Cardiorespiratory, analgesic and gastrointestinal effects of fentanyl and lidocaine in rabbits undergoing ovariohysterectomy

Abstract

Background

Despite high analgesic efficacy, full mu agonist opioids are used with caution in rabbits largely due to the potential for gastrointestinal side effects. Systemic lidocaine enhances intestinal motility and reduces nociception and inflammatory responses. This study aimed to evaluate the cardiorespiratory, analgesic, and gastrointestinal effects of continuous infusion of fentanyl and lidocaine in rabbits undergoing elective ovariohysterectomy (OVH).

Methods

Nineteen New Zealand White rabbits were assigned to 3 groups: lidocaine (LG), fentanyl (FG), and fentanyl+lidocaine (FLG). Drugs were administered as follows: L - 2 mg kg-1 IV and continuous rate infusion (CRI) at 6 mg kg-1 hour-1; F – 0.002 mg kg-1 IV and CRI at 0.01 mg kg-1 hour-1. Measured variables included cardiorespiratory parameters, expired fraction of isoflurane (FE'Iso), plasma glucose concentration, body weight, food and water consumption, fecal output and pain scores.

Results

Fentanyl reduced heart and respiratory rate in FG and FLG. Reduction in mean arterial pressure and a higher FE'Iso compared to baseline was observed in LG. There was no difference in pain scores between groups, but 2 animals from LG and one from FLG required analgesic rescue. FG and FLG had a reduction in body weight, water and food intake and fecal output, mostly on the first and second postoperative days.

Conclusions and clinical relevance

The CRI of fentanyl and/or lidocaine may contribute to analgesia in rabbits undergoing OVH, but lidocaine CRI should be included within a multimodal analgesia protocol. Fentanyl affects intestinal motility in rabbits and the addition of lidocaine does not appear to prevent the effect of the opioid on the gastrointestinal tract.