In a 72-year-old patient with type 2 diabetes who requires 1–10 units of insulin per hour, how many units of regular insulin should be added to a total parenteral nutrition bag containing 180 g of dextrose?

Insulin Dosing for TPN in a 72-Year-Old with Type 2 Diabetes

Direct Answer

Add 18 units of regular insulin to the TPN bag containing 180 grams of dextrose, using the standard ratio of 1 unit per 10 grams of carbohydrate. 1, 2, 3

Calculation and Rationale

The American Diabetes Association and American College of Clinical Endocrinologists recommend starting with 1 unit of regular insulin for every 10 grams of dextrose in TPN. 1, 2, 3

• For 180 grams of dextrose: 180 g ÷ 10 = 18 units of regular insulin added directly to the TPN bag 1, 2, 3
• This patient's current requirement of 1-10 units per hour suggests insulin resistance, but the standard 1:10 ratio remains the appropriate starting point 2, 3
• Only regular human insulin should be added to TPN bags—never use rapid-acting analogs (lispro, aspart, glulisine) as they are incompatible with parenteral nutrition solutions 3

Essential Concurrent Management

Continue the patient's basal insulin separately, even though TPN provides all nutrition. 1, 3

• The basal insulin requirement does not disappear when TPN is initiated 1
• Patients with type 2 diabetes must maintain their background insulin to prevent ketosis and maintain baseline glycemic control 1, 3

Monitoring Protocol

Check capillary blood glucose every 6 hours initially, targeting 140-180 mg/dL. 1, 2, 3

• If blood glucose remains >180 mg/dL despite the initial dose, increase monitoring to every 4 hours 3
• If >20 units of correctional insulin are required in any 24-hour period, add that total amount to the next day's TPN bag. 1, 2, 3
• For persistent hyperglycemia, increase the TPN-bag insulin by 10-20% daily 3
• If blood glucose drops <70 mg/dL, reduce the TPN-bag insulin by 10-20% immediately 3

Correctional Insulin Regimen

Provide subcutaneous correctional insulin separately from the TPN-bag insulin. 1, 3

• Administer regular insulin every 6 hours OR rapid-acting insulin every 4 hours for hyperglycemia 1, 3
• This correctional insulin is in addition to the 18 units already in the TPN bag 3
• Do not rely solely on sliding-scale insulin—this practice is discouraged by major guidelines due to erratic glucose control 3

Critical Safety Measures

If TPN is unexpectedly interrupted or stopped, immediately start 10% dextrose infusion at 50-100 mL/hour. 1, 2, 3

• The 18 units of regular insulin already mixed in the TPN bag will continue to be absorbed for several hours after discontinuation 1, 3
• This creates a high risk of severe hypoglycemia if dextrose delivery stops abruptly 1, 2
• Check blood glucose every 2-4 hours until stable after any TPN interruption 3

Important Caveats for This Patient

Type 2 diabetes patients often require higher insulin doses than the standard 1:10 ratio due to insulin resistance. 2, 3

• Given this patient's current requirement of 1-10 units per hour (24-240 units daily), expect to escalate the TPN-bag insulin rapidly over the first 48-72 hours 2, 3
• If supplemental insulin requirements exceed 0.2 units per gram of dextrose (>36 units for 180 g), consider adjusting the TPN formulation by increasing lipid calories and decreasing dextrose calories 3
• When increasing lipids, keep serum triglycerides <400 mg/dL 3

Adsorption Considerations

Be aware that 5-56% of insulin may adsorb to ethylene vinyl acetate (EVA) TPN bags, reducing bioavailability. 4

• Glass containers have significantly less insulin adsorption than EVA bags 4
• Despite this adsorption, clinical studies show that adding insulin to TPN achieves reasonable glycemic control with low hypoglycemia rates 5, 6, 7
• The standard 1:10 ratio accounts for typical adsorption losses in clinical practice 1, 2, 3

Alternative Regimen (If Insulin Cannot Be Added to TPN)

If institutional policy prohibits adding insulin to TPN bags, use a subcutaneous basal-bolus approach. 3

• Deliver 50% of total daily insulin as long-acting basal insulin (glargine or detemir) once daily 3
• Provide the remaining 50% as NPH insulin every 12 hours to match continuous nutrient infusion 3
• Add correctional insulin every 4-6 hours based on glucose readings 3
• This approach is less preferred because it offers less precise alignment of insulin delivery with nutrient infusion 3