CARDIORESPIRATORY, ENDOCRINE AND METABOLIC CHANGES IN PONIES UNDERGOING INTRAVENOUS OR INHALATION ANESTHESIA

Six Welsh gelding ponies (weight 246 +/- 6 kg) were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) followed by 0.02 mg/kg of detomidine i.v. Anaesthesia was induced with 2 mg/kg of ketamine i .v. Ponies were intubated and lay in left lateral recumbency. On one o ccasion anaesthesia was maintained for 2 h using 1.2% halothane in oxy gen. The same group of ponies were anaesthetized 1 month later using t he same induction regime and anaesthesia was maintained with a combina tion of detomidine, ketamine and guaiphenesin, while the ponies breath ed oxygen-enriched air, Electrocardiogram, heart rate, mean arterial b lood pressure, cardiac output, respiratory rate, blood gases, temperat ure, haematocrit, glucose, lactate and cortisol were measured and card iac index and systemic vascular resistance were calculated in both gro ups. Beta-endorphin, met-enkephalin, dynorphin, arginine vasopressin ( AVP), adrenocorticotrophic hormone (ACTH) and catecholamines were meas ured in the halothane anaesthesia group only and 11-deoxycortisol duri ng total intravenous anaesthesia (TIVA) only, Cardiorespiratory depres sion was more marked during halothane anaesthesia, Hyperglycaemia deve loped in both groups, Lactate and AVP increased during halothane anaes thesia. Cortisol increased during halothane and decreased during TIVA. There were no changes in the other hormones during anaesthesia. Recov ery was smooth in both groups, TIVA produced better cardiorespiratory performance and suppressed the endocrine stress response observed duri ng halothane anaesthesia.