A 40-year-old obese man comes to the physician because of exertional dyspnea, fatigue, and poor energy over the past year. He was diagnosed with obstructive sleep apnea and started on nocturnal continuous positive airway pressure (CPAP) six months ago with mild improvement of his symptoms. He reports compliance with CPAP "most of the time." He denies cough, chest pain, dizziness, or syncope. His other medical problems include hypertension, glucose intolerance, and pain in both hips and knees which increases at the end of the day. He does not use tobacco, alcohol, or illicit drugs.
His blood pressure is 152/90 mm Hg, pulse is 70/min, and respirations are 16/min. Oxygen saturation is 94% on room air. His BMI is 44 kg/m². Jugular venous pressure is difficult to estimate. Lungs are clear to auscultation. Heart sounds are distant but no murmurs are heard. There is 2+ symmetric peripheral edema.
His hemoglobin level is 16.2 g/dL and his serum TSH is 2.5 mU/L.
Chest x-ray shows low lung volumes but is unremarkable otherwise. Spirometry shows an FEV1 of 70% predicted and an FEV1/FVC ratio of 90%. Transthoracic echocardiography is limited by body habitus, but shows mild right ventricular enlargement.
Which of the following is the best next step in managing this patient?

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Quizplus · Accepted Answer

11ec193a_98d0_2cc2_853d_71a976c0cb51_MD0002_00 This patient most likely has obesity hypoventilation syndrome (OHS). The vast majority of patients with OHS have symptoms of obstructive sleep apnea (OSA). In contrast to OSA, patients with OHS frequently complain of dyspnea and may have signs and symptoms of cor pulmonale. All patients with OHS are obese, and the majority have a BMI > 35 kg/m². Physical examination findings may include a florid complexion, cyanosis, an enlarged neck circumference, crowded oropharynx, and signs of right-sided heart failure. ² An ABG on room air should be obtained in any patient with suspected OHS to confirm the presence of daytime hypercapnia and hypoxemia. The A-a gradient should also be calculated since a normal A-a gradient on room air makes pulmonary parenchymal or airway disease unlikely. In addition, an elevated serum bicarbonate level and secondary erythrocytosis may be a clue that chronic hypercapnia and chronic hypoxemia are present, respectively. If hypercapnia is present, additional studies (see table) should be performed to exclude other causes of hypercapnia. Also, drugs or medications (e.g., excessive alcohol, sedative-hypnotics, narcotics) that can aggravate chronic hypoventilation should be avoided if possible. Patients with OHS should be strongly urged to lose weight. They should also be referred for nighttime polysomnography testing to identify the underlying sleep disorder and to individualize treatment with either continuous positive airway pressure or noninvasive mechanical ventilation. (Choice B) Although exercise testing should be part of the initial evaluation of any patient with heart failure, this patient's symptoms are suggestive of OHS, which warrants an ABG to evaluate for daytime hypercapnia. (Choice C) Further work-up may include high-resolution CT scanning, but this should be considered after obtaining an ABG, PFTs, and a chest x-ray. (Choice D) This patient has already been diagnosed with obstructive sleep apnea. He now requires a diagnosis of OHS, which is best done by demonstrating daytime hypercapnia on ABG. (Choice E) Pulmonary embolism is a frequent cause of death in patients with OHS. Furthermore, chronic thromboembolic pulmonary hypertension (CTEPH) can present similarly with right-sided heart failure, sometimes even without prior diagnosis of DVT or PE. However, in this patient OHS is more likely than CTEPH and an ABG is helpful to rule out OHS. Educational objective: Obesity hypoventilation syndrome is defined as daytime hypercapnia and hypoxemia (PaCO₂ > 45 mm Hg and PaO₂ < 70 mm Hg) in an obese patient (BMI > 30 kg/m²) in the absence of any other cause of hypoventilation. Arterial blood gas analysis identifies alveolar hypoventilation and should be obtained in any patient with morbid obesity and unexplained hypoxemia or signs and symptoms of cor pulmonale. ² __________ References: The effect of obesity on chronic respiratory diseases: pathophysiology and therapeutic strategies. (http://www.ncbi.nlm.nih.gov/pubmed/16636330) The obesity hypoventilation syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/16164877)

A 40-Year-Old Obese Man Comes to the Physician Because of Exertional