A 24-year-old woman with type 1 diabetes presents with vomiting, Kussmaul breathing, glucose 540 mg/dL, pH 7.12, and serum potassium 3.0 mEq/L. After starting isotonic saline, what is the correct next step regarding insulin therapy?

• A Give an IV regular insulin bolus of 0.1 units/kg immediately
• B Add 5% dextrose to the fluids and start insulin concurrently
• C Start an insulin infusion only after the pH normalises
• D Withhold insulin, replace potassium, and begin insulin once potassium exceeds 3.3 mEq/L ✓

Explanation

Insulin drives potassium into cells and can precipitate fatal hypokalaemia and cardiac arrhythmia when the serum potassium is below 3.3 mEq/L. Standard protocol is to delay insulin, give 20 to 30 mEq of potassium per litre of fluid, and start the infusion once potassium exceeds 3.3 mEq/L. An immediate bolus (option A) is contraindicated here. Dextrose is added only once glucose falls below about 250 mg/dL.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.