A 26-year-old woman with type 1 diabetes presents with diabetic ketoacidosis: glucose 540 mg/dL, pH 7.08, bicarbonate 6 mEq/L, serum potassium 4.6 mEq/L. Intravenous fluids are started and regular insulin infusion at 0.1 U/kg/hour is begun. Which of the following is the correct approach to potassium?

• A Withhold all potassium because the admission level is normal
• B Wait until serum potassium falls below 3.0 mEq/L before replacing
• C Give a bolus of 40 mEq potassium chloride intravenously over 15 minutes
• D Add potassium 20 to 30 mEq/L to each litre of intravenous fluid immediately ✓

Explanation

Insulin drives potassium into cells and levels fall predictably during therapy. ADA guidance is to add potassium 20 to 30 mEq/L once the level is below 5.3 mEq/L, provided urine output is adequate, so replacement should start immediately here. Withholding until frank hypokalaemia risks fatal arrhythmia. Potassium below 3.3 mEq/L is the only situation where insulin is delayed and potassium replaced first.

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

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Written and medically reviewed by the StethoPrep medical team.