In a patient on insulin scheduled for surgery requiring pre‑operative NPO status, when should the rapid‑acting and basal insulin doses be held or reduced?

Perioperative Insulin Management: When to Hold Insulin Before Surgery

For patients on insulin scheduled for surgery, hold all rapid-acting/short-acting (prandial) insulin on the morning of surgery, reduce basal insulin to 75-80% of the usual long-acting analog dose (or 50% of NPH) on the morning of surgery, and reduce the evening basal insulin dose by 25% the night before surgery. 1, 2

Basal Insulin Adjustments

The Night Before Surgery

• Reduce the evening basal insulin dose by 25% from the usual dose the night before surgery 1, 2
• This single intervention is the most evidence-based strategy to achieve perioperative glucose targets (100-180 mg/dL) while minimizing hypoglycemia risk, which peaks overnight when 78% of hypoglycemic episodes occur 2

Morning of Surgery

• Give 75-80% of the usual long-acting basal insulin analog (glargine, detemir, degludec) dose on the morning of surgery 1, 3
• Give 50% of the usual NPH insulin dose if using intermediate-acting insulin 1, 3
• Never discontinue basal insulin entirely while NPO—this is a critical error that leads to hyperglycemia and worse perioperative outcomes 2

Rapid-Acting/Short-Acting (Prandial) Insulin

• Hold all rapid-acting and short-acting insulin on the morning of surgery 1
• Do not give any prandial insulin doses while the patient is NPO 1
• Use rapid-acting or short-acting insulin only for correction doses if blood glucose exceeds 180 mg/dL during the NPO period 1, 2

Blood Glucose Monitoring While NPO

• Monitor blood glucose every 2-4 hours throughout the NPO period, including overnight 1, 2
• Target range: 100-180 mg/dL (5.6-10.0 mmol/L) 1, 3
• Administer correction doses of rapid-acting or short-acting insulin when glucose exceeds 180 mg/dL 1, 2

Other Diabetes Medications to Hold

• Metformin: Hold on the day of surgery (can be taken with dinner the night before) 1, 4
• SGLT2 inhibitors: Discontinue 3-4 days before surgery due to euglycemic ketoacidosis risk 1, 3
• All other oral glucose-lowering agents: Hold on the morning of surgery 1

Dextrose Infusion Considerations

• D5 infusion is NOT routinely necessary for all NPO patients on reduced basal insulin 2
• Start D5 infusion only if blood glucose falls below 70 mg/dL or is trending downward despite the reduced basal insulin dose 2
• The 75-80% basal insulin dosing strategy is designed to maintain euglycemia without requiring routine dextrose supplementation 2

Critical Pitfalls to Avoid

Most Common Error

Failing to reduce the basal insulin dose the evening before surgery is the single most critical error, significantly increasing overnight hypoglycemia risk 2

Second Most Common Error

Discontinuing basal insulin entirely while NPO leads to hyperglycemia and increased perioperative complications 2

Third Common Error

Using correction-only ("sliding scale") insulin without basal insulin coverage is associated with poorer glycemic control and higher complication rates in surgical patients 3

Dosing Error

Inappropriately increasing basal insulin to control postprandial hyperglycemia will cause hypoglycemia in the fasting state—basal insulin doses in excess of basal requirements are dangerous when NPO 5

Perioperative Glucose Targets

• Target range: 100-180 mg/dL (5.6-10.0 mmol/L) throughout the perioperative period 1, 3
• Stricter targets (<100 mg/dL or 80-180 mg/dL) do not improve outcomes and significantly increase hypoglycemia risk 1, 3
• For elective surgeries, aim for HbA1c <8% when possible to reduce surgical risk 1, 3