Motor effects of fentanyl in isoflurane-anaesthetized pigs and the subsequent effect of ketanserin or naloxone.

OBJECTIVE

To examine the effect of ketanserin and naloxone on fentanyl-induced motor activity in isoflurane-anaesthetized pigs.

STUDY

DESIGN

Randomized, blinded, prospective two-group study.

ANIMALS: A group of 12 crossbred pigs weighing 22-31 kg.

METHODS

Fentanyl was administered to isoflurane-anaesthetized pigs at 7.5 μg kg-1 hour-1 for 40 minutes intravenously, followed by an intravenous injection of naloxone 0.1 mg kg-1 or ketanserin 1 mg kg-1. Electromyography (EMG) and accelerometry were used to record motor unit activity and tremors, respectively. To test the effect of drug administration on motor activity, data from a 5 minute period at baseline, immediately before and after antagonist injection were compared in a mixed model; p < 0.05.

RESULTS

Results are reported with the median difference, 95% confidence intervals and corresponding p-values in brackets. Fentanyl significantly increased EMG activity [30.51 (1.84-81.02) μV, p = 0.004] and induced tremors [0.09 (0.02-0.18) m s-2, p < 0.001] in 10 of 12 pigs. Ketanserin significantly reduced EMG [32.22 (6.29-136.80) μV, p = 0.001] and tremor [0.10 (0.03-0.15) m s-2, p = 0.007] activity. No significant effect was found for naloxone on EMG [26.76 (-13.28-91.17) μV, p = 0.4] or tremors [0.08 (-0.01-0.19) m s-2, p = 0.08].

CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl can induce motor activity in anaesthetized pigs, with a suggested link to the serotonergic system. This study shows that ketanserin can antagonize this activity, which supports the role of serotonin. This knowledge contributes to the general understanding of the motor effects of fentanyl and especially the problem of tremors in anaesthetized pigs.