A 68-year-old man is brought to the emergency department due to a syncopal episode at home… — USMLE Step 2 CK

A 68-year-old man is brought to the emergency department due to a syncopal episode at home. Over the past 3 days, he has experienced progressively worsening shortness of breath and a dry cough. His medical history is significant for severe chronic obstructive pulmonary disease (COPD), type 2 diabetes mellitus, and a recent diagnosis of prostate cancer. His current medications include inhaled tiotropium, inhaled albuterol as needed, and metformin.

On arrival, his temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $82/50\text{ mm Hg}$ , pulse is $122/\text{min}$ , and respirations are $28/\text{min}$ . Pulse oximetry shows $84\%$ on room air.

Physical examination reveals significant jugular venous distention to the angle of the jaw. Cardiac auscultation demonstrates a loud second heart sound ( $P_2$ ) at the left upper sternal border and a holosystolic murmur at the left lower sternal border that increases in intensity with inspiration. Lung auscultation reveals faint, bilateral end-expiratory wheezes without crackles. The right calf is visibly swollen and tender to palpation.

A bedside echocardiogram demonstrates a severely dilated, hypokinetic right ventricle with bowing of the interventricular septum into the left ventricle.

Arterial blood gas analysis on room air reveals:
pH: $7.29$
$\text{PaCO}_2$ : $32\text{ mm Hg}$
$\text{PaO}_2$ : $52\text{ mm Hg}$
$\text{HCO}_3^-$ : $15\text{ mEq/L}$

Serum lactic acid is $5.4\text{ mmol/L}$ .

Which of the following is the most appropriate next step in management?

Intravenous alteplaseAnswer
B
Systemic glucocorticoids and nebulized bronchodilators
C
Intravenous furosemide and noninvasive positive pressure ventilation
D
Intravenous vancomycin and cefepime
E
Endotracheal intubation and permissive hypercapnia

Answer

The most appropriate next step in management is the administration of intravenous alteplase.

This patient's presentation of syncope, hypotension, right ventricular strain (JVD, loud

P_2

, tricuspid regurgitation murmur), right calf swelling, and a history of malignancy points strongly to a massive pulmonary embolism (PE). A massive PE is defined by the presence of hemodynamic instability (systolic blood pressure

<90\text{ mm Hg}

). The large clot burden drastically increases pulmonary vascular resistance, causing acute right ventricular (RV) dilation, hypokinesis, and bowing of the interventricular septum into the left ventricle (LV). This septal bowing impairs LV filling (preload), leading to drastically reduced cardiac output, obstructive shock, and subsequent lactic acidosis. In patients with massive PE and no absolute contraindications, immediate systemic thrombolysis (e.g., intravenous alteplase) is the treatment of choice to rapidly restore pulmonary perfusion and stabilize hemodynamics.

Step-by-Step Solution

Analyze the patient's clinical presentation and vital signs.

The patient has obstructive shock characterized by hypotension (

82/50\text{ mm Hg}

), tachycardia, and hypoxia, accompanied by right heart strain signs (JVD, loud

P_2

, tricuspid regurgitation murmur) and a likely DVT (swollen right calf).

Identifying the shock phenotype is the crucial first step to directing lifesaving therapy.

Interpret the bedside echocardiogram findings.

The echocardiogram shows severe right ventricular dilation and hypokinesis with septal bowing, confirming acute cor pulmonale/RV failure.

This confirms that the hemodynamic collapse is due to acute pulmonary hypertension secondary to a massive pulmonary embolism.

Evaluate the arterial blood gas values and serum lactate.

The patient has a primary metabolic acidosis (lactic acidosis from hypoperfusion). Winter's formula (Expected

\text{PaCO}_2 = 1.5 \times 15 + 8 = 30.5 \pm 2\text{ mm Hg}

) confirms the measured

\text{PaCO}_2

32\text{ mm Hg}

is appropriate respiratory compensation.

Ruling out a primary uncompensated respiratory acidosis prevents the critical error of initiating mechanical ventilation, which could be fatal.

Determine the optimal intervention for massive PE.

The definitive treatment for massive (hemodynamically unstable) pulmonary embolism is systemic thrombolysis with an agent like alteplase.

Thrombolytics rapidly dissolve the massive clot burden, decreasing pulmonary vascular resistance, improving RV forward flow, and reversing the obstructive shock.

Key Concept

Massive pulmonary embolism presents with obstructive shock, right ventricular failure, and profound hypoxemia; it requires immediate systemic thrombolysis.

Estimated Time:2m 0s

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