In a 50-year-old man with bulky diffuse large B-cell lymphoma who develops tumor-lysis syndrome after the first R-CHOP cycle (potassium 6 mmol/L, phosphate 3 mmol/L, calcium 1.2 mmol/L, uric acid ≈570 µmol/L) and oliguria, what medication should be added to aggressive intravenous hydration?

Management of Tumor Lysis Syndrome with Oliguria After R-CHOP

This patient requires immediate rasburicase 0.2 mg/kg IV plus aggressive IV hydration, with urgent nephrology consultation for hemodialysis given the combination of anuria and severe hyperkalemia (K 6 mmol/L). 1, 2

Immediate Pharmacologic Interventions

Rasburicase Administration

• Rasburicase must be given immediately at 0.2 mg/kg IV over 30 minutes through central venous access if available, as this patient meets criteria for clinical TLS (hyperkalemia, hyperphosphatemia, hypocalcemia, hyperuricemia plus acute kidney injury with oliguria). 1, 2
• Rasburicase rapidly converts uric acid to allantoin, providing uric acid clearance of 70-100 mL/min—far superior to any diuretic therapy—and reduces plasma uric acid by approximately 50% within 4 hours. 1
• Even in anuric patients, rasburicase reduces metabolic burden and facilitates earlier renal recovery once dialysis is initiated. 1
• Randomized trials demonstrate rasburicase achieves 97-100% response rates for uric acid control versus allopurinol (mean uric acid AUC: 128 ± 70 vs 329 ± 129 mg/dL·h, p < 0.001). 1

Cardiac Membrane Stabilization

• Administer calcium gluconate 50-100 mg/kg IV over 2-5 minutes immediately to stabilize the myocardial membrane against hyperkalemia-induced arrhythmias (K = 6 mmol/L). 1, 2
• Effects begin within 1-3 minutes but last only 30-60 minutes; this does not lower serum potassium. 1

Intracellular Potassium Shift

• Give rapid insulin 0.1 units/kg IV plus 25% dextrose 2 mL/kg IV to shift potassium intracellularly, with onset in 15-30 minutes and duration of 4-6 hours. 1, 2
• Add sodium polystyrene sulfonate 1 g/kg orally or by enema for ongoing potassium removal. 1

Aggressive Hydration Strategy

• Increase IV hydration to 150-200 mL/hour (approximately 4-5 L/m²/day) through central venous access to achieve target urine output ≥100 mL/hour. 1, 2
• The standard rate of 100 mL/hour is insufficient for TLS and predisposes to uric acid nephropathy. 1

Why Loop Diuretics Are NOT Appropriate Here

• Furosemide (Lasix) is contraindicated in this patient with established oliguria/anuria despite adequate hydration because loop diuretics require residual renal function to work. 1, 2
• Loop diuretics may only be added after rasburicase and only if the patient is adequately volume-resuscitated, still producing urine (not anuric), has no obstructive uropathy, and urine output remains <100 mL/hour despite hydration. 1, 2
• This patient's 24-hour oliguria despite presumed hydration indicates complete or near-complete renal shutdown, making diuretics ineffective. 1

Why Allopurinol Is NOT Appropriate Here

• Allopurinol is a prophylactic agent that prevents uric acid formation by inhibiting xanthine oxidase; it should be started 24-48 hours before chemotherapy, not after TLS has developed. 1
• In established clinical TLS with oliguria, allopurinol cannot rapidly reduce existing hyperuricemia and may cause xanthine accumulation. 1, 2
• Never give allopurinol concurrently with rasburicase, as this removes substrate for rasburicase and causes xanthine precipitation. 2

Urgent Hemodialysis Indications

• This patient requires immediate nephrology consultation for hemodialysis based on the following absolute indications: 1, 2
  • Persistent anuria/oliguria despite aggressive hydration
  • Severe refractory hyperkalemia (K = 6 mmol/L)
  • The combination of anuria plus K ≥6 mmol/L constitutes an emergent dialysis indication
• Hemodialysis provides uric acid clearance of 70-100 mL/min and lowers plasma uric acid by 50% per 6-hour session while simultaneously correcting life-threatening hyperkalemia. 1
• Additional dialysis indications include progressive respiratory distress from fluid overload and symptomatic hypocalcemia refractory to treatment. 1, 2

Hypocalcemia Management

• Do NOT treat asymptomatic hypocalcemia beyond the initial calcium gluconate dose used for cardiac membrane stabilization, as calcium administration can precipitate calcium-phosphate crystals in renal tubules and worsen kidney injury. 1, 2
• Only treat hypocalcemia if tetany, seizures, or prolonged QT interval develops. 1

Hyperphosphatemia Management

• For persistent hyperphosphatemia >1.62 mmol/L (this patient has PO₄ = 3 mmol/L), consider aluminum hydroxide 50-100 mg/kg/day divided every 6 hours. 1, 2

Critical Monitoring Parameters

• Continuous ECG monitoring is mandatory to detect hyperkalemia-induced arrhythmias (peaked T waves, widened QRS, prolonged PR interval). 1, 2
• Recheck potassium every 2-4 hours after initial treatment. 1, 2
• Monitor uric acid, electrolytes, phosphate, and calcium every 4-6 hours for the first 24 hours. 1, 2
• Measure hourly urine output targeting ≥100 mL/hour. 1, 2
• Assess respiratory status every 30-60 minutes for signs of fluid overload (crepitations, increased work of breathing, falling oxygen saturation). 1

Common Pitfalls to Avoid

• Do not use loop diuretics in anuric patients—they are ineffective without residual renal function and delay definitive dialysis. 1, 2
• Do not delay rasburicase while waiting for allopurinol to work—rasburicase provides immediate uric acid reduction in clinical TLS. 1, 2
• Do not aggressively treat asymptomatic hypocalcemia when hyperphosphatemia is present, as this precipitates calcium-phosphate crystals and worsens renal injury. 1, 2
• Do not continue inadequate hydration at 100 mL/hour—this predisposes to uric acid nephropathy and acute kidney injury. 1