Perioperative plasma cortisol concentration in the horse

The cortisol response to anaesthesia and surgery was studied in 2 groups of horses undergoing either abdominal or non-abdominal surgery. The preoperative mean plasma cortisol concentration (pcc) of 381.7 nmol/l (s.d. 254.7) was markedly higher in the abdominal group than the early-morning mean pcc of 115.6 nmol/l (s.d. 78.4) in the non-abdominal group. During halothane anaesthesia and surgery the mean pcc increased significantly (p < 0.05) from the preoperative mean of 119.2 to 215.9 nmol/l (s.d. 79.8) after 30 min of surgery in the non-abdominal group. In the abdominal group a decrease occurred after induction of anaesthesia and surgical preparation, but increased during surgery to a mean pcc of 418.1 nmol/l (s.d. 236.5). In the postoperative period a large decrease in the mean pcc occurred after 24 h in the abdominal group. It was only after 60 h that the pcc (153.2 nmol/l) equalled the pcc of the non-abdominal group (171.4 nmol/l) at 24 h. The slow decline over 60 h could be an indication of the prolonged recovery associated with abdominal surgery in the horse.