Clinical Predictors of Obesity Hypoventilation Syndrome in Obese Subjects With Obstructive Sleep Apnea

Abstract

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/m 2 , 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 S pO 2 < 90% (P < .001) compared with subjects with pure OSA (n ‫؍‬ 88). They also had lower daytime P aO 2 (P < .001), sleep efficiency (P ‫؍‬ .032), mean S pO 2 (P < .001), and nadir S pO 2 (P < .001) . Serum bicarbonate levels and nadir S pO 2 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 S pO 2 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 S pO 2 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.

What can anthropometric measurements tell us about obstructive sleep apnoea?

“…It is thought that high value of this parameter demonstrates the size of pharynx entrance and so it makes the air stream easier. Statistical analysis showed that there is a significant difference between the two groups [3,16,24].…”

“…Muller's manoeuvre has been the most investigated research subject till now. Different length and angular values were examined for the analyses of pharyngeal structure in radiographic studies [3,8,16,24,25]. It is believed in this study that bigonial width is one of the important parameters which determine pharyngeal entrance of human.…”

Bicarbonate Level for Early Diagnosis of Obesity Hypoventilation Syndrome: Still Defining Boundaries—Reply

“…1 As opposed to the latter, no large public health campaign has yet been conducted to improve the diagnostic process of OHS, and the disease is largely underrecognized, usually discovered at an advanced stage when acute respiratory failure occurs. 2 In their prospective observational study, Bingol et al 3 compare the clinical characteristics and polysomnographic parameters of OHS subjects with those of obese subjects with pure OSAS.…”

“…1 The International Classification of Sleep Disorders, 3rd edition, 2 defines obesity hypoventilation syndrome (OHS) as the combined presence of obesity (body mass index Ͼ30 kg/m 2 ) with awake arterial hypercapnia (P aCO 2 Ͼ 45 mm Hg) and sleep-disordered breathing in the absence of other causes of alveolar hypoventilation, such as COPD. It is an important cause of chronic respiratory failure.…”

Bicarbonate Level for Early Diagnosis of Obesity Hypoventilation Syndrome: Still Defining Boundaries

“…Second, even when admitted to the ICU for an episode of acute respiratory failure, up to 75% of the morbidly obese patients with OHS are misdiagnosed as having COPD or asthma. 3 So the point is not to prevent a puncture of the radial artery to make the diagnosis less invasive in specialized sleep centers; this seems from a practical point of view crucial when some respiratory diseases like pulmonary hypertension require a pulmonary arterial catheter for assessment. Furthermore, these patients will continue to have many arterial punctures in the ICU and sometimes an endotracheal tube as a bonus if we do not improve the early diagnostic process and management of the disease.…”