Pupillary assessment of sensory block level during combined epidural/general anesthesia.
BACKGROUND
Currently, no reliable method exists to determine the level of sensory block during combined epidural/general anesthesia. However, the pupil dilates markedly in response to noxious electrical stimulation during general anesthesia. Presumably, sensory block produced by epidural anesthesia decreases or obliterates this autonomic response. Accordingly, we tested the hypothesis that pupillary dilation in response to noxious stimulation would predict the level of sensory block achieved during combined epidural/general anesthesia.


METHODS
We studied eight volunteers and ten patients during combined epidural/general anesthesia. The volunteers were given an epidural infusion of 2% 2-chloroprocaine while general anesthesia was maintained with 0.8% isoflurane and 60% N2O. In the patients, an epidural infusion of 0.25% bupivacaine was combined with isoflurane and vecuronium. Noxious electrical stimulation was administered to dermatomal segments in a caudal-to-rostral progression. A twofold increase in pupil size following electrical stimulation was considered the predicted block level in volunteers. In patients, an increase in pupil size exceeding 50% was considered the predicted level. After general anesthesia was discontinued, observers blinded to the pupillary measurements independently determined the actual epidural block level using pain in response to a pinprick as the criterion.


RESULTS
The level predicted by pupillary responses was within two dermatomal segments of the actual level in all the volunteers. The predicted and actual block levels were within two segments in eight of the ten patients and never differed by more than four dermatomes.


CONCLUSIONS
We conclude that dilation of the pupil in response to electrical stimulation is an accurate test of the sensory block level during combined epidural/general anesthesia.
Larson
M D
MD
Department of Anesthesia, University of California, San Francisco 94143-0648.
Sessler
D I
DI
Ozaki
M
M
McGuire
J
J
Schroeder
M
M
D000328:Adult; D000767:Anesthesia, Epidural / Q000379:methods*; D000768:Anesthesia, General / Q000379:methods*; D001340:Autonomic Nerve Block; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011597:Psychomotor Performance / Q000187:drug effects; D011680:Pupil / Q000187:drug effects*; D012025:Reflex, Pupillary / Q000187:drug effects*