16th February 2025

Obesity hypoventilation syndrome (OHS)

Diagnosis of OHS

Obesity hypoventilation syndrome is a diagnosis of exclusion, defined as where a patient with BMI > 30 has an awake pCO₂ > 6 kPa, with no other explanation.

Patients present non-specifically with features similar to OSA and, in severe cases, may additionally show features of right-heart failure. A minority of patients present acutely with severe type II respiratory failure requiring hospital admission.

Management of OHS

Non-invasive ventilation (NIV) is typically started in the presence of acidosis, somnolence or cor pulmonale.

• OSA is co-morbid in 90% of patients, and for these patients typically nighttime CPAP is the initial mode, with escalation to BiPAP (bilevel positive airway pressure) for those who fail to respond adequately
• For the remaining 10% of patients who have few obstructive events during sleep and for patients who present acutely, nighttime BiPAP is the initial treatment

BiPAP may be started with an inspiratory positive airway pressure (IPAP) of 8 cmH2O and an expiratory positive airway pressure (EPAP) of 4 cmH2O. These pressures can then be titrated up. The EPAP will improve airway opening, and the driving pressure (IPAP – EPAP) will improve tidal volumes.

As per management of OSA, conservative or surgical measures to encourage weight loss also form part of OHS management.

Patients should be assessed and treated for complications of OHS, which include:

• Pulmonary hypertension (present in 60%) – all patients should have ECG and echocardiography
• Hypertension, congestive cardiac failure, insulin resistance

References

• Chapman SJ, Robinson GV, Shrimanker R, Turnbull CD, Wrightson JM. Oxford handbook of respiratory medicine. 4th ed. London, England: Oxford University Press; 2021
• Bourke SJ. Respiratory medicine: Lecture notes, 10th edition: Lecture Notes. 10th ed. Hoboken, NJ: Wiley-Blackwell; 2022
• Kline LR. Clinical presentation and diagnosis of obstructive sleep apnea in adults [Internet]. Collop N, editor. UpToDate. 2022 [cited 2022 Dec 9]. Available from: https://www.uptodate.com/contents/clinical-presentation-and-diagnosis-of-obstructive-sleep-apnea-in-adults
• Piper A, Yee B. Clinical manifestations and diagnosis of obesity hypoventilation syndrome [Internet]. Safwan Badr M, editor. UpToDate. 2022 [cited 2022 Dec 9]. Available from: https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-obesity-hypoventilation-syndrome
• Martin T. Treatment and prognosis of the obesity hypoventilation syndrome [Internet]. Safwan Badr M, editor. UpToDate. 2022 [cited 2022 Dec 9]. Available from: https://www.uptodate.com/contents/treatment-and-prognosis-of-the-obesity-hypoventilation-syndrome
• Safwan Badr M. Central sleep apnea: Risk factors, clinical presentation, and diagnosis [Internet]. Chervin R, editor. UpToDate. 2022 [cited 2022 Dec 9]. Available from: https://www.uptodate.com/contents/central-sleep-apnea-risk-factors-clinical-presentation-and-diagnosis