A nurse is caring for a 45-year-old patient with acute lymphoblastic leukemia receiving high-dose chemotherapy who develops tumor lysis syndrome. Which nursing intervention should be the highest priority?

Tumor lysis syndrome with hyperkalemia (K+ 6.2 mEq/L) poses immediate risk of fatal cardiac arrhythmias, making continuous cardiac monitoring the highest priority. Other interventions address symptoms or electrolyte imbalances but do not prevent life-threatening complications.

Understanding the Clinical Scenario

The patient is exhibiting classic signs of tumor lysis syndrome (TLS), an oncologic emergency. The rapid destruction of malignant cells by high-dose chemotherapy releases massive amounts of intracellular contents into the bloodstream, overwhelming the body's homeostatic mechanisms. The laboratory values confirm severe metabolic derangements: a potassium level of 6.2 mEq/L (hyperkalemia), phosphorus of 6.8 mg/dL (hyperphosphatemia), calcium of 7.1 mg/dL (hypocalcemia, secondary to the elevated phosphorus binding calcium), and uric acid of 12.5 mg/dL (hyperuricemia). The patient's subjective complaints of muscle cramps and perioral tingling are neurological manifestations of hypocalcemia, while the nausea is a common symptom of the uremic state and electrolyte chaos. The most critical finding is the precipitous drop in urine output to 20 mL/hour, signaling acute kidney injury from uric acid crystal deposition and calcium-phosphate precipitation in the renal tubules. This oliguric state further compromises the body's ability to excrete potassium, creating a vicious cycle that accelerates the primary life threat.

Priority Intervention Analysis

In a patient with TLS, the immediate threat to life is a cardiac arrhythmia or arrest stemming from the synergistic effects of severe hyperkalemia and hypocalcemia. The 2025 Korean Guidelines for Cardiopulmonary Resuscitation acknowledge the critical nature of acute hyperkalemia in special circumstances, noting the need for immediate interventions such as intravenous insulin with glucose to shift potassium intracellularly ^[1]. While the guidelines state that evidence is insufficient to recommend for or against routine calcium administration in hyperkalemic cardiac arrest, in the non-arrest setting with a profoundly elevated potassium and concurrent hypocalcemia, the physiological priority is to stabilize the myocardial cell membrane. Hyperkalemia depolarizes the resting membrane potential, bringing it dangerously close to the threshold potential, which can trigger ventricular tachycardia or fibrillation. Hypocalcemia exacerbates this instability by increasing sodium permeability, further reducing the threshold for excitation. The patient's reported muscle cramps and perioral tingling are clinical signs of this heightened neuromuscular and cardiac irritability. A simulation-based study on TLS in pediatrics reinforces that prompt recognition and treatment of hyperkalemia-induced tachyarrhythmias is vital, as these are life-threatening events . Therefore, the nurse's highest priority is not to address the underlying cause or a single symptom, but to directly manage the imminent risk of a fatal cardiac event.

Why Other Options Are Not the Priority

Administering antiemetics (Option 1) addresses the patient's comfort but does nothing to mitigate the immediate, life-threatening cardiac risk. Providing oral calcium supplements (Option 2) is inappropriate and dangerous; oral calcium has a slow, unpredictable onset and does not provide the rapid ionized calcium needed to antagonize the cardiotoxic effects of hyperkalemia at the myocardial cell membrane. Furthermore, in the context of hyperphosphatemia, additional calcium could worsen metastatic calcification. Encouraging increased fluid intake (Option 3) is a core component of TLS prevention and management to promote uric acid excretion, but it is a secondary intervention in this acute crisis. With a urine output of only 20 mL/hour, the patient is likely in acute kidney injury and may be anuric, making increased oral intake ineffective and potentially harmful. The priority is to first stabilize the cardiac membrane, then rapidly implement measures to lower serum potassium and manage fluid status, often with aggressive intravenous hydration and diuretics, or in refractory cases, renal replacement therapy. The scoping review on nursing roles in advanced cancer care highlights that nurses are central to symptom assessment and care coordination, which in this context means recognizing the cluster of symptoms as a life-threatening emergency and acting on the most critical one first . The recognition and management of such oncologic emergencies remain a critical gap in many settings, underscoring the importance of the nurse's role in immediate identification and prioritization . Continuous cardiac monitoring allows for the detection of evolving rhythm disturbances, such as peaked T-waves, loss of P-waves, and a widened QRS complex, which are precursors to lethal arrhythmias, enabling the nurse to activate the emergency response system and prepare to administer intravenous calcium gluconate or calcium chloride as the first-line membrane-stabilizing agent.