What are the recommendations for adjusting insulin dosing (insulin therapy) preoperatively for patients with diabetes mellitus (DM) undergoing surgery?

Preoperative Insulin Dosing for Patients with Diabetes

Reduce basal insulin by 25% the evening before surgery to achieve optimal perioperative glucose control with the lowest risk of hypoglycemia. 1

Preoperative Optimization Timeline

Days Before Surgery

• Discontinue SGLT2 inhibitors 3-4 days before surgery to prevent life-threatening euglycemic diabetic ketoacidosis, which can occur even with normal glucose levels 1, 2, 3
• Target A1C <8% for elective surgeries whenever possible to reduce surgical risk, mortality, and infection rates 1, 2

Evening Before Surgery

• Administer 75-80% of usual long-acting insulin analog dose (or 50% of NPH dose if using intermediate-acting insulin) 1
• This 20-25% reduction is more effective than usual dosing for achieving target perioperative glucose (100-180 mg/dL) with significantly lower hypoglycemia risk 1, 2, 4
• Research demonstrates that patients taking 60-87% of their usual dose (optimal around 75%) had the highest proportion achieving target glucose range 4

Morning of Surgery

• Hold all oral glucose-lowering agents on the morning of surgery 1
• Hold metformin on the day of surgery 1, 2
• Do not administer rapid-acting or short-acting insulin unless specifically treating hyperglycemia 1

Intraoperative and Immediate Perioperative Management

Target Glucose Range

• Maintain blood glucose 100-180 mg/dL (5.6-10.0 mmol/L) within 4 hours of surgery and throughout the perioperative period 1, 2, 5
• Do not pursue stricter targets (<100 mg/dL or 80-180 mg/dL) as they increase hypoglycemia risk without improving outcomes 1, 2

Monitoring Protocol

• Monitor blood glucose at least every 2-4 hours while the patient is NPO 1, 2
• Do not use continuous glucose monitoring (CGM) alone for glucose monitoring during surgery 1

Insulin Administration While NPO

• Administer short- or rapid-acting insulin as needed to maintain target range based on frequent monitoring 1
• For critically ill patients, continuous intravenous insulin is the standard of care 1

Postoperative Insulin Management

Preferred Regimen

• Use basal-bolus insulin regimens (basal insulin plus premeal short/rapid-acting insulin) rather than correction-only insulin in noncardiac general surgery patients 1, 2
• This approach improves glycemic outcomes and reduces perioperative complications compared to reactive correction-only insulin without basal coverage 1

Transitioning from IV to Subcutaneous Insulin

• Administer basal insulin 2-4 hours before stopping IV insulin to prevent rebound hyperglycemia and recurrent ketoacidosis 1, 2

Special Situations

Glucocorticoid Therapy

• Glucocorticoids induce hyperglycemia in 56-86% of hospitalized patients, increasing mortality and morbidity risk 1
• Substantially increase prandial and correction insulin (40-60% or more) in addition to basal insulin when patients receive glucocorticoids 2
• Morning steroid therapy causes disproportionate daytime hyperglycemia requiring adjusted insulin timing 1

Insulin Pump Management

• Adjust pump basal rates based on type of diabetes and clinical judgment 1

Critical Pitfalls to Avoid

• Never continue full-dose basal insulin the evening before surgery—this increases hypoglycemia risk without benefit 1, 4
• Never use correction-only insulin without basal insulin in general surgery patients—this worsens outcomes and increases complications 1, 2
• Never continue SGLT2 inhibitors within 3-4 days of surgery—this poses unacceptable risk of euglycemic DKA 1, 2, 3
• Never stop IV insulin without prior subcutaneous basal insulin—this causes rebound hyperglycemia 1, 2
• Never pursue glucose targets <100 mg/dL perioperatively—this increases hypoglycemia without clinical benefit 1, 2
• Never underestimate hypoglycemia risk in patients presenting with low-normal glucose (70-89 mg/dL)—these patients have higher perioperative hypoglycemia rates than those treated for hyperglycemia 6

Evidence Quality Considerations

The 25% basal insulin reduction recommendation is supported by the highest quality evidence from the 2024 American Diabetes Association guidelines 1 and corroborated by prospective research demonstrating optimal glucose control with this approach 4. The basal-bolus superiority over correction-only insulin is consistently demonstrated across multiple studies in noncardiac surgery populations 1.