Evaluation and Management of Obesity Hypoventilation Syndrome

Publication Date: August 1, 2019
Last Updated: December 15, 2022


1A: For obese patients with sleep-disordered breathing with a high pre-test probability of having OHS, the ATS suggests measuring PaCO2 rather than serum bicarbonate or SpO2 to diagnose OHS. (C, VL)
Patients with a high pre-test probability of having OHS are usually severely obese with typical signs and symptoms of OHS and can be mildly hypoxemic during wake and/or significantly hypoxemic during sleep. This is a recommendation for screening for OHS in patients with sleep-disordered breathing, most typically obstructive sleep apnea (OSA).

1B: For patients with low to moderate probability of having OHS (<20%), the ATS suggests using serum bicarbonate levels to decide when to measure PaCO2: in patients with serum bicarbonate <27 mmol/l clinicians might forego measuring PaCO2, since the diagnosis of OHS in them is very unlikely. In patients with serum bicarbonate ≥27 mmol/l clinicians might need to measure PaCO2 to confirm or rule out the diagnosis of OHS. (C, VL)
Using a 27 mmol/l threshold in serum bicarbonate in obese patients with OSA and low to moderate clinical suspicion of OHS (initial probability of OHS not more than 20%) would likely permit forgoing further testing such as arterial blood gases in those with bicarbonate level <27 mmol/l (64% to 74% of obese patients with OSA) and perform arterial blood gas analysis only in those with serum bicarbonate ≥27 mmol/l (26% to 36% of obese patients with OSA). The ATS found insufficient evidence for serum bicarbonate thresholds other than 27 mmol/l.

1C: The ATS suggests that clinicians avoid using oxygen saturation by pulse oximetry (SpO2) during wakefulness to decide when to measure PaCO2 in patients suspected of having OHS until more data about the usefulness of SpO2 in this context become available. (C, VL)
The ATS found insufficient data to investigate the clinical usefulness of any threshold of wake SpO2 for screening for OHS in obese patients with OSA. Guideline panel members thought that relevant studies have to be done before the clinical usefulness of wake SpO2 in this context can be assessed. This is a temporary recommendation reflecting lack of evidence about a potentially useful intervention, rather than evidence that it is not useful. Thus, this recommendation should not be used as an argument against additional research and will likely change once additional data are available.

2: For stable ambulatory patients diagnosed with OHS, the ATS suggests treatment with PAP during sleep. (C, VL)
Note: Patients with symptomatic OHS who have significant comorbidities and those with chronic respiratory failure following an episode of acute-on-chronic hypercapnic respiratory failure may particularly benefit from using PAP.

3: For stable ambulatory patients diagnosed with OHS and concomitant severe OSA (apnea-hypopnea index ≥30 events/hour), the ATS suggests initiating 1st line treatment with CPAP therapy rather than noninvasive ventilation (NIV). (C, VL)
More than 70% of patients with OHS also have severe OSA; therefore, this recommendation applies to the majority of patients with OHS who have concomitant severe OSA. However, panel members lacked certainty on the clinical benefits of initiating treatment with CPAP, rather than NIV, in patients with OHS who have sleep hypoventilation without severe OSA.

4: The ATS suggests that hospitalized patients with respiratory failure suspected of having OHS be started on NIV therapy before being discharged from the hospital until they undergo outpatient workup and titration of PAP therapy in the sleep laboratory, ideally within the first 3 months after hospital discharge. (C, VL)
Note: Discharging patients from hospital with NIV should not be a substitute for arranging the outpatient sleep study and PAP titration in the sleep laboratory, as soon as it is feasible.

5: For patients with OHS the ATS suggests using weight-loss interventions that produce sustained weight loss of 25-30% of actual body weight. This level of weight loss is most likely required to achieve resolution of hypoventilation. (C, VL)
Note: many patients may not be able to achieve this degree of sustained weight loss despite participating in multifaceted comprehensive weight-loss lifestyle intervention program. Those who have no contraindications may benefit from being evaluated for bariatric surgery.

Recommendation Grading




Evaluation and Management of Obesity Hypoventilation Syndrome

Authoring Organization

Publication Month/Year

August 1, 2019

Last Updated Month/Year

December 15, 2022

Document Type


External Publication Status


Country of Publication


Document Objectives

The purpose of this guideline is to improve early recognition of obesity hypoventilation syndrome (OHS) and advise clinicians concerning the management of OHS, with the goal of reducing variability in clinical practice. 

Inclusion Criteria

Female, Male, Adult

Health Care Settings

Ambulatory, Emergency care, Hospital

Intended Users

Nurse, nurse practitioner, physician, physician assistant


Diagnosis, Management


obesity, sleep, hypercapnia, obesity hypoventilation syndrome, pickwickian, sleep-disordered breathing, chronic hypercapnic respiratory failure, bilevel PAP

Source Citation

Mokhlesi B, Masa JF, Brozek JL, et al. Evaluation and management of obesity hypoventilation syndrome. An official American thoracic society clinical practice guideline. Am J Respir Crit Care Med. 2019 Aug 1;200:e6-e24. 

Supplemental Methodology Resources

Data Supplement