Treatment of Metabolic Acidosis
The treatment of metabolic acidosis must be directed at the underlying cause while simultaneously correcting severe acidemia with bicarbonate therapy when pH is below 7.2 or serum bicarbonate is severely decreased. 1, 2
Diagnostic Approach
First, determine the type of metabolic acidosis:
- Anion gap metabolic acidosis: Normal anion gap is 8-12 mEq/L; elevated anion gap (>12 mEq/L) indicates accumulation of unmeasured acids 1
- Normal anion gap (hyperchloremic) metabolic acidosis: Due to bicarbonate loss or impaired renal acidification 3
Treatment Algorithm
Step 1: Address the Underlying Cause
- Diabetic ketoacidosis: Insulin therapy plus fluid resuscitation with isotonic saline at 15-20 mL/kg/hr initially 1, 4
- Lactic acidosis: Improve tissue oxygenation and treat shock or hypoperfusion 5
- Toxic alcohol ingestion: Fomepizole or ethanol and hemodialysis for severe cases 1
- Renal tubular acidosis: Alkali replacement therapy 1
- Diarrhea-induced acidosis: Fluid and bicarbonate replacement 2
Step 2: Bicarbonate Therapy
For severe acidosis (pH <7.2 or bicarbonate severely decreased):
- Initial dosing: 1-2 mEq/kg sodium bicarbonate IV over 1 hour 1, 2
- Cardiac arrest: Rapid IV dose of 44.6-100 mEq (1-2 50mL vials) initially, followed by 44.6-50 mEq every 5-10 minutes if necessary 2
- Less urgent metabolic acidosis: 2-5 mEq/kg body weight over 4-8 hours 2
Step 3: Monitoring and Adjustment
- Monitor arterial blood gases, serum electrolytes, and clinical response 2
- Target: Aim for serum bicarbonate ≥22 mmol/L 1
- Caution: Avoid rapid full correction of bicarbonate in first 24 hours to prevent iatrogenic alkalosis 2
Special Considerations
Chronic Kidney Disease
- Maintain serum bicarbonate above 22 mmol/L to prevent bone and muscle complications 4, 6
- Avoid citrate-containing alkali in patients exposed to aluminum 4
Diabetic Ketoacidosis
- Fluid resuscitation with 0.9% NaCl at 15-20 mL/kg/hr during first hour 4
- Subsequent fluid choice depends on hydration status and electrolytes 4
- Include potassium (20-30 mEq/L) in fluids once renal function is assured 4
Chronic Metabolic Acidosis
- Long-term oral bicarbonate therapy is beneficial for preventing bone and muscle loss 6
- Increasing fruit and vegetable consumption can provide alternative alkali source 1
Pitfalls to Avoid
- Overcorrection: Achieving normal total CO2 too quickly can cause alkalosis due to ventilatory lag 2
- Sodium overload: Bicarbonate solutions are hypertonic and may cause hypernatremia 2
- Inadequate monitoring: Serial blood gas measurements are essential to guide therapy 1
- Ignoring potassium: Correction of acidosis can lower serum potassium, requiring supplementation 4
- Citrate use in aluminum exposure: Avoid citrate-containing alkali in patients exposed to aluminum salts 4
By systematically identifying the cause and severity of metabolic acidosis, and applying appropriate treatment strategies, morbidity and mortality can be significantly reduced.