A 25-year-old man comes to the hospital due to acute-onset shortness of breath. The patient has a history of cystic fibrosis and multiple hospitalizations for recurrent pneumonia. He has a frequent productive cough at baseline. He does not use tobacco. Blood pressure is 80/50 mm Hg, pulse is 110/min, and respirations are 24/min. Examination shows mild cyanosis and subcutaneous crepitus. Breath sounds are decreased on the left. Which of the following is most likely responsible for this patient's acute symptoms?

Question

A 25-year-old man comes to the hospital due to acute-onset shortness of breath.  The patient has a history of cystic fibrosis and multiple hospitalizations for recurrent pneumonia.  He has a frequent productive cough at baseline.  He does not use tobacco.  Blood pressure is 80/50 mm Hg, pulse is 110/min, and respirations are 24/min.  Examination shows mild cyanosis and subcutaneous crepitus.  Breath sounds are decreased on the left.  Which of the following is most likely responsible for this patient's acute symptoms?

Quizplus · Accepted Answer

11ec160b_3b44_83c9_9249_8147007bbaa7_MD0001_00 This patient with sudden-onset shortness of breath and a physical examination showing subcutaneous crepitus and unilaterally decreased breath sounds most likely has a pneumothorax. In cystic fibrosis, chronic lung damage, combined with mucus plugging and large alveolar pressure surges (eg, coughing), predisposes to spontaneous alveolar rupture. Pressure in the lungs is normally equivalent to atmospheric pressure (ie, 0 cm H₂O) at end expiration, and the pressure in the intrapleural space is negative (eg, −5 cm H₂O) due to the expanding tendency of the chest wall and collapsing tendency of the lungs. Alveolar rupture creates continuity between the lungs and the pleural space, with pressure equalization and loss of intrapleural negative pressure. Shortness of breath results from inability to expand the ruptured lung, and during rupture, air may be forced into the subcutaneous tissues of the chest wall to cause crepitus. Simple pneumothorax is most common, but tension pneumothorax can develop if the rupture creates a one-way tissue valve that opens during inspiration to allow air into the pleural space and then closes during expiration to trap that air. As a result, intrapleural pressure increases with each breath and leads to contralateral mediastinal shift with vena cava collapse and decreased venous return to the heart. The reduced cardiac output causes hypotension and tachycardia (ie, obstructive shock) and can rapidly lead to cardiac arrest; therefore, emergent decompression of the pleural space is needed. (Choice A) Alveolar consolidation with inflammatory exudate occurs with pneumonia, which can cause hypotension (ie, septic shock). However, increased breath sounds are expected with pneumonia, and it would not explain subcutaneous crepitus. (Choice B) Bronchial obstruction with alveolar air reabsorption describes atelectasis (eg, due to a large mucus plug). Shortness of breath and decreased breath sounds are typical, but hypotension and subcutaneous crepitus are not expected. (Choice C) Diffuse bronchiolar constriction occurs with asthma exacerbation and is not typical of cystic fibrosis. Hypotension and unilaterally decreased breath sounds are not expected with asthma exacerbation. (Choice D) Increased dead-space ventilation occurs with pulmonary embolism. Although hypotension (ie, obstructive shock) can occur, decreased breath sounds and subcutaneous crepitus are not typical. Educational objective: Spontaneous pneumothorax is common in cystic fibrosis and involves alveolar rupture, leading to loss of intrapleural negative pressure. Patients have sudden-onset shortness of breath, unilaterally decreased breath sounds, and, sometimes, subcutaneous crepitus. Hypotension and tachycardia suggest the development of tension pathophysiology. __________ References: Pneumothorax in cystic fibrosis. (http://www.ncbi.nlm.nih.gov/pubmed/25337406)

A 25-Year-Old Man Comes to the Hospital Due to Acute-Onset