Quantitative Assessment of Pupillary Light Reflex in Acute Carbon Monoxide Poisoning

Quantitative Assessment of Pupillary Light Reflex for the Prediction of Neurocognitive Outcomes of Acute Carbon Monoxide Poisoning: A Prospective Observational Study

Neurological complications after acute carbon monoxide (CO) poisoning can range from transient headache or dizziness to cognitive dysfunction, seizure, permanent anoxic brain damages or death. A recent study reported that a lack of standard pupillary light reflex (sPLR), assessed using a pen light, was a predictor of 30-day neurological sequelae in patients with CO poisoning. Given that the basic sPLR has a poor inter-rater reliability, more objective and quantitative methods are required in the assessment of PLR.

An automated pupillometer has been used in the intensive care unit to quantitatively assess the PLR. Therefore, we hypothesized that quantitative assessment of PLR might be associated with neurocognitive sequelae after acute CO poisoning. The purpose of this study was to assess the value of quantitative pupillary reactivity (NPi and qPLR) in comparison to that of sPLR in predicting neurocognitive outcome at 1 month after acute CO poisoning.

Neurological complications after acute carbon monoxide (CO) poisoning can range from transient headache or dizziness to cognitive dysfunction, seizure, permanent anoxic brain damages or death. Although hyperbaric oxygen therapy (HBO2) has been tried to minimize the neurological complications, a significant percentage of patients still suffer from neurocognitive sequelae after acute CO poisoning. A recent study reported that a lack of standard pupillary light reflex (sPLR), assessed using a pen light, was a predictor of 30-day neurological sequelae in patients with CO poisoning. Given that the basic sPLR has a poor inter-rater reliability, more objective and quantitative methods are required in the assessment of PLR.

An automated pupillometer has been used in the intensive care unit to quantitatively assess the PLR. Quantitative PLR (qPLR), which is expressed as the percentage pupillary constriction in response to a calibrated light stimulus, was better in predicting neurological outcome after cardiac arrest (CA) compared to standard light reflex. In addition, the Neurological Pupil index (NPi) has been validated as a tool for assessing prognosis after CA because it is not influenced by medications (especially opioids and neuromuscular blocking agents) or small pupil size.

Therefore, the investigators hypothesized that quantitative assessment of PLR might be associated with neurocognitive sequelae after acute CO poisoning. The purpose of this study was to assess the value of quantitative pupillary reactivity (NPi and qPLR) in comparison to that of sPLR in predicting neurocognitive outcome at 1 month after acute CO poisoning.

Inclusion Criteria:

• Acute CO poisoning

Exclusion Criteria:

• Age <19 years
• Patients with a history of ophthalmic surgery which might have affected the PLR
• Patients with baseline cognitive deficit
• Refusal to enroll in this study
• Discharge from the ED or transfer to another hospital within 24 hours
• Expired in the ED
• Co-ingestion of drugs, such as hypnotics, that may affect the PLR
• No follow-up for the neurocognitive outcome