Continuing management

All patients should be observed with ECG monitoring for at least 6 h after ingestion. Patients who are symptomatic after this time should be admitted and monitored until asymptomatic; those who are asymptomatic can be discharged. Electrolytes and arterial blood gas status should be measured and corrected, and adequate oxygenation and ventilation maintained.

Intravenous fluids should be used to maintain the blood pressure if necessary. Inotropic agents usually have little effect on tricyclic-induced hypotension, but glucagon may be effective. Once oxygenation has been attended to, diazepam is the treatment of choice for convulsions, taking care not to cause respiratory depression.

If the patient is acidotic, is showing definite signs of toxicity, or has cardiovascular instablity or a wide QRS complex on the ECG, sodium bicarbonate should be administered to maintain the arterial blood pH between 7.45 and 7.55. This often produces a marked improvement. The initial dose is 1 to 2 mmol/kg by slow intravenous infusion. The plasma potassium concentration should also be maintained at the upper end of normal.

Drug therapy should be avoided where possible, but if arrhythmias are unresponsive to sodium bicarbonate, phenytoin may be effective (18 mg/kg intravenously over 20 min). Intravenous esmolol or atenolol may also be given for arrhythmias and repeated as necessary. Lidocaine (lignocaine) has been used to treat ventricular dysrhythmias, but may precipitate convulsions.

Glucagon has been successfully used to treat a massive imipramine overdose (S®n§L§L§! 1995). In this case, 10 mg intravenously immediately raised the blood pressure from 71/30 to 110/70 mmHg and the QRS interval shortened from 129 to 89 ms. It should be considered in hypotensive cases which fail to respond to volume expansion and sodium bicarbonate administration. Magnesium sulfate has been successful in reversing tricyclic-induced ventricular tachycardia in experimental animals, but human data are limited.

Class Ia antiarrhythmic drugs (quinidine, procainamide, and disopyramide) are contraindicated because their effects on myocardial contractility are similar to those of tricyclics and they will exacerbate the cardiotoxic effects. Use of physostigmine is no longer recommended to treat tricyclic poisoning as it has caused convulsions, dysrhythmias, and cardiac arrest. Flumazenil should not be used to reverse a concomitant benzodiazepine overdose. It has produced convulsions and ventricular dysrhythmias in the presence of tricyclic drugs.

If there is evidence of pulmonary edema or if respiratory depression is causing hypoxemia, assisted ventilation should be commenced. If there is severe unresponsive hypotension or a cardiac arrest occurs, the circulation should be supported by external chest compression for as long as necessary. This should be done in the case of asystole and should be employed even when electromechanical dissociation is apparent on the ECG. This has been carried out for 3 to 5 h with full recovery ( O.EL.

and Bramble.. .1981). In an ICU setting an aortic balloon pump or cardiopulmonary bypass may be necessary. Measures such as these are justified in severe tricyclic antidepressant overdose because this type of poisoning is essentially reversible, provided that hypoxic cerebral damage can be prevented.

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