A simple method for assessing analgesic requirements and efficacy in rodents.

Evaluation of pain in the clinical setting is an ongoing challenge for veterinarians, researchers and IACUCs. Behavioral assessment, a common technique for evaluating pain, is subjective and difficult to translate into quantifiable data. The authors propose measuring changes in body weight, food consumption and water consumption as a simple and objective method for evaluating postsurgical pain and analgesic efficacy in rodents.

Duration of clinical effects and absence of referred hyperalgesia after femoral vein cannulation in rats.

The goal of this study was to assess the duration of pain-related clinical effects and referred hyperalgesia after surgery in rats. Isoflurane anesthesia with or without femoral vein cannulation was performed (n = 6 per group). Body weight and food and water consumption were monitored daily for 48 h, and tail-flick latency was measured twice daily for 24 h after surgery. Water consumption at 24 h after surgery was significantly decreased in the surgical group compared with baseline values and those of the anesthesia group. Body weight change and food consumption showed nonsignificant decreases compared with baseline in both groups 24 h after the procedure. There was a trend toward decreased food consumption after surgery compared with that for the anesthesia-alone group. Tail-flick latency was nonsignificantly decreased the afternoon after surgery compared with baseline values or that after anesthesia alone. Tail-flick latency was similar to baseline and between groups 24 h after surgery. All parameters were similar between groups and compared with baseline by 48 h after surgery. Our results show some changes in postsurgical pain-related parameters only during the initial 24-h period after femoral cannulation surgery, but only the change in water consumption was significant. Although this study involved only a small number of animals, our findings suggest that femoral vein cannulation produces a less painful stimulus than that seen in studies assessing these parameters after abdominal surgery. Hyperalgesia from a distant painful stimulus could not be measured in this model by using the tail-flick assay.

Duration of effects on clinical parameters and referred hyperalgesia in rats after abdominal surgery and multiple doses of analgesic.

This study evaluated the duration of clinical effects and referred hyperalgesia in rats (n = 10 per group) undergo ing abdominal surgery with analgesics (ketoprofen at 3 mg/kg and buprenorphine at 0.01 or 0.1 mg/kg) administered intramuscularly twice daily for 72 h beginning prior to surgery; no-surgery and no-analgesia control groups were included. Food and water consumption and body weight were monitored daily. As a measure of referred hyperalgesia, tail-flick latency was measured daily, before and 4 h after analgesia administration. Compared with those of the no-surgery controls, significant decreases in food consumption and body weight occurred 24 h after surgery without analgesics. There were nonsignificant reductions in these effects by analgesics, but the benefits were not significantly different than those of saline. These parameters continued to be decreased with variable significance in the buprenorphine groups at 48 and 72 h after surgery. In both buprenorphine-treated groups, water consumption was significantly increased at 24 h after surgery but not at 48 or 72 h. Tail-flick latency was not significantly different between the no-surgery and no-analgesia groups but was significantly increased 4 h after high-dose buprenorphine administration and declined nonsignificantly over time in the other groups. We conclude that painful effects from surgery are present primarily during the first 24 h after surgery. The analgesic regimens tested did not completely reduce these effects. Buprenorphine was associated with adverse effects for as long as 72 h after surgery. Referred hyperalgesia from this abdominal surgery could not be measured using the tail-flick assay.