Obesity is epidemic in the United States and is a major cause of morbidity and mortality. In addition to obstructive sleep apnea, obesity is associated with obesity hypoventilation syndrome (OHS), characterized by daytime hypercapnia. OHS is associated with significant morbidity and mortality. In order to initiate therapy with non invasive positive pressure ventilation (NIPPV), a sleep study is required. We perrformed a study to determine the prevalence of daytime hypercapnia in morbidly obese patients referred for evaluation of dyspnea and to evaluate if body mass index or pulmonary function test help distinguish simple obesity from OHS.
All subjects who underwent pulmonary function test (PFT) at our institution from January 2003 to December 2004 were screened. Inclusion criteria was a BMI ≥ 35 kg/m2, ≤ 20 pack years history of smoking, an FEV1 > 50%, an FEV1 / FVC >70, and absence of neuromuscular disorder. Simple Obesity (SO) was defined as a BMI ≥ 35 kg/m2 in the absence of daytime hypercapnea. OHS was defined as a BMI ≥ 35 Kg/m2 and daytime hypercapnia (arterial PaCO2 ≥ 45 mm Hg). Data on subjects age, gender, height, weight, smoking history, pulmonary function tests (PFT’s), arterial blood gas (ABG), polysomnography and use of NIPPV were collected by chart review.
1904 PFT’s were performed during the study period. 122 patients met the inclusion criteria. Seventy six (62%) patients had complete PFT’s and an ABG available for review. Twelve (16%) subjects had daytime hypercapnia.
OHS is common in morbidly obese patients. Clinical parameters such as BMI and pulmonary function test do not help distinguish OHS from SO. Arterial blood gas measurements are necessary to establish a diagnosis of OHS.
Morbidly obese individuals with unexplained dyspnea should have arterial blood gas measurements to exclude daytime hypercapnia. Polysomnography should be considered in patients with daytime hypercapnia to determine the presence of sleep disordered breathing and to initiate noninvasive positive pressure ventilation.
Farooq Sattar, None.