Insulin Glargine Dosing for Postoperative Surgical Patients
For adult postoperative surgical patients transitioning from IV insulin to subcutaneous insulin glargine, administer 50% of the total 24-hour IV insulin requirement as a single dose of glargine, given 2 hours before discontinuing the IV infusion. 1, 2, 3, 4
Prerequisites Before Transition
Before converting to subcutaneous insulin glargine, ensure the following conditions are met:
- Blood glucose must be stable at ≤180 mg/dL for at least 24 hours 1, 2, 3
- Patient must have resumed oral feeding 1, 2, 3
- IV insulin infusion rate must be ≤3 U/hour - rates exceeding this indicate severe insulin resistance and increased risk of postoperative complications, requiring continued IV therapy 1, 2
Calculating the Glargine Dose
Step 1: Calculate total 24-hour IV insulin requirement
- Sum the total units of IV insulin administered during the most recent 24-hour period when glucose was stable 1, 2, 3
Step 2: Determine basal insulin dose
- Glargine dose = 50% of the 24-hour IV insulin total 1, 2, 3, 4
- Example: If patient received 40 units IV insulin over 24 hours, give 20 units glargine
Step 3: Calculate prandial insulin
- The remaining 50% becomes prandial insulin, divided by 3 meals 1, 2, 3
- Use ultra-rapid insulin analogue (lispro, aspart, or glulisine) before each meal 1, 2, 3
- Example: Remaining 20 units ÷ 3 = approximately 7 units before each meal
Critical Timing for Administration
Administer glargine 2 hours before discontinuing IV insulin - this overlap prevents dangerous rebound hyperglycemia and diabetic ketoacidosis 2, 3, 4
Optimal timing for glargine injection is 20:00 hours (8 PM) 1
Alternative Dosing for Insulin-Naive Patients
If the patient received IV insulin for <24 hours, was not previously on insulin, and remains hyperglycemic postoperatively:
- Start with 0.5-1 units/kg total daily insulin 1
- Divide as 50% basal glargine and 50% prandial rapid-acting insulin 1
- For type 2 diabetes patients never treated with insulin: start with 0.2 units/kg or up to 10 units once daily 5
Monitoring Requirements
Capillary blood glucose monitoring frequency:
- Every 1-2 hours while NPO 2, 3, 4
- Before each meal and at bedtime once eating 2, 3, 4
- Continue daily adjustments based on glucose patterns 2, 3
Hypoglycemia Management Protocol
For blood glucose <60 mg/dL (3.3 mmol/L):
- Administer 15-20 grams IV dextrose immediately, even without symptoms 2, 3, 4
- Post-pancreatectomy patients lack glucagon counter-regulation and cannot wait for symptomatic confirmation 2, 3
- Recheck glucose every 15 minutes until >100 mg/dL 2, 3
Hyperglycemia Management Protocol
For blood glucose >300 mg/dL (16.5 mmol/L):
- Check for ketosis immediately 2, 3, 4
- If ketonuria = 0 or ketonemia <0.5 mmol/L: give 6 units ultra-rapid insulin subcutaneously 2, 3, 4
- Ensure adequate hydration 2, 3
- Recheck glucose in 3 hours 2, 3, 4
Common Pitfalls to Avoid
Never discontinue IV insulin before administering subcutaneous glargine - this creates a dangerous gap in insulin coverage that can precipitate diabetic ketoacidosis 4
Do not transition if IV insulin rate exceeds 3 U/hour - this indicates severe insulin resistance requiring continued IV therapy 1, 2
Do not mix or dilute glargine with other insulins - administer as separate injections 5
Rotate injection sites (abdomen, thigh, deltoid) to reduce risk of lipodystrophy 5
Evidence Supporting Basal-Bolus Regimen
The basal-bolus scheme significantly reduces postoperative complications compared to sliding-scale insulin alone (composite complications 8.6% vs 24.3%, OR 3.39, P=0.003) 2, 3
This regimen more faithfully replicates normal pancreatic physiology with continuous basal coverage plus meal-related insulin spikes 1, 2, 3