Some metabolic and hormonal changes associated with general anaesthesia and surgery in the horse

Abstract

Summary Three different anaesthetic techniques were studied in normal, healthy Thoroughbred or Thoroughbred type horses. These were (a) acepromazine, thiopentone and suxamethonium; (b) acepromazine, glyceryl guaiacolate and a ‘half‐dose’ of thiopentone; and (c) xylazine and ketamine. Anaesthesia was maintained with halothane vaporised in oxygen and nitrous oxide. All horses underwent either laryngeal or body surface surgery. Heart rate, packed cell colume, blood glucose and lactate, plasma non‐esterified fatty acids, insulin and Cortisol were measured before, during and after surgery. The greatest metabolic and hormonal changes occurred immediately after anaesthetic induction and were different in each group. The combination of acepromazine, glyceryl guaiacolate and a ‘half‐dose’ of thiopentone was associated with the least change in the physiological and metabolic variables measured.

Effects of intravenous xylazine hydrochloride on blood glucose, plasma insulin and rectal temperature in neonatal foals

“…No change in rectal temperature has been reported in adult horses following xylazine administration (Kerr et a/ 1972a(Kerr et a/ , 1972bMuir et a1 1977). Sweating occurs in some horses after xylazine injection (Hoffman 1974;Robertson 1984) but does not appear to be a response to changes in body temperature. In the present study, xylazine caused a significant drop in rectal temperature at 30 mins post-administration in both 10 and 28 day old foals, when ambient temperature was maintained between 21 and 23'C.…”

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

“…Robertson (1987) and Robertson et al . (1990 ) have reported similarly enhanced endocrine and metabolic activity in horses during minor surgery under halothane anaesthesia.…”

“…(1990 ) have reported similarly enhanced endocrine and metabolic activity in horses during minor surgery under halothane anaesthesia. However, none of the studies investigating equine endocrine responses under anaesthesia has identified the stimulus to the stress response, particularly those that do not distinguish between the effects of surgery and anaesthesia ( Robertson, 1987; Taylor, 1989b; Robertson et al ., 1990 ; Taylor, 1991). Taylor (1990) raised the possibility that halothane‐induced hypotension acted as a stimulus to adrenocortical activity during anaesthesia, as barbiturate anaesthesia did not induce either hypotension or adrenocortical stimulation.…”

Feeding management pre- and post-surgery

“…In addition to a cortisol response, anesthesia and surgery result in other endocrine and metabolic responses, including increases in circulating catecholamines (Robertson 1987, Wagner et al 1990 and changes in insulin and glucose levels. The pre-anesthetic and anesthetic induction drugs can also affect insulin responses and glucose metabolism (Robertson 1987).…”

“…Alpha-2-adrenergic agents (such as xylazine) can inhibit insulin release by stimulating alpha-2adrenoceptors in pancreatic beta cells, thereby resulting in hyperglycemia (Thurmon et al 1982). Feed intake pre-and post-surgery will also affect the insulin response, with fasting resulting in a suppression of the insulin response, and refeeding enhancing insulin release (Robertson 1987, Taylor 1989, Robertson et al 1990. Surgery in humans generally causes hyperglycemia (Clarke 1973), but in horses this response appears to be more variable, and some anesthetic drugs may actually result in hypoglycemia (Robertson 1987, Taylor 1989, Robertson et al 1990.…”