A 55-year-old man comes to the hospital due to exertional dyspnea and orthopnea for 24 hours. A week ago, the patient underwent coronary artery bypass surgery for exertional chest pain and was discharged in stable condition. He started physical therapy but had to stop due to dyspnea. He has no cough but is unable to sleep well. Prior to surgery, the patient never had respiratory difficulty. He has a 20-pack-year smoking history but quit just before the surgery. Temperature is 37 C (98.6 F), blood pressure is 120/80 mm Hg, pulse is 88/min, and respirations are 18/min. Oxygen saturation is 95% on room air. Examination shows normal jugular venous pressure, clear lung sounds, and normal heart sounds. The sternal wound is clean and dry. When the patient is placed supine on the examination table, he reports worsening dyspnea and has paradoxical movement of the abdomen during inspiration. There is no peripheral edema. Neurologic examination is normal. What is the most likely cause of this patient's symptoms?

Question

A 55-year-old man comes to the hospital due to exertional dyspnea and orthopnea for 24 hours.  A week ago, the patient underwent coronary artery bypass surgery for exertional chest pain and was discharged in stable condition.  He started physical therapy but had to stop due to dyspnea.  He has no cough but is unable to sleep well.  Prior to surgery, the patient never had respiratory difficulty.  He has a 20-pack-year smoking history but quit just before the surgery.  Temperature is 37 C (98.6 F), blood pressure is 120/80 mm Hg, pulse is 88/min, and respirations are 18/min.  Oxygen saturation is 95% on room air.  Examination shows normal jugular venous pressure, clear lung sounds, and normal heart sounds.  The sternal wound is clean and dry.  When the patient is placed supine on the examination table, he reports worsening dyspnea and has paradoxical movement of the abdomen during inspiration.  There is no peripheral edema.  Neurologic examination is normal.  What is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

11ec25c8_d88d_a0de_bc81_f95f535b519c_MD0003_00 This patient has exertional dyspnea, orthopnea, and paradoxical movement of the abdomen during inspiration, findings suspicious for diaphragmatic weakness. In the setting of a recent coronary artery bypass graft (CABG) procedure, this is most likely due to phrenic nerve injury. The phrenic nerves originate from C3-C5 and descend through the mediastinum along the sides of the heart to innervate the diaphragm. Phrenic nerve injury can occur during cardiac surgery due to inadvertent cutting or stretching of the nerve. The nerve can also be damaged by the application of iced slush used for cardioprotection during bypass. phrenic nerves When the diaphragm is weak, accessory inspiratory muscles are used to raise the rib cage and decrease intrathoracic pressure. This draws the flaccid diaphragm upward and the abdominal wall inward during inspiration, which is opposite (ie, paradoxical) to their typical movement. Patients with unilateral diaphragmatic weakness and no underlying heart or lung disease are usually asymptomatic at rest but can develop dyspnea with exertion. Orthopnea occurs because in a recumbent position, gravity opposes chest wall and lung expansion. (Choices A and D) Bronchospasm and pleural effusion can both cause exertional dyspnea but would also likely result in wheezing (bronchospasm) or decreased breath sounds (effusion). In addition, neither would cause paradoxical movement of the abdomen. (Choice B) Pericardial effusion can occur after cardiac surgery due to immune-mediated inflammatory damage to the pericardium (ie, postpericardiotomy syndrome). However, this typically presents a few weeks after surgery with distant, muffled heart sounds and signs of decreased cardiac output (eg, tachycardia, increased jugular venous pressure). (Choice E) Heart failure, a potential complication of a CABG procedure, can result in cardiogenic pulmonary edema and orthopnea. However, this patient has no other signs of heart failure (eg, jugular venous distension, peripheral edema), and heart failure would not cause paradoxical movement of the abdomen. (Choice F) Surgery is a risk factor for pulmonary embolism, which can present with dyspnea. However, this patient has no lower extremity swelling, tachycardia, or other clinical signs of deep venous thrombosis (Wells criteria score = 1.5), and diaphragmatic paralysis is more likely given the paradoxical movement of the abdomen. Wells criteria Educational objective: The phrenic nerve can be injured during cardiac surgery. Patients can have dyspnea on exertion, orthopnea, and paradoxical breathing movement (ie, abdomen moving inward on inspiration).

A 55-Year-Old Man Comes to the Hospital Due to Exertional