A 72-year-old woman is brought to the emergency department by her daughter due to severe, … — USMLE Step 2 CK

A 72-year-old woman is brought to the emergency department by her daughter due to severe, worsening shortness of breath and a persistent cough for the past 48 hours. The patient reports that her breathing is significantly worse when she attempts to lie flat in bed, forcing her to sleep in a recliner last night. Her medical history includes type 2 diabetes mellitus, essential hypertension, severe obesity (BMI $43\text{ kg/m}^2$ ), and a 35-pack-year history of cigarette smoking. Home medications include metformin, lisinopril, and an as-needed albuterol inhaler.

Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure of $182/104\text{ mm Hg}$ , heart rate of $115/\text{min}$ , and respiratory rate of $28/\text{min}$ . Pulse oximetry on ambient air is 88%.

On physical examination, the patient is speaking in short phrases and using accessory muscles of respiration. Jugular venous distention cannot be accurately assessed due to her body habitus. Pulmonary auscultation reveals a prolonged expiratory phase with diffuse, high-pitched polyphonic wheezing bilaterally, along with dullness to percussion at the lung bases. Cardiac auscultation reveals a rapid, regular rhythm; an extra low-frequency sound is heard just after S2 at the cardiac apex. The lower extremities show 2+ bilateral pitting edema.

Laboratory evaluation reveals the following:

Test	Result	Reference Range
Leukocyte count	$8,200/\text{mm}^3$	$4,500–11,000/\text{mm}^3$
B-type natriuretic peptide (BNP)	$145\text{ pg/mL}$	$<100\text{ pg/mL}$
Thyroid-stimulating hormone (TSH)	$1.2\text{ }\mu\text{U/mL}$	$0.5–5.0\text{ }\mu\text{U/mL}$
Free thyroxine (T4)	$0.5\text{ ng/dL}$	$0.9–1.7\text{ ng/dL}$

Arterial blood gas analysis on ambient air:

Parameter	Value	Reference Range
pH	7.49	7.35–7.45
PaCO2	$30\text{ mm Hg}$	$35–45\text{ mm Hg}$
PaO2	$56\text{ mm Hg}$	$75–105\text{ mm Hg}$
HCO3-	$22\text{ mEq/L}$	$22–28\text{ mEq/L}$

Chest radiography reveals prominent upper lobe pulmonary vasculature and indistinct vascular margins, but no lobar consolidation or pneumothorax is seen.

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

Intravenous furosemideAnswer
B
Systemic methylprednisolone and nebulized albuterol
C
Intravenous ceftriaxone and azithromycin
D
Intravenous sodium bicarbonate
E
Oral levothyroxine

Answer

Intravenous furosemide

The correct answer is intravenous furosemide. This patient is presenting with acute decompensated heart failure (ADHF) characterized by severe orthopnea, an S3 gallop (the 'extra low-frequency sound heard just after S2'), and radiologic evidence of pulmonary venous hypertension (prominent upper lobe vessels, peribronchial cuffing). Her presentation of diffuse wheezing is a manifestation of 'cardiac asthma,' where peribronchial edema leads to airway narrowing. A critical learning point is that her B-type natriuretic peptide (BNP) is only mildly elevated (

145\text{ pg/mL}

); severe obesity significantly increases the clearance of natriuretic peptides via adipose tissue clearance receptors, often resulting in falsely low BNP levels despite severe volume overload. The initial management of ADHF requires intravenous loop diuretics (e.g., furosemide) to reduce preload.

Step-by-Step Solution

Analyze the clinical presentation and physical exam.

The patient presents with severe orthopnea, an S3 gallop (extra low-frequency sound after S2), and diffuse wheezing.

These findings strongly suggest acute decompensated heart failure (ADHF). The wheezing represents 'cardiac asthma' resulting from peribronchial edema.

Interpret the laboratory findings, specifically the BNP in the context of the patient's BMI.

BNP is

145\text{ pg/mL}

(mildly elevated), which is highly significant in a patient with a BMI of

43\text{ kg/m}^2

Adipose tissue possesses clearance receptors for natriuretic peptides. Therefore, patients with severe obesity frequently have falsely low or 'normal' BNP levels despite significant volume overload.

Evaluate the arterial blood gas.

pH is 7.49 and PaCO2 is

30\text{ mm Hg}

, indicating a primary respiratory alkalosis.

This is a typical finding in early ADHF and pulmonary edema due to hypoxia-driven hyperventilation. It rules out primary metabolic acidosis.

Assess the thyroid panel.

TSH is normal and free T4 is low.

This pattern indicates euthyroid sick syndrome (non-thyroidal illness syndrome), common in acutely ill patients, which requires observation rather than hormone replacement.

Determine the next best step in management.

Administer intravenous furosemide.

Intravenous loop diuretics are the cornerstone of initial therapy for ADHF to reduce intravascular volume and alleviate pulmonary congestion.

Key Concept

Acute decompensated heart failure can present with wheezing ('cardiac asthma'), and diagnostic biomarkers like BNP can be falsely lowered in patients with severe obesity due to increased clearance by adipocytes.

Estimated Time:2m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic