What is the diagnosis and treatment for Obesity Hypoventilation Syndrome (OHS)?

From the Guidelines

Obesity hypoventilation syndrome (OHS) should be treated with positive airway pressure therapy, typically CPAP or BiPAP, and weight-loss interventions that produce sustained weight loss of 25% to 30% of body weight. The initial settings for BiPAP typically include an inspiratory pressure of 12-16 cmH2O and expiratory pressure of 4-6 cmH2O, adjusted based on patient response 1.

Diagnosis and Treatment

OHS is defined by the combination of obesity (body mass index [BMI] > 30 kg/m2), sleep-disordered breathing, and awake daytime hypercapnia (awake resting PaCO2 > 45 mm Hg at sea level), after excluding other causes for hypoventilation 1. The American Thoracic Society recommends using a serum bicarbonate level < 27 mmol/L to exclude the diagnosis of OHS in obese patients with sleep-disordered breathing when suspicion for OHS is not very high (< 20%) but to measure arterial blood gases in patients strongly suspected of having OHS 1.

Weight Loss and Bariatric Surgery

Weight loss is crucial for long-term management, with a goal of 10% reduction in body weight through dietary changes and increased physical activity. Bariatric surgery may be considered for patients with BMI >40 kg/m² or >35 kg/m² with comorbidities who haven't responded to lifestyle interventions 1.

Positive Airway Pressure Therapy

The choice between CPAP and BiPAP depends on the presence of severe obstructive sleep apnea (OSA), with CPAP preferred for patients with coexistent severe OSA 1. Supplemental oxygen therapy may be needed if hypoxemia persists despite positive airway pressure. OHS requires treatment because chronic hypercapnia leads to respiratory acidosis, pulmonary hypertension, and right heart failure. The underlying mechanism involves a combination of increased mechanical load on the respiratory system from excess weight, altered respiratory drive, and often coexisting obstructive sleep apnea, creating a vicious cycle of worsening hypoventilation and hypercapnia.

Some key points to consider in the treatment of OHS include:

• The importance of early diagnosis and treatment to prevent long-term complications
• The need for individualized treatment plans that take into account the patient's specific needs and medical history
• The potential benefits of bariatric surgery for patients with severe obesity who have not responded to lifestyle interventions
• The importance of close monitoring and follow-up to adjust treatment plans as needed and to prevent complications.

From the Research

Definition and Characteristics of Obesity Hypoventilation Syndrome

• Obesity hypoventilation syndrome (OHS) is characterized by obesity, daytime hypercapnia, and sleep-disordered breathing in the absence of other known causes of hypercapnia 2, 3, 4.
• OHS is defined as a combination of obesity (body mass index ≥30 kg·m-2), daytime hypercapnia (arterial carbon dioxide tension ≥45 mmHg), and sleep-disordered breathing 3.
• The presence of daytime hypercapnia is explained by several co-existing mechanisms, such as obesity-related changes in the respiratory system, alterations in respiratory drive, and breathing abnormalities during sleep 3.

Diagnosis and Treatment of OHS

• The diagnosis of OHS is firmly established after arterial blood gases and a sleep study 3.
• Both continuous positive airway pressure (CPAP) and noninvasive ventilation (NIV) improve clinical symptoms, quality of life, gas exchange, and sleep-disordered breathing in patients with OHS 3, 5, 6.
• CPAP is considered the first-line treatment modality for OHS phenotype with concomitant severe obstructive sleep apnea, whereas NIV is preferred in patients with hypoventilation during sleep with no or milder forms of obstructive sleep apnea 3.
• A randomized controlled trial found no difference in treatment failure between Bi-level PAP and CPAP for initial treatment of severe OHS 5.

Morbidity and Mortality Associated with OHS

• Patients with OHS have increased healthcare expenses and are at higher risk of developing serious cardiovascular disease leading to early mortality 2, 4.
• The prevalence of OHS has been estimated to be approximately 0.4% of the adult population 3.
• Appropriate management of comorbidities, including medications and rehabilitation programs, is key to improving prognosis in patients with OHS 3.