ADRENOCORTICAL AND METABOLIC RESPONSES TO DOBUTAMINE INFUSION DURING HALOTHANE ANESTHESIA IN PONIES

The study investigated whether hypotension in halothane-anaesthetised ponies is the stimulus inducing an endocrine stress response by assess ing the effect of maintenance of normotension with a dobutamine infusi on, Groups of six ponies were studied. After premedication with acepro mazine (0.04 mg/kg) anaesthesia was induced with thiopentone (10 mg/kg ) and maintained for 120 min with halothane (group AN). Dobutamine was infused to effect (1.1-4.4 mu g/kg/min) to maintain arterial pressure at pre anaesthetic levels. The conscious group (CON) were prepared as for AN and then received only dobutamine infusion 1.0 mu g/kg/min for 120 min, Arterial blood pressure, pH, oxygen and carbon dioxide tensi on, pulse rate, haematocrit, and plasma cortisol, glucose and lactate concentrations were measured before, at 20 min intervals during anaest hesia, and 20 and 120 min after anaesthesia ceased. Blood pressure rem ained close to control in both groups. The AN group became hypercapnic and acidotic, pulse rate and haematocrit increased, cortisol increase d more than twofold and plasma glucose and lactate did not change. All values remained at control in the CON group except for small increase s in haematocrit and decreases in pulse rate. Maintenance of normotens ion during halothane anaesthesia did not blunt the adrenocortical resp onse to anaesthesia nor did the same dose of dobutamine alone increase plasma cortisol, Hypotension appears not to be the sole stimulus to e quine adrenocortical activity during halothane anaesthesia.