How is long-acting insulin dose calculated for ICU patients over 24 hours?

Calculating Long-Acting Insulin Requirements in ICU Patients Over 24 Hours

Primary Calculation Method: The 50% Rule

Calculate the total units of IV insulin infused over the previous 24 hours when glucose levels have been stable (ideally <180 mg/dL), then give 50% of this total as once-daily subcutaneous long-acting basal insulin (such as glargine), administered in the evening. 1, 2, 3

Step-by-Step Algorithm

Step 1: Determine the 24-Hour IV Insulin Total

• Calculate the average hourly IV insulin infusion rate during the prior 6-8 hours when glucose levels have been stable 2
• Multiply this hourly rate by 24 to get the total daily insulin requirement 2
• For example: If a patient received an average of 1.5 units/hour during stable glycemic control, the estimated total daily dose would be 36 units (1.5 × 24 = 36 units) 2

Step 2: Calculate the Basal Insulin Dose

• Give 50% of the calculated 24-hour IV insulin total as once-daily long-acting basal insulin 1, 2, 3
• Using the example above: 36 units × 0.5 = 18 units of long-acting insulin 2

Step 3: Calculate the Prandial Insulin Component

• Divide the remaining 50% equally into three doses of rapid-acting insulin before each meal 1, 2, 3
• Using the example: 18 units ÷ 3 = 6 units of rapid-acting insulin before each meal 2
• If the patient has insufficient caloric supply, give half of the planned prandial dose 3

Critical Timing to Prevent Rebound Hyperglycemia

Administer the subcutaneous basal insulin exactly 2 hours before discontinuing the IV insulin infusion to allow adequate absorption and prevent dangerous rebound hyperglycemia, recurrent DKA/HHS, and increased hospital complications. 2, 1

• For basal insulin given in the evening, administer it immediately after stopping the IV infusion to prevent rebound hyperglycemia 1
• The IV insulin infusion must overlap with subcutaneous insulin administration 1
• Never stop the IV insulin infusion before administering subcutaneous basal insulin—this single error causes rebound hyperglycemia and recurrent metabolic crises 2

Prerequisites Before Transition

Ensure glucose levels have been stable for at least 4-6 hours consecutively on the IV insulin infusion before initiating transition. 2

• Confirm hemodynamic stability and that the patient has a stable nutrition plan or is able to eat 2
• For HHS specifically, resolution criteria must be met: calculated serum osmolality <315 mOsm/kg, patient alert and able to tolerate oral intake, and glucose target 200-250 mg/dL during HHS treatment 1

Dose Adjustments for Special Populations

Reduce the starting dose to 0.15-0.2 units/kg total daily dose in elderly patients (>65 years), those with renal insufficiency, or patients with poor oral intake to minimize hypoglycemia risk. 2, 4

• For hospitalized patients on high-dose home insulin (≥0.6 units/kg/day), reduce their home total daily dose by 20% rather than calculating from IV insulin rates 2
• For patients without diabetes on steroids, consider adding 0.1-0.3 units/kg/day glargine to the usual insulin regimen 4

Intensive Monitoring Requirements

Check capillary blood glucose before each meal and at bedtime during the first 24-48 hours after transition. 2

• Intensive glucose monitoring is mandatory during transition, with capillary blood glucose checked every 2-4 hours initially 1
• Monitor serum potassium closely as insulin drives potassium intracellularly, potentially causing life-threatening hypokalemia and cardiac arrhythmias 2, 1
• Ensure adequate renal function before full insulin dosing 1

Adding Correctional Insulin

Prescribe supplemental rapid-acting insulin using a correction scale to address hyperglycemia between scheduled doses. 2

• A typical correction factor is 1 unit of rapid-acting insulin per 50 mg/dL above target glucose 2
• Never use sliding scale (correction-only) insulin alone without scheduled basal and prandial insulin in patients with known diabetes, as this approach is associated with worse outcomes and higher complication rates 2

Alternative Dosing Strategy for Non-Eating Patients

While the 50/50 split (50% basal, 50% prandial) is most widely recommended, one approach suggests using 80% of the calculated dose as basal insulin only for patients not eating or on continuous enteral nutrition, with correction doses every 4-6 hours. 2

Common Pitfalls to Avoid

• Never continue premixed insulin regimens in ICU patients, as randomized trials show significantly increased hypoglycemia rates compared to basal-bolus therapy 4
• Do not use point-of-care capillary blood glucose measurements without caution, as they may not accurately estimate arterial blood or plasma glucose values 3
• Use arterial blood rather than capillary blood for point-of-care testing if patients have arterial catheters 3
• For insulin-naive type 2 diabetes patients, this basal-bolus regimen may be temporary, and once stable, many patients can transition to oral agents plus basal insulin only 1