During morning rounds, a physician evaluates a patient hospitalized for the treatment of h… — USMLE Step 2 CK

During morning rounds, a physician evaluates a patient hospitalized for the treatment of high-grade Burkitt lymphoma. The patient received his first cycle of cytotoxic chemotherapy 24 hours ago. He now complains of severe muscle cramps, perioral numbness, and progressive nausea.

Vital signs are temperature $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), blood pressure $108/65 \text{ mm Hg}$ , pulse $115/\text{min}$ , and respirations $18/\text{min}$ . Physical examination reveals hyperactive deep tendon reflexes and a positive Chvostek sign.

Laboratory evaluation reveals the following:
* Sodium: $137 \text{ mEq/L}$
* Potassium: $7.3 \text{ mEq/L}$
* Bicarbonate: $18 \text{ mEq/L}$
* Blood urea nitrogen: $52 \text{ mg/dL}$
* Creatinine: $3.1 \text{ mg/dL}$ (baseline $0.9 \text{ mg/dL}$ )
* Calcium: $6.2 \text{ mg/dL}$
* Phosphorus: $9.1 \text{ mg/dL}$
* Uric acid: $16.4 \text{ mg/dL}$

A 12-lead electrocardiogram demonstrates peaked T waves and widening of the QRS complex. Which of the following is the most appropriate initial intervention?

Provide an infusion of calcium gluconateAnswer
B
Give calcitonin and zoledronic acid
C
Start empiric meropenem therapy
D
Provide a rapid infusion of sodium bicarbonate
E
Transfer to radiology for an abdominal computed tomography scan

Answer

Provide an infusion of calcium gluconate

The correct answer is to provide an infusion of calcium gluconate. This patient's presentation of severe hyperkalemia (potassium

7.3 \text{ mEq/L}

), hyperuricemia, hyperphosphatemia, hypocalcemia, and acute kidney injury following induction chemotherapy for a high-grade hematologic malignancy (Burkitt lymphoma) is pathognomonic for tumor lysis syndrome (TLS). The massive release of intracellular contents outpaces renal clearance. The most immediate threat to this patient's life is hyperkalemia-induced cardiac arrhythmia, evidenced by peaked T waves and QRS widening on the electrocardiogram. The initial step in managing severe hyperkalemia with electrocardiographic changes is stabilizing the myocardial membrane with intravenous calcium (calcium gluconate or calcium chloride). This does not lower serum potassium but prevents fatal arrhythmias while other potassium-lowering therapies (e.g., insulin with glucose, gastrointestinal cation exchangers, or dialysis) are prepared.

Step-by-Step Solution

Identify the primary clinical syndrome based on the patient's history and laboratory values.

The patient has hyperkalemia, hyperphosphatemia, hypocalcemia, hyperuricemia, and acute kidney injury following induction chemotherapy, which is diagnostic for Tumor Lysis Syndrome.

Recognizing the syndrome is essential to prioritize the various metabolic derangements.

Assess the immediate life-threatening complications of the syndrome.

The electrocardiogram shows peaked T waves and QRS widening in the setting of a potassium level of

7.3 \text{ mEq/L}

Severe hyperkalemia can rapidly progress to ventricular fibrillation or asystole.

Determine the most appropriate initial pharmacological intervention.

Intravenous calcium gluconate is selected.

Calcium antagonizes the membrane actions of hyperkalemia, stabilizing the myocardium and preventing fatal arrhythmias, taking precedence over potassium-lowering agents.

Key Concept

In Tumor Lysis Syndrome, severe hyperkalemia with electrocardiographic changes requires immediate myocardial stabilization with intravenous calcium before implementing other therapies.

Estimated Time:1m 30s

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