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Previously undiagnosed obesity hypoventilation syndrome

There are approximately 300 million obese individuals (body mass index (BMI) 30 kg/m2 or higher) worldwide,1 and in the UK nearly one quarter of all adults are classified as clinically obese.2 Obesity hypoventilation syndrome (OHS) describes a subgroup of obese individuals who develop chronic daytime hypercapnia (arterial carbon dioxide tension (Paco2) >6 kPa) and hypoxia (arterial oxygen tension (Pao2) <8 kPa) in the absence of chronic obstructive pulmonary disease (COPD).3,4 Presentation is usually indolent, with symptoms arising due to hypercapnia and sustained hypoventilation (hypersomnolence, alterations in cognitive function, headache, peripheral oedema, hypertension, congestive cardiac failure).5 At Southend Hospital we have noticed an increase in acute admissions in obese individuals with type II respiratory failure of initially unknown cause in whom a diagnosis of OHS was eventually made.

We collected data on 11 patients (seven men) diagnosed with OHS from 1996 to 2005 from the respiratory disease register. Patients with possible overlap syndrome were excluded (smokers with forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) ratio <70%). Patient demographics, lung function and Epworth sleep score (ESS) were documented. The results of initial sleep studies on air were analysed. Initial management was recorded and follow-up data were reviewed regarding ESS, blood gases, long-term use of continuous positive airway pressure (CPAP) or non-invasive ventilation (NIV, using bi-level pressure support ventilation).

The mean (SD) age of the 11 patients was 59 (12) years and the mean (SD) BMI was 52.7 (16.6) kg/m2 (range 37–102). Two patients were current smokers, one an ex-smoker and …