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Obesity Hypoventilation Syndrome (OHS) is a severe respiratory illness that is comorbid with obesity (BMI ?30 kg/m2) and is characterised by daytime hypercapnia (PaCO? > 45 mmHg) and hypoxaemia after the exclusion of any lung or neuromuscular disorders. This condition is caused by decreased respiratory mechanics due to excess chest weight, impaired breathing control, and leptin dysfunction that affects the respiratory drive.

The main symptoms include poor sleep quality, obstructive sleep apnoea, daytime sleepiness, morning headaches, depression, and exhaustion resulting from persistent hypoxia. Patients often struggle to breathe and get exhausted even with minor exertion. If ignored, OHS leads to major cardiovascular consequences over time. This includes pulmonary hypertension, right ventricular hypertrophy, and ultimately heart failure due to the prolonged low oxygen levels constricting capillaries in the lungs.

Diagnosis includes blood tests indicating increased carbon dioxide, nocturnal sleep studies showing significant hypoxaemia, and assessment of BMI. The primary treatment is positive airway pressure therapy, in which CPAP keeps the airway open during sleep, and BiPAP provides active assistance with breathing to increase oxygen intake and carbon dioxide removal. It can be difficult, but losing weight is important and can reverse OHS. Oxygen therapy alone is not enough. OHS can lead to serious disability or death if left untreated, highlighting the necessity of early diagnosis and regular use of CPAP/BiPAP as indicated.