How to manage metabolic acidosis after urostomy?

Management of Metabolic Acidosis After Urostomy

Oral sodium bicarbonate at doses of 2-4 g/day (25-50 mEq/L) should be administered as first-line therapy to correct serum bicarbonate to ≥22 mmol/L in patients with metabolic acidosis after urostomy. 1

Pathophysiology and Diagnosis

Metabolic acidosis after urostomy occurs due to:

• Absorption of urinary chloride by intestinal segments used for urinary diversion
• Loss of bicarbonate from intestinal mucosa
• Impaired renal acid excretion

Diagnostic Approach:

• Obtain arterial blood gas to assess pH (<7.3), bicarbonate (<22 mEq/L), and PaCO₂ (≤45 mmHg)
• Calculate anion gap = Na⁺ - (Cl⁻ + HCO₃⁻)
  • Typically presents as hyperchloremic (non-anion gap) metabolic acidosis 2, 3
• Monitor serum electrolytes, particularly potassium (hypokalemia commonly accompanies acidosis) 4
• Check serum calcium and phosphorus every three months 1

Treatment Algorithm

1. Mild to Moderate Acidosis (pH >7.15, bicarbonate 15-22 mEq/L):

• First-line: Oral sodium bicarbonate 2-4 g/day (25-50 mEq/day) 1
  • Titrate dose to maintain serum bicarbonate ≥22 mmol/L
  • Monitor serum bicarbonate every three months
• Alternative: Potassium citrate if hypokalemia is present 5
  • Preferred over sodium citrate as sodium load may increase urinary calcium excretion

2. Severe Acidosis (pH <7.15 with hemodynamic instability):

• Intravenous sodium bicarbonate 1-2 mEq/kg over 10-15 minutes 1
• Consider nephrology consultation for possible renal replacement therapy in refractory cases

3. Adjunctive Therapies:

• Nicotinic acid may reduce the requirement for alkali supplementation 6
• Chlorpromazine has shown benefit in animal models for reducing metabolic acidosis severity 6

Monitoring and Follow-up

• Monitor serum bicarbonate at least every three months 1
• Check serum electrolytes, particularly potassium, calcium, and phosphorus
• Assess for clinical symptoms of acidosis:
  • Fatigue
  • Muscle weakness
  • Bone pain
  • Respiratory compensation (tachypnea)

Prevention of Complications

• Hypokalemia: Monitor and correct promptly as it commonly accompanies metabolic acidosis in urostomy patients 4

  • Severe hypokalemia can lead to paralysis and intestinal dysfunction

• Fluid Balance:

  • Avoid fluid overload which can lead to tissue edema and impaired wound healing
  • Ensure adequate hydration to prevent urinary stasis and infection

• Urinary Tract Infection:

  • Promptly treat infections as they can worsen metabolic derangements 3
  • Consider prophylactic antibiotics if recurrent infections occur

Long-term Considerations

• Chronic mild acidosis may lead to:

  • Protein degradation
  • Decreased albumin synthesis
  • Poor nutritional status
  • Reduced bone mineral content and osteomalacic lesions 7

• Regular follow-up with both urology and nephrology is recommended to monitor for and manage these potential complications

• Patients with ileal neobladders or ureterosigmoidostomies should be educated about the importance of compliance with bicarbonate supplementation and regular monitoring

While metabolic acidosis after urostomy is often mild and asymptomatic, prompt recognition and treatment are essential to prevent long-term complications related to chronic acidosis, including bone demineralization and protein catabolism.