PT  - JOURNAL ARTICLE
AU  - Zuleyha Bingol
AU  - Aylin Pihtili
AU  - Penbe Cagatay
AU  - Gulfer Okumus
AU  - Esen Kiyan
TI  - Clinical Predictors of Obesity Hypoventilation Syndrome in Obese Subjects With Obstructive Sleep Apnea
AID  - 10.4187/respcare.03733
DP  - 2015 Jan 13
TA  - Respiratory Care
PG  - respcare.03733
4099  - http://rc.rcjournal.com/content/early/2015/01/13/respcare.03733.short
4100  - http://rc.rcjournal.com/content/early/2015/01/13/respcare.03733.full
AB  - BACKGROUND: Arterial blood gas (ABG) analysis is not a routine test in sleep laboratories due to its invasive nature. Therefore, the diagnosis of obesity hypoventilation syndrome (OHS) is underestimated. We aimed to evaluate the differences in subjects with OHS and pure obstructive sleep apnea (OSA) and to determine clinical predictors of OHS in obese subjects. METHODS: Demographics, body mass index (BMI), Epworth Sleepiness Scale score, polysomnographic data, ABG, spirometric measurements, and serum bicarbonate levels were recorded. RESULTS: Of 152 obese subjects with OSA (79 females/73 males, mean age of 50.3 ± 10.6 y, BMI of 40.1 ± 5.6 kg/m2, 51.9% with severe OSA), 42.1% (n = 64) had OHS. Subjects with OHS had higher BMI (P = .02), neck circumference (P < .001), waist circumference (P < .001), waist/hip ratio (P = .02), Epworth Sleepiness Scale scores (P = .036), ABG and serum bicarbonate levels (P < .001), apnea-hypopnea index (P = .01), oxygen desaturation index (P < .001), and total sleep time with SpO2 < 90% (P < .001) compared with subjects with pure OSA (n = 88). They also had lower daytime PaO2 (P < .001), sleep efficiency (P = .032), mean SpO2 (P < .001), and nadir SpO2 (P < .001) . Serum bicarbonate levels and nadir SpO2 were the only independent predictive factors for OHS. A serum bicarbonate level of ≥ 27 mmol/L as the cutoff gives a satisfactory discrimination for the diagnosis of OHS (sensitivity of 76.6%, specificity of 74.6%, positive predictive value of 54.5%, negative predictive value of 88.9%). A nadir SpO2 of < 80% as the cutoff gives a satisfactory discrimination for the diagnosis of OHS (sensitivity of 82.8%, specificity of 54.5%, positive predictive value of 56.9%, negative predictive value of 81.4%). When we used a serum bicarbonate level of ≥ 27 mmol/L and/or a nadir SpO2 of < 80% as a screening measure, only 3 of 64 subjects with OHS were missed. CONCLUSIONS: Serum bicarbonate level and nadir saturation were independent predictive factors for the diagnosis of OHS.