Intraoperatively, switching to IV insulin may be appropriate for stabilizing glycemia, depending on the type of surgery. A number of IV insulin protocols have been proposed, although no consistent comparisons of efficacy or safety among these protocols have been published.
Postoperatively, patients eventually should be transitioned from IV to subcutaneous insulin when glycemic control stabilizes. This transition may be complicated for many reasons. Oral intake may be inconsistent. The surgery and surrounding environment can induce stressors, promote susceptibility to infection, and increase insulin resistance. Additionally, some patients may be on hyperalimentation. Specific instructions for the transition from IV to subcutaneous insulin are covered later in this article.
PREOPERATIVE GLYCEMIC MANAGEMENT
In patients with type 2 diabetes, oral agents pose certain safety risks and should be discontinued prior to surgery.
Sulfonylureas may induce hypoglycemia in patients who are placed on NPO (“nothing by mouth”) orders and should be held in patients who are fasting.
Metformin can induce lactic acidosis if kidney function declines and should be withheld 1 to 2 days before planned surgery if a need for IV contrast is anticipated or the procedure could potentially lead to hemodynamic instability and reduced renal perfusion.
Thiazolidinediones may cause fluid retention that can complicate the postoperative period; they can be discontinued several days prior to a planned surgery.
GLP-1 agonists, such as exenatide, can slow gastric motility and potentially delay gastrointestinal recovery after major surgery; they should be held the day of surgery.
DPP-4 inhibitors (incretin enhancers) , such as sitagliptin, do not have significant side effects and, if need be, can be continued. Because incretin therapies act via a glucose-dependent mechanism, they are unlikely to cause hypoglycemia, even in a patient whose oral intake is held or delayed. On the other hand, since their effect is mostly in reducing postprandial glycemia, there may be little need to use them in a patient who is NPO.
Patients with type 1 diabetes must continue basal insulin replacement preoperatively (0.2 to 0.3 U/kg/day of a long-acting insulin). Patients with type 2 diabetes may benefit from basal insulin replacement, as previously noted.
Supplemental insulin scales are used to correct hyperglycemia regardless of a patient’s oral intake status. They can be individualized based on the estimated total daily insulin dose and require glycemic targets to be established. Fingerstick glucose monitoring should be done every 4 to 6 hours in a patient who is NPO, and supplemental-scale insulin should be used to correct glucose values that exceed target. For supplemental-scale coverage, rapid-acting insulin analogs have a shorter duration of action than human regular insulin and may be given subcutaneously every 4 to 6 hours, whereas regular insulin should not be given more often than every 6 hours to correct hyperglycemia. These differences in action duration should be kept in mind to minimize the potential for insulin stacking.
INTRAOPERATIVE GLYCEMIC MANAGEMENT
Procedure length is an important determinant
Strategies for intraoperative glucose management vary according to the length of the procedure.
For minor, short procedures, the preoperative glucose management orders may be continued.