For a patient on basal insulin like glargine (insulin glargine) given at night and NPO (nil per os) till surgery, should blood glucose levels be checked every 4 hours overnight and is D5 (5% dextrose) necessary?

Perioperative Glucose Monitoring and Dextrose Management for NPO Patients on Basal Insulin

For a patient on nighttime basal insulin (like glargine) who is NPO for surgery, you should check blood glucose every 2-4 hours overnight, and D5 is generally NOT necessary unless hypoglycemia occurs or the patient is at high risk for it. 1

Blood Glucose Monitoring Frequency

Check blood glucose at least every 2-4 hours while the patient is NPO. 1

• The most recent 2024 American Diabetes Association guidelines explicitly recommend monitoring "at least every 2-4 h while the individual takes nothing by mouth" 1
• Earlier 2018 guidelines suggested every 4-6 hours, but this has been tightened to 2-4 hours in more recent recommendations 1
• More frequent monitoring (every 2-4 hours rather than 4-6 hours) is particularly important overnight when hypoglycemia risk peaks between midnight and 6:00 AM in patients on basal insulin 1

Basal Insulin Dosing Adjustment

Reduce the evening basal insulin dose by approximately 25% (giving 75-80% of the usual dose) the night before surgery. 1

• The 2024 ADA guidelines recommend "a reduction by 25% of basal insulin given the evening before surgery is more likely to achieve perioperative blood glucose goals with a lower risk for hypoglycemia" 1
• This translates to giving 75-80% of the normal long-acting analog dose 1
• A 2017 observational study of 150 patients found that those taking 60-87% of their usual glargine dose (with optimal results at approximately 75%) had the highest proportion (78%) achieving target glucose range with minimal hypoglycemia 2

Dextrose Infusion: When Is It Necessary?

D5 infusion is NOT routinely necessary for all NPO patients on basal insulin, but should be started if hypoglycemia occurs or is anticipated. 1

When to START D5:

• If blood glucose falls below 70 mg/dL (treat hypoglycemia) 1
• If blood glucose is trending downward despite reduced basal insulin dose
• In patients at high risk for hypoglycemia, including:
  • Those with history of severe hypoglycemia during the current admission (84% of patients with severe hypoglycemia had a preceding episode) 1
  • Patients with impaired counterregulation 1
  • Those on higher doses of basal insulin who may have received inadequate dose reduction

When D5 is NOT needed:

• If glucose remains in target range (100-180 mg/dL) with the reduced basal insulin dose 1
• The basal insulin dose reduction (to 75-80%) is specifically designed to maintain euglycemia without requiring dextrose supplementation 1, 2

Target Blood Glucose Range

Maintain perioperative blood glucose between 100-180 mg/dL (5.6-10.0 mmol/L). 1

• Tighter targets (80-180 mg/dL) were used in older guidelines but are no longer recommended 1
• Stricter perioperative glycemic goals "may not improve outcomes and are associated with more hypoglycemia" 1

Correction Insulin Protocol

Use short- or rapid-acting insulin for correction doses as needed based on point-of-care glucose monitoring. 1

• Administer correction insulin when glucose exceeds 180 mg/dL 1
• Continue basal insulin coverage even while NPO—do not rely solely on correction insulin, as this "sliding scale only" approach is associated with worse outcomes 1

Common Pitfalls to Avoid

The most critical error is failing to reduce the basal insulin dose the evening before surgery, which significantly increases hypoglycemia risk, particularly overnight when 78% of hypoglycemic episodes occur in patients on basal insulin 1

Another common mistake is discontinuing basal insulin entirely while NPO, which leads to hyperglycemia and worse perioperative outcomes 1

Failing to adjust insulin doses after recognizing hypoglycemia: In one study, 75% of patients who experienced hypoglycemia did not have their basal insulin dose changed before the next administration 1

Practical Algorithm

1. Evening before surgery: Give 75% of usual glargine dose 1, 2
2. Overnight monitoring: Check glucose every 2-4 hours 1
3. If glucose 100-180 mg/dL: Continue monitoring, no intervention needed
4. If glucose >180 mg/dL: Give correction dose of rapid-acting insulin 1
5. If glucose <70 mg/dL or trending down: Treat hypoglycemia and consider starting D5 infusion
6. Morning of surgery: Hold oral agents, continue reduced basal insulin coverage 1