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Latency of pupillary reflex dilation during general anesthesia
Merlin D Larson1, Peter D Berry, Jacqueline May
1Department of Anesthesia and Perioperative Care, University of California, San Francisco, CA 94143-0648, USA. larsonm@anesthesia.ucsf.edu
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 13, 2004
Summary
Pupillary reflex dilation during anesthesia is not initiated by slow C fibers. Fentanyl depresses this reflex, but it returns over time, with only a small initial latency increase.
Area of Science:
- Anesthesiology
- Neuroscience
- Pain Research
Background:
- Neuraxial anesthesia and peripheral nerve blocks induce insensibility.
- Pupillary reflex dilation failure indicates insensibility during general anesthesia.
Purpose of the Study:
- Examine pupillary reflex dilation latency during anesthesia.
- Investigate fentanyl's effect on this reflex latency.
- Test hypotheses regarding C-fiber involvement and fentanyl's impact.
Main Methods:
- Measured pupillary reflex dilation latency using infrared pupillometry in nine volunteers.
- Stimulated L4 and C5 dermatomes before and after intravenous fentanyl (3 microg/kg).
- Observed reflex recovery after naloxone administration.
Main Results:
- Pupillary reflex dilation exhibited long latency with early and late phases.
- No latency difference between L4 and C5 stimulation, before or after fentanyl.
- High-dose fentanyl largely abolished the reflex, with gradual return of early and late phases.
- Fentanyl caused a minor increase in early dilation latency.
Conclusions:
- Pupillary reflex dilation during anesthesia is not initiated by slowly conducting C fibers.
- Fentanyl depresses the pupillary reflex dilation in a predictable manner.
- The reflex demonstrates distinct phases and recovery patterns post-fentanyl.