Adrenocortical and metabolic responses to dobutamine infusion during halothane anaesthesia in ponies

Abstract

The study investigated whether hypotension in halothane-anaesthetised ponies is the stimulus inducing an endocrine stress response by assessing the effect of maintenance of normotension with a dobutamine infusion. Groups of six ponies were studied. After premedication with acepromazine (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 microg/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 microg/kg/min for 120 min. Arterial blood pressure, pH, oxygen and carbon dioxide tension, pulse rate, haematocrit, and plasma cortisol, glucose and lactate concentrations were measured before, at 20 min intervals during anaesthesia, and 20 and 120 min after anaesthesia ceased. Blood pressure remained close to control in both groups. The AN group became hypercapnic and acidotic, pulse rate and haematocrit increased, cortisol increased more than twofold and plasma glucose and lactate did not change. All values remained at control in the CON group except for small increases in haematocrit and decreases in pulse rate. Maintenance of normotension during halothane anaesthesia did not blunt the adrenocortical response to anaesthesia nor did the same dose of dobutamine alone increase plasma cortisol. Hypotension appears not to be the sole stimulus to equine adrenocortical activity during halothane anaesthesia.

Cardiopulmonary effects associated with head–down position in halothane–anesthetized ponies with or without capnoperitoneum

“…Whole blood lactate concentration did not significantly differ within, or between, treatments. The values obtained are similar to those of other studies of halothane‐anesthetized horses (Taylor 1998). Tissue perfusion and oxygen delivery may be assumed to be similar in both treatments, although the ER was significantly greater in the insufflated animals, only during the horizontal‐position phase.…”

Endocrine, haematological and metabolic responses to sevoflurane anaesthesia in lambs

“…1994) and horses (Taylor 1989, 1991, 1998a), and probably occurred in the current study, as levels of both reached a maximum 1 hour after the end of surgery. Hypotension caused by inhalation anaesthesia is one of the most important causes of pituitary–adrenocortical activation in ponies (Taylor 1989, 1998b; Taylor & Silver 1990) and sheep (Taylor 1998a,c, 1999), and most inhalation anaesthetics produce pituitary–adrenocortical activation (Oyama et al. 1979, 1989; Hall 1984; Taylor 1989).…”

Plasma arginine vasopressin concentration in horses undergoing surgery for colic

“…The increase in plasma AVP observed in our control horses at T90 and T120 might have been part of a compensatory response to vasodilation and hypotension caused by isoflurane. However, ponies anesthetized with halothane had increased levels of stress‐related hormones despite receiving dobutamine that maintained normotension 17 . The increased plasma AVP values in our control horses suggests that AVP release was stimulated by some other unidentified factor.…”

“…Horses may have a 10‐fold greater mortality rate during emergency general anesthesia for colic surgery 11–13 . In normal horses arterial hypotension and stress are common features of general anesthesia, 14–18 and plasma AVP concentration increases significantly during general anesthesia of healthy equids 19,20 . Endotoxemia occurs frequently in horses with colic, especially those with strangulating lesions of the intestinal tract.…”