Objective To compare the anti-nociceptive effect of tramadol, a combination of tramadol-lidocaine, and lidocaine alone when administered in the epidural space.
Study design Experimental randomized cross-over study.
Animals Seven healthy male goats, aged 9–11 months, weight 17.5–25.5 kg.
Methods Treatments were lidocaine, 2.86 mg kg−1, tramadol-lidocaine (1 mg kg−1 and 2.46 mg kg−1, respectively) and tramadol (1 mg kg−1) given into the epidural space. The volume of all treatments was 0.143 mL kg−1. Nociception was tested by pin prick and by pressure from a haemostat clamp. Times to the onset and duration of anti-nociception in the perineal region were recorded. Recumbency and ataxia were noted. Rectal temperature, heart rate and respiratory rate were recorded before and at 15 minute intervals for 2 hours after the administration of each treatment. Statistical comparison used one-way anova with a post hoc Duncan’s test as a post hoc. Significance was taken as p < 0.05.
Results Times (mean ± SD) to onset of and duration of loss of sensation, respectively in minutes were; lidocaine, 3 ± 1 and 85 ± 11), tramadol-lidocaine 4 ± 1 and 140 ± 2; tramadol 12 ± 1 and 235 ± 18. Onset and duration times were significantly longer with tramadol than the other two treatments. Duration was significantly longer with tramadol-lidocaine than with lidocaine alone. With lidocaine treatment all goats were severely ataxic or recumbent, after tramadol-lidocaine mildly ataxic, and after tramadol not ataxic. Rectal temperature, heart and respiratory rates did not differ significantly from baseline after any treatment.
Conclusions and clinical relevance The combination of tramadol-lidocaine given by epidural injection produced an anti-nociceptive effect in the perineal region, which was rapid in onset and had a longer duration of action than lidocaine alone. This combination might prove useful clinically to provide analgesia in goats for long-duration obstetrical and surgical procedures but surgical stimuli were not investigated in this study.