Management of Metabolic Acidosis
The primary recommendation for treating metabolic acidosis is to correct the underlying cause while providing supportive care, with sodium bicarbonate therapy indicated for severe acidosis (pH < 7.1) or when serum bicarbonate is < 22 mmol/L in chronic kidney disease patients. 1, 2
Diagnostic Approach
- Determine type of metabolic acidosis:
- High anion gap: lactic acidosis, ketoacidosis, renal failure, toxins
- Normal anion gap (hyperchloremic): GI bicarbonate loss, renal tubular acidosis
- Calculate anion gap: [Na+] - ([HCO3-] + [Cl-])
- Assess severity through arterial blood gases and serum bicarbonate levels
- Monitor serum electrolytes (Na, K, Cl, HCO3) every 4-6 hours in acute cases 1
Treatment Algorithm
1. Severe Metabolic Acidosis (pH < 7.0-7.1)
- Sodium bicarbonate administration is indicated 1, 2
- Dosage: 1-2 mEq/kg IV given slowly for acute situations
- Goal: Increase bicarbonate levels toward normal range without exceeding it
- Monitor for complications of bicarbonate therapy:
- Sodium and fluid overload
- Decreased ionized calcium
- Paradoxical intracellular acidosis
- Hypernatremia
2. Specific Etiologies
Diabetic Ketoacidosis
- Primary treatment: Insulin therapy and fluid resuscitation
- Bicarbonate only if pH < 7.0 or life-threatening hyperkalemia 1
Lactic Acidosis
- Focus on improving tissue perfusion and treating underlying cause (sepsis, shock)
- Bicarbonate therapy remains controversial but indicated in severe cases (pH < 7.1) 2
Renal Tubular Acidosis
- Alkali therapy (sodium bicarbonate or potassium citrate)
- Target urinary citrate levels >320 mg/day and urinary pH 6.0-7.0 1
- Regular monitoring of serum electrolytes and renal function
Chronic Kidney Disease
- Sodium bicarbonate supplementation when serum bicarbonate < 18 mmol/L
- Target serum bicarbonate ≥ 22 mmol/L 1, 3
- Normalization of predialysis serum bicarbonate can be achieved through higher dialysate bicarbonate (38 mmol/L) or oral sodium bicarbonate (2-4 g/day or 25-50 mEq/day) 3
Special Considerations
Infants and Children
- Infants with methemoglobinemia from diarrhea and acidosis may improve with aggressive hydration and bicarbonate correction alone if methemoglobin level < 20% 3
- Monitor closely with strict input/output records and frequent vital signs 1
Critically Ill Patients
- In shock states, correct volume deficits first (20-40 ml/kg of either 0.9% saline or 4.5% human albumin solution) 3
- For patients with shock and coma, human albumin solution may be preferred over saline 3
- Avoid rapid correction of PCO2 in ventilated patients with severe acidosis 3
Monitoring Response to Treatment
- Regular laboratory monitoring:
- Serum electrolytes
- Arterial or venous blood gases
- Renal function tests
- For chronic conditions, monitor 24-hour urinary citrate, pH, and calcium excretion 1
- Ultrasound monitoring for nephrocalcinosis in renal tubular acidosis every 12-24 months 1
Benefits of Correcting Acidosis
- In dialysis patients, correction of acidemia has been associated with:
- Increased serum albumin
- Decreased protein degradation rates
- Increased plasma concentrations of essential amino acids
- Potential for greater body weight gain and improved nutritional status
- Fewer hospitalizations in peritoneal dialysis patients 3
Cautions and Pitfalls
- Bicarbonate therapy has not consistently reduced morbidity or mortality in lactic acidosis and ketoacidosis
- Potential adverse effects include worsening intracellular acidosis and reduced ionized calcium
- Avoid excessive alkali therapy which can lead to metabolic alkalosis
- In patients with respiratory compromise, bicarbonate administration may worsen hypercapnia
The management of metabolic acidosis requires a balanced approach that addresses the underlying cause while providing appropriate supportive care. While sodium bicarbonate remains the primary treatment for severe acidosis, its use should be guided by the severity of acidosis, the underlying etiology, and careful monitoring of the patient's response to therapy.