Calculating Total Daily Insulin Dose
The total daily insulin dose (TDD) can be calculated from the average hourly insulin infusion rate multiplied by 24, or by using weight-based formulas of 0.3-0.5 units/kg/day for insulin-naive patients. 1
Methods to Calculate Total Daily Insulin Dose
From IV Insulin Infusion
- Transition from IV to SQ insulin: Calculate TDD based on the average hourly insulin infusion rate over the previous 12 hours 1
- Formula: Average hourly rate (units/hour) × 24 = TDD
- Example: If average insulin infusion is 1.5 units/hour, TDD = 1.5 × 24 = 36 units/day
Weight-Based Calculation
- For insulin-naive patients: 0.3-0.5 units/kg/day 1
- Lower doses (0.3 units/kg) for patients with higher hypoglycemia risk:
- Elderly patients (>65 years)
- Renal impairment
- Poor oral intake
- Higher doses (0.5 units/kg) for patients with greater insulin resistance
- Lower doses (0.3 units/kg) for patients with higher hypoglycemia risk:
- For patients already on insulin at home with doses ≥0.6 units/kg/day: Reduce home TDD by 20% when hospitalizing to prevent hypoglycemia 1
Distribution of Total Daily Dose
Basal-Bolus Approach
- Basal insulin: 50% of TDD 1
- Given once or twice daily depending on insulin type
- Prandial (bolus) insulin: 50% of TDD 1
- Divided into three doses before meals
- Alternative calculation: 1 unit per 10-15g of carbohydrates 1
For Patients on Enteral/Parenteral Nutrition
- Basal insulin needs: 30-50% of TDD 1
- For continuous tube feedings: Calculate as 1 unit per 10-15g carbohydrate per day or 50-70% of TDD 1
Insulin Dose Adjustment Formulas
Carbohydrate-to-Insulin Ratio (CIR)
- Standard formula: CIR = 300-400 ÷ TDD 2
- Breakfast: CIR = 300 ÷ TDD
- Lunch and dinner: CIR = 400 ÷ TDD
- More recent research suggests: CIR = (217 ÷ TDD) + 3 3
Correction Factor (CF)
Monitoring and Adjustment
- Adjust basal insulin every 3 days based on fasting glucose patterns 5
- Adjust prandial insulin based on 2-hour postprandial glucose values 5
- Relationship between dosing factors: 100 ÷ Total Basal Dose = CIR = CF ÷ 4.5 4
Important Considerations and Pitfalls
- Avoid sliding scale insulin alone for patients with type 1 diabetes as it's associated with poor glycemic control 1
- Never abruptly discontinue insulin infusions, especially in type 1 diabetes patients, even if feedings are stopped 5
- Hypoglycemia risk increases 4-6 times with basal-bolus compared to sliding scale insulin 1
- Premixed insulin therapy (70/30) is associated with high rates of hypoglycemia and is not recommended for hospitalized patients 1
By following these evidence-based approaches to calculating and adjusting insulin doses, you can optimize glycemic control while minimizing the risk of hypoglycemia, ultimately improving patient outcomes.