When to Give Sodium Bicarbonate Based on Arterial Blood Gas Results
Administer sodium bicarbonate when arterial pH is less than 7.1 AND base excess is less than -10 mmol/L, but only after ensuring effective ventilation is established. 1
Primary Indications Based on ABG Criteria
Severe metabolic acidosis requires:
- Arterial pH < 7.1 1, 2
- Base excess < -10 mmol/L 1
- Effective ventilation already established (to eliminate CO₂ produced by bicarbonate) 1, 2
The initial dose is 50 mmol (50 mL of 8.4% solution) given slowly IV, with repeat dosing guided by serial ABG measurements every 2-4 hours. 1, 3
Specific Clinical Scenarios Where ABG Guides Bicarbonate Use
Diabetic Ketoacidosis
- Give bicarbonate only if pH < 6.9 after initial hydration 2, 4
- For pH 6.9-7.0: administer 50 mmol in 200 mL sterile water at 200 mL/hour 2, 4
- For pH < 6.9: administer 100 mmol in 400 mL sterile water at 200 mL/hour 2, 4
- Do not give bicarbonate if pH ≥ 7.0, as insulin therapy alone resolves the acidosis 2, 4
Cardiac Arrest
- Consider bicarbonate after first epinephrine dose fails and documented pH < 7.1 1, 4
- Dose: 1-2 mEq/kg (44.6-100 mEq) as rapid IV bolus 4, 3
- Repeat every 5-10 minutes guided by arterial pH monitoring 4, 3
- Routine use is not recommended as it does not improve survival 1
Special Toxicologic Emergencies (Independent of pH Threshold)
- Tricyclic antidepressant or sodium channel blocker overdose with QRS > 120 ms: give 50-150 mEq bolus targeting pH 7.45-7.55 2, 4
- Life-threatening hyperkalemia: give 1-2 mEq/kg as temporizing measure while definitive therapy is initiated 1, 2, 4
Absolute Contraindications Based on ABG
Do NOT give bicarbonate when:
- pH ≥ 7.15 in hypoperfusion-induced lactic acidosis – two blinded RCTs showed no hemodynamic benefit and identified harms including increased lactate, sodium/fluid overload, increased PaCO₂, and decreased ionized calcium 1, 5
- pH ≥ 7.15 in sepsis-related acidosis – strong evidence demonstrates lack of benefit and potential harm 1, 2
- Respiratory acidosis without adequate ventilation established – bicarbonate generates CO₂ that worsens intracellular acidosis if not eliminated 1, 2
Critical Pre-Administration Requirements
Before giving bicarbonate, you must:
- Ensure adequate ventilation (mechanical or spontaneous) to eliminate CO₂ generated by bicarbonate reaction 1, 2
- Target minute ventilation to achieve PaCO₂ 30-35 mmHg for synergistic alkalinization 2, 4
- Obtain baseline ABG to document pH < 7.1 and base excess < -10 1
- Use separate IV line from calcium-containing solutions and vasoactive amines 2, 4
Monitoring Protocol During Therapy
Every 2-4 hours during active bicarbonate therapy, measure: 2, 4
- Arterial blood gases (pH, PaCO₂, bicarbonate)
- Serum sodium (stop if > 150-155 mEq/L)
- Serum potassium (replace as needed; alkalinization shifts K⁺ intracellularly)
- Ionized calcium (replace if symptomatic)
Target pH is 7.2-7.3, NOT complete normalization – avoid pH > 7.50-7.55 as this causes hypokalemia and impaired oxygen delivery. 2, 4
Common Pitfalls to Avoid
- Never give bicarbonate without ensuring adequate ventilation first – this is the most dangerous error and causes paradoxical intracellular acidosis 1, 2
- Do not treat pH ≥ 7.15 with bicarbonate in lactic acidosis or sepsis – clear evidence shows lack of benefit and potential harm 1, 5
- Do not calculate total bicarbonate deficit and give it all at once – use stepwise approach over 4-8 hours as response is unpredictable 4, 3
- Do not mix bicarbonate with calcium or catecholamines – causes precipitation or inactivation 2, 4
- Do not ignore the underlying cause – bicarbonate buys time but does not treat the disease; restoration of adequate circulation is definitive therapy 1