

Studies have shown that these markers change in relation to pain and it can be considered a valuable tool for pain measurement but there are multiple factors like psychological and emotional factors which affect these markers.

Conclusion

There is lack of evidence to show which marker can be used for measuring pain accurately. This narrative review is an attempt to look into the various pain-related markers that can be used and it calls for further studies including clinical trials with different diseases and taking into accounts different factors affecting pain to give an accurate measurement of pain.

Modern Sedation and Analgesia Strategies in Neurocritical Care

PURPOSE OF REVIEW

Patients with acute neurologic injury require a specialized approach to critical care, particularly with regard to sedation and analgesia. This article reviews the most recent advances in methodology, pharmacology, and best practices of sedation and analgesia for the neurocritical care population.

RECENT FINDINGS

In addition to established agents such as propofol and midazolam, dexmedetomidine and ketamine are two sedative agents that play an increasingly central role, as they have a favorable side effect profile on cerebral hemodynamics and rapid offset can facilitate repeated neurologic exams. Recent evidence suggests that dexmedetomidine is also an effective component when managing delirium. Combined analgo-sedation with low doses of short-acting opiates is a preferred sedation strategy to facilitate neurologic exams as well as patient-ventilator synchrony. Optimal care for patients in the neurocritical care population requires an adaptation of general ICU strategies that incorporates understanding of neurophysiology and the need for close neuromonitoring. Recent data continues to improve care tailored to this population.

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.

Pupillometry is not sensitive to gas narcosis in divers breathing hyperbaric air or normobaric nitrous oxide

INTRODUCTION

Gas narcosis impairs divers when diving deeper. Pupillometry is sensitive to alcohol intoxication and it has been used in anaesthesia to assess nitrous oxide narcosis. It is a potential novel method to quantify narcosis in diving. The aim of this study was to evaluate pupillometry for objective measurement of narcosis during exposure to hyperbaric air or nitrous oxide.

METHOD

Pupil size in 16 subjects was recorded directly at surface pressure and during air breathing at 608 kPa (equivalent to 50 metres' seawater depth) in a hyperbaric chamber. Another 12 subjects were exposed to nitrous oxide at end-tidal percentages of 20, 30 and 40% in random order at surface pressure. Pupil size and pupil light reflex were recorded at baseline and at each level of nitrous oxide exposure.

RESULTS

Pupil size did not significantly change during exposure to hyperbaric air or nitrous oxide. The pupil light reflex, evaluated using percentage constriction and minimum diameter after exposure to a light stimulus, was affected significantly only during the highest nitrous oxide exposure - an end-tidal level of 40%.

CONCLUSION

Pupillometry is insensitive to the narcotic effect of air at 608 kPa in the dry hyperbaric environment and to the effects of low dose nitrous oxide. Pupillometry is not suitable as a monitoring method for gas narcosis in diving.

Prognostic value of automated pupillometry: an unselected cohort from a cardiac intensive care unit

Background:

Patients admitted to a cardiac intensive care unit are often unconscious with uncertain prognosis. Automated infrared pupillometry for neurological assessment in the intensive care unit may provide early prognostic information. This study aimed to determine the prognostic value of automated pupillometry in different subgroups of patients in a cardiac intensive care unit with 30-day mortality as the primary endpoint and neurological outcome as the secondary endpoint.

Methods:

A total of 221 comatose patients were divided into three groups: out-of-hospital cardiac arrest, in-hospital cardiac arrest and others (i.e. patients with cardiac diagnoses other than cardiac arrest). Automated pupillometry was serially performed until discharge or death and pupil measurements were analysed using the neurological pupil index algorithm. We applied receiver operating characteristic curves in univariable and multivariable logistic regression models and a calculated Youden index identified neurological pupil index cut-off values at different specificities.

Results:

In out-of-hospital cardiac arrest patients higher neurological pupil index values were independently associated with lower 30-day mortality. The univariable model for 30-day mortality had an area under the curve of 0.87 and the multivariable model achieved an area under the curve of 0.94. The Youden index identified a neurological pupil index cut-off in out-of-hospital cardiac arrest patients of 2.40 for a specificity of 100%. For patients with in-hospital cardiac arrest and other cardiac diagnoses, we found no association between neurological pupil index values and 30-day mortality, and the univariable models showed poor predictive values.

Conclusion:

Automated infrared pupillometry has promising predictive value after out-of-hospital cardiac arrest, but poor predictive value in patients with in-hospital cardiac arrest or cardiac diagnoses unrelated to cardiac arrest. Our data suggest a possible neurological pupil index cut-off of 2.40 for poor outcome in out-of-hospital cardiac arrest patients.

Acepromazine and Chlorpromazine as Pharmaceutical-grade Alternatives to Chlorprothixene for Pupillary Light Reflex Imaging in Mice

Studies of visual responses in isoflurane-anesthetized mice often use the sedative chlorprothixene to decrease the amount of isoflurane used because excessive isoflurane could adversely affect light-evoked responses. However, data are not available to justify the use of this nonpharmaceutical-grade chemical. The current study tested whether pharmaceutical-grade sedatives would be appropriate alternatives for imaging pupillary light reflexes. Male 15-wk-old mice were injected intraperitoneally with 1 mg/kg chlorprothixene, 5 mg/kg acepromazine, 10 mg/kg chlorpromazine, or saline. After anesthetic induction, anesthesia maintenance used 0.5% and 1% isoflurane for sedative- and saline-injected mice, respectively. A photostimulus (16.0 log photons cm^-2 s^-1; 470 nm) was presented to the right eye for 20 min, during which the left eye was imaged for consensual pupillary constriction and involuntary pupil drift. Time to immobilization, loss of righting reflex, physiologic parameters, gain of righting reflex, and degree of recovery were assessed also. The sedative groups were statistically indistinguishable for all measures. By contrast, pupillary drift occurred far more often in saline-treated mice than in the sedative groups. Furthermore, saline-treated mice took longer to reach maximal pupil constriction than all sedative groups and had lower heart rates compared with chlorpromazine- and chlorprothixene-sedated mice. Full recovery (as defined by purposeful movement, response to tactile stimuli, and full alertness) was not regularly achieved in any sedative group. In conclusion, at the doses tested, acepromazine and chlorpromazine are suitable pharmaceutical-grade alternatives to chlorprothixene for pupil imaging and conceivably other in vivo photoresponse measurements; however, given the lack of full recovery, lower dosages should be investigated further for use in survival procedures.

Enhanced pupillary light reflex in infancy is associated with autism diagnosis in toddlerhood

Autism spectrum disorder (ASD) is a neurodevelopmental condition affecting around 1% of the population. We previously discovered that infant siblings of children with ASD had stronger pupillary light reflexes compared to low-risk infants, a result which contrasts sharply with the weak pupillary light reflex typically seen in both children and adults with ASD. Here, we show that on average the relative constriction of the pupillary light reflex is larger in 9-10-month-old high risk infant siblings who receive an ASD diagnosis at 36 months, compared both to those who do not and to low-risk controls. We also found that the magnitude of the pupillary light reflex in infancy is associated with symptom severity at follow-up. This study indicates an important role of sensory atypicalities in the etiology of ASD, and suggests that pupillometry, if further developed and refined, could facilitate risk assessment in infants.

Pupillary reflex dilation in response to incremental nociceptive stimuli in patients receiving intravenous ketamine

Pupillometry is a non-invasive monitoring technique, which allows dynamic pupillary diameter measurement by an infrared camera. Pupillary diameter increases in response to nociceptive stimuli. In patients anesthetized with propofol or volatile agents, the magnitude of this pupillary dilation is related to the intensity of the stimulus. Pupillary response to nociceptive stimuli has never been studied under ketamine anesthesia. Our objective was to describe pupillary reflex dilation after calibrated tetanic stimulations in patients receiving intravenous ketamine. After written consent, 24 patients of our pediatric burn care unit were included. They received an oral morphine premedication (0.3 mg kg^-1) 1 h before their scheduled daily dressing change. Just before the procedure, they received 1 mg kg^-1 of intravenous ketamine. Two minutes after this bolus, tetanic stimulations of incremental intensities were performed on the arm of each patient (5-10-20-30-40-60 mA, 60 s interval between stimulations). Pupillary diameter, heart rate and movements were recorded before and after each stimulation. Tetanic stimulations were associated with changes in pupillary diameter and heart rate. The magnitude of these changes was significantly influenced by the intensity of stimulation (ANOVA for repeated measures, p < 0.001). Movement was associated with a 32% increase in diameter (ROC curves, AUC 0.758) with 65% sensitivity and 77% specificity. In children, pupillary reflex dilation to nociceptive stimuli persists under deep sedation obtained with 1 mg kg^-1 of intravenous ketamine combined with a 0.3 mg kg^-1 oral morphine premedication, and its magnitude depends on the intensity of the stimulation. Our results confirm that pupillometry could be a relevant way to monitor nociception in anaesthetised subjects, including those receiving ketamine. Trial registration clinicaltrials.gov, NCT 02648412.

The relevance of pupillometry for evaluation of analgesia before noxious procedures in the intensive care unit

BACKGROUND

Many patients in the intensive care unit are unable to communicate verbally. Accurately predicting whether such patients will exhibit painful behaviors during noxious procedures and assessing the adequacy of analgesia during those procedures is a challenge. In addition to observational pain assessment tools such as the Behavioral Pain Scale, physiologic indicators such as the pupillary response have been proposed. The pupil is innervated by both divisions of the autonomic nervous system and is affected by pain and analgesic medications. We evaluated the pupillary response to a light stimulus before noxious procedures as a method to predict pain during the procedure.

METHODS

We correlated different aspects of the pupillary light reflex with established strategies for pain assessment to evaluate the adequacy of analgesia before surgical dressing changes performed in the intensive care unit in patients with cellulitis associated with mediastinitis or not.

RESULTS

We found that a percentage of variation in pupil size >19% predicted the presence of pain as assessed by a Behavioral Pain Scale score of >3 with a sensitivity of 100% (95% confidence interval, 100%-100%) and a specificity of 77% (95% confidence interval, 54%-100%).

CONCLUSIONS

In patients unable to communicate verbally, pupillometry may potentially guide caregivers to adjust analgesia before noxious procedures.

Assessing pain objectively: the use of physiological markers

Pain diagnosis and management would benefit from the development of objective markers of nociception and pain. Current research addressing this issue has focused on five main strategies, each with its own advantages and disadvantages. These encompass: (i) monitoring changes in the autonomic nervous system; (ii) biopotentials; (iii) neuroimaging; (iv) biological (bio-) markers; and (v) composite algorithms. Although each strategy has shown areas of promise, there are currently no validated objective markers of nociception or pain that can be recommended for clinical use. This article introduces the most important developments in the field and highlights shortcomings, with the aim of allowing the reader to make informed decisions about what trends to watch in the future.

Pharmacologically stimulated pupil and accommodative changes in Guinea pigs

PURPOSE

The guinea pig is being used increasingly as a model of human myopia. As accommodation may influence the effects of manipulations used in experimental myopia models, understanding the accommodative ability of guinea pigs is important. Here, nonselective muscarinic agonists were used as pharmacological tools to study guinea pig accommodation.

METHODS

Measurements were made on 15 pigmented guinea pigs. For in vivo testing, animals were anesthetized and, following baseline measurements, 2% pilocarpine was applied topically. Measurements included A-scan ultrasonography, optical coherence tomography (OCT) imaging, corneal topography, and refraction. In vitro lens scanning experiments were performed using anterior segment preparations, with measurements before and during exposure to carbachol. Anterior segment structures were examined histologically and immunohistochemistry was done to characterize the muscarinic receptor subtypes present.

RESULTS

In vivo, pilocarpine induced a myopic shift in refractive error coupled to a small, but consistent decrease in anterior chamber depth (ACD), a smaller and more variable increase in lens thickness, and a decrease in pupil size. Lens thickness increases were short-lived (10 minutes), while ACD and pupil size decreased over 20 minutes. Corneal curvature was not significantly affected. Carbachol tested on anterior segment preparations in vitro was without effect on lens back vertex distance, but did stimulate pupil constriction. Immunohistochemistry indicated the presence of muscarinic receptor subtypes 1 to 5 in the iris and ciliary body.

CONCLUSIONS

The observed pilocarpine-induced changes in ACD, lens thickness, and refraction are consistent with active accommodation in the guinea pig, through cholinergic muscarinic stimulation.

Evaluation of the depth of sedation in an intensive care unit based on the photo motor reflex variations measured by video pupillometry

Background

Evaluating depth of sedation in the intensive care unit (ICU) is crucial for the management of mechanically ventilated patients but can be challenging in some situations. Because the depth of hypnosis is correlated with the decrease in photomotor reflex (PMR), we suggest using pupillometric video as an automated, noninvasive, simple, and reproducible technique to evaluate the depth of sedation in ICU patients. We compare the effectiveness of this procedure to the bispectral index (BIS).

Methods

Thirty-one patients requiring sedation and ventilation were included in this monocentric, observational study. The posology of hypnotics and morphinics were based on the Richmond Agitation and Sedation Scale (RASS). PMR was measured by the Neurolight® (IDMED) system and BIS value by BIS Vista® (Anandic Medical Systems). RASS, PMR, and BIS were measured three times daily in all patients. Data acquired by pupillometric video included variation in pupillary diameter (ΔPD), latency time (LT), and maximal speed of pupillary constriction (Vmax). These parameters were analyzed after having classified BIS values in three groups (<40 heavy sedation; 40 ≤ BIS ≤ 60 acceptable sedation; >60 light sedation). Exclusion criteria were neurological or ophthalmologic pathologies that could interfere with PMR.

Results

There was a significant difference in Vmax and ΔPD between the BIS < 40 group and 40 ≤ BIS ≤ 60 groups (p < 0.0001 for each) and between the BIS < 40 and BIS > 60 groups (p < 0.0001 for each). There were no significant differences in Vmax and ΔPD between the 40 ≤ BIS ≤ 60 and BIS > 60 groups. There was no correlation between any of the BIS groups and LT.

Conclusions

Vmax and ΔPD seem to be relevant criteria compared with the BIS and the RASS. Pupillometric video monitoring of depth of sedation could be beneficial in ICU patients, especially for those under myorelaxant drugs, where no clinical evaluation of sedation is possible.

L-Carnitine rescues ketamine-induced attenuated heart rate and MAPK (ERK) activity in zebrafish embryos

Ketamine, an antagonist of the N-methyl-D-aspartate (NMDA)-type glutamate receptors, is a pediatric anesthetic. Ketamine has been shown to be neurotoxic and cardiotoxic in mammals. Here, we show that after 2 h of exposure, 5 mM ketamine significantly reduced heart rate in 26 h old zebrafish embryos. In 52 h old embryos, 1 mM ketamine was effective after 2 h and 0.5 mM ketamine at 20 h of exposure. Ketamine also induced significant reductions in activated MAPK (ERK) levels. Treatment of the embryos with the ERK inhibitor, PD 98059, also significantly reduced heart rate whereas the p38/SAPK inhibitor, SB203580, was ineffective. Ketamine is known to inhibit lipolysis and a decrease of ATP content in the heart. Co-treatment with l-carnitine that enhances fatty acid metabolism effectively rescued ketamine-induced attenuated heart rate and ERK activity. These findings demonstrate that l-carnitine counteracts ketamine's negative effects on heart rate and ERK activity in zebrafish embryos.