Mixed Overdose With Wide QRS and Seizure
22-year-old woman is brought in after intentional ingestion of unknown pills. She was somnolent at home, then had a 2-minute tonic-clonic seizure in the ED. Heart rate 118 beats/min, blood pressure 82/48 mm Hg, QRS 138 ms, terminal R wave in aVR. She received 2 mg lorazepam IV and the seizure stopped. She remains somnolent but withdraws to painful stimuli. Arterial blood gas: pH 7.28, lactate 6.8 mmol/L. Bedside glucose 140 mg/dL. ECG shows sinus tachycardia. Empty bottles at home include amitriptyline and alprazolam.
1. Identify the toxidrome and the most dangerous agent. Why is flumazenil contraindicated?
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The toxidrome is consistent with tricyclic antidepressant (TCA) toxicity: tachycardia, hypotension, widened QRS, terminal R wave in aVR, seizures, and acidosis. The most dangerous agent is amitriptyline. Alprazolam contributes to sedation but is not the primary threat. Flumazenil is contraindicated because it reverses benzodiazepine effect and can precipitate seizures and life-threatening arrhythmias in patients with TCA overdose. The seizure risk is high, and flumazenil may also unmask the proconvulsant effects of the TCA. Do not give flumazenil in mixed overdose with a proconvulsant agent.
2. What are your immediate treatment priorities, including sodium bicarbonate dosing and goals?
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Prioritize airway, breathing, and circulation. Intubate if the patient cannot protect her airway or has recurrent seizures. Give sodium bicarbonate 1-2 mEq/kg IV bolus for a QRS >100 ms or ventricular arrhythmia, and repeat until the QRS narrows and the pH is 7.45-7.55. The goals are a narrow QRS (<120 ms) and alkaline serum pH. Avoid hyperventilation as the primary treatment. Give isotonic fluids for hypotension; if needed, start norepinephrine. Treat seizures with benzodiazepines (lorazepam 2-4 mg IV) and consider a second agent. Avoid class IA and IC antiarrhythmics (e.g., procainamide, flecainide). Magnesium may be used for torsades de pointes. Monitor ECG continuously.
3. What is the appropriate disposition and monitoring plan, and what complications do you anticipate?
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Admit to the intensive care unit for continuous cardiac monitoring, serial ECGs, and arterial blood gas monitoring. Observe for at least 24 hours after ingestion or until the QRS and pH normalize. Anticipate complications: ventricular arrhythmias, heart block, seizures, aspiration pneumonitis, pulmonary edema, and delayed deterioration. Obtain a psychiatric evaluation once medically stable. Check acetaminophen and salicylate levels, and consider a urine drug screen. Monitor electrolytes and renal function. The patient may develop anticholinergic delirium. Do not discharge from the ED, even if the QRS narrows initially, because TCA toxicity can be delayed and recurrent.