Effects of bupivacaine and morphine on the electroencephalogram and postoperative pain in castrated dogs.

OBJECTIVE

To compare the effects of locally administered bupivacaine and systemic morphine, separately or in combination, on the electroencephalogram (EEG) and postoperative pain in castrated dogs.

STUDY

DESIGN

Randomized blinded clinical study.

ANIMALS: A group of 21 healthy mixed-breed dogs.

METHODS

Dogs were randomly assigned to one of three groups (n = 7 per group): morphine (0.5 mg kg-1), bupivacaine (2 mg kg-1) or a combination of both. Premedication consisted of acepromazine (0.05 mg kg-1) (all groups) and morphine (morphine and combination groups only) administered subcutaneously. Anaesthesia was induced with intravenous propofol to effect and maintained with halothane in oxygen. Bupivacaine was infiltrated at the incision site 30 minutes prior to surgery in bupivacaine and combination groups. Systolic arterial blood pressure (SAP), heart rate (HR) and haemoglobin oxygen saturation (SpO2) were recorded. All dogs underwent an open castration via a routine prescrotal approach. EEG was recorded throughout anaesthesia. Median frequency (F50), 95% spectral edge frequency (F95) and total power (Ptot) were derived from raw EEG traces. Postoperative pain was assessed at 1, 3, 6 and 9 hours using a short form of the Glasgow Composite Measure Pain Scale. EEG and pain scores were compared among groups using a generalized linear mixed model and Wilcoxon-Mann-Whitney odds macro, respectively. Data were presented as mean ± standard deviation (p < 0.05).

RESULTS

The morphine and bupivacaine groups had a significantly higher F50 and F95 and a lower Ptot than the combination group during castration. Postoperative pain scores did not significantly differ between bupivacaine and combination groups; both groups had significantly lower pain scores than the morphine group. SAP, HR and SpO2 did not differ significantly among groups.

CONCLUSIONS AND CLINICAL RELEVANCE: Presurgical incisional infiltration of bupivacaine, alone or with a systemic opioid, reduces intraoperative nociception and postoperative pain in dogs undergoing castration.