During morning rounds, the internal medicine team evaluates a patient who was recently adm… — USMLE Step 2 CK

During morning rounds, the internal medicine team evaluates a patient who was recently admitted for high-grade non-Hodgkin lymphoma. The patient, a $48$ -year-old male, started induction chemotherapy $48$ hours ago. The nursing staff reports that he acutely developed profound nausea, intense muscle cramping, and palpitations over the last hour. Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure of $100/60$ mm Hg, an irregular pulse of $118$ /min, and a respiratory rate of $20$ /min. He appears visibly lethargic. Cardiac auscultation reveals an irregular rhythm without murmurs, and the lungs are clear to auscultation. A stat electrocardiogram (ECG) is obtained, which reveals tall, peaked T waves and a prolonged PR interval. Laboratory analysis yields the following results:

Test	Result
Potassium	$6.8$ mEq/L
Calcium	$6.8$ mg/dL
Phosphorus	$6.5$ mg/dL
Uric acid	$14.2$ mg/dL
Blood urea nitrogen	$45$ mg/dL
Creatinine	$2.8$ mg/dL

Based on the clinical presentation and laboratory findings, which of the following is the most appropriate initial step in the management of this patient?

Administration of calcium gluconate via intravenous infusionAnswer
B
Administration of intravenous furosemide and non-invasive positive pressure ventilation
C
Commencement of empiric broad-spectrum antimicrobial therapy
D
Measurement of arterial blood gases to calculate expected respiratory compensation
E
Placement of a nasogastric tube to decompress the gastrointestinal tract

Answer

The most appropriate initial step is the administration of calcium gluconate via intravenous infusion.

The correct intervention is the administration of intravenous calcium gluconate. This patient is experiencing Tumor Lysis Syndrome (TLS), an oncologic emergency characterized by the massive release of intracellular contents following the initiation of cytotoxic therapy for rapidly proliferating tumors. This results in hyperkalemia, hyperphosphatemia, hyperuricemia, and secondary hypocalcemia. The most life-threatening complication is hyperkalemia, evidenced by his elevated level of

6.8

mEq/L and characteristic ECG changes (peaked T waves, prolonged PR interval). The immediate, most critical step in management is myocardial stabilization with intravenous calcium gluconate (or calcium chloride) to raise the threshold potential and prevent fatal ventricular arrhythmias. Once the myocardium is stabilized, subsequent therapies to shift potassium intracellularly (e.g., insulin and glucose) and treat the underlying TLS (e.g., aggressive hydration, rasburicase) should be initiated.

Step-by-Step Solution

Analyze the patient's history and current presentation.

A patient with newly treated high-grade lymphoma presents acutely with muscle cramps, arrhythmias, and acute kidney injury.

Recent initiation of cytotoxic chemotherapy in high-grade lymphomas strongly predisposes to massive cellular breakdown.

Interpret the laboratory and ECG findings.

Labs show hyperkalemia, hyperuricemia, hyperphosphatemia, and hypocalcemia. ECG shows peaked T waves and prolonged PR interval.

These findings definitively confirm Tumor Lysis Syndrome (TLS) complicated by severe, symptomatic hyperkalemia.

Determine the most critical priority in management.

The most immediate threat to the patient's life is a fatal ventricular arrhythmia induced by the hyperkalemia.

While treating the underlying TLS (e.g., hydration, rasburicase) and lowering total body potassium are necessary, stabilizing the cardiac membrane is the most urgent, time-sensitive intervention.

Key Concept

Tumor Lysis Syndrome (TLS) can cause life-threatening hyperkalemia; when accompanied by ECG changes, the immediate priority is myocardial stabilization with intravenous calcium.

Estimated Time:1m 30s

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