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Obesity Hypoventilation Syndrome (OHS)

People with Class 1 obesity and above are at risk for developing obesity hypoventilation syndrome (OHS).  Read more…


People with Class 1 obesity and above are at risk for developing obesity hypoventilation syndrome (OHS).  OHS causes you to have too much carbon dioxide and too little oxygen in your blood. Without treatment it can lead to serious and even life-threatening health problems. It occurs when the body does not receive enough oxygen and cannot blow off enough carbon dioxide from breathing during sleep.  OHS can cause extreme daytime sleepiness and lead to life threatening medical complications.  OHS is easily treated with an assistive breathing device that is worn during sleep.  Achieving and maintaining a healthy weight can actually eliminate the condition in many people.


The actual underlying cause is unclear though researchers suspect patients may also have a problem with the way their brain controls their breathing. It may also involve too much pressure on the chest from body fat that prevents deep breathing during sleep and may produce hormones that affect your body’s breathing patterns. Most people who have obesity hypoventilation syndrome also have apnea.

OHS is not the same thing as sleep apnea, although many people with OHS have sleep apnea.  Sleep apnea is a condition in which people stop breathing numerous times when they sleep, causing then to wake up and gasp for air.  With OHS alone, breathing does not stop, but it is inefficient, resulting in poor oxygen and carbon dioxide exchange.


OHS can lead to sleep deprivation.  You may feel excessively tired during the day, and even fall asleep at unexpected times.  You may feel depressed, moody, and irritable.  You may develop poor concentration and memory.
Untreated OHS can cause low blood oxygen levels, termed hypoxia causing you to feel tired after minimal activity.  Symptoms include:

  • Your lips, fingers, or toes appearing blue appear blue. 

  • Shortness of breath

  • Feeling tired after minimal activity

  • Swollen legs, ankles and feet


Untreated OHS can lead to life-threatening medical complications including high blood pressure, pulmonary hypertension; right-sided heart failure also known as cor pulmonale, and death.


You should contact your GP if you are obese and excessively drowsy during the day or other symptoms mentioned above.  Your GP will review your medical history, perform a physical examination, measure your weight and height, calculate your body mass index (BMI), and measure your waist and neck circumference
conduct some simple tests and refer you to your local hospital.  

An arterial blood gas test is used to check the amount of carbon dioxide and oxygen in your blood.  A high level of carbon dioxide in the blood while a person is awake indicates OHS and rather than sleep apnea.  Pulmonary function tests are used to evaluate the efficiency of your lungs.  Such tests usually involve breathing into a device while measurements are taken.  

You may be referred for a sleep study.  A sleep study is helpful for diagnosing OHS, sleep apnea, and other sleep disorders.  A sleep study is used to take measurements of basic body functions, such as heart rate, blood pressure, and blood oxygen levels, while you sleep.  A sleep study may be conducted at a sleep clinic or in some cases, it may be conducted at your home. 


You GP may initially recommend healthy lifestyle changes such as weight loss and increasing you physical activity. You may be prescribed Continuous Positive Airway Pressure (PAP). CPAP is the most common treatment for people with OHS.  CPAP involves wearing a device over your nose and/or mouth while you sleep.  The device generates gentle air pressure to keep your airway open.  The machine senses when you are inhaling and delivers more air pressure during that time.  CPAP is an effective way to treat OHS.  Some patients may require the use of oxygen in addition to PAP therapy to keep blood oxygen levels up in the normal range. 

Losing weight and maintaining a healthy weight can be a long-term solution and actually eliminate OHS.  You should ask your doctor about a safe weight loss plan for you.  Your doctor may refer you to a dietitian, exercise specialist, or support group for more information and emotional support.  Weight loss surgery may also be an option for some patients.