Paramedics arrive at the emergency department with a 24-year-old graduate student who was … — USMLE Step 3

Paramedics arrive at the emergency department with a $24$ -year-old graduate student who was discovered obtunded in her apartment. An empty pill container labeled amitriptyline was found nearby. En route, the prehospital crew secured her airway with an advanced device and initiated mechanical ventilation due to severe central nervous system depression. Upon transfer to the resuscitation bay, her temperature is $38.1^\circ\text{C}$ ( $100.6^\circ\text{F}$ ), heart rate is $142/\text{min}$ , blood pressure is $76/40\text{ mm Hg}$ , and oxygen saturation is $98\%$ on the ventilator. Her pupils are $6\text{ mm}$ and sluggishly reactive to light. A $12$ -lead electrocardiogram is immediately obtained and demonstrates sinus tachycardia with a QRS complex duration of $145\text{ ms}$ and a prominent terminal R wave in lead aVR. Which of the following is the most appropriate next step in the stabilization of this patient?

Intravenous bolus of sodium bicarbonateCevap
B
Administration of intravenous physostigmine
C
Initiation of an amiodarone infusion
D
Non-contrast computed tomography of the head
E
Administration of activated charcoal via orogastric tube

Cevap

Intravenous bolus of sodium bicarbonate

The correct answer identifies that the patient is suffering from severe tricyclic antidepressant (TCA) overdose, complicated by cardiac sodium channel blockade. This is evidenced by the wide QRS complex (

145\text{ ms}

) and profound hypotension. In the setting of TCA toxicity, a QRS duration

>100\text{ ms}

is highly predictive of seizures, and a QRS

>160\text{ ms}

is highly predictive of ventricular dysrhythmias. The primary stabilization mechanism is the immediate administration of intravenous hypertonic sodium bicarbonate. The concentrated sodium load physically overcomes the competitive sodium channel blockade at the His-Purkinje system, while the induced serum alkalinization favors the non-ionized form of the TCA, which binds less effectively to the sodium channels. This rapidly narrows the QRS complex and improves the blood pressure.

Adım Adım Çözüm

Analyze the patient's presentation and vital signs.

The patient presents with coma, hypotension, fever, tachycardia, dilated pupils, and an amitriptyline bottle, indicating severe tricyclic antidepressant (TCA) toxicity.

Recognizing the toxidrome is essential to determining the specific antidote required.

Interpret the diagnostic data (ECG).

The ECG reveals sinus tachycardia with a QRS duration of

145\text{ ms}

and an abnormal aVR axis.

TCA overdose causes blockade of fast cardiac sodium channels, manifesting as a QRS duration

>100\text{ ms}

, which strongly correlates with the risk of life-threatening ventricular arrhythmias and seizures.

Select the most urgent stabilization intervention.

Administer sodium bicarbonate.

Sodium bicarbonate provides a sodium load to overcome the channel blockade and alkalinizes the blood, which decreases the active, unbound fraction of the TCA, rapidly correcting the QRS widening and hypotension.

Anahtar Kavram

Patients with tricyclic antidepressant overdose and a QRS duration greater than

100\text{ ms}

or hemodynamic instability require immediate stabilization with hypertonic sodium bicarbonate to reverse sodium channel blockade.

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

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