How do I manage hyperuricemia in a pediatric cardiac surgery patient?

Management of Hyperuricemia in Pediatric Cardiac Surgery Patients

In pediatric cardiac surgery patients with hyperuricemia, prioritize aggressive hydration (2-3 L/m²/day) while carefully monitoring cardiac function and fluid status, and use allopurinol (10 mg/kg/day divided every 8 hours, maximum 800 mg/day) as first-line pharmacologic therapy, with dose reduction by 50% or more if renal impairment develops. 1

Critical Context for Cardiac Surgery Patients

The management approach must be modified from standard hyperuricemia protocols due to the unique constraints of cardiac surgery patients:

• Fluid management is fundamentally different: While standard hyperuricemia guidelines recommend vigorous hydration at 2-3 L/m²/day, this must be adapted to the patient's cardiac function and volume status 1
• Cardiac surgery patients often have compromised cardiac output and may not tolerate aggressive fluid loading
• Urine output targets of 80-100 mL/m²/h (4-6 mL/kg/h if <10 kg) should guide fluid administration, but cardiac function takes precedence 1

Hydration Strategy (Modified for Cardiac Patients)

• Administer IV fluids using one-quarter normal saline with 5% dextrose, but volume must be adapted to cardiac function and urine output 1
• Monitor urine-specific gravity and maintain at 1.010 1
• Withhold potassium, calcium, and phosphate from hydration fluids initially due to risks of hyperkalemia, hyperphosphatemia, and calcium phosphate precipitation 1
• Use diuretics cautiously to maintain urine output only if there is no hypovolemia or obstructive uropathy 1
• The goal is equal fluid intake and urinary output when cardiac function permits 1

Pharmacologic Management

First-Line: Allopurinol

Allopurinol is the appropriate first-line agent for most pediatric cardiac surgery patients unless severe pre-existing hyperuricemia (≥7.5 mg/dL) is present 1:

• Dosing: 10 mg/kg/day divided every 8 hours orally (maximum 800 mg/day) or 50-100 mg/m² every 8 hours (maximum 300 mg/m²/day) 1
• IV alternative: 200-400 mg/m²/day in 1-3 divided doses (maximum 600 mg/day) if oral intake is restricted 1, 2
• IV allopurinol normalized or improved uric acid levels in 95% of pediatric patients 3

Critical Dose Adjustments in Renal Impairment

Reduce allopurinol dose by 50% or more in renal failure, which is common post-cardiac surgery 1, 2:

• Creatinine clearance 10-20 mL/min: 200 mg daily maximum 2
• Creatinine clearance <10 mL/min: 100 mg daily maximum 2
• Creatinine clearance <3 mL/min: extend dosing intervals beyond daily 2

When to Use Rasburicase Instead

Rasburicase is preferred over allopurinol if pre-existing hyperuricemia ≥7.5 mg/dL (450 μmol/L) is present 1:

• Allopurinol only prevents new uric acid formation and takes several days to reduce levels 1
• Rasburicase rapidly degrades existing uric acid to allantoin, which is 5-10 times more soluble 4
• Contraindicated in G6PD deficiency (screen patients of African American, Mediterranean, or Southeast Asian descent) 1
• Administered IV over 30 minutes 1
• Blood samples for uric acid monitoring must be placed immediately on ice to prevent ex vivo enzymatic degradation 1

Alkalinization: NOT Recommended

Do not routinely alkalinize urine with sodium bicarbonate 1:

• No unequivocal evidence of efficacy 1
• Increases risk of calcium phosphate crystal precipitation 1
• May promote xanthine crystal deposition in renal tubules when using allopurinol 1
• Only indicated if metabolic acidosis develops 1
• Not required with rasburicase 1

Monitoring Parameters

• Serum uric acid levels: Monitor regularly to guide therapy 1
• Renal function: Creatinine clearance determines allopurinol dosing 2, 5
• Urine output: Target 80-100 mL/m²/h but adjust for cardiac status 1
• Electrolytes: Watch for hyperkalemia and hyperphosphatemia 1
• Fluid balance: Critical in cardiac surgery patients to avoid volume overload 1

Common Pitfalls to Avoid

• Do not use standard aggressive hydration protocols without considering cardiac function—this can precipitate heart failure 1
• Do not continue full-dose allopurinol in renal impairment—this increases toxicity risk including hypersensitivity syndrome 2, 5
• Do not use allopurinol alone if uric acid is already ≥7.5 mg/dL—it will not reduce pre-existing levels quickly enough 1
• Do not add potassium to IV fluids initially—hyperkalemia risk is significant 1
• Do not forget to screen for G6PD deficiency before considering rasburicase 1

Drug Interactions Relevant to Cardiac Surgery

• Allopurinol requires dose adjustment with concurrent thiazide diuretics, cyclosporine (often used post-transplant), and dicumarol 1
• If patient is on 6-mercaptopurine or azathioprine (immunosuppression), reduce these doses by 65-75% when starting allopurinol 1