When do you start bridging therapy for anion gap (a difference in the measured cations and anions in the blood) metabolic acidosis?

Bicarbonate Therapy for Anion Gap Metabolic Acidosis

Bicarbonate therapy should be initiated for anion gap metabolic acidosis when the pH is <7.2 or bicarbonate is <15 mEq/L, with severe cases (pH <6.9) requiring immediate intervention. 1

Assessment of Severity

The decision to start bicarbonate therapy depends primarily on the severity of acidosis:

• Mild acidosis: Total CO2 ≥19 mmol/L - generally does not require bicarbonate therapy
• Moderate to severe acidosis: Total CO2 <19 mmol/L - consider bicarbonate therapy 1

pH thresholds for intervention:

• pH 7.0-7.2: Consider bicarbonate therapy
• pH <7.0: Strongly indicated
• pH <6.9: Urgent indication for bicarbonate therapy 2, 1

Dosing Guidelines

When bicarbonate therapy is indicated:

• Severe acidosis (pH <6.9): 100 mmol sodium bicarbonate in 400 ml sterile water at 200 ml/h 2
• Moderate acidosis (pH 6.9-7.0): 50 mmol sodium bicarbonate in 200 ml sterile water at 200 ml/h 2
• Cardiac arrest with acidosis: 44.6-100 mEq (1-2 vials of 50 mL) IV initially, may continue at 44.6-50 mEq every 5-10 minutes as needed based on arterial pH 3
• Less urgent metabolic acidosis: 2-5 mEq/kg body weight over 4-8 hours 3

Important Considerations

• Avoid overcorrection: Do not attempt full correction of low total CO2 content during the first 24 hours to prevent rebound alkalosis 3
• Target: Aim for total CO2 content of about 20 mEq/L at the end of the first day 3
• Stepwise approach: Plan bicarbonate therapy in a stepwise fashion as response is not precisely predictable 3
• Monitoring: Serial arterial or venous blood gases should be performed every 2-4 hours to assess response to therapy 2, 1

Special Situations

Diabetic Ketoacidosis (DKA)

• Bicarbonate is generally not necessary if pH is ≥7.0 2
• For DKA with pH <6.9, bicarbonate therapy is prudent 2
• Insulin therapy is the primary treatment for ketoacidosis 1

Toxic Alcohol Ingestion

• Hemodialysis is recommended for severe acidosis, renal failure, or toxic alcohol levels ≥50 mg/dL 1
• For ethylene glycol poisoning, treatment includes fomepizole or ethanol and hemodialysis 1

Chronic Kidney Disease

• Target serum bicarbonate level of ≥22 mmol/L with alkali replacement therapy 1

Potential Pitfalls

• Hypernatremia risk: Bicarbonate solutions are hypertonic and may produce an undesirable rise in plasma sodium 3
• Paradoxical CSF acidosis: Rapid correction can worsen central nervous system acidosis
• Hypocalcemia: Alkalinization increases calcium binding to proteins
• Volume overload: Monitor fluid status, especially in patients with heart failure or renal dysfunction

Remember that the primary goal is to identify and treat the underlying cause of the anion gap metabolic acidosis while supporting the patient through the acute phase with appropriate bicarbonate therapy when indicated by severity.