A 25-year-old man is brought to the emergency department after a high-speed motor vehicle collision. The patient was restrained, but there was prolonged extrication due to extensive vehicular damage. Supplemental oxygen and intravenous fluids were administered on the way to the hospital. On arrival, the patient is alert and can speak but appears to have increased work of breathing. Blood pressure is 110/66 mm Hg, pulse is 120/min, and respirations are 34/min. Pulse oximetry is 88% on 10 L oxygen via nonrebreather mask. The trachea is midline and the neck veins are flat. There are several chest wall and abdominal bruises. A portion of the anterior left chest moves inward during inspiration. Breath sounds are diminished in the anterior left lung but normal elsewhere. The abdomen is nondistended, soft, and nontender to palpation. The left thigh is deformed, but compartments are soft and distal pulses are intact. There are no focal neurologic deficits. Which of the following is the most likely cause of this patient's hypoxia?

Question

A 25-year-old man is brought to the emergency department after a high-speed motor vehicle collision.  The patient was restrained, but there was prolonged extrication due to extensive vehicular damage.  Supplemental oxygen and intravenous fluids were administered on the way to the hospital.  On arrival, the patient is alert and can speak but appears to have increased work of breathing.  Blood pressure is 110/66 mm Hg, pulse is 120/min, and respirations are 34/min.  Pulse oximetry is 88% on 10 L oxygen via nonrebreather mask.  The trachea is midline and the neck veins are flat.  There are several chest wall and abdominal bruises.  A portion of the anterior left chest moves inward during inspiration.  Breath sounds are diminished in the anterior left lung but normal elsewhere.  The abdomen is nondistended, soft, and nontender to palpation.  The left thigh is deformed, but compartments are soft and distal pulses are intact.  There are no focal neurologic deficits.  Which of the following is the most likely cause of this patient's hypoxia?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d953_3af7_bc81_17d8df8b67e4_MD0003_00 This patient with tachypnea, hypoxia, and a segment of the chest wall that moves inward during inspiration most likely has flail chest. Flail chest occurs when fracture of ≥3 contiguous ribs in ≥2 locations creates an isolated chest wall segment (flail segment) that moves paradoxically (opposite) to the rest of the rib cage during respiration. Typically, the extreme trauma to the chest wall that creates the flail segment also contuses the underlying lung (eg, causing diminished anterior breath sounds beneath this patient's anterior flail segment). Flail chest negatively impacts respiration and oxygenation in multiple ways, including the following: Impaired generation of negative intrathoracic pressure during inspiration and increased dead space during expiration cause ineffective ventilation. Pulmonary contusion (with alveolar hemorrhage and edema) in the underlying lung impedes oxygen diffusion. Fracture-related pain causes respiratory splinting (ie, decreased inspiratory effort) and bibasilar atelectasis. Flail chest often results in respiratory failure requiring mechanical positive pressure ventilation, which, due to positive pressure, can force the flail segment to move outward with the rest of the rib cage during inspiration. (Choices A and C) Injury to the tracheobronchial tree can cause extensive air leakage into the mediastinum and pleural space. This can result in pneumothorax (often tension pneumothorax). Massive pneumothorax or hemothorax can increase intrapleural pressure, compress the lung, and prevent adequate ventilation, leading to hypoxia. However, such a large intrapleural collection of air or blood typically causes diffusely diminished or absent breath sounds and/or tracheal deviation from mass effect. This patient's breath sounds are only diminished anteriorly in the lung underlying the flail segment (ie, pulmonary contusion), and his trachea is midline. (Choice D) Fat embolism, which is most commonly associated with long bone fracture (especially femur fracture, as in this patient), can occlude pulmonary capillaries, leading to hypoxia. However, this is typically associated with neurologic deficits (not present in this patient) and does not manifest until 24-72 hours after the initial insult. (Choice E) Myocardial contusion from blunt thoracic trauma can lead to myocardial dysfunction and cardiogenic shock. The resulting left heart failure can lead to pulmonary edema and hypoxia; however, it typically also causes hypotension (not seen in this patient) from forward pump failure. Educational objective Fracture of ≥3 contiguous ribs in ≥2 locations can result in flail chest, with paradoxical movement of the fractured flail segment during respiration. Flail chest can cause hypoxia due to ineffective ventilation, pulmonary contusion, and atelectasis. 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 25-Year-Old Man Is Brought to the Emergency Department After