How should I dose a continuous IV insulin infusion using a preparation of 100 units regular insulin in 100 mL normal saline (1 U/mL) for an adult patient?

Continuous IV Insulin Infusion Dosing Protocol

For adult patients requiring continuous IV insulin therapy, prepare a standardized solution of 100 units regular insulin in 100 mL normal saline (1 U/mL concentration), prime the tubing with 20 mL waste volume, and initiate at 0.1 units/kg/hour for diabetic ketoacidosis or 0.5–1 U/hour for general ICU hyperglycemia, targeting glucose 140–180 mg/dL in most critically ill patients. 1, 2

Standard Preparation and Priming

• Mix 100 units of regular human insulin into 100 mL of 0.9% sodium chloride to create a 1 U/mL concentration; this standardized preparation minimizes dosing errors and enables consistent titration across all ICU settings 1, 2

• Prime the infusion tubing with 20 mL of the prepared solution before connecting to the patient to ensure accurate concentration delivery and prevent insulin adsorption to the tubing walls 1

• Regular (short-acting) insulin is the only insulin formulation approved for intravenous administration; rapid-acting analogs (lispro, aspart, glulisine) must never be given IV 2

Diabetic Ketoacidosis (DKA) Protocol

Initial Dosing

• Administer 0.1 units/kg IV bolus of regular insulin as a direct push in adults with moderate-to-severe DKA, followed immediately by continuous infusion at 0.1 units/kg/hour 1, 2

• Pediatric patients should NOT receive an initial bolus; start continuous infusion at 0.05–0.1 units/kg/hour to minimize cerebral edema risk 1, 2

• Do not initiate insulin if serum potassium is <3.3 mEq/L; aggressively replete potassium first to prevent life-threatening cardiac arrhythmias (Class A evidence) 1, 2

Glucose Management During DKA

• Target glucose decline of 50–75 mg/dL per hour; if glucose does not fall by 50 mg/dL in the first hour, verify adequate hydration status and double the insulin infusion rate hourly until achieving steady decline 1, 2

• When plasma glucose reaches 250 mg/dL, switch IV fluid to D5W combined with 0.45–0.75% NaCl while continuing insulin infusion at the same rate to clear ketones 1, 2

• In euglycemic DKA (initial glucose <250 mg/dL), start D5W with normal saline from the outset of insulin therapy to prevent hypoglycemia while allowing ketone clearance 2

Potassium Replacement During DKA

• Add 20–30 mEq/L potassium to each liter of IV fluid once serum potassium falls below 5.5 mEq/L and adequate urine output (≥0.5 mL/kg/hour) is confirmed 1, 2

• Use a mixture of 2/3 potassium chloride (or potassium acetate) and 1/3 potassium phosphate to address concurrent phosphate depletion 1, 2

• Maintain serum potassium between 4.0–5.0 mEq/L throughout DKA treatment; monitor every 2–4 hours during active therapy 1, 2

General ICU Hyperglycemia Management

• Start insulin infusion at 0.5–1 U per hour for non-DKA hyperglycemia in critically ill patients, adjusting based on glucose measurements every 1–2 hours 1, 2

• Target glucose range of 140–180 mg/dL (7.8–10.0 mmol/L) for the majority of critically ill patients; tighter control (110–140 mg/dL) may be considered in selected cardiac surgery patients 1

• Use validated written or computerized protocols for dose adjustments to minimize hypoglycemia risk and improve glycemic control 3

Monitoring Requirements

• Check blood glucose every 1–2 hours during initial titration phase, then every 2–4 hours once stable 1, 2

• Measure serum potassium, electrolytes, venous pH, bicarbonate, anion gap, BUN, creatinine, and osmolality every 2–4 hours in DKA patients until metabolically stable 1, 2

• Monitor for hypoglycemia continuously; if glucose falls below 70 mg/dL, administer D50W and reduce insulin infusion rate rather than stopping insulin 2

Transition to Subcutaneous Insulin

Timing and Overlap Protocol

• Administer long-acting basal insulin (glargine or detemir) subcutaneously 2–4 hours BEFORE stopping the IV insulin infusion to ensure continuous insulin coverage and prevent rebound hyperglycemia or DKA recurrence 1, 2

• Continue IV insulin infusion for 1–2 hours after subcutaneous basal insulin administration to allow adequate absorption of the subcutaneous dose 1, 2

DKA Resolution Criteria

• All of the following must be met before transitioning: glucose <200 mg/dL, serum bicarbonate ≥18 mEq/L, venous pH >7.3, anion gap ≤12 mEq/L, and patient able to tolerate oral intake 2

Subcutaneous Dose Calculation

• Use approximately 50% of the total 24-hour IV insulin dose as a single daily injection of long-acting basal insulin 2

• Divide the remaining 50% of the 24-hour IV insulin dose equally among three daily meals as rapid-acting prandial insulin 2

High-Dose Insulin for Toxicological Emergencies

• For beta-blocker or calcium channel blocker overdose with refractory shock, administer 1 U/kg regular insulin as IV bolus with 0.5 g/kg dextrose, followed by continuous infusions of 0.5–1 U/kg/hour insulin and 0.5 g/kg/hour dextrose 3

• Concentrated insulin solutions (16 units/mL) may be prepared for high-dose insulin therapy to minimize fluid volume overload; this concentration remains stable for 14 days refrigerated or at room temperature 4

• Monitor glucose every 15 minutes initially during high-dose insulin-dextrose therapy; moderate hypokalemia (target 2.5–2.8 mEq/L) is expected 3

Critical Safety Considerations

Absolute Contraindications

• Never administer insulin IV if serum potassium <3.3 mEq/L; this is the single most important safety threshold (Class A evidence) 1, 2

• Never use rapid-acting insulin analogs intravenously; only regular human insulin is approved for IV administration 2

Common Pitfalls to Avoid

• Never stop IV insulin abruptly without prior subcutaneous basal insulin overlap; this is the most common cause of recurrent DKA 1, 2

• Never hold insulin when glucose falls during DKA treatment; instead add dextrose to IV fluid while maintaining insulin infusion to clear ketones 2

• Never tie potassium delivery to insulin infusion rate; maintain separate IV lines to allow independent titration of each therapy 2

• Never supplement potassium without first checking and correcting magnesium; hypomagnesemia (target >0.6 mmol/L) is the most common cause of refractory hypokalemia 2, 5

Indications for IV vs. Subcutaneous Insulin

• IV insulin infusion is preferred for: hemodynamically unstable patients requiring vasopressor support, type 1 diabetic patients in the ICU, and whenever rapid flexible titration is needed for strict glycemic control 1, 2

• Subcutaneous insulin regimens become acceptable once the patient is hemodynamically stable, alert, has resolved acute critical illness, and can tolerate oral intake 1, 2