The recent NICE-SUGAR study of aggressive glucose control in the ICU randomized patients to a target blood glucose of 81 to 108 mg/dL (intensive group) or 180 mg/dL or less (control group). 12 At study’s end, the groups’ mean blood glucose levels were 115 mg/dL and 144 mg/dL, respectively, while rates of severe hypoglycemia (blood glucose < 40 mg/dL) were 6.8% and 0.5%, respectively. Mortality rates were higher in the intensive therapy group (27.5%) than in the control group (24.9%), driven by severe hypoglycemic events. Notably, blood glucose monitoring in this and other studies was conducted at a frequency of anywhere between 1 and 4 hours.
The conclusions of the available data would support, for the time being, a modified glycemic target in critically ill patients, with strict avoidance of severe hypoglycemia. The recent consensus statement from the American Association of Clinical Endocrinologists and the American Diabetes Association recommends using insulin therapy if blood glucose levels exceed 180 mg/dL, with target glucose levels less than 180 mg/dL in critically ill patients and less than 140 mg/dL in non–critically ill patients. 13 Development and implementation of safer insulin infusion algorithms and more frequent and accurate blood glucose monitoring in this setting should enable us to achieve better glycemic targets with lower risk.
ELEMENTS OF PHYSIOLOGIC INSULIN REPLACEMENT
In hospitalized patients with hyperglycemia, three different components of insulin replacement require management 1:
Basal insulin replacement consists of a long-acting insulin preparation administered regardless of the patient’s oral intake status, with the premise of matching hepatic (endogenous) glucose production
Prandial insulin replacement requires a rapid-acting insulin preparation given to cover nutritional needs
Supplemental (or correction) insulin replacement requires a rapid-acting preparation (usually the same insulin type as for prandial coverage) to correct blood glucose values that exceed predetermined glycemic targets.
For most patients, basal insulin replacement might be appropriate preoperatively to control fasting glucose, whereas during surgery, especially if prolonged or high risk, an intravenous (IV) insulin drip is the most effective means of glucose control. The postoperative transition from the IV insulin drip usually involves basal insulin replacement plus supplemental rapid-acting insulin. Prandial or nutritional insulin should be started once the patient begins to receive nutrition (oral, enteral, or hyperalimentation).
GOALS OF PERIOPERATIVE GLYCEMIC CONTROL
Perioperative glycemic management has several key objectives:
- Avoidance of clinically significant hyper- or hypoglycemia
- Maintenance of electrolyte and fluid balance
- Prevention of ketoacidosis, which is imperative in patients with type 1 diabetes, who require insulin at all times
- Achievement of specific glycemic targets, as discussed above—ie, less than 180 mg/dL in critically ill patients and less than 140 mg/dL in stable patients. 13
Strategies differ across the perioperative timeline
Strategies for perioperative glycemic control differ before, during, and after surgery, as summarized immediately below and detailed in the following sections.
Preoperatively, glycemia should be stabilized, typically with subcutaneous insulin, if there is enough time to do so. For patients who have not previously been on insulin, placing them on an insulin supplemental scale to correct glycemia to desired targets might be a first step. In the setting of hyperglycemia, these patients may also be started on a low dose of basal insulin, with preference given to basal insulin analogs, given their consistent and relatively peakless action profile and lower risk of hypoglycemia. A starting dose of 0.2 to 0.4 U/kg is appropriate and carries a low risk of hypoglycemia. For patients already using insulin on an outpatient basis, continuing their basal insulin dose, possibly at a reduced dosage (25% less), together with supplemental-scale insulin coverage, should stabilize blood glucose levels. For patients on combination insulin or premixed insulin types, the basal insulin dose for preoperative management can be estimated by taking the patient’s usual total daily dose and delivering 40% to 50% of that dose as a basal insulin analog injection. Clearly, a supplemental scale should be implemented along with basal insulin replacement.