ICU · toxicology

Acute Tricyclic Antidepressant (TCA) Poisoning — Comprehensive ICU Management

Also known as Tricyclic antidepressant poisoning · TCA overdose · Amitriptyline overdose · Sodium channel blockade poisoning · Sodium bicarbonate antidote · Membrane stabilising agent toxicity · Wide QRS toxicology · Lipid emulsion rescue

Acute tricyclic antidepressant (TCA) poisoning — the classic 'membrane stabilising' overdose. The lethal mechanism is a QUINIDINE-LIKE block of fast cardiac sodium channels: phase 0 depolarisation slows in the His-Purkinje system and myocardium → WIDE QRS, AV block, impaired automaticity → HYPOTENSION and VENTRICULAR DYSRHYTHMIAS. Alongside this: CNS depression (lethargy to coma), SEIZURES (20% in one prospective cohort), sinus tachycardia and QTc prolongation. Severity is read off the ECG, not the drug level: QRS >100 ms is the consensus trigger for sodium bicarbonate; a terminal R wave ≥3 mm in aVR (or R/S ratio ≥0.7 in aVR) independently predicts seizures and ventricular arrhythmias; QRS <100 ms within the first 6 h of confirmed intoxication excludes adverse cardiac events. Referral dose thresholds: >5 mg/kg for most TCAs (>2.5 mg/kg for desipramine, nortriptyline, trimipramine; >1 mg/kg for protriptyline). Management: HYPERTONIC SODIUM BICARBONATE 1–2 mmol/kg IV BOLUS, repeated while the patient remains unstable, to a MAXIMUM of 6 mmol/kg, combined with mechanical ventilation and hyperventilation to achieve serum alkalinisation (pH ~7.45–7.55) — sodium loading and alkalaemia are both part of the mechanism. Correct the hypokalaemia and hypocalcaemia bicarbonate causes (both prolong QT and can trigger torsades). Seizures: BENZODIAZEPINES (treat fast — seizure after presentation predicted death with OR ~41). Hypotension: IV fluids, vasopressors per ACLS; terlipressin is described for catecholamine-refractory shock. AVOID class Ia/Ic antiarrhythmics (they add phase-0 sodium-channel depression); phenytoin evidence is weak — lidocaine is the better-studied class Ib adjunct when bicarbonate is insufficient. AVOID flumazenil (consensus: not recommended in TCA poisoning). CAUTION with physostigmine (asystole reported in TCA case series). Activated charcoal only if early (up to 1 h) with a protected airway; whole-bowel irrigation is not routine. Lipid emulsion 20% (1.5 mL/kg bolus then 15 mL/kg/h) is rescue therapy for refractory cardiovascular compromise. Not a filtration problem: large volume of distribution and saturable kinetics — massive overdoses can need prolonged bicarbonate for days. Prognosis: 3% ICU mortality in a prospective cohort; TCA poisoning death rates ~10× those of SSRIs per million prescriptions.