Effects of hypercapnia on endocrine and metabolic responses to anaesthesia in ponies

Some metabolic and endocrine effects of hypercapnia were studied in six ponies during halothane anaesthesia with neuromuscular blockade and controlled ventilation. Each was anaesthetised twice, once with a 40-minute-period of hypercapnia (10 kPa) and once when normocapnia (5.3 kPa) was maintained throughout two hour's anaesthesia. Routine cardiovascular monitoring was performed and blood samples were taken for assay of cortisol, insulin, glucose, lactate, muscle and liver enzymes and total protein. Anaesthesia induced hypotension and lacticacidaemia which were slightly ameliorated during hypercapnia. Hyperglycaemia was more marked during hypercapnia. Plasma cortisol increased in a similar manner in both groups and insulin tended to decrease. There were no major changes in the other variables measured. It was concluded that 40 minutes of hypercapnia during halothane anaesthesia in ponies may have improved perfusion and did not markedly alter the stress response.