A 22-year-old man is brought to the emergency department after a high-speed motor vehicle collision. Blood pressure is 102/60 mm Hg, pulse is 122/min, and respirations are 40/min. Pulse oximetry is 88% on 6 L oxygen. The patient is alert but appears to be in respiratory distress. Breath sounds are diminished bilaterally, and bilateral chest tubes are placed. The patient's respiratory status initially improves; however, over the next hour, he develops respiratory failure, requiring intubation and mechanical ventilation. Postintubation chest x-ray is shown below. Which of the following is the most likely cause of this patient's need for mechanical ventilation?

Question

A 22-year-old man is brought to the emergency department after a high-speed motor vehicle collision.  Blood pressure is 102/60 mm Hg, pulse is 122/min, and respirations are 40/min.  Pulse oximetry is 88% on 6 L oxygen.  The patient is alert but appears to be in respiratory distress.  Breath sounds are diminished bilaterally, and bilateral chest tubes are placed.  The patient's respiratory status initially improves; however, over the next hour, he develops respiratory failure, requiring intubation and mechanical ventilation.  Postintubation chest x-ray is shown below.  Which of the following is the most likely cause of this patient's need for mechanical ventilation?

Quizplus · Accepted Answer

11ec25c8_d93f_3dae_bc81_1753d441655d_MD0003_00 This patient with respiratory distress and multiple rib fractures on chest x-ray likely has flail chest. Flail chest occurs when fracture of ≥3 adjacent ribs in ≥2 locations (multiple x-ray views are usually required to see both locations) creates an isolated chest wall segment that moves paradoxically to the remaining rib cage during respiration. The paradoxical motion impairs generation of negative intrathoracic pressure during inspiration. As a result, tidal volume decreases and work of breathing increases. In addition, the extreme blunt force required to create flail chest typically injures the underlying lung. The resulting pulmonary contusion (eg, seen on x-ray as infiltrates underlying this patient's rib fractures) decreases oxygen diffusion (due to alveolar hemorrhage and edema). As a result, patients must breathe harder to maintain oxygenation. The combination of increased work of breathing and decreased oxygenation causes many patients, such as this one, to fatigue and develop respiratory failure, requiring mechanical ventilation. (Choice A) This patient is at risk for acute respiratory distress syndrome (ARDS) from both trauma and pulmonary contusion. However, ARDS typically takes 6-72 hours (or longer) to evolve after the inciting event (while the inflammatory response builds) and causes more diffuse bilateral infiltrates on x-ray. (Choice B) Blunt cardiac injury can cause myocardial dysfunction leading to cardiogenic pulmonary edema and hypoxia. However, concomitant hypotension (from acute pump failure) is expected in addition to more symmetric bilateral alveolar infiltrates. (Choice C) Diaphragmatic rupture can alter respiratory mechanics and cause respiratory distress; however, it typically causes loss of diaphragmatic contour and/or visualization of abdominal organs within the thoracic cavity (eg, intrathoracic nasogastric tube). (Choice D) Fat embolism can cause hypoxemia but typically occurs after long bone or pelvic fracture and does not manifest until 24-72 hours after the inciting event. (Choice F) Although this patient likely had bilateral pneumothoraces upon arrival, bilateral tube thoracostomy initially improved his respiratory status. Recurrent (especially tension) pneumothorax is unlikely given functioning chest tubes and would be seen on x-ray as an area without lung markings bordered by a visceral pleural line. visceral pleural line Educational objective: Flail chest should be suspected in patients with respiratory distress and multiple rib fractures. Flail chest increases work of breathing and may injure the underlying lung, often leading to respiratory failure. References: Chest wall trauma. (http://www.ncbi.nlm.nih.gov/pubmed/28363365) Disorders of the chest wall: clinical manifestations. (http://www.ncbi.nlm.nih.gov/pubmed/29779595)

A 22-Year-Old Man Is Brought to the Emergency Department After