A 64-year-old man on maintenance hemodialysis presents to the emergency department with severe weakness, palpitations, and near-syncope. He missed his last two dialysis sessions. Serum potassium is 8.4 mEq/L. The 12-lead ECG shows loss of P waves, progressive QRS widening (>200 ms), and blending of the QRS complex with the T wave to form a characteristic **sine wave** morphology, as marked **A** in the diagram. Blood pressure is 80/40 mm Hg. Which of the following is the most appropriate IMMEDIATE first-line intervention?
A. Intravenous regular insulin 10 units with 50% dextrose to shift potassium intracellularly
B. Nebulized salbutamol 10–20 mg to promote potassium shift via β2-agonism
C. Emergent hemodialysis to eliminate potassium from the circulation
D. Intravenous calcium gluconate 10% over 2–3 minutes to stabilize the cardiac membrane
Explanation
Why intravenous calcium gluconate 10% over 2–3 minutes is correct
The sine wave pattern marked A represents a pre-arrest ECG finding in severe hyperkalemia (K+ >9 mEq/L), indicating imminent ventricular fibrillation or asystole. According to Harrison 21e Chapter 313 and ACLS hyperkalemia algorithms, membrane stabilization with IV calcium gluconate is the IMMEDIATE first-line intervention when ECG changes of this severity are present. Calcium antagonizes the depolarizing effect of potassium on cardiomyocyte membranes within 1–3 minutes and buys time for intracellular shift therapies to work. The effect lasts 30–60 minutes and can be repeated if ECG changes persist. This is a true cardiac emergency — calcium must be given BEFORE waiting for confirmatory serum potassium levels or other interventions.
Why each distractor is wrong
Intravenous regular insulin 10 units with 50% dextrose: While this is Phase 2 (intracellular shift) and is essential, it takes 15–30 minutes to lower potassium by 0.5–1.2 mEq/L. In a pre-arrest sine wave pattern, this delay is dangerous. Insulin is given AFTER or SIMULTANEOUSLY with calcium, not instead of it.
Emergent hemodialysis: Although dialysis is the definitive Phase 3 (potassium elimination) therapy and is mandatory for this dialysis-dependent patient, it requires vascular access setup and takes time. Calcium stabilization must occur first to prevent cardiac arrest during dialysis preparation.
Nebulized salbutamol 10–20 mg: This is an adjunctive Phase 2 therapy that promotes β2-mediated potassium shift (lowers K+ by ~0.5 mEq/L) but is slower and less cardioprotective than calcium. It is used alongside insulin, not as first-line monotherapy in a pre-arrest rhythm.
High-YieldNEET PG
Sine wave = pre-arrest hyperkalemia; give IV calcium FIRST (membrane stabilization), then insulin + dextrose (intracellular shift), then dialysis (elimination). Do not delay calcium for labs.
Harrison 21e Ch 313; ACLS hyperkalemia algorithm
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