What is the role of sodium bicarbonate in treating metabolic acidosis?

Role of Sodium Bicarbonate in Treating Metabolic Acidosis

Sodium bicarbonate therapy is indicated for severe metabolic acidosis (arterial pH < 7.1 and base deficit < 10) and specific conditions like hyperkalemia or tricyclic antidepressant overdose, rather than for routine use in all cases of metabolic acidosis. 1

Indications for Sodium Bicarbonate Therapy

• FDA-approved uses include treatment of metabolic acidosis occurring in severe renal disease, uncontrolled diabetes, circulatory insufficiency due to shock, severe dehydration, extracorporeal circulation of blood, cardiac arrest, and severe primary lactic acidosis 2
• Sodium bicarbonate is also indicated for certain drug intoxications (barbiturates, salicylates, methyl alcohol), hemolytic reactions requiring urine alkalinization, and severe diarrhea with significant bicarbonate loss 2
• Treatment with sodium bicarbonate should ideally be used alongside measures addressing the underlying cause of acidosis (e.g., insulin in diabetes, volume restoration in shock) 2

When to Avoid Routine Use

• Not recommended for routine use in metabolic acidosis arising from tissue hypoperfusion, particularly when arterial pH is >7.15 1
• The American College of Cardiology recommends against routine use in cardiac arrest 1
• In tumor lysis syndrome, sodium bicarbonate is only indicated for patients with documented metabolic acidosis 3
• The best method of reversing acidosis is to treat the underlying cause and restore adequate circulation 3, 1

Dosing and Administration

• Standard dose is 1-2 mEq/kg IV given slowly 1
• For maintenance dialysis patients, serum bicarbonate should be maintained at or above 22 mmol/L 3
• In patients with chronic renal failure or maintenance dialysis, oral sodium bicarbonate at 2-4 g/day (25-50 mEq/day) can effectively increase serum bicarbonate concentrations 3
• Do not mix sodium bicarbonate with vasoactive amines or calcium 1

Evidence from Clinical Research

• The BICAR-ICU trial (2018) found that in patients with severe metabolic acidemia, sodium bicarbonate had no significant effect on the composite outcome of death and organ failure in the overall population 4
• However, in the subgroup of patients with acute kidney injury, sodium bicarbonate was associated with improved survival at day 28 (54% vs 37%) 4
• Recent observational data suggests that in vasopressor-dependent patients with metabolic acidosis, early sodium bicarbonate administration may be associated with higher mean arterial pressure at 6 hours 5

Potential Adverse Effects

• Can cause extracellular alkalosis, shifting the oxyhemoglobin curve and inhibiting oxygen release 1
• May lead to hypernatremia and hyperosmolarity 1
• Can produce excess CO2, potentially causing paradoxical intracellular acidosis 1
• May inactivate simultaneously administered catecholamines 1
• Sodium bicarbonate increases PaCO2, making it contraindicated in patients with mixed acidosis with high PaCO2 levels 6

Special Considerations

• In patients with hyperkalemia, sodium bicarbonate can help shift potassium into cells 1
• For patients with hypernatremia, alternative alkalizing agents like THAM may be preferred as sodium bicarbonate increases serum sodium while THAM decreases it 6
• In patients with chronic kidney disease, correction of acidemia has been associated with increased serum albumin, decreased protein degradation, increased plasma concentrations of branched chain amino acids, and fewer hospitalizations 3

Clinical Decision Algorithm

1. Assess severity of acidosis:

   • If pH < 7.1 and base deficit < 10: Consider sodium bicarbonate 1
   • If pH ≥ 7.15: Generally avoid sodium bicarbonate 1

2. Evaluate specific conditions:

   • Hyperkalemia: Sodium bicarbonate recommended 1
   • Tricyclic antidepressant overdose: Sodium bicarbonate recommended 1
   • Acute kidney injury with severe acidosis: Consider sodium bicarbonate (improved survival in clinical trials) 4
   • Cardiac arrest: Not routinely recommended unless specific indications present 1
   • Mixed acidosis with high PaCO2: Avoid sodium bicarbonate 6

3. Always prioritize treating the underlying cause of acidosis while considering bicarbonate therapy 2