A 65-year-old man with chronic obstructive pulmonary disease is hospitalized due to worsening shortness of breath, coughing, and wheezing. On arrival to the emergency department, the patient was in severe respiratory distress with bilateral wheezing. Chest x-ray revealed hyperinflated lungs without infiltrates. Endotracheal intubation was performed and mechanical ventilation initiated. Inhaled bronchodilators, systemic glucocorticoids, and empiric antibiotics were administered. Respiratory status gradually improved, and the patient was admitted to the intensive care unit. Now, 45 minutes later, progressive hypoxemia with elevated peak and plateau pressures has developed. Blood pressure is 150/86 mm Hg, pulse is 108/min, and respirations are 22/min. Oxygen saturation is 88% despite an increase in the fraction of inspired oxygen (FiO₂) to 70%. There is no wheezing, but breath sounds are decreased on the right. Tracheal suctioning yields no mucus. Which of the following is the most likely cause of the deterioration in this patient's condition?

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This patient with a severe chronic obstructive pulmonary disease (COPD) exacerbation (eg, wheezing, dyspnea, cough) requiring mechanical ventilation developed abrupt-onset hypoxemia associated with elevated peak and plateau pressures (measured on the ventilator) and decreased right-sided breath sounds. This presentation suggests a pneumothorax, or the presence of air within the pleural space. Pneumothoraxes may occur spontaneously or secondary to underlying lung disease, trauma, or iatrogenic injury. Positive pressure ventilation (eg, mechanical ventilation) poses the risk of pulmonary barotrauma, leading to alveolar rupture and pneumothorax formation. Patients with COPD are at higher risk due to preexisting pulmonary hyperinflation and the presence of bullae or blebs, which can rupture. air within the pleural space Patients with a large pneumothorax often demonstrate abrupt-onset tachycardia, tachypnea, hypoxemia, and decreased or absent breath sounds on the affected side. The collapsed lung, receiving a relatively stable volume of air from the ventilator, results in increased peak pressure (a measure of increased resistance to air flow from the ventilator) and increased plateau pressure (a measure of the lung's decreased ability to expand [compliance]). Management of pneumothorax involves placement of a chest tube, which allows reexpansion of the lung. (Choice A) Acute respiratory distress syndrome causes hypoxemia but is associated with diffuse pulmonary infiltrates; this patient's x-ray is clear. In addition, this syndrome typically takes multiple hours to days to manifest and is not associated with asymmetric breath sounds. (Choice C) A large pulmonary embolism can cause acute hypoxemia but would not cause elevated ventilatory pressures or decreased unilateral breath sounds. (Choice D) Right mainstem bronchus intubation would cause hypoxemia and elevated peak and plateau pressures due to the limited volume of the ventilated right lung but would cause decreased breath sounds in the left, unventilated lung (rather than the right lung, as in this patient). (Choice E) Ventilator-associated pneumonia can cause hypoxemia, but it occurs after >48 hours of mechanical ventilation. In addition, pneumonias typically cause crackles or rhonchi, not decreased breath sounds. Educational objective: Positive pressure ventilation improves gas exchange but poses the risk of pulmonary barotrauma, leading to alveolar rupture and subsequent pneumothorax formation. Patients with a large pneumothorax often demonstrate rapid-onset tachycardia, tachypnea, hypoxemia, and decreased or absent breath sounds on the affected side. References: Management of pneumothorax and prolonged air leak. (http://www.ncbi.nlm.nih.gov/pubmed/25463161)

A 65-Year-Old Man with Chronic Obstructive Pulmonary Disease Is Hospitalized