Paramedics bring a 72-year-old man to the emergency department due to a 1-day history of s… — USMLE Step 2 CK

Paramedics bring a 72-year-old man to the emergency department due to a 1-day history of severe dyspnea and increasing somnolence. His medical history includes severe chronic obstructive pulmonary disease (COPD) requiring continuous home oxygen, heart failure with a left ventricular ejection fraction of $35\%$ , and essential hypertension. Upon arrival, his temperature is $37.1^\circ$ C ( $98.8^\circ$ F), blood pressure is $165/95$ mm Hg, heart rate is $118$ /min, and respiratory rate is $28$ /min. Oxygen saturation is $84\%$ on his baseline $2$ L/min via nasal cannula. He is lethargic but arouses to loud verbal stimuli. Physical examination reveals an elevated jugular venous pressure of $13$ cm $H_2O$ . Lung auscultation demonstrates diffuse, bilateral expiratory wheezing and prominent bibasilar fine crackles. Cardiac auscultation reveals a regular tachycardia with a distinct third heart sound ( $S_3$ ). There is $2+$ bilateral pitting edema of the lower extremities. Laboratory studies show a leukocyte count of $8,500/mm^3$ . An arterial blood gas analysis obtained on $2$ L/min of oxygen reveals:

$pH$ : $7.22$
$PaCO_2$ : $72$ mm Hg
$PaO_2$ : $52$ mm Hg
$HCO_3^-$ : $30$ mEq/L

A trial of noninvasive positive pressure ventilation (NIPPV) is immediately initiated. Which of the following is the most appropriate additional next step in the management of this patient?

Intravenous administration of a loop diureticAnswer
B
Administration of systemic methylprednisolone
C
Initiation of empiric piperacillin-tazobactam
D
Intravenous administration of sodium bicarbonate
E
Titration of supplemental oxygen to a target saturation of $98\%$

Answer

Intravenous administration of a loop diuretic

This patient is presenting with acute hypercapnic respiratory failure and hypercapnic encephalopathy (lethargy, somnolence). Despite his history of COPD and the presence of expiratory wheezing, his physical examination is diagnostic of acute decompensated heart failure (ADHF). The combination of an elevated jugular venous pressure, an

S_3

gallop, bibasilar crackles, and peripheral edema provides overwhelming evidence of cardiogenic volume overload. In patients with ADHF, peribronchial interstitial edema can cause narrowing of the small airways, presenting as wheezing (often termed 'cardiac asthma'). The arterial blood gas confirms an acute-on-chronic respiratory acidosis; the elevated bicarbonate reflects his baseline renal compensation for chronic hypercapnia, while the acute drop in pH is caused by the sudden onset of pulmonary edema. The most appropriate management for this patient includes noninvasive positive pressure ventilation (NIPPV) to provide ventilatory support and decrease both preload and afterload, accompanied immediately by intravenous loop diuretics (e.g., furosemide) to reduce the volume overload.

Step-by-Step Solution

Analyze the patient's vital signs and physical examination findings.

The patient is hypoxic and hypertensive with an elevated JVP, an

S_3

gallop, bibasilar crackles, and bilateral pitting edema.

These are classic hallmark signs of severe volume overload and acute decompensated heart failure (ADHF).

Evaluate the lung exam findings in the context of the cardiovascular signs.

Diffuse wheezing is present, but given the strong evidence of ADHF, this represents 'cardiac asthma'.

Peribronchial edema in ADHF can cause small airway narrowing and wheezing, which must be differentiated from a primary COPD exacerbation.

Interpret the arterial blood gas (ABG) values.

The ABG shows an acidemia (

pH = 7.22

) with severe hypercapnia (

PaCO_2 = 72

mm Hg) and elevated bicarbonate (

HCO_3^- = 30

mEq/L).

This indicates an acute-on-chronic respiratory acidosis. The high bicarbonate is a chronic metabolic compensation for his baseline COPD, while the acute drop in pH is driven by acute pulmonary edema impairing gas exchange.

Determine the most appropriate therapeutic interventions.

Continue NIPPV for ventilatory support and administer an intravenous loop diuretic.

NIPPV reduces the work of breathing and decreases cardiac preload/afterload. Intravenous furosemide is essential to aggressively remove the excess fluid driving the cardiogenic pulmonary edema.

Key Concept

Differentiating acute decompensated heart failure from a COPD exacerbation and managing acute-on-chronic hypercapnic respiratory failure.

Estimated Time:1m 30s

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