title: Diagnostic predictors of obesity-hypoventilation syndrome in patients suspected of having sleep disordered breathing.
abstract: BACKGROUND
  Obesity-hypoventilation syndrome (OHS) is associated with significant morbidity and mortality and requires measurement of arterial pCO2 for diagnosis.
  
  
  OBJECTIVE
  To determine diagnostic predictors of OHS among obese patients with suspected obstructive sleep apnea/hypopnea syndrome (OSAHS).
  
  
  METHODS
  Retrospective analysis of data on 525 sleep clinic patients (mean age 51.4 ± 12.7 years; 65.7% males; mean BMI 34.5 ± 8.1). All patients had sleep studies, and arterialized capillary blood gases (CBG) were measured in obese subjects (BMI > 30 kg/m2).
  
  
  RESULTS
  Of 525 patients, 65.5% were obese, 37.2% were morbidly obese (BMI > 40 kg/m2); 52.3% had confirmed OSAHS. Hypercapnia (pCO2 > 6 kPa or 45 mm Hg) was present in 20.6% obese and 22.1% OSAHS patients. Analysis of OHS predictors showed significant correlations between pCO2 and BMI, FEV1, FVC, AHI, mean and minimum nocturnal SpO2, sleep time with SpO2 < 90%, pO2, and calculated HCO3 from the CBG. PO2 and HCO3 were independent predictors of OHS, explaining 27.7% of pCO2 variance (p < 0.0001). A calculated HCO3 cutoff > 27 mmol/L had 85.7% sensitivity and 89.5% specificity for diagnosis of OHS, with 68.1% positive and 95.9% negative predictive value.
  
  
  CONCLUSIONS
  We confirmed a high prevalence of OHS in obese OSAHS patients (22.1%) and high calculated HCO3 level (> 27 mmol/L) to be a sensitive and specific predictor for the diagnosis of OHS.
authors.affiliation: Sleep and Ventilation Unit, Department of Respiratory Medicine, North Middlesex University Hospital, London, UK. vladimirmacavei@gmail.com
authors.forename: Vladimir M
authors.initials: VM
authors.lastname: Macavei
authors.forename: Kristofer J
authors.initials: KJ
authors.lastname: Spurling
authors.forename: Janine
authors.initials: J
authors.lastname: Loft
authors.forename: Himender K
authors.initials: HK
authors.lastname: Makker
mesh_terms: D015992:Body Mass Index; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000150:complications; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D009765:Obesity / Q000150:complications; D010845:Obesity Hypoventilation Syndrome / Q000175:diagnosis / Q000209:etiology*; D009767:Obesity, Morbid / Q000150:complications; D010092:Oximetry; D012189:Retrospective Studies; D012307:Risk Factors; D012891:Sleep Apnea Syndromes / Q000175:diagnosis / Q000209:etiology*; D013147:Spirometry
keywords: Obstructive sleep apnea; obesity hypoventilation syndrome