Outline perioperative management alternatives for the diabetic patient.
The goals of perioperative management are to avoid hyperglycemia and hypoglycemia. Severe hyperglycemia pre-disposes patients to osmotic diuresis as well as ketosis or nonketotic hyperosmolar states. Hypoglycemia risks CNS damage. Recent studies from the ICU and cardiac surgery indicate that serum glucose concentrations above 120 mg/dL may significantly increase mortality and morbidity. Traditionally, the perioperative target for serum glucose was 120–200 mg/dL, to minimize the potential for hypo-glycemia. This is probably still a reasonable goal for minor or moderately invasive procedures in noncritically ill patients. Patients who are critically ill or are having major procedures should have tighter glycemic control, in the range of 80–110 mg/dL. Protocols for tight glycemic control are still evolving, and several have been published (see Suggested Readings). This tighter control is more labor- and resource-intensive, and is currently not practical for all diabetic patients.
Oral hypoglycemic agents should be discontinued while patients are fasting. Residual hypoglycemic effects are opposed by administering 5% dextrose, if needed. The frequency of blood glucose measurements to monitor for hyperglycemia and hypoglycemia depends on the desired degree of control.
Because patients refrain from eating and drinking before surgery and anesthesia, insulin doses may be with-held or reduced, depending on the underlying physiology. Type I diabetics need insulin to avoid DKA. Type II diabet-ics with elevated fasting glucose concentrations also bene-fit from insulin therapy while fasting. Frequently, one half of the usual subcutaneous insulin dose is administered. Blood glucose concentrations determine the need for 5% dextrose infusion, typically started at 100 mL/hr. Insulin and dextrose infusions are adjusted based on blood glucose determinations at 1-hour intervals for major procedures or critically ill patients, and up to 4-hour intervals for minor procedures. Intravenous administration is far more reliable than subcutaneous dosing during periods of hemody-namic instability, vasoconstrictor administration, and/or hypothermia.
Bolus intravenous insulin dosing results in rapid decline of glucose levels for short periods of time. In contrast, con-tinuous intravenous administration of 0.01–0.02 U/kg/hr provides the optimal and easiest means of controlling serum glucose concentrations. The most reliable control is obtained with separate infusions of 5% dextrose and insulin mixed with half-normal saline to a concentration of 0.1 U/cc. Flushing the intravenous tubing with the insulin solution prevents significant loss of insulin to the plastic tubing. During periods of rapid glucose fluxes, blood glucose determinations are performed every hour. Measurements can be made every 4 hours after a steady state has been reached.
Autonomic dysfunction and/or severe cardiac disease may indicate invasive monitoring. Autonomic neuropathy predisposes patients to hypotension accompanying regional anesthesia and increases the risk of aspiration pneumonitis from gastroparesis. Aspiration prophylaxis and rapid sequence induction may be indicated. Peripheral neuropathies require particular care during positioning and moving to avoid traumatic injury. Hyperglycemia-induced osmotic diuresis indicates urinary bladder drainage.
Postoperatively, rapid resolution of sepsis and decreased levels of circulating catecholamines contribute to acute hypoglycemia.