Chest
RECENT ADVANCES IN CHEST MEDICINERecent Advances in Obesity Hypoventilation Syndrome
Section snippets
Definitions
OHS is defined as a combination of obesity (ie, BMI ≥ 30 kg/m2) and awake chronic hypercapnia (ie, Paco2 ≥ 45 mm Hg) accompanied by sleep-disordered breathing.910 It is important to recognize that OHS is a diagnosis of exclusion and should be distinguished from other conditions that are commonly associated with hypercapnia (Table 1). In approximately 90% of patients with OHS, the sleep-disordered breathing consists of obstructive sleep apnea (OSA).111213 Due to this association, the term
Clinical Presentation and Diagnosis
In general, patients with OHS are middle-aged with a 2:1 male-to-female ratio. These patients tend to be extremely obese and experience significant sleep-disordered breathing. On presentation, the patients usually report the classic symptoms of OSA such as fatigue, hypersomnolence, loud habitual snoring, nocturnal choking episodes, and morning headaches. In contrast to patients with simple OSA, dyspnea, lower extremity edema, and low oxygen saturation measured by pulse oximetry during
Epidemiology
As measurement of arterial blood gases is not a standard practice in patients with OSA or extreme obesity, the precise prevalence of OHS in the general population remains uncertain. Table 3 summarizes several studies from various geographical regions that estimated the prevalence of OHS among patients with OSA. The prevalence ranges between 10% and 20%11132526293132 and is higher in the subgroup of patients with extreme obesity (ie, BMI > 40 kg/m2) [Fig 2].132630 Two studies2737 reported a much
Morbidity and Mortality
Compared to eucapnic patients with OSA, patients with OHS have a lower quality of life, higher health-care expenses, and a greater risk of pulmonary hypertension. Even patients with mild OHS (ie, Paco2 between 46 to 50 mm Hg) are more somnolent and have a lower quality of life than patients with OSA when matched for age, BMI, and lung function.43 Compared to patients with similar degrees of obesity, patients with OHS have increased medical resource utilization and are more likely to be
Pathophysiology
Paco2 is determined by the balance between CO2 production and elimination (ie, minute ventilation and the fraction of dead space ventilation). In patients with OHS, short-term treatment with continuous PAP (CPAP) or bilevel PAP improves hypercapnia without any significant changes in body weight, CO2 production, or the volume of dead space. Therefore, this disorder is entirely due to hypoventilation.35
The exact mechanisms that lead to hypoventilation in obese individuals remain controversial.
Treatment
The optimal management of patients with OHS remains uncertain. Several studies have reported improvement in chronic daytime hypercapnia and hypoxia with PAP therapy (CPAP or bilevel PAP). Approximately half of patients with OHS require oxygen therapy in addition to PAP therapy upon initiation of treatment. Although PAP is the mainstay of therapy in both OSA and OHS patients, there is no standard protocol for its titration.95Figure 5 provides a therapeutic algorithm during polysomnography in
Conclusion
With such a global epidemic of obesity, the prevalence of OHS is likely to increase. Despite the significant morbidity and mortality associated with OHS, it is often unrecognized, and treatment is frequently delayed. It is essential for clinicians to maintain a high index of suspicion, particularly because early recognition and treatment improve outcomes. Further research is needed to better understand the pathophysiology and long-term treatment outcomes of patients with OHS.
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The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.