Intravenous glucose tolerance test during anaesthesia in dogs: insulin response and glucose clearance

To evaluate the insulin response and the rates of disappearance of glucose from plasma during high spinal analgesia and various types of general anaesthesia, a series of intravenous glucose tolerance tests was performed in six dogs. Plasma glucose and insulin levels were measured during the intravenous glucose tolerance tests. Insulinogenic indices were calculated. The values obtained during anaesthesia were compared to those obtained during an unanaesthetized state. The insulinogenic index was increased significantly during high spinal analgesia and thiopentone infusion. Halothane and enflurane anaesthesia decreased the insulinogenic index significantly while Innovar-nitrous oxide also decreased it, but not significantly. These findings suggest that insulin secretion in response to hyperglycaemia is stimulated by spinal analgesia and thiopentone anaesthesia, depressed by halothane and enflurane anaesthesia and unchanged during neuroleptanesthesia. A diuresis was observed in the thiopentone anaesthetic and spinal analgesic groups as compared to the other general anaesthetic groups. Urinary losses of insulin and glucose paralleled urinary output; yet the greatest mean urinary loss of glucose did not exceed 4.5 per cent of the load of glucose administered. Accordingly, 95 per cent of the administered glucose remained within the body, presumably available for utilization.