Preoperative Glycemic Management

Preoperative Glycemic Management

In patients using insulin, frequent glucose monitoring should be utilized to ensure that glucose values are within normal ranges. Patients should monitor blood glucose levels vigilantly including before and after meals as well as before sleeping. Additionally, finger stick glucose monitoring should be completed every 4 to 6 hours in any patient who is nil per os (NPO), with supplemental insulin used to correct hyperglycemia back to normal values [57]. When using supplemental-scale coverage, short-acting insulin (humulin, novolin) has a shorter duration of action than human insulin and may be given subcutaneously every 4 to 6 hours; however to prevent insulin stacking regular human insulin should not be given more than every 6 hours to correct hyperglycemia [57]. Traditionally, long-acting insulin (glargine, ultralente) is discontinued two to three days prior to surgery; glucose levels are instead stabilized by a combination of intermediate insulin (NPH) with short-acting insulin twice daily or regular insulin before meals and intermediate-acting insulin at bedtime [62]. However, if glycemic control is well managed in a patient being treated with glargine, it is acceptable to continue the same insulin regimen until the day of surgery [63]. Finally, it is important to confirm the form of diabetes present, as patients with type 1 diabetes must continue a basal rate insulin replacement preoperatively (0.2 to 0.3 U/kg/day of a long-acting insulin) [57].

Along with careful insulin regulation, there are a number of oral glycemic control drugs that should be discontinued before surgery. Biguanides (metformin) sensitize specific tissues to insulin, mediating efficient uptake of glucose in muscle and fat while preventing hepatic glucose formation. Metformin usage is discontinued before surgery in the United States and Europe due to renal function complications that may arise intraoperatively (such as hemodynamic instability or decreased renal perfusion), increasing the risk of lactic acidosis [64, 65]. Alpha glucosidase inhibitors (acarbose, miglitol) weaken the effect of oligosaccharidases and disaccharidases in the intestinal brush border, effectively lowering the absorption of glucose after meals. However, in preoperative fasting states, this drug has no effect and thus should be discontinued until the patient resumes eating [66]. Thiazolidinediones (pioglitazone, rosiglitazone) mechanism of action is similar to that of metformin and however is not associated with lactic acidosis. Nevertheless, these drugs are generally discontinued as they are not insulin secretagogues and may also cause fluid retention in the postoperative phase [57, 67]. Sulfonylureas (glibenclamide, glimepiride, and glipizide) trigger insulin production and may induce hypoglycemia in a fasting preoperative patient. If a patient has mistakenly taken a sulfonylurea on the day of surgery, the operation may still be completed; however, careful glucose monitoring is imperative and IV dextrose may be required [65, 68]. Glucagon-like peptide-1 (GLP-1) agonists (exenatide, liraglutide) are held the day of surgery as they slow gastric motility and may delay restoration of proper gastrointestinal function during recovery. Finally, because dipeptidyl peptidase-4 (DPP-4) inhibitors (sitagliptin, linagliptin) work by a glucose dependent mechanism (reducing the risk of hypoglycemia even in fasting patients) they may be continued if necessary; however, these medications primarily reduce glycemic levels after meals and their effects will be greatly marginalized in preoperative NPO patients [57].

There currently exists no evidence-based guideline dictating when to cancel surgery due to hyperglycemia. As a rule, elective surgery should not be performed on patients in a compromised metabolic state (DKA, HHS, etc.). Although no strict standard for surgical cancellation has been determined, the Yale New-Haven Hospital recommends postponing surgery if glucose is greater than 400 mg/dL. Similarly, at Boston Medical Center, it is recommended to postpone nonurgent surgical procedures if glucose is >500 mg/dL. In the event surgical cancellation is required, physicians should first manage any metabolic pathologies if present. After resolution of any underlying metabolic abnormalities, clinicians may then aim to restore blood glucose back to target range using combination insulin therapy as described above [69].