What are the diagnostic criteria for Obesity Hypoventilation Syndrome (OHS)?

From the Guidelines

To diagnose obesity hypoventilation syndrome (OHS), clinicians should evaluate patients with obesity (BMI > 30 kg/m²) who demonstrate awake daytime hypercapnia (PaCO₂ > 45 mmHg) and sleep-disordered breathing, after excluding other causes of hypoventilation, as recommended by the American Thoracic Society clinical practice guideline 1. The diagnostic process begins with a comprehensive clinical assessment, looking for symptoms such as:

• Excessive daytime sleepiness
• Morning headaches
• Fatigue
• Disturbed sleep Arterial blood gas analysis is essential to confirm hypercapnia while awake, with a PaCO₂ level greater than 45 mmHg at sea level 1. Polysomnography or sleep respiratory polygraphy should be performed to identify sleep-disordered breathing, particularly obstructive sleep apnea, which coexists in approximately 90% of OHS cases 1. Pulmonary function tests help exclude other causes of hypoventilation such as COPD or restrictive lung diseases. Additional testing may include chest imaging, thyroid function tests, and assessment for neuromuscular disorders. The pathophysiology involves a combination of increased mechanical load from obesity, blunted respiratory drive, and sleep-disordered breathing leading to chronic hypercapnia and hypoxemia 1. Early diagnosis is critical as OHS is associated with significant morbidity, including pulmonary hypertension, right heart failure, and increased mortality compared to simple obesity or obstructive sleep apnea alone 1.

From the Research

Diagnostic Criteria for Obesity Hypoventilation Syndrome

To diagnose a patient with obesity hypoventilation syndrome (OHS), the following criteria should be considered:

• The presence of obesity, defined as a body mass index (BMI) ≥ 30 kg/m² 2, 3
• Daytime arterial hypercapnia, defined as a PaCO2 ≥ 45 mmHg 2, 3
• The absence of other causes of hypoventilation 2, 3

Clinical Predictors of OHS

Several clinical predictors can help identify patients with OHS, including:

• Higher BMI, neck circumference, waist circumference, and waist/hip ratio 4, 5
• Higher Epworth Sleepiness Scale scores 4, 5
• Lower daytime PaO2 and sleep efficiency 4
• Higher serum bicarbonate levels and nadir S(pO2) 4, 5

Diagnostic Tools

The following diagnostic tools can be used to diagnose OHS:

• Arterial blood gas (ABG) analysis to measure PaCO2 and PaO2 2, 4
• Polysomnography to assess sleep-disordered breathing 6
• Serum bicarbonate levels and nadir S(pO2) as independent predictive factors for OHS 4, 5

Screening Measures

Screening measures, such as serum bicarbonate levels ≥ 27 mmol/L and/or nadir S(pO2) < 80%, can help identify patients with OHS 4, 5

• A serum bicarbonate level of ≥ 27 mmol/L has a sensitivity of 76.6% and specificity of 74.6% for diagnosing OHS 4
• A nadir S(pO2) of < 80% has a sensitivity of 82.8% and specificity of 54.5% for diagnosing OHS 4