The goal of management for all diabetic patients is the prevention of severe hyper- or hypoglycemia in the perioperative period. In addition, patients with type 1 diabetes are at risk for developing ketoacidosis. Increased secretion of cortisol, epinephrine, glucagon, and growth hormone during and after surgery causes insulin resistance and hyperglycemia in diabetic patients. Conversely, reduced caloric intake after surgery and frequent, unpredictable periods of fasting increase the risk for hypoglycemia. Thus, all surgical diabetic patients require frequent blood glucose monitoring. Ideally, patients with diabetes should undergo surgery early in the morning. The specific pharmacologic management of diabetes during the perioperative period depends on the type of diabetes (insulin-dependent or not), the level of glycemic control, and the type and length of surgery.
Poor preoperative glycemic control, as indicated by an elevated hemoglobin A1c level, is associated with a greater risk of surgical complications, particularly infections. However, a strategy of delaying surgery until glycemic control improves has not been rigorously studied. The ideal postoperative blood glucose target is also unknown. Trials have demonstrated that tighter perioperative glycemic control leads to better clinical outcomes in cardiac surgery patients in a critical care unit. This finding is not generally applicable to other surgical patients, however, since a subsequent trial demonstrated increased mortality with tight control in surgical patients in an ICU. Data are lacking on risks and benefits of tight control in patients outside of ICUs. Based on trials that showed increased mortality in hospitalized patients randomized to tight control, the American College of Physicians recommends maintaining serum glucose between 140 mg/dL and 200 mg/dL (7.8–11.1 mmol/L), whereas the British National Health Service guidelines recommend a range of 108–180 mg/dL (6–10 mmol/L). Even for coronary artery bypass patients, the Society of Thoracic Surgeons recommends a blood glucose range of 121–180 mg/dL (6.7–10 mmol/L).
A. Diabetes Controlled by Diet
For people with diabetes controlled with diet alone, no special precautions must be taken unless diabetic control is markedly disturbed by the procedure. If this occurs, small doses of short-acting insulin as needed will correct the hyperglycemia.
B. Diabetes Treated with Oral Hypoglycemic Agents
Most oral hypoglycemic agents should be held on the day of surgery. However, the sodium-glucose transporter 2 inhibitors (eg, canagliflozin) should be held for 3–4 days before surgery due to their long half-life and associated risk of ketoacidosis. Oral hypoglycemic agents should not be restarted after surgery until patients are clinically stable and oral intake is adequate and unlikely to be interrupted. Patients who experience significant hyperglycemia when oral agents are held should be treated in the same way as patients with type 2 diabetes who require insulin, as described below. Postoperative kidney function should be checked with a serum creatinine level prior to restarting metformin.
C. Diabetes Treated with Insulin