Obesity hypoventilation syndrome

Background

Pathophysiology

• Caused by a combination of lectin deficiency causing muscle weakness, increased extrathoracic pressure from soft tissue, and increased airway resistance

Clinical Manifestations

• Almost all (90%) have concurrent obstructive sleep apnea, and 70% have severe OSA

Investigations

• Serum bicarbonate <27 has a 97% negative predictive value
• Polysomnography is used for diagnosis

Diagnosis

• Obesity (BMI ≥30 kg·m−2)
• Daytime hypercapnia with PaCO₂ ≥45 mmHg
• Sleep disordered breathing
  • Obstructive sleep apnea (90%), or
  • Non-obstructive sleep hypoventilation (10%), defined as either
    • PaCO₂ (or surrogate such as ETCO₂ or transcutaneous CO₂) >55 mmHg for >10 min, or
    • An increase in PaCO₂ (or surrogate) >10 mmHg compared to an awake supine value to a value >50 mmHg for >10 min
• Exclusion of other causes of hypoventilation

Management

• Treated with CPAP

Further Reading

• Obesity hypoventilation syndrome. European Respir Rev. 2019;28:180097. doi: 10.1183/16000617.0097-2018