What is Obesity Hypoventilation Syndrome (OHS)?

From the Guidelines

Obesity hypoventilation syndrome (OHS) should be managed with positive airway pressure therapy, typically with bilevel positive airway pressure (BiPAP), and weight-loss interventions that produce sustained weight loss of 25% to 30% of body weight, as recommended by the American Thoracic Society clinical practice guideline 1.

Diagnosis and Treatment

OHS is a condition characterized by obesity (BMI over 30 kg/m²) and chronic hypoventilation leading to daytime hypercapnia (elevated carbon dioxide levels in the blood) and hypoxemia (low oxygen levels) 1. The diagnosis of OHS requires a sleep study (polysomnography or respiratory polygraphy) to establish the presence of sleep-disordered breathing (SDB) and a measurement of arterial blood gases during wakefulness to establish the presence of hypercapnia 1.

Key Recommendations

The American Thoracic Society clinical practice guideline recommends the following:

• Stable ambulatory patients with OHS should receive positive airway pressure (PAP) therapy 1
• Continuous positive airway pressure (CPAP) rather than noninvasive ventilation should be offered as the first-line treatment to stable ambulatory patients with OHS and coexistent severe obstructive sleep apnea 1
• Patients hospitalized with respiratory failure and suspected of having OHS should be discharged with noninvasive ventilation until they undergo outpatient diagnostic procedures and PAP titration in the sleep laboratory 1
• Patients with OHS should use weight-loss interventions that produce sustained weight loss of 25% to 30% of body weight to achieve resolution of OHS, which is more likely to be obtained with bariatric surgery 1

Monitoring and Follow-up

Regular follow-up with pulmonary function tests and arterial blood gas measurements is necessary to monitor treatment effectiveness 1. Supplemental oxygen therapy may be needed if hypoxemia persists despite BiPAP, and medications like acetazolamide (250-500 mg twice daily) can help stimulate breathing in some patients by creating a mild metabolic acidosis.

Complications

Without treatment, OHS can lead to serious complications including pulmonary hypertension, right heart failure, and increased mortality 1. Therefore, early diagnosis and treatment are crucial to improve outcomes in patients with OHS.

From the Research

Definition and Epidemiology of Obesity Hypoventilation Syndrome

• Obesity hypoventilation syndrome (OHS) is defined as the triad of obesity, daytime hypoventilation, and sleep-disordered breathing in the absence of an alternative neuromuscular, mechanical or metabolic explanation for hypoventilation 2.
• The prevalence of OHS has increased worldwide due to the rising prevalence of extreme obesity 3, 2.

Clinical Features and Pathophysiology

• OHS results in symptoms based on a diverse spectrum of interactions between obesity, ventilatory drive, and sleep's impact on respiration 4.
• Patients with OHS have a lower quality of life and a higher risk of unfavorable cardiometabolic consequences 3.
• The syndrome worsens morbidity and mortality far beyond that of more typical sleep-disordered breathing 4.

Treatment Modalities

• Effective treatment can lead to significant improvement in patient outcomes, underscoring the importance of early diagnosis 3, 2.
• Non-invasive ventilation (NIV) and continuous positive airway pressure (CPAP) therapy are commonly used to treat OHS 5, 6.
• Both NIV and CPAP appear safe and effective in patients with obesity-related respiratory failure and OSA, with or without COPD 5.
• It is feasible to switch most stable OHS patients from NIV to CPAP therapy, which could significantly reduce health-related costs 6.

Treatment Outcomes

• Treatment with NIV or CPAP can improve respiratory failure, health-related quality of life, reduce healthcare utilization, and reduce mortality 5.
• A study found that 71% of OHS patients maintained daytime partial pressure of carbon dioxide (PaCO2) levels ≤45 mm Hg after switching to CPAP therapy 6.
• Patients who switched to CPAP therapy showed no further impairment in quality of life, sleep parameters, or lung function 6.