POSTOPERATIVE CENTRAL HYPERSENSITIVITY AND PAIN - THE PREEMPTIVE VALUE OF PETHIDINE FOR OVARIOHYSTERECTOMY

The effect of timing of analgesic drug administration on the severity of post-operative pain was investigated in dogs undergoing ovariohyste rectomy using both subjective visual assessment scoring systems (VAS) and objective mechanical nociceptive threshold measurements using a no vel handheld anti-nociceptiometric device. Forty dogs undergoing routi ne elective ovariohysterectomy were included in a randomised and doubl e-blind study and assigned to one of three groups: (i) pre-operative a nalgesics; (ii) post-operative analgesics; (iii) no analgesics (saline injections). The analgesic used was pethidine (a short acting predomi nantly mu-opioid agonist), at a dose of 5.0 mg/kg (intramuscular). The post-operative administration of pethidine resulted in significantly higher sedation scores and significantly lower pain scores in the earl y post-operative period, but the dogs given pethidine pre-operatively had significantly lower pain scores than both the other,groups at 8, 1 2 and 20 h post-extubation (P < 0.01, ANOVA). Mechanical thresholds me asured at the distal tibia demonstrated the development of allodynia a t 12 and 20 h post-extubation, and this was significantly prevented by the pre-(P < 0.01 at 12 h, P < 0.05 at 20 h, Kruskal-Wallis and post hoc Dunn's), but not by the post-operative administration of pethidine . Mechanical nociceptive thresholds measured at the ventral midline (s ite of surgery) demonstrated post-operative hyperalgesia in all groups ; this hyperalgesia was least in the pre-operative pethidine group. In summary, this study clearly shows pethidine to be an effective analge sic in dogs, albeit of short duration of action, when administered pos t-operatively, and, importantly, that it has a positive benefit in ter ms of post-operative outcome measures, when administered pre-operative ly, possibly as a result of blocking or preventing the development of central sensitisation following surgical stimulation. (C) 1997 Interna tional Association for the Study of Pain. Published by Elsevier Scienc e B.V.