A 55-year-old man is evaluated for new-onset shortness of breath after a right hemicolectomy 3 days ago. He has no chest pain, cough, or hemoptysis. The patient came to the hospital 4 days ago with a history of constipation, weight loss, and abdominal distension. He was found to have an obstructing cecal mass and underwent right hemicolectomy with ileocolic anastomosis. The patient has no significant medical history other than a 35-pack-year smoking history. Temperature is 37.2 C (99 F), blood pressure is 120/80 mm Hg, pulse is 98/min, and respirations are 22/min. Pulse oximetry shows 88% on room air. Lung examination reveals dullness to percussion and absence of breath sounds on the left. Chest x-ray is shown below. Chest x-ray at the time of admission was normal. Which of the following is the most likely cause of this patient's pulmonary findings?

Question

A 55-year-old man is evaluated for new-onset shortness of breath after a right hemicolectomy 3 days ago.  He has no chest pain, cough, or hemoptysis.  The patient came to the hospital 4 days ago with a history of constipation, weight loss, and abdominal distension.  He was found to have an obstructing cecal mass and underwent right hemicolectomy with ileocolic anastomosis.  The patient has no significant medical history other than a 35-pack-year smoking history.  Temperature is 37.2 C (99 F), blood pressure is 120/80 mm Hg, pulse is 98/min, and respirations are 22/min.  Pulse oximetry shows 88% on room air.  Lung examination reveals dullness to percussion and absence of breath sounds on the left.  Chest x-ray is shown below.  Chest x-ray at the time of admission was normal.  Which of the following is the most likely cause of this patient's pulmonary findings?

Quizplus · Accepted Answer

11ec25c8_d93a_0d85_bc81_83ac5fd785c0_MD0003_00 This patient likely has atelectasis of the left lung due to a left mainstem bronchial mucus plug. Airway obstruction (eg, mucus, tumor, foreign body) creates distal air trapping in the alveoli. Eventually, the trapped air molecules diffuse into the bloodstream; because no additional air can enter the obstructed airway, the alveoli become devoid of matter and collapse. To occupy the vacated space, mediastinal structures (eg, carina, heart) are pulled toward the atelectasis (assuming the atelectasis is large). Patients typically present with respiratory distress (eg, dyspnea, tachypnea, tachycardia) and hypoxemia, and lung examination reveals dullness to percussion and absence of breath sounds in the affected lung area. Chest x-ray demonstrates opacification of the affected lung area with mediastinal shifting toward the side of opacification. In addition, rib spacing becomes narrower in the affected hemithorax. Surgery (under anesthesia) and smoking increase the risk of mucus plugging. Chest physiotherapy is often useful in preventing mucus plugging and can be used to treat relatively minor atelectasis due to mucus plugging. Large-volume atelectasis typically requires bronchoscopy to remove the mucus plug. (Choice B) Diaphragmatic perforation is usually caused by blunt abdominal trauma and typically presents with respiratory distress or signs of small bowel obstruction (eg, vomiting, colicky pain). Chest x-ray demonstrates stomach or bowel herniating into the thoracic cavity. (Choice C) An endobronchial tumor can lead to obstructive atelectasis; however, this patient's lack of cough or hemoptysis and his acute presentation following surgery make bronchial mucus plugging more likely. (Choice D) A large pleural effusion can cause large opacification on chest x-ray. However, because the effusion is occupying space, the mediastinum will be shifted away from (rather than toward) the side of effusion. (Choice E) Multilobar pneumonia can cause opacification of an entire hemithorax on chest x-ray. However, the mediastinum does not typically shift in either direction, and fever and cough would be expected. (Choice F) A tension pneumothorax typically demonstrates radiolucency (rather than opacification) of the affected lung field with shifting of the mediastinum away from (rather than toward) the side of the pneumothorax. Educational objective: Mucus plugging can lead to large-volume atelectasis (lung collapse) due to airway obstruction. Chest x-ray demonstrates opacification of the affected lung area and mediastinal shifting toward the side of atelectasis. References: Postoperative atelectasis. (http://www.ncbi.nlm.nih.gov/pubmed/9742334)

A 55-Year-Old Man Is Evaluated for New-Onset Shortness of Breath