Diagnosing Obesity Hypoventilation Syndrome in Patients with COPD

Diagnostic Criteria and Approach

The American Thoracic Society defines Obesity Hypoventilation Syndrome (OHS) as the combination of obesity (BMI > 30 kg/m²), sleep-disordered breathing, and awake daytime hypercapnia (PaCO₂ > 45 mm Hg at sea level), after excluding other causes for hypoventilation 1, 2
For patients with both obesity and COPD with a high pretest probability of having OHS, measuring PaCO₂ through arterial blood gas analysis is recommended rather than relying solely on serum bicarbonate or SpO₂ 1
The American Journal of Respiratory and Critical Care Medicine recommends that for patients with low to moderate probability of having OHS (<20%), serum bicarbonate can be used as an initial screening tool: If serum bicarbonate < 27 mmol/L, OHS is very unlikely 2, 4
Avoid using SpO₂ during wakefulness alone to decide when to measure PaCO₂ in patients suspected of having OHS 5

Clinical features that suggest OHS rather than COPD-only hypercapnia include severe obesity (especially BMI > 40 kg/m²) 1
Evidence of sleep-disordered breathing, particularly severe OSA (AHI > 30 events/h), suggests OHS rather than COPD-only hypercapnia 1

Polysomnography or sleep respiratory polygraphy is required to determine the pattern of sleep-disordered breathing (obstructive or nonobstructive) and tailor treatment appropriately 1
Arterial blood gas analysis to document awake hypercapnia (PaCO₂ > 45 mm Hg) is necessary for diagnosis 1, 2

For stable ambulatory patients with both OHS and COPD, positive airway pressure (PAP) therapy during sleep is recommended 2
For patients with both OHS and severe OSA (AHI > 30 events/h), CPAP is suggested as first-line treatment rather than NIV 3
Weight loss interventions that produce sustained weight loss of 25-30% of actual body weight should be pursued to achieve resolution of hypoventilation 6