- Obesity hypoventilation syndrome (OHS) is defined by the combination of obesity (body mass index [BMI] ≥30 kg/m2), sleep-disordered breathing (SDB) and awake daytime hypercapnia (awake resting partial pressure of arterial CO2 or PaCO2 ≥45 mmHg at sea level), after excluding other causes for hypoventilation.
- OHS is the most severe form of obesity-induced respiratory compromise and leads to serious sequelae, including increased rates of mortality, chronic heart failure, pulmonary hypertension, and hospitalization due to acute-on-chronic hypercapnic respiratory failure, among others.
- While the definition of OHS suggests a diurnal pathology, polysomnography or sleep respiratory polygraphy is required to determine the pattern of SDB and hypoventilation (obstructive or non-obstructive), to tailor treatment, and to establish the optimal settings of positive airway pressure (PAP) therapy.
- PAP has become the primary management option for controlling SDB and reversing awake hypoventilation in patients with OHS.
Figure 1. Summary Guideline Flowchart
Flowchart summarizing the ATS panel’s recommendations. OHS may be suspected when symptoms lead to pulmonary or sleep consultation in stable conditions as an outpatient or during an episode of hospitalization due to acute-on-chronic hypercapnic respiratory failure. In the outpatient setting, the ATS panel recommends to perform a measurement of arterial blood gases (ABG) to confirm daytime hypercapnia for patients with high pre-test probability of OHS (for example, very symptomatic patients with a BMI >40 kg/m2) or assess serum bicarbonate levels in cases in which there is a moderate or low pre-test probability of OHS (for example, less symptomatic patients with a BMI of 30-40 kg/m2). When the bicarbonate level is ≥27 mmol/l, the ATS panel recommends a confirmatory measurement of ABG to confirm the presence of hypercapnia and to carry out a sleep study to ascertain the presence and severity of sleep-disordered breathing. If the serum bicarbonate level is <27 mmol/l, OHS is highly unlikely. For management of hospitalized patients in acute-on-chronic respiratory failure treated with NIV treatment, the ATS panel recommends that patients be discharged on empiric NIV settings due to high risk of short-term (3 month) mortality without therapy. The panel also recommends evaluation with a sleep study and PAP titration in the sleep laboratory as early as possible after discharge from the hospital, ideally within 3 months of discharge. If the sleep evaluation demonstrates OHS and severe OSA (AHI ≥30), the ATS panel recommends CPAP titration and treatment. If, on the other hand, the sleep study demonstrates OHS with no OSA or mild to moderate OSA, the ATS panel recommends NIV titration and treatment. In patients initially treated with CPAP who do not have adequate response to therapy (lack of symptom resolution or insufficient improvement in gas exchange during wakefulness or sleep), the ATS panel recommends changing to NIV therapy. The panel also recommends that patients with OHS should be considered for bariatric surgery. All recommendations are conditional due to the very low level of certainty in the evidence.
a It is important to note that OHS is a diagnosis of exclusion and other causes of hypercapnia need to be investigated and excluded.
b In healthcare settings with limited or no access to NIV, discharging patients on auto-PAP would be preferable to no PAP, particularly that 70% of patients with OHS have co-existent severe OSA.
Reprinted with permission of the American Thoracic Society. Copyright © 2019 American Thoracic Society. Mokhlesi B et al. Evaluation and management of obesity hypoventilation syndrome: an official American Thoracic Society clinical practice guideline. Am J Respir Crit Care Med 2019;200(4): e6–e24. The American Journal of Respiratory and Critical Care Medicine is an official journal of the American Thoracic Society.