Approach to Workup and Management of Acidosis
The workup of acidosis requires arterial blood gas analysis, calculation of anion gap, and identification of the underlying cause to guide appropriate management. 1, 2
Initial Assessment
Step 1: Confirm Acidosis
- Arterial blood gas (ABG) analysis: pH < 7.35 defines acidosis 1
- Serum bicarbonate: < 22 mmol/L indicates metabolic component 1
Step 2: Determine Type of Acidosis
- Respiratory acidosis: Elevated PaCO₂ > 45 mmHg (hypercapnia) 1
- Metabolic acidosis: Reduced serum bicarbonate < 22 mmol/L 1
- Mixed disorders: Both respiratory and metabolic components present
Detailed Metabolic Acidosis Workup
Step 3: Calculate Anion Gap (AG)
- AG = [Na⁺] - ([HCO₃⁻] + [Cl⁻]) 3
- Normal AG: 8-12 mEq/L
- Elevated AG (> 12 mEq/L): Suggests addition of unmeasured acids
Step 4: Classify Metabolic Acidosis
High Anion Gap Metabolic Acidosis (HAGMA):
- Lactic acidosis: Check serum lactate (> 2 mmol/L) 1
- Causes: Shock, severe dehydration, circulatory insufficiency, sepsis
- Ketoacidosis: Check urine/serum ketones
- Causes: Diabetic ketoacidosis, alcoholic ketoacidosis, starvation
- Renal failure: Check BUN/creatinine
- Toxins/Ingestions: Salicylates, methanol, ethylene glycol
Normal Anion Gap Metabolic Acidosis (NAGMA):
- GI bicarbonate loss: Diarrhea, intestinal fistulas
- Renal tubular acidosis: Check urine pH, electrolytes
- Iatrogenic: IV fluids with high chloride content
Step 5: Assess for Compensation
- Expected respiratory compensation for metabolic acidosis:
- PaCO₂ = 1.5 × [HCO₃⁻] + 8 (± 2)
- Inadequate compensation suggests mixed disorder
Management Approach
General Principles
- Treat the underlying cause - This is the most important step 2
- Supportive care - Maintain hemodynamics and oxygenation
Specific Management Based on Etiology
Lactic Acidosis
- Restore tissue perfusion with fluids/vasopressors if shock present
- Identify and treat source of hypoperfusion (sepsis, hemorrhage)
- Monitor lactate clearance to assess response 1
Diabetic Ketoacidosis
- IV fluids, insulin therapy, and electrolyte replacement
- For mild/moderate DKA: Subcutaneous insulin may be appropriate
- For severe DKA: Continuous IV insulin until resolution of ketosis 1
Respiratory Acidosis
- For acute hypercapnic respiratory failure: Controlled oxygen therapy targeting SpO₂ 88-92% 1
- Consider non-invasive ventilation (NIV) when pH < 7.35 and pCO₂ > 6.5 kPa despite optimal medical therapy 1
- Mechanical ventilation for severe acidosis with deteriorating clinical status
Renal Acidosis
- For chronic kidney disease with GFR < 30 ml/min/1.73m²:
Sodium Bicarbonate Therapy
Indications for sodium bicarbonate:
- Severe metabolic acidosis (pH < 7.1) with hemodynamic instability 1
- Drug intoxications (salicylates, barbiturates, methanol poisoning)
- Hyperkalemia with acidosis
- Renal tubular acidosis
Dosing:
- Initial dose: 1-2 mEq/kg IV over 10-15 minutes in severe cases
- For less urgent acidosis: 2-5 mEq/kg over 4-8 hours 2
- Avoid rapid correction which may cause paradoxical CNS acidosis and hypernatremia
Monitoring Response
- Serial ABGs to assess pH correction
- Electrolyte monitoring (especially potassium, calcium)
- Clinical assessment of hemodynamic response
- Lactate clearance in lactic acidosis
Common Pitfalls to Avoid
- Treating the numbers rather than the patient's clinical condition
- Overlooking mixed acid-base disorders
- Rapid overcorrection of chronic acidosis
- Failure to identify and address the underlying cause
- Excessive sodium bicarbonate administration causing paradoxical intracellular acidosis and volume overload
Remember that the ultimate goal of treatment is to improve morbidity and mortality by addressing the underlying cause while supporting organ function during the acute phase of illness.