The effect of two doses of fentanyl on chest wall rigidity at equipotent doses of isoflurane in dogs.

Abstract

OBJECTIVE\nTo evaluate the effect of two doses of fentanyl upon chest wall rigidity of dogs anesthetized at equipotent doses of isoflurane [1.3 minimum alveolar concentration (MACISO) of each dose of fentanyl].\n\n\nSTUDY DESIGN\nProspective crossover randomized study.\n\n\nANIMALS\nA group of eight male Beagle dogs, approximately 1 year old and weighing 12.1 ± 1.6 kg (mean ± standard deviation).\n\n\nMETHODS\nThe dogs were anesthetized with isoflurane and instrumented for the measurement of esophageal pressure (PESO), flow (V˙) and volume (V). Chest wall elastance (ECW) was estimated by multiple linear regression of the model. PESO(t)\xa0= V˙(t)\xa0× RCW\xa0+ V(t)\xa0× ECW\xa0+ EEPESO where t is time, RCW is chest wall resistance and EEPESO is end-expiratory PESO. Chest wall compliance (CCW) was calculated as 1/ECW and normalized to the body weight of each dog (mL cmH2O-1 kg-1). Anesthesia was maintained at 1.3 MACISO for at least 15 minutes and CCW recorded (CCW-ISO). The dogs were randomly assigned to the lower fentanyl dose [loading dose (33 μg kg-1) and infusion (0.2 μg kg-1 minute-1)] or the higher fentanyl dose [loading dose (102 μg kg-1) and infusion (0.8 μg kg-1 minute-1)]. After 60 minutes of fentanyl infusion, CCW was recorded for each dose (CCW-FENT). During fentanyl infusion, the dogs were maintained at equipotent doses of isoflurane (1.3 MACISO for each fentanyl dose). A two-way analysis of variance followed by a Bonferroni test was used to compare CCW-ISO and CCW-FENT in both treatments and CCW-FENT between treatments. A p value <0.05 was considered significant.\n\n\nRESULTS\nNeither of the fentanyl doses decreased CCW and there was no difference in CCW-FENT between doses.\n\n\nCONCLUSIONS AND CLINICAL RELEVANCE\nFentanyl at the studied doses did not result in chest wall rigidity in dogs anesthetized with equipotent doses of isoflurane (1.3 MACISO).