• M D Larson and P D Berry.
• Department of Anesthesia, the University of California, San Francisco 94143-0648, USA.
• Reg Anesth Pain Med. 2000 Jan 1;25(1):60-6.

Background And ObjectivesEpidural fentanyl has been shown to gain rapid access to the circulation resulting in supraspinal effects. We compared the supraspinal effects of fentanyl via epidural versus intravenous (IV) routes, during isoflurane anesthesia. Supraspinal fentanyl effect was evaluated as a reduction of pupillary reflex dilation (PRD) measured with infrared pupillometry.MethodsEighteen patients undergoing abdominal procedures were studied during combined epidural and general anesthesia. General anesthesia was provided by 0.55 to 0.70% end-tidal isofurane in air:oxygen (50:50). Sensory block of the surgical field was established with bupivacaine 0.375% and confirmed by absence of PRD to cutaneous stimulation. A high cervical dermatome was then stimulated (60 to 70 mA) at 5-minute intervals via cutaneous needle electrodes, and PRD was measured with each stimulation, using infrared pupillometry. Baseline PRD was determined and then a randomized injection of cpidueral saline (n = 6), epidural fentanyl 3 microg/kg (n = 6), or IV fentanyl 3 microg/kg (n = 6) was given. Subsequently, PRD was measured at 5, 10, 20, 30, 40, 60, and 80 minutes. Maximum change in PRD and time to maximum change were calculated for each group.ResultsFollowing epidural injection, suppression of PRD was highly variable among subjects. The maximum suppression was 70+/-15% at 23.3+/-10.3 minutes for the epidural group and 96+/-3% at 10.8+/-7.4 min for the IV group (P<.0001). Epidural saline produced no effect.ConclusionsSupraspinal effects of epidural fentanyl can be assessed during general anesthesia using infrared pupillometry. Epidural fentanyl 3 microg/kg produces significant but variable supraspinal effects during 0.5 minimum alveolar concentration isoflurane anesthesia.

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