How should a tricyclic antidepressant (TCA) and mixed drug overdose be managed in the emergency setting?

Management of Tricyclic Antidepressant (TCA) and Mixed Drug Overdose

Administer sodium bicarbonate 1-2 mEq/kg IV bolus immediately if QRS duration >100 ms is present, and prioritize airway management with mechanical ventilation while maintaining alkalemia (pH 7.45-7.55) to prevent life-threatening cardiotoxicity. 1, 2

Immediate Assessment and Stabilization

Airway and Breathing

• Establish airway control early with endotracheal intubation for patients showing respiratory depression, altered mental status, or inability to protect their airway 2
• Maintain mild hyperventilation during mechanical ventilation to support alkalemia (pH 7.45-7.55) and avoid respiratory acidosis, which potentiates cardiotoxicity 2
• Never allow respiratory acidosis to develop—this is a critical pitfall that worsens sodium channel blockade 2

Cardiac Monitoring

• Obtain an ECG or rhythm strip immediately during initial assessment 2, 3
• QRS duration >100 ms indicates severe toxicity requiring immediate sodium bicarbonate administration 1, 2, 3
• Continuous cardiac monitoring is mandatory to detect ventricular dysrhythmias, heart block, or asystole 2
• Terminal rightward axis deviation in lead aVR is characteristic and precedes ventricular dysrhythmias 1

Sodium Bicarbonate Therapy (First-Line Treatment)

Indications and Dosing

• Administer hypertonic sodium bicarbonate 1-2 mEq/kg IV bolus for QRS prolongation >100 ms or any life-threatening cardiotoxicity 1, 2, 4
• Repeat boluses every 5-10 minutes as needed to achieve target arterial pH 7.45-7.55 1, 2, 4
• Use hypertonic solutions: 1000 mEq/L in adults, 500 mEq/L in children 1, 4

Monitoring During Bicarbonate Therapy

• Monitor serum sodium frequently and maintain <150-155 mEq/L to avoid hypernatremia 2, 4
• Monitor arterial pH and maintain 7.45-7.55 (not >7.55) 2, 4
• Monitor serum potassium as hypokalemia may develop during therapy 2
• Ensure adequate ventilation to eliminate CO2 generated by bicarbonate, as inadequate ventilation worsens intracellular acidosis 4

Management of Hypotension

• Administer IV fluid boluses of 10 mL/kg normal saline for initial hypotension management 2
• Continue sodium bicarbonate therapy for persistent hypotension despite fluid resuscitation 2
• Consider vasopressors if hypotension remains refractory to fluids and bicarbonate 2

Seizure Management

• Administer benzodiazepines (diazepam or midazolam) as first-line therapy for TCA-associated seizures 1, 3
• Benzodiazepines are the only recommended anticonvulsant in this setting 1

Refractory Cardiotoxicity: Escalation Algorithm

Second-Line: Lidocaine

• Administer lidocaine 1-1.5 mg/kg IV bolus slowly for persistent wide-complex tachycardia after optimized bicarbonate therapy 1, 2
• Lidocaine (Class Ib antiarrhythmic) may be reasonable for life-threatening cardiotoxicity refractory to sodium bicarbonate 1, 2
• Expected effect: QRS narrowing and hemodynamic improvement 2

Third-Line: Intravenous Lipid Emulsion (ILE)

• Administer 20% lipid emulsion 1.5 mL/kg bolus over 1 minute, followed by continuous infusion at 0.25 mL/kg/min for refractory toxicity 2
• ILE is reasonable for life-threatening sodium channel blocker poisoning unresponsive to bicarbonate and lidocaine 1, 2
• The "lipid sink" effect sequesters lipophilic TCAs, reducing free plasma concentration 2

Fourth-Line: VA-ECMO

• Consider veno-arterial ECMO for cardiac arrest or refractory cardiogenic shock unresponsive to high-dose vasopressors, bicarbonate, lidocaine, and ILE 1, 2
• Early ECMO consultation improves outcomes, especially when initiated before prolonged cardiac arrest 2
• VA-ECMO provides mechanical circulatory support while allowing time for drug metabolism and elimination 1, 2

Gastrointestinal Decontamination

• Administer activated charcoal if the patient presents within 1-2 hours of ingestion and has a protected airway 3
• Do not induce emesis 3
• Do not delay transport or definitive care to administer charcoal 3

Critical Medications to AVOID

Absolutely Contraindicated

• Never administer flumazenil, even if benzodiazepine co-ingestion is suspected—it precipitates seizures and arrhythmias in TCA overdose 2, 3
• Never use physostigmine for anticholinergic symptoms—it worsens cardiac toxicity 2

Contraindicated Antiarrhythmics

• Avoid Class Ia antiarrhythmics (quinidine, procainamide)—they exacerbate sodium channel blockade 1, 2
• Avoid Class Ic antiarrhythmics (flecainide)—they worsen conduction delays 1, 2
• Avoid Class III antiarrhythmics (amiodarone)—they may worsen cardiotoxicity 1, 2
• Avoid beta-blockers (Class II)—they precipitate hypotension and cardiac arrest 2

Special Considerations for Mixed Overdose

Opioid Co-Ingestion

• If respiratory arrest is present with suspected opioid co-ingestion, administer naloxone in addition to standard BLS/ALS care 1
• For cardiac arrest, prioritize high-quality CPR over naloxone administration 1
• Do not delay emergency activation while awaiting response to naloxone 1

Benzodiazepine Co-Ingestion

• Benzodiazepine co-ingestion may complicate the clinical picture but does not change TCA management 3
• Again, never administer flumazenil in this setting 2, 3

Supportive Care

• Maintain normothermia—hyperthermia worsens TCA toxicity 1, 2
• Treat anticholinergic symptoms (hyperthermia, flushing, ileus) with supportive measures only 5
• Continue cardiac monitoring for at least 6 hours after clinical recovery, as life-threatening complications develop within 6 hours or not at all 3, 6

Disposition and Observation

• All symptomatic patients (weak, drowsy, dizzy, tremulous, palpitations) require emergency department referral 3
• Asymptomatic patients are unlikely to develop symptoms if >6 hours have elapsed since ingestion 3
• Patients with suspected self-harm require immediate psychiatric evaluation regardless of medical stability 3