How to manage metabolic acidosis after urostomy surgery?

Management of Metabolic Acidosis After Urostomy Surgery

Metabolic acidosis following urostomy surgery should be treated by correcting serum bicarbonate to ≥22 mmol/L using oral sodium bicarbonate supplementation, typically at doses of 2-4 g/day (25-50 mEq/day), while monitoring electrolytes regularly. 1

Pathophysiology of Post-Urostomy Metabolic Acidosis

Metabolic acidosis after urostomy surgery occurs due to:

• Absorption of urinary chloride by intestinal segments used for urinary diversion
• Loss of bicarbonate through intestinal mucosa
• Impaired renal acid excretion in patients with compromised kidney function

This typically presents as a hyperchloremic non-anion gap metabolic acidosis 2, 3.

Diagnostic Approach

• Monitor serum bicarbonate at least every three months in patients with GFR <30 ml/min/1.73m² 1
• Obtain arterial blood gas to assess pH, bicarbonate level, PaCO₂, and calculate anion gap 4
• Calculate anion gap = Na⁺ - (Cl⁻ + HCO₃⁻), with normal range being 8-12 mEq/L 4
• Check serum potassium levels, as hypokalemia frequently accompanies metabolic acidosis in these patients 5

Treatment Algorithm

1. Correct Serum Bicarbonate

• Target serum bicarbonate ≥22 mmol/L 1
• Administer oral sodium bicarbonate at doses of 2-4 g/day (25-50 mEq/day) 1
• Adjust dose based on regular monitoring of serum bicarbonate levels

2. Fluid Management

• Use balanced crystalloid solutions rather than 0.9% saline to avoid worsening hyperchloremic acidosis 4
• Maintain euvolemia with careful fluid administration and monitoring 4
• Avoid fluid overload which can lead to tissue edema and impaired wound healing 4

3. Electrolyte Management

• Monitor and correct hypokalemia, which commonly accompanies metabolic acidosis in urostomy patients 5
• Check serum calcium and phosphorus at least every three months 1
• Monitor iPTH levels if calcium/phosphorus levels are abnormal 1

4. Severe Acidosis Management

• For severe acidosis (pH <7.15) with hemodynamic instability, consider intravenous sodium bicarbonate at 1-2 mEq/kg over 10-15 minutes 4
• In cases of severe, refractory acidosis, consider nephrology consultation for possible renal replacement therapy 1

Monitoring and Follow-up

• Monitor serum bicarbonate at least every three months 1
• Check electrolytes more frequently (every 4-6 hours initially) in severe cases 4
• Assess fluid balance at least every 8 hours in acute settings 4
• Monitor for signs of improved continence, as this may correlate with increased risk of metabolic acidosis in neobladder patients 3

Special Considerations

• Patients with ileal neobladders are particularly susceptible to non-anion gap metabolic acidosis 2
• Urinary tract infections can exacerbate metabolic acidosis in patients with urinary diversions 2
• Urinary retention in patients with enterovesical fistulas can lead to severe metabolic acidosis 6
• Improved continence in neobladder patients may increase risk of metabolic acidosis due to greater contact time between urine and intestinal mucosa 3

Pitfalls to Avoid

• Don't use normal saline for fluid resuscitation as it can worsen hyperchloremic acidosis 4
• Don't overlook hypokalemia, which can lead to paralysis and intestinal dysfunction 5
• Don't delay treatment of metabolic acidosis, as it can lead to protein degradation, decreased albumin synthesis, and poor nutritional status 1
• Don't forget to monitor acid-base status more frequently during periods of improving continence in neobladder patients 3