What is OHS?

OHS is defined as chronic daytime hypercapnia (PaCO2 of over 45 mm Hg) in obese patients (those with a BMI of > 30kg/m)2 after ruling out any other causes of hypoventilation.1

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

OHS symptoms include:

  • dyspnea2
  • Excessive Daytime Sleepiness (EDS)2
  • morning headache2
  • depression

As many as 90% of patients with OHS also suffer from obstructive sleep apnea (OSA).


  • 01

    Olson AL, Zwillich C. The obesity hypoventilation syndrome. Am J Med. 2005 Sep 118(9): 948-56

  • 02

    Mokhlesi B, Kryger MH, Grunstein RR. (2008) Assessment and management of patients with obesity hypoventilation syndrome. Proc Am Thorac Soc 5:218–225

  • 03

    Kessler R, Chaouat A, Schinkewitch P, Faller M, Casel S, Krieger J, Weitzenblum E. (2001) The obesity-hypoventilation syndrome revisited: A prospective study of 34 consecutive cases. Chest 120:369–376

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