Perioperative stress response in the dog: Effect of pre-emptive administration of medetomidine

Objective-To determine the effect of medetomidine on the stress response in duced by ovariohysterectomy in isoflurane-anesthetized dogs. Study Design-Prospective randomized study. Animals-Twelve healthy adult female purpose-bred dogs, weighing 16.8 to 25 kg. Methods-Two treatments were randomly administered to each of twelve dogs at weekly intervals: (1) Saline injected IM followed in 15 minutes by isoflur ane anesthesia (ISO) induced by mask and maintained at an end-tidal concent ration of 1.8% for 60 minutes; and (2) Medetomidine, 15 mu g/kg IM followed in 15 minutes by isoflurane anesthesia (ISO&MED) induced by mask and maint ained at an end-tidal concentration of 1.0% for 60 minutes. One week after completion of these two treatments, all dogs were ovariohysterectomized, si x receiving each treatment (SURG and SURG&MED). Central venous blood sample s (10 mL) were obtained immediately before medetomidine or saline (baseline ) and at 30, 75, and 195 minutes and 2 1 hours after administration of mede tomidine or saline in ISO and ISO&MED. In SURG and SURG&MED, samples were o btained immediately prior to injection of medetomidine or saline (baseline) and at 30 (before skin incision), 45 (after severence of the ovarian ligam ent), 75 (after skin closure), 105 (30 minutes after skin closure, dog reco vered and in sternal recumbency), 135, 195, 375 minutes, and 24 hours after the initial sample. Samples were analyzed for epinephrine, norepinephrine, adrenocorticotrophic hormone (ACTH), cortisol, insulin, and glucose. Data were analyzed by analysis of variance and where significant differences wer e found, a least significant difference test was applied. Results-Premedication with medetomidine prevented or delayed the stress res ponse induced by ovariohysterectomy in isoflurane-anesthetized dogs. Conclusions-The stress response induced by ovariohysterectomy, although sig nificant, is of short duration. Medetomidine safely and effectively reduced surgically-induced stress responses. Clinical Relevance-Surgically induced stress responses can be obtunded or p revented by administration of medetomidine. (C)Copyright 2000 by The Americ an College of Veterinary Surgeons.