Transported via emergency medical services with severe, acute-onset respiratory distress, … — USMLE Step 2 CK

Transported via emergency medical services with severe, acute-onset respiratory distress, a 71-year-old individual is evaluated in the resuscitation bay. The patient has a history of a remote myocardial infarction and a 35-pack-year smoking history. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 172/98 mm Hg, heart rate of 118/min, and respiratory rate of 28/min. Oxygen saturation is 85% on room air.

Physical examination reveals a patient sitting upright and using accessory muscles of respiration. The jugular venous pressure is elevated to 11 cm $H_2O$ . Cardiac auscultation reveals a regular tachycardia with a prominent S3 gallop. Lung auscultation demonstrates diffuse, bilateral end-expiratory wheezing without focal crackles. Bilateral trace pitting edema is present in the lower extremities.

Arterial blood gas analysis on room air shows:
$pH$ : 7.26
$PaCO_2$ : 58 mm Hg
$PaO_2$ : 52 mm Hg
$HCO_3^-$ : 25 mEq/L

Laboratory evaluation reveals a leukocyte count of 8,200/mm³ and a thyroid-stimulating hormone (TSH) level of 5.8 mU/L (normal: 0.4-4.0 mU/L).

Which of the following is the most appropriate initial pharmacological intervention for this patient?

Intravenous torsemideAnswer
B
Systemic methylprednisolone and nebulized bronchodilators
C
Intravenous sodium bicarbonate
D
Empiric intravenous levofloxacin
E
Oral levothyroxine

Answer

Intravenous torsemide

Intravenous loop diuretics (such as torsemide) are the mainstay of pharmacological therapy for acute decompensated heart failure. They act rapidly to induce venodilation (decreasing preload immediately) followed by a potent diuresis, which clears the pulmonary edema causing the patient's severe respiratory distress, hypoxia, and secondary respiratory acidosis.

Step-by-Step Solution

Analyze the physical examination findings to differentiate the cause of respiratory distress.

The patient exhibits an S3 gallop, elevated jugular venous pressure (JVP), and hypertension.

These findings are highly specific for volume overload and left ventricular failure, indicating acute decompensated heart failure.

Interpret the presence of wheezing in the context of the cardiac findings.

The wheezing represents 'cardiac asthma' caused by peribronchial edema, rather than primary bronchospasm.

Fluid accumulation in the interstitial spaces compresses the bronchioles, simulating the wheezing seen in COPD or asthma.

Evaluate the arterial blood gas (ABG) results.

The ABG shows an acute, uncompensated respiratory acidosis.

Severe pulmonary edema impairs gas exchange and lung compliance, leading to fatigue and

CO_2

retention.

Select the appropriate pharmacological management.

A rapid-acting intravenous loop diuretic is the definitive pharmacological therapy.

Loop diuretics reduce intravascular volume and venous return (preload), thereby directly alleviating the pulmonary congestion driving the respiratory failure.

Key Concept

Differentiation and acute management of acute decompensated heart failure (ADHF) masquerading as a COPD exacerbation (cardiac asthma).

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