TCA Poisoning

Major effects of TCA antidepressant 1. Sodium channel blockade 2. α1-Adrenoreceptor blockade 3. Inhibition of reuptake of biogenic amines (e.g.. Norepinephrine, serotonin) 4. Muscarinic receptor blockade (anticholinergic effects) 5. Histamine receptor blockade (antihistaminic effects) 6. Potassium efflux blockade 7. Indirect GABA antagonism

TCA toxicity should be considered in all patients with decreased level of consciousness (LOC) and prolonged QRS complex. A dose greater than 10 mg/kg or 1000 mg in an adult should be considered life threatening.

ECG

ECG after therapy

Clinical condition improving? History or clinical suspicion of ingestion absent Reassess at 6 hours: Still no major signs of poisoning? Bowel sounds present? Clinical condition improving? IV line establishment Cardiac monitoring Pulse oximetry ECG Immediate and continuous observation No Psychologic consultation Discharge Consider activated charcoal Major signs of poisoning: Decreased level of consciousness Respiratory depression Hypotension Dysrhythmias Conduction block (ORS > 100 msec) Seizures Yes present Admit

Management airway and breathing: when in doubt, intubate. Ventilatory support to avoid respiratory acidosis is critical. If ingestion is recent: activated charcoal Physostigmine is contraindicated in CA overdose.

Management Hypotension: isotonic crystalloids. If the QRS is more than 100 msec or if the patient is acidemic, intravenous (IV) sodium bicarbonate (NaHCO3) should also be administered. NaHCO3 is administered by IV boluses of I to 2 mEq/kg until hypotension resolves and the QRS narrows to 100 msec or until serum pH increases to 7.55.

Management Afler obtaining the desired endpoint with IV NaHCO3 boluses, isotonic continuous IV infusion is initiated by adding three ampules of NaHCO3(50 mEq/ampule) to 1 L of D5W. The initial IV infusion is started at a usual maintenance rate for IV fluids. This initial NaHCO3 infusion rate must often be maintained for at least 4 to 6 hours before the rate can be decreased. For a hypertonic continuous IV solution. four ampules of NaHCO3 are added to I L of D5W. This is occasionally necessary for refractory hypotension with a prolonged QRS or refractory ventricular dysrhythmias.

If the patient's hypotension does not resolve, norepinephrine or dopamine is recommended. High dosage dopamine (up to 30 µg/kg/min) and norepinephrine (up to 1 µg/kg/min) may be necessary.

Tachydysrhytmia NaHCO3 is the treatment of choice for ventricular tachycardia. No antiarrhytmia. Wide-complex tachycardia is not necessarily ventricular tachycardia and can be caused by sinus tachycardia with aberrant conduction

Treatment of Neurologic Complications of TCA Poisoning Coma Endotrachcal intubation mechanical ventilation Supportive care Seizures Lorazepam or diazepam Phenobarbital or continuous intravenous midazolam infusion Hyperthermia Cessation of seizures with benzodiazepine and phenobarbital Neuromuscular blockade with vecuronium during phenobarbital loading General anesthesia Evaporativc cooling Ice water bath