If a patient receives 6 units of regular insulin in total parenteral nutrition (TPN) with 100 g dextrose, how many units of insulin should be added when the dextrose is increased to 170 g?

Insulin Adjustment in TPN: Proportional Scaling Based on Dextrose Content

When dextrose in TPN increases from 100 g to 170 g, increase the insulin dose proportionally from 6 units to approximately 10 units of regular insulin. 1

Calculation Method

• The standard insulin-to-dextrose ratio in TPN is 0.1 units per gram of dextrose (equivalent to 1 unit per 10 g of carbohydrate). 1
• For 100 g dextrose: 100 g × 0.1 = 10 units would be the standard starting dose, but the patient is currently receiving 6 units (a ratio of 0.06 units/g). 1
• To maintain the same ratio when increasing to 170 g: 170 g × 0.06 = 10.2 units (round to 10 units). 1
• Alternatively, using the standard 0.1 ratio: 170 g × 0.1 = 17 units would be appropriate if glycemic control has been suboptimal on the current regimen. 1

Recommended Approach

• Start with 10 units of regular insulin in the new 170 g dextrose TPN bag to maintain the current insulin-to-dextrose ratio. 1
• If blood glucose has been consistently >180 mg/dL on the previous regimen, consider starting with 12–15 units instead. 1
• Monitor capillary glucose every 6 hours during the first 24–48 hours after the TPN change. 1

Daily Adjustment Protocol

• If >20 units of correctional insulin are required in any 24-hour period, add the total correctional insulin used to the next day's TPN bag. 1
• When glucose remains >180 mg/dL despite adjustments, raise the TPN-bag insulin by 10–20% per day. 1
• If glucose falls <70 mg/dL, reduce the TPN-bag insulin by 10–20% immediately. 1

Safety Thresholds

• The insulin-to-dextrose ratio should remain below 0.2 units/g (34 units for 170 g dextrose). 1
• If the ratio exceeds 0.2 units/g, reformulate the TPN to increase lipid calories and decrease dextrose rather than continuing to escalate insulin. 1
• Maintain serum triglycerides <400 mg/dL (maximum 700–800 mg/dL) when increasing lipid content. 1

Correctional Insulin Protocol

• Provide separate subcutaneous correctional insulin using regular insulin every 6 hours or rapid-acting insulin every 4 hours. 1
• Simplified correction scale: 2 units for glucose 250–350 mg/dL; 4 units for glucose >350 mg/dL. 1
• These correction doses are in addition to the scheduled insulin in the TPN bag. 1

Critical Pitfalls to Avoid

• Do not rely solely on sliding-scale insulin for TPN patients; this practice is discouraged by major guidelines due to erratic glucose control. 1
• Only regular insulin should be added to TPN bags; rapid-acting insulin analogs (lispro, aspart, glulisine) are incompatible with parenteral nutrition solutions. 1, 2
• Never omit basal insulin in type 1 diabetes or insulin-dependent type 2 diabetes, even when TPN supplies all calories. 1
• If TPN is unexpectedly stopped, start a 10% dextrose infusion at 50–100 mL/h immediately to prevent hypoglycemia, as insulin already mixed in the discontinued TPN bag continues to be absorbed for several hours. 1, 2

Special Considerations

• For patients with known diabetes, the 1:10 ratio (0.1 U/g) is appropriate; those with type 2 diabetes and insulin resistance may require 1 unit per 8–10 g carbohydrate (0.1–0.125 U/g). 1
• For insulin-naïve patients, start conservatively with 1 unit per 15 g carbohydrate (≈0.067 U/g dextrose) and titrate upward over 24–48 hours. 1
• In patients with eGFR <30 mL/min or severe hepatic dysfunction, reduce the initial insulin dose by 25–50% (start with 0.05–0.075 units/g dextrose) and monitor glucose every 4–6 hours. 1