A 55-year-old woman is brought to the emergency department after being found unconscious in her apartment. En route to the hospital, the patient had a seizure and was urgently intubated for airway protection. Medical history is significant for treatment-resistant major depression, hypertension, and hyperlipidemia. The patient takes imipramine, atorvastatin, and lisinopril. Temperature is 38.2 C (100.7 F), blood pressure is 90/50 mm Hg, pulse is 120/min, and respirations are 14/min. Oxygen saturation is 98% on 40% fraction of inspired oxygen. Examination shows bilateral dilated pupils that are minimally reactive to light. The skin appears flushed. Cardiopulmonary examination reveals clear lungs and normal heart sounds. The abdomen is slightly distended with decreased bowel sounds. Muscle tone and reflexes are normal. Sodium bicarbonate therapy is administered. Sodium bicarbonate is indicated in this patient primarily to treat which of the following?

Question

A 55-year-old woman is brought to the emergency department after being found unconscious in her apartment.  En route to the hospital, the patient had a seizure and was urgently intubated for airway protection.  Medical history is significant for treatment-resistant major depression, hypertension, and hyperlipidemia.  The patient takes imipramine, atorvastatin, and lisinopril.  Temperature is 38.2 C (100.7 F), blood pressure is 90/50 mm Hg, pulse is 120/min, and respirations are 14/min.  Oxygen saturation is 98% on 40% fraction of inspired oxygen.  Examination shows bilateral dilated pupils that are minimally reactive to light.  The skin appears flushed.  Cardiopulmonary examination reveals clear lungs and normal heart sounds.  The abdomen is slightly distended with decreased bowel sounds.  Muscle tone and reflexes are normal.  Sodium bicarbonate therapy is administered.  Sodium bicarbonate is indicated in this patient primarily to treat which of the following?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d1df_bb1d_bc81_83b3c8e198cf_MD0003_00 This patient has likely overdosed on imipramine, a tricyclic antidepressant (TCA). Because of the inhibitory effects of TCAs on multiple receptor types, overdose can cause a variety of symptoms, including CNS toxicity (eg, unconsciousness, seizures), anticholinergic toxicity (eg, hyperthermia, dilated pupils, intestinal ileus, flushed skin), hypotension, and cardiac toxicity. Cardiac toxicity is caused by TCA inhibition of fast sodium channels in the His-Purkinje system and myocardium. This decreases conduction velocity, increases the duration of repolarization, and prolongs absolute refractory periods. QRS prolongation and ventricular arrhythmias (eg, ventricular tachycardia, ventricular fibrillation) may result. A QRS interval >100 msec or ventricular arrhythmia in the setting of TCA overdose is an indication for sodium bicarbonate therapy. Sodium bicarbonate likely improves cardiac toxicity through the following mechanisms: Increasing serum pH makes the TCA less pharmacologically active, decreasing its avidity for sodium channels. Increasing extracellular sodium concentration raises the electrochemical gradient across cardiac cell membranes, decreasing the impact of the TCA-induced sodium channel blockade. Sodium bicarbonate infusion also improves TCA-induced hypotension, which is caused by alpha-1 adrenergic receptor antagonism in combination with cardiac toxicity, and is the leading cause of mortality in TCA overdose. (Choice B) Sodium bicarbonate is an adjunctive therapy for treating severe hyperkalemia (or rapidly increasing serum potassium) associated with ECG changes (eg, peaked T waves, short QT interval, increased QRS interval). However, TCA overdose is not associated with severe hyperkalemia. (Choice C) TCA overdose causes hyperthermia via its anticholinergic effect (ie, muscarinic receptor inhibition) on sweat glands, which decreases sweating and heat dissipation. This anticholinergic effect is typically unaltered by sodium bicarbonate administration. (Choice D) Sodium bicarbonate administration may increase serum sodium levels; however, this medication is administered to treat cardiac toxicity rather than hyponatremia, which is not typically associated with TCA overdose. In addition, 3% saline, rather than sodium bicarbonate, is the preferred medication for treating severe hyponatremia. (Choice E) Respiration depression is not directly caused by TCA overdose but can occur indirectly because of CNS depression (ie, antihistamine effects) or complications of seizure activity. Sodium bicarbonate is unlikely to improve these indirect causes of respiratory depression. Educational objective: Tricyclic antidepressant (TCA) overdose can cause CNS toxicity, anticholinergic findings, hypotension, and cardiac toxicity. Cardiac toxicity is due to the inhibition of fast sodium channels and may result in QRS prolongation and ventricular arrhythmia. Sodium bicarbonate can improve both cardiac toxicity and TCA-induced hypotension. References: A literature review of the use of sodium bicarbonate for the treatment of QRS widening. (http://www.ncbi.nlm.nih.gov/pubmed/26159649)

A 55-Year-Old Woman Is Brought to the Emergency Department After