EFFECTS OF HYPERCAPNIA ON ENDOCRINE AND METABOLIC RESPONSES TO ANESTHESIA IN PONIES

Some metabolic and endocrine effects of hypercapnia were studied in si x ponies during halothane anaesthesia with neuromuscular blockade and controlled ventilation. Each was anaesthetised twice, once with a 40-m inute-period of hypercapnia (10 kPa) and once when normocapnia (5.3 kP a) was maintained throughout two hour's anaesthesia. Routine cardiovas cular monitoring was performed and blood samples were taken for assay of cortisol, insulin, glucose, lactate, muscle and liver enzymes and t otal protein. Anaesthesia induced hypotension and lacticacidaemia whic h were slightly ameliorated during hypercapnia. Hyperglycaemia was mor e marked during hypercapnia. Plasma cortisol increased in a similar ma nner in both groups and insulin tended to decrease. There were no majo r changes in the other variables measured. It was concluded that 40 mi nutes of hypercapnia during halothane anaesthesia in ponies may have i mproved perfusion and did not markedly alter the stress response.