Evaluation of five common induction protocols by comparison of hemodynamic responses to surgical manipulation in halothane-anesthetized horses.

OBJECTIVE

To determine whether hemodynamic responses of halothane-anesthetized horses undergoing surgical procedures depended on anesthetic induction protocols used, and to determine whether hemodynamic responses to surgical manipulation could be detected.

DESIGN

Prospective experimental study without controls.

ANIMALS

36 clinically normal horses.

PROCEDURE

Horses were allotted to 5 groups according to anesthetic induction protocol: acepromazine/guaifenesin/thiamylal, acepromazine/guaifenesin/ketamine, xylazine/guaifenesin/thiamylal, xylazine/guaifenesin/ketamine, and xylazine/diazepam/ketamine. Anesthesia was maintained with halothane. Hemodynamic measurements and blood gas values were obtained prior to the start of surgery, during surgery, and after surgery.

RESULTS

Few differences in hemodynamic measurements existed between horses in which anesthesia was induced by 5 anesthetic induction protocols, whether prior to the start of surgery or for pooled values for all 3 measurement periods. Hemodynamic responses to surgical manipulation were marked and included increased mean arterial pressure and systemic vascular resistance, and decreased cardiac index and oxygen delivery.

CLINICAL IMPLICATIONS

Choice of anesthetic induction protocol has little impact on hemodynamic function during surgery in halothane-anesthetized horses. Surgical stimulation may increase blood pressure, but does not improve cardiac index or oxygen delivery.