Obesity Hypoventilation Syndrome (OHS)

Overview

Obesity hypoventilation syndrome (OHS) is a breathing disorder that affects some people with severe obesity. In OHS, breathing is too shallow and slow to keep the blood gases normal, so oxygen levels fall and carbon dioxide builds up, especially during sleep. The extra weight on the chest and abdomen makes the work of breathing harder, and the body's drive to breathe may also be reduced.

OHS is diagnosed when these blood gas changes are present and other causes have been ruled out. Many people with OHS also have obstructive sleep apnea, in which the airway repeatedly blocks during sleep. Left untreated, OHS can strain the heart and lungs and lead to serious complications, but it usually improves with breathing support and weight management. Recognizing and treating it can greatly improve symptoms and health.

Symptoms

Symptoms often overlap with those of sleep apnea and may build up slowly:

• Loud snoring and pauses in breathing during sleep
• Excessive daytime sleepiness and fatigue
• Morning headaches
• Shortness of breath, especially with activity
• Difficulty concentrating and low mood
• A bluish tinge to the lips or fingertips in more advanced cases
• Swelling in the legs and signs of heart strain over time

Because the changes are gradual, OHS is sometimes only recognized when a person becomes seriously unwell or is evaluated for sleep problems.

Causes

OHS results from a combination of factors related to severe obesity.

• Mechanical load: Excess weight on the chest and abdomen makes it harder to expand the lungs and take full breaths.
• Reduced breathing drive: The brain's response that normally increases breathing when carbon dioxide rises may be blunted.
• Sleep-disordered breathing: Coexisting obstructive sleep apnea worsens nighttime breathing.

Together these lead to underbreathing, low oxygen, and a buildup of carbon dioxide, particularly during sleep.

Risk Factors

• Severe obesity, especially with weight carried around the abdomen
• Obstructive sleep apnea
• Being middle-aged
• Other breathing or heart conditions
• Use of sedating medications that further reduce breathing

Diagnosis

OHS is diagnosed in a person with obesity who has a raised carbon dioxide level in the blood, after excluding other causes of underbreathing.

• Blood tests: An arterial or venous blood gas shows elevated carbon dioxide; blood may also reveal effects of long-standing low oxygen.
• Oxygen monitoring: Shows low oxygen levels, often worst during sleep.
• Sleep study: Assesses for obstructive sleep apnea and breathing patterns overnight.
• Other tests: Lung function tests, chest imaging, and heart tests help rule out other conditions and assess complications.

Treatment

Treatment aims to improve breathing, normalize blood gases, and address the underlying obesity.

• Positive airway pressure: CPAP or BiPAP machines used during sleep keep the airway open and support breathing, and are the mainstay of treatment.
• Weight management: Sustained weight loss, through lifestyle changes and sometimes medical or surgical treatment of obesity, can significantly improve or even resolve OHS.
• Oxygen therapy: Added in some cases, usually together with breathing support.
• Avoiding sedatives: Limiting alcohol and sedating medicines that further depress breathing.
• Treating complications: Managing heart strain and other related problems.

Severe cases with very low oxygen or high carbon dioxide may need urgent hospital care.

Self-Care and Prevention

• Work toward and maintain a healthier weight with professional support
• Use prescribed breathing support consistently every night
• Avoid alcohol and sedating medicines, especially before sleep
• Stay physically active within your ability
• Attend follow-up to monitor breathing, weight, and heart health

When to See a Doctor

See a healthcare provider if you have severe obesity along with loud snoring, daytime sleepiness, morning headaches, or breathlessness, so your breathing and blood gases can be checked. Seek emergency care for severe shortness of breath, confusion or unusual drowsiness, a bluish color of the lips or face, or chest pain, as these can signal dangerously low oxygen or high carbon dioxide that needs immediate treatment.

Related Topics

Frequently Asked Questions

References

1. American Thoracic Society. Obesity Hypoventilation Syndrome.
2. MedlinePlus, U.S. National Library of Medicine. Obesity hypoventilation syndrome.
3. National Heart, Lung, and Blood Institute (NHLBI). Sleep-related breathing disorders.