What is OHS?

OHS is defined as chronic daytime hypercapnia in obese patients (those with a BMI of > 30kg/m2), in the absence of other known causes for hypoventilation1.

As a result of poor breathing, those with OHS suffer from too much carbon dioxide (hypoventilation) and too little oxygen in their blood (hypoxemia).

OHS is characterised by dyspnoea, excessive daytime sleepiness, morning headache and depression.

OHS is typified by a chronically diminished respiratory drive during sleep, resulting in permanently low oxygen saturation levels, as well as daytime hypercapnia2. As many as 90% of patients with OHS also suffer from obstructive sleep apnoea (OSA).

OHS is diagnosed by a daytime PaCO2 > 45 mmHg after exclusion of other causes of hypoventilation.

Excessive weight in patients is a major cause of OHS. About half of all adults in Europe are overweight and one third of these are already obese (BMI>30 kg/m2), with numbers increasing3.



Olson AL, Zwillich C. The obesity hypoventilation syndrome. Am J Med.2005 Sep;


Nowbar S, Burkart KM, Gonzales R, Fedorowicz A, Gozansky WS, Gaudio JC, Taylor MR, Zwillich CW. Obesity-associated hypoventilation in hospitalised patients: prevalence, effects, and outcome. Am J Med. 2004 Jan 1;


WHO European Ministerial Conference on Counteracting Obesity, 15?17 November 2006.