Which statement defines obesity hypoventilation syndrome?

Which statement defines obesity hypoventilation syndrome?

• A. Hypoxemia during sleep only
• B. Hypercapnia with PaCO2 >45 mmHg in BMI >30 kg/m2
• C. Elevated BMI but normal CO2
• D. Restrictive pattern on spirometry

Answer: (B)

Obesity hypoventilation syndrome is characterized by persistent daytime hypercapnia in an obese individual, defined by a PaCO2 greater than 45 mmHg in someone with a body mass index above 30. The key is that the elevated CO2 is present when awake, not just during sleep, and other causes of hypoventilation, such as neuromuscular disease, severe lung disease, or chest wall disorders, are excluded. This distinguishes it from conditions where CO2 rises only at night or not at all despite obesity. While many patients with this syndrome also have sleep-disordered breathing and may experience hypoxemia, the defining finding is the chronic daytime hypercapnia. An elevated BMI with normal CO2 does not meet the diagnosis, and spirometry showing a restrictive pattern alone is not defining for this condition.

Obesity hypoventilation syndrome is characterized by persistent daytime hypercapnia in an obese individual, defined by a PaCO2 greater than 45 mmHg in someone with a body mass index above 30. The key is that the elevated CO2 is present when awake, not just during sleep, and other causes of hypoventilation, such as neuromuscular disease, severe lung disease, or chest wall disorders, are excluded. This distinguishes it from conditions where CO2 rises only at night or not at all despite obesity. While many patients with this syndrome also have sleep-disordered breathing and may experience hypoxemia, the defining finding is the chronic daytime hypercapnia. An elevated BMI with normal CO2 does not meet the diagnosis, and spirometry showing a restrictive pattern alone is not defining for this condition.