Sodium Bicarbonate Dosing in TCA Cardiac Arrest: Upper Limits and Monitoring
In TCA overdose with cardiac arrest, sodium bicarbonate should be titrated to clinical response (QRS narrowing, hemodynamic stability) while avoiding serum sodium >150-155 mEq/L and pH >7.50-7.55—there is no absolute upper dose limit if these parameters remain within target and the patient continues to improve. 1
Primary Dosing Strategy
Initial bolus administration should be 1-2 mEq/kg (50-100 mL of 8.4% solution) given as a slow IV push, repeated every 5-10 minutes as needed based on arterial blood gas monitoring and ECG response. 1, 2 In the case report of massive imipramine overdose with ventricular fibrillation, a total of 400 mmol (approximately 8 mEq/kg for a 70 kg patient) of sodium bicarbonate was successfully administered over 50 minutes of cardiac arrest with full neurological recovery. 3
Continuous infusion following initial boluses should use a 150 mEq/L solution at 1-3 mL/kg/hour to maintain alkalinization if the patient shows ongoing improvement. 1, 4
Critical Safety Thresholds (Not Absolute Dose Limits)
The American Heart Association establishes physiologic boundaries rather than maximum doses: 1
- Serum sodium: Must not exceed 150-155 mEq/L
- Arterial pH: Target 7.45-7.55, do not exceed 7.50-7.55
- Monitor and replace potassium: Alkalemia shifts potassium intracellularly, causing potentially dangerous hypokalemia
These are the true "upper limits"—not a specific milliequivalent dose. 1, 5
Monitoring Requirements During Aggressive Therapy
Arterial blood gases and serum electrolytes must be checked every 2-4 hours during active resuscitation to guide ongoing bicarbonate administration. 4 The FDA label emphasizes that "the degree of response from a given dose is not precisely predictable," requiring stepwise titration rather than calculated total deficit replacement. 2
Continuous ECG monitoring for QRS duration is essential—bicarbonate should be continued as long as QRS remains >100-120 ms and the patient demonstrates hemodynamic improvement. 1, 5, 6
Clinical Decision Algorithm
Continue bicarbonate if:
- QRS duration remains >100-120 ms 1, 6
- Hemodynamic instability persists (hypotension, arrhythmias) 1, 5
- Serum sodium <150 mEq/L 1
- pH <7.50 1
Stop or reduce bicarbonate when:
- QRS normalizes and hemodynamics stabilize 1, 5
- Serum sodium approaches 150-155 mEq/L 1
- pH exceeds 7.50-7.55 1
- Severe hypokalemia develops despite replacement 1
Evidence from Extreme Cases
The published case of successful resuscitation after 400 mmol sodium bicarbonate administration demonstrates that very large cumulative doses can be safely given when titrated to clinical response and monitored appropriately. 3 This patient had a peak TCA level of 6000 ng/ml (the highest reported in literature at that time) and required 50 minutes of cardiac arrest management with aggressive bicarbonate therapy, ultimately achieving complete neurological recovery. 3
Important Caveats
Ensure adequate ventilation before and during bicarbonate administration, as each dose generates CO2 that must be eliminated to prevent paradoxical intracellular acidosis. 1, 4 In cardiac arrest, mechanical ventilation should maintain minute ventilation sufficient to achieve PaCO2 of 30-35 mmHg. 4
Do not mix bicarbonate with calcium-containing solutions or catecholamines (epinephrine, norepinephrine) in the same IV line—flush with normal saline before and after bicarbonate administration. 4, 2
Consider ECMO/VA-ECMO for refractory cardiogenic shock despite maximal bicarbonate therapy, as TCA toxicity is a reversible cause of cardiac arrest. 1, 5
Practical Approach in Ongoing Cardiac Arrest
In the setting of persistent cardiac arrest with ongoing QRS widening, prioritize clinical response over arbitrary dose limits. The literature supports repeated boluses of 50-100 mEq every 5-10 minutes as long as serum sodium and pH remain within acceptable ranges. 1, 2, 3 The case evidence demonstrates that cumulative doses exceeding 400 mmol can be life-saving when appropriately monitored. 3