A nurse is caring for a 45-year-old patient with acute lymphoblastic leukemia who received chemotherapy 24 hours ago and now presents with altered mental status, muscle cramps, and decreased urine output, suggesting tumor lysis syndrome. Which nursing intervention should be the priority?

Ensuring adequate hydration and urine output is the priority to prevent acute renal failure in tumor lysis syndrome by promoting excretion of uric acid and toxic metabolites. Other options are important but not immediate interventions.

Clinical Presentation Analysis

The patient exhibits the classic triad of tumor lysis syndrome (TLS): altered mental status, muscle cramps, and decreased urine output. These findings occur because rapid cell lysis after chemotherapy releases massive amounts of intracellular contents — potassium, phosphate, and nucleic acids (metabolized to uric acid) — into the bloodstream faster than the kidneys can clear them ^[1]. The altered mental status and muscle cramps strongly suggest hyperkalemia, which destabilizes cardiac resting membrane potentials and can rapidly progress to life-threatening arrhythmias or cardiac arrest ^[1]. Decreased urine output indicates that uric acid and calcium phosphate crystals may already be obstructing renal tubules, further impairing the body’s ability to excrete potassium.

Priority Intervention Rationale

The correct priority intervention is ensuring adequate hydration and urine output (Option 4). Aggressive intravenous fluid administration, typically with normal saline at 200–250 mL/hour, serves as the cornerstone of TLS management by addressing the underlying pathophysiology through two mechanisms. First, volume expansion increases renal blood flow and glomerular filtration rate, directly enhancing the kidneys’ capacity to excrete potassium, uric acid, and phosphate. Second, higher urine flow rates dilute intratubular concentrations of uric acid and calcium phosphate, preventing crystal precipitation that would otherwise worsen acute kidney injury ^[1]. Without adequate urine output, all other interventions become ineffective or dangerous — potassium cannot be eliminated, and medications like calcium gluconate provide only temporary cardiac membrane stabilization without resolving the potassium excess.

Why Other Options Are Not the Priority

Option	Clinical Reasoning
1. Administer calcium gluconate	Calcium gluconate antagonizes the cardiac effects of hyperkalemia by stabilizing myocardial cell membranes, but it does not lower serum potassium levels [1]. It is indicated when ECG changes (peaked T waves, widened QRS) or arrhythmias are present, serving as a temporizing measure while definitive potassium-lowering therapies are initiated. In the absence of documented ECG changes or arrhythmia, establishing renal elimination through hydration takes precedence.
2. Restrict fluid intake	Fluid restriction is contraindicated in TLS. The syndrome’s primary danger is renal obstruction from crystal deposition, which aggressive hydration prevents. Restricting fluids would concentrate urinary solutes, accelerate tubular blockage, and worsen both hyperkalemia and renal failure [1].
3. Monitor serum potassium every 4 hours	While potassium monitoring is essential in TLS, checking every 4 hours is insufficient during the acute phase when cell lysis peaks 24–72 hours post-chemotherapy. More frequent monitoring (every 4–6 hours initially, or more often if levels are rising rapidly) is required. More importantly, monitoring alone does not treat the underlying problem — the immediate nursing action must be to facilitate potassium excretion through hydration and urine output [1].

Pathophysiology-to-Practice Connection

In TLS, the sudden release of intracellular potassium overwhelms the sodium-potassium ATPase pump mechanism that normally maintains the steep potassium gradient across cell membranes. As extracellular potassium rises, the resting membrane potential of cardiac and skeletal muscle cells becomes less negative (partial depolarization), initially making cells more excitable — hence the muscle cramps. As potassium continues to rise, sodium channels become inactivated, leading to decreased excitability, weakness, and ultimately cardiac conduction blocks and asystole ^[1]. The nurse’s priority must target the root cause: removing excess potassium from the body. Hydration achieves this by maximizing renal clearance, while simultaneously preventing the secondary renal injury that would create a vicious cycle of worsening hyperkalemia. If urine output does not improve despite adequate hydration, the nurse must promptly notify the provider for escalation to rasburicase (for uric acid reduction) or renal replacement therapy ^[1].