Cardiorespiratory responses and plasma cortisol concentrations in dogs treated with medetomidine before undergoing ovariohysterectomy

Objective-To evaluate effects of medetomidine on anesthetic dose requiremen ts, cardiorespiratory variables, plasma cortisol concentrations, and behavi oral pain scores in dogs undergoing ovariohysterectomy. Design-Randomized, prospective study. Animals-12 healthy Walker-type hound dogs. Procedure-Dogs received medetomidine (40 mu g/kg [18.2 mu g/lb] of body wei ght, IM; n = 6) or saline (0.9% NaCl) solution (1 ml, IM; 6) prior to anest hesia induction with thiopental; thiopental dose needed for endotracheal in tubation was compared between groups. Ovariohysterectomy was performed duri ng halothane anesthesia. Blood samples were obtained at various times befor e drug administration until 300 minutes after extubation. Various physiolog ic measurements and end-tidal halothane concentrations were recorded. Results-In medetomidine-treated dogs, heart rate was significantly lower th an in controls, and blood pressure did not change significantly from baseli ne. Plasma cortisol concentrations did not increase significantly until 60 minutes after extubation in medetomidine-treated dogs, whereas values in co ntrol dogs were increased from time of surgery until the end of the recordi ng period. Control dogs had higher pain scores than treated dogs from extub ation until the end of the recording period. Conclusion and Clinical Relevance-Administration of medetomidine reduced do se requirements for thiopental and halothane and provided postoperative ana lgesia up to 90 minutes after extubation. Dogs undergoing ovariohysterectom y by use of thiopental induction and halothane anesthesia benefit from anal gesia induced by medetomidine administered prior to anesthesia induction. A dditional analgesia is appropriate 60 minutes after extubation.