A 72-year-old man presents to the emergency department with a 3-day history of progressive… — USMLE Step 2 CK

A $72$ -year-old man presents to the emergency department with a $3$ -day history of progressively worsening shortness of breath. He reports that his breathing becomes particularly difficult when he lies down, forcing him to sleep in a recliner chair for the past two nights. His medical history is significant for moderate chronic obstructive pulmonary disease (COPD), type 2 diabetes mellitus, hypertension, and a myocardial infarction $3$ years ago. His current medications include an albuterol inhaler, metformin, lisinopril, and metoprolol. Temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $168/94\text{ mm Hg}$ , pulse is $108/\text{min}$ and regular, and respirations are $26/\text{min}$ . Pulse oximetry shows $86\%$ on room air. Jugular venous pressure is estimated at $12\text{ cm H}_2\text{O}$ . Chest auscultation reveals diffuse bilateral wheezing with a markedly prolonged expiratory phase; no focal crackles are heard. Cardiac auscultation reveals distant heart sounds, but a faint third heart sound (S3) is appreciated at the apex. Bilateral $2+$ pitting edema is present up to the mid-calves.

Laboratory results are as follows:
Sodium: $136\text{ mEq/L}$
Potassium: $4.0\text{ mEq/L}$
Chloride: $100\text{ mEq/L}$
Bicarbonate: $24\text{ mEq/L}$
Blood urea nitrogen: $25\text{ mg/dL}$
Serum creatinine: $1.2\text{ mg/dL}$
Thyroid-stimulating hormone (TSH): $6.5\text{ }\mu\text{U/mL}$ (Normal: $0.4-4.0$ )
Free T4: $1.1\text{ ng/dL}$ (Normal: $0.9-1.7$ )

Arterial blood gas (room air):
pH: $7.26$
$\text{PaCO}_2$ : $58\text{ mm Hg}$
$\text{PaO}_2$ : $54\text{ mm Hg}$

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

Intravenous furosemideAnswer
B
Systemic glucocorticoids and nebulized albuterol
C
Intravenous ceftriaxone and azithromycin
D
Intravenous sodium bicarbonate
E
Initiation of oral levothyroxine

Answer

The most appropriate next step is to administer intravenous furosemide to treat acute decompensated heart failure.

The patient's presentation of orthopnea, elevated jugular venous pressure, an S3 gallop, and bilateral lower extremity edema is highly characteristic of acute decompensated heart failure (ADHF). Although the patient has a history of COPD and presents with diffuse wheezing, this is a classic manifestation of 'cardiac asthma', where peribronchial fluid accumulation leads to airway narrowing. The arterial blood gas confirms a pure acute respiratory acidosis (for a

\text{PaCO}_2

increase of

18\text{ mm Hg}

above normal, the pH drops by

1.8 \times 0.08 \approx 0.14

, yielding an expected pH of

7.26

). Furthermore, the normal serum bicarbonate is inconsistent with a chronic COPD retainer, who would typically have a compensatory metabolic alkalosis. The most appropriate initial step in management is to reduce pulmonary congestion and preload with a loop diuretic, such as intravenous furosemide.

Step-by-Step Solution

Analyze the physical examination findings to differentiate between possible causes of dyspnea and wheezing.

The presence of orthopnea, elevated jugular venous pressure (

12\text{ cm H}_2\text{O}

), an S3 gallop, and bilateral lower extremity edema points strongly to volume overload and acute decompensated heart failure.

While the patient has a history of COPD and diffuse wheezing, these findings represent 'cardiac asthma', where peribronchial edema causes airway narrowing.

Evaluate the arterial blood gas (ABG) to determine the acid-base status and calculate the expected compensation.

The ABG shows a primary respiratory acidosis (pH

7.26

\text{PaCO}_2

58\text{ mm Hg}

). For an acute respiratory acidosis, the pH drops by

0.08

for every

10\text{ mm Hg}

increase in

\text{PaCO}_2

. (

1.8 \times 0.08 = 0.144

; expected pH =

7.40 - 0.144 = 7.256

, which matches the patient's pH of

7.26

The pure acute respiratory acidosis with a normal bicarbonate (

24\text{ mEq/L}

) confirms this is an acute event, rather than an acute-on-chronic COPD exacerbation in a CO2 retainer (who would exhibit an elevated baseline bicarbonate).

Synthesize the clinical and laboratory data to determine the correct initial intervention.

The primary pathology is acute decompensated heart failure. The correct initial treatment involves loop diuretics to reduce pulmonary congestion.

Intravenous furosemide rapidly reduces preload and relieves the peribronchial edema causing the respiratory failure.

Key Concept

Patients with acute decompensated heart failure can present with wheezing (cardiac asthma) that mimics a COPD exacerbation; differentiation requires identifying signs of left and right ventricular failure (S3 gallop, elevated JVP, orthopnea) and interpreting acid-base status.

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