QUANTITATIVE ELECTROENCEPHALOGRAPHIC EVALUATION TO DETERMINE THE QUALITY OF ANALGESIA DURING ANESTHESIA OF HORSES FOR ARTHROSCOPIC SURGERY

We compared the anesthetic combination of detomidine, ketamine, and ha lothane in control horses not undergoing apparently painful procedures with that in horses during arthroscopic surgery. The effectiveness of this regimen in suppressing neurologic response to surgery was, thus, evaluated. In this study, significant differences were not observed i n electroencephalographic total amplitude, spectral edge, or beta-to-d elta frequency ratio between surgically treated and nonsurgically trea ted (control) horses. On the basis of its attenuation of encephalograp hic responses, we conclude that detomidine (20 mu g/kg of body weight, IV) and ketamine (2.2 mg/kg, IV) induction of anesthesia followed by maintenance with halothane is an effective regimen for control of pain in horses during arthroscopic surgery. The insignificant frequency ch anges observed without any other signs of inadequate anesthesia or pai n may indicate a surgical stress response. We hypothesize that brain a ctivity monitoring may give an earlier index to initiation of surgical ly induced stress than do hormonal responses, because endocrine altera tions are not as rapidly perceived as is the electroencephalogram. Ana lysis of spectral edge frequency changes could be used to evaluate ane sthetic regimens to find those that cause the least stress to the CNS during surgery in horses. Differences in species responses to an anest hetic agent or the regimen's effectiveness in prevention of pain durin g surgery may be identified by adoption of the study model. Evaluation of cardiopulmonary variables during anesthesia, with and without surg ery, did not reveal any alterations that would be relevant to CNS resp onses. Blood pressure, heart rate, Pao, Pace, and pH were stabilized b y use of intermittent positive-pressure ventilation in all horses, and dobutamine was administered, as needed, to avoid bias of electroencep halogram data.