A 7-year-old boy is admitted to the pediatric intensive care unit for the initiation of ch… — USMLE Step 2 CK

A $7$ -year-old boy is admitted to the pediatric intensive care unit for the initiation of chemotherapy for newly diagnosed, advanced-stage Burkitt lymphoma. He has a massive abdominal tumor burden. A central venous port was placed $48$ hours ago. Twelve hours after receiving his first dose of chemotherapy, he becomes lethargic and his urine output drops to $0.2 \text{ mL/kg/hr}$ .

Continuous telemetry reveals peaked T waves and a widened QRS complex.

Temperature is $38.6^\circ \text{C}$ ( $101.5^\circ \text{F}$ ), blood pressure is $90/55 \text{ mm Hg}$ , pulse is $135/\text{min}$ , and respiratory rate is $28/\text{min}$ . Initial blood cultures drawn from the port at the time of admission are now growing *Escherichia coli* that is susceptible to ceftriaxone.

Laboratory studies reveal the following:

Laboratory Parameter	Value
Sodium ( $Na^+$ )	$134 \text{ mEq/L}$
Potassium ( $K^+$ )	$7.2 \text{ mEq/L}$
Chloride ( $Cl^-$ )	$98 \text{ mEq/L}$
Bicarbonate ( $HCO_3^-$ )	$12 \text{ mEq/L}$
Calcium ( $Ca^{2+}$ )	$6.1 \text{ mg/dL}$
Phosphorus	$9.5 \text{ mg/dL}$
Uric acid	$16.2 \text{ mg/dL}$
Blood urea nitrogen (BUN)	$58 \text{ mg/dL}$
Creatinine	$2.4 \text{ mg/dL}$ (baseline $0.6 \text{ mg/dL}$ )

An arterial blood gas on room air shows a pH of $7.26$ , $pCO_2$ of $26 \text{ mm Hg}$ , and $pO_2$ of $92 \text{ mm Hg}$ . Upon reviewing his chart, the parents note he missed his $4$ -year-old immunization boosters and ask if they can be updated while he is hospitalized.

Which of the following is the most appropriate initial step in the management of this patient?

A
Administer intravenous sodium bicarbonate infusion to correct the uncompensated respiratory acidosis that is shifting potassium extracellularly
B
Initiate broad-spectrum intravenous vancomycin and meropenem to provide empiric coverage for his bacteremia despite current culture sensitivities
Administer intravenous calcium gluconate followed by regular insulin with dextrose, and prepare for emergent hemodialysisCevap
D
Order a venous Doppler ultrasound of the upper extremity, as fever occurring exactly 48 hours postoperatively is most characteristic of deep vein thrombosis
E
Administer the live-attenuated measles, mumps, and rubella (MMR) and varicella vaccines to protect his immunocompromised system prior to discharge

Cevap

The most appropriate initial step is to administer intravenous calcium gluconate followed by regular insulin with dextrose, and prepare for emergent hemodialysis.

This patient is presenting with severe Tumor Lysis Syndrome (TLS), a rapidly developing oncologic emergency characterized by the massive release of intracellular contents following the destruction of malignant cells (especially in highly proliferative tumors like Burkitt lymphoma). He has the hallmark laboratory triad of hyperuricemia, hyperkalemia, and hyperphosphatemia with secondary hypocalcemia. The most immediate threat to his life is the potassium of

7.2 \text{ mEq/L}

with accompanying EKG changes (peaked T waves, widened QRS), indicating imminent cardiac arrest. The immediate next step must be intravenous calcium gluconate to stabilize the myocardial membrane, followed by regular insulin (with dextrose) to shift potassium intracellularly. Because he is oliguric with acute kidney injury, these bridging measures must be immediately followed by emergent hemodialysis for definitive clearance.

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Analyze the patient's clinical presentation and comprehensive laboratory profile.

The patient has hyperuricemia, hyperphosphatemia, hypocalcemia, hyperkalemia, and oliguric acute kidney injury following the initiation of chemotherapy for Burkitt lymphoma.

These findings represent the classic triad of metabolic derangements diagnostic of severe Tumor Lysis Syndrome (TLS), complicated by acute renal failure.

Evaluate the telemetry findings and specific electrolyte critical values.

The potassium level is critically elevated at

7.2 \text{ mEq/L}

, accompanied by peaked T waves and a widened QRS complex on the electrocardiogram.

Severe hyperkalemia with EKG changes is an immediate, life-threatening medical emergency that can rapidly degenerate into ventricular fibrillation or asystole.

Determine the prioritized management sequence based on the most immediate threat to life.

The immediate priority is to stabilize the cardiac membrane with intravenous calcium gluconate, shift potassium intracellularly using insulin with dextrose, and prepare for emergent hemodialysis to definitively clear the potassium and uric acid.

While the patient has concurrent issues (bacteremia, acidosis), preventing imminent cardiac arrest from hyperkalemia supersedes all other diagnostic and therapeutic interventions.

Anahtar Kavram

Management of life-threatening hyperkalemia in Tumor Lysis Syndrome

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