title: Is a raised bicarbonate, without hypercapnia, part of the physiologic spectrum of obesity-related hypoventilation?
abstract: BACKGROUND
  Obesity hypoventilation syndrome (OHS) conventionally includes awake hypercapnia, but an isolated raised bicarbonate, even in the absence of awake hypercapnia, may represent evidence of "early" OHS. We investigated whether such individuals exhibit certain features characteristic of established OHS.
  
  
  METHODS
  Obese subjects (BMI > 30 kg/m(2)) were identified from a variety of sources and divided into those with (1) normal blood gas measurements and normal acid-base balance, (2) an isolated raised base excess (BE) (≥ 2 mmol/L), and (3) awake hypercapnia (> 6 kPa; ie, established OHS). Two-point ventilatory responses to hypoxia and hypercapnia were performed. Polygraphic sleep studies were done to identify intermittent and prolonged hypoxia.
  
  
  RESULTS
  Seventy-one subjects (BMI, 47.2; SD, 9.8; age, 52.1 years; SD, 8.8 years) were recruited into three groups (33, 22, and 16 respectively). The Paco2 and BE values were 5.15, 5.42, 6.62 kPa, and +0.12, +3.01, +4.78 mmol/L, respectively. For nearly all the ventilatory response and sleep study measures, group 2 (with only an isolated raised BE) represented an intermediate group, and for some of the measures they were more similar to the third group with established OHS.
  
  
  CONCLUSIONS
  These data suggest that obese individuals with a raised BE, despite normocapnia while awake, should probably be regarded as having early obesity-related hypoventilation. This has important implications for clinical management as well as randomized controlled treatment trials, as they may represent a group with a more reversible disease process.
  
  
  BACKGROUND
  ClinicalTrials.gov; No.: NCT01380418; URL: www.clinicaltrials.gov.
authors: Oxford Centre for Respiratory Research, Oxford Biomedical Research Centre, Churchill Campus, Oxford University Hospitals NHS Trust, Oxford. Electronic address: ari.manuel@ouh.nhs.uk.
authors: Ari R G
authors: ARG
authors: Manuel
authors: Lane Fox Clinical Respiratory Physiology Centre, St. Thomas' Hospital, Guy's and St. Thomas' NHS Foundation Trust, London, England.
authors: Nicholas
authors: N
authors: Hart
authors: Oxford Centre for Respiratory Research, Oxford Biomedical Research Centre, Churchill Campus, Oxford University Hospitals NHS Trust, Oxford.
authors: John R
authors: JR
authors: Stradling
mesh_terms: D000328:Adult; D001639:Bicarbonates / Q000097:blood*; D001784:Blood Gas Analysis; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010845:Obesity Hypoventilation Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D017286:Polysomnography; D011446:Prospective Studies; D012890:Sleep / Q000502:physiology
chemical_list: D001639:Bicarbonates