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Chapter 28. Acute Lung Injury and the Acute Respiratory Distress Syndrome: Pathophysiology and Treatment

A 59-year-old woman presents with shortness of breath that worsened in the past 24 hours. She is severely dyspneic and cannot complete a full sentence. Vitals include radial pulse = 116 beats/min and respiratory f = 40 breaths/min. Diffuse bilateral crackles are heard on posterior exam; a chest x-ray shows diffuse airspace disease. Which criteria would best distinguish between ARDS and congestive heart failure in this patient?

a. The subacute onset of her symptoms

b. A calculated PaO2/FIO2 ratio ≥250 in this woman

c. Bilateral infiltrates and a pulmonary wedge pressure of ≤18 mm Hg

d. An improved clinical profile following intubation and PEEP ventilation

e. Responsiveness to antibiotics against community-acquired pathogens

The most correct answer is c.

Regardless of how this patient's pulmonary complaint arose, the presence of bilateral infiltrates in the absence of a significantly elevated wedge pressure would be definitive of ARDS, while a PaO2 /FIO2 >250 mm Hg in itself (answer b) would tend to exclude ARDS. She might indeed have community-acquired pneumonia that worsened overnight (answer a) and that would respond to antibiotics (answer e), but those issues do not in themselves rule out congestive heart failure (CHF). Since both ARDS and CHF patients can have pulmonary edema, each could develop atelectasis and thus respond favorably to mechanical ventilation with PEEP (answer d).

A 41-year-old man is hospitalized after attempting to synthesize methamphetamine. He was found unconscious in a room with strong ammonia fumes. A chest x-ray shows left upper lobe and right middle lobes infiltrates. Blood gases on 100% O2 show pHa = 7.31, PaCO2 = 50 mm Hg, PaO2 = 180 mm Hg. His status does not improve, and 72 hours later a repeat chest x-ray shows infiltrates in the left upper, left lower, right upper, and right middle lobes. What underlying lung pathophysiology is most likely involved?

a. Ammonia-enhanced reabsorption of alveolar fluid and protein

b. Excessive surfactant release with resultant alveolar instability

c. CNS depression, insufficient ventilation, and reduced PAO2

d. Alveolar overdistention causing increased functional residual capacity

e. Sloughed epithelium, endothelial cell injury, and surfactant inactivation

The most correct answer is e.

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