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Updated: Oct 21, 2025
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Objective Nociceptive Assessment in Ventilated ICU Patients: A Feasibility Study Using Pupillometry and the Nociceptive Flexion Reflex
Published on: July 4, 2018
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Detection of opioid effect with pupillometry
Rachel Eshima McKay1, Merlín D Larson1
1Department of Anesthesia and Perioperative Care, University of California San Francisco (UCSF), San Francisco, CA, United States of America.
Autonomic Neuroscience : Basic & Clinical
|September 2, 2021
Summary
Opioid administration significantly reduces pupillary unrest in ambient light (PUAL), serving as a specific indicator of central opioid effects. This finding is crucial for monitoring patients receiving opioids.
Area of Science:
- Neuroscience
- Pharmacology
- Ophthalmology
Background:
- Opioids are known to cause pupillary constriction.
- The effects of opioids on pupillary unrest and dynamic pupillary light reflex parameters remain uncharacterized.
- Distinguishing opioid-induced pupillary changes from brain insults is vital, especially with portable pupillometry in critical care.
Purpose of the Study:
- To investigate the impact of remifentanil infusion on pupillary unrest and dynamic pupillary light reflex parameters.
- To determine which pupillary responses are most consistently affected by remifentanil.
- To assess the utility of pupillary unrest in identifying central opioid effects.
Main Methods:
- Eighteen volunteers were studied using two portable infrared pupillometers.
- Pupillary unrest in ambient light (PUAL) was measured.
- Neurological pupillary index (NPi), constriction velocity (CV), pupil diameter (PD), latency, and % reflex (% reflex) were assessed following light stimulation.
- Remifentanil was administered progressively to achieve opioid effect concentrations associated with respiratory depression.
Main Results:
- Remifentanil administration ablated pupillary unrest in ambient light (PUAL), decreasing it by 94% from baseline.
- Other pupillary measurements (PD, CV, % reflex) decreased by 50-65%, with wide scattering at oxyhemoglobin desaturation.
- Neurological pupillary index (NPi) remained unchanged.
- PUAL consistently approached zero at maximum drug effect.
Conclusions:
- Pupillary unrest in ambient light (PUAL) is a highly specific indicator of central opioid effects.
- PUAL offers a non-invasive method for clinicians to monitor patients receiving opioids.
- This finding aids in differentiating opioid-induced pupillary changes from neurological insults.
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