What is Obesity Hypoventilation Syndrome? (Diagnosis and Treatment)



Very obese children and adults who have daytime fatigue and difficulty concentrating may be suffering from obstructive sleep apnea — but in up to 20% of cases, the diagnosis may be even more serious. Obesity Hypoventilation Syndrome, or OHS, is a sleep-related respiratory problem that can cause serious and in some cases irreversible damage to the body, greatly increasing mortality risk over a fairly short period of time.

The key to managing this condition is knowing how to spot it early. 

What Is Obesity Hypoventilation Syndrome (OHS)?

OHS, sometimes referred to as hypercapnic sleep apnea or Pickwickian Syndrome, is form of sleep-disordered breathing. It’s characterized by the following:

  1. Patients are seriously overweight (obese), with a BMI greater than 30.
  2. They have a higher-than-normal amount of carbon dioxide, or CO2, in the bloodstream (a condition called hypercapnia). This hypercapnia is present during the daytime but gets worse during sleep, sometimes leading to severe oxygen deprivation in the arterial blood supply.
  3. This hypercapnia is caused by hypoventilation, or respiratory depression: episodes of shallow breathing or slower-than-normal breathing that are not caused by a lung disease, a neurologic disorder, or muscle weakness. People with OHS tend to hypoventilate more during REM sleep than in non-REM sleep. Sometimes their breath ceases altogether (similar to an apnea event). 

This disease is associated exclusively with obesity. About 90% of patients diagnosed with OHS also have Obstructive Sleep Apnea (OSA).

OHS is dangerous because the high CO2 levels, combined with a lack of sufficient oxygen in the blood, can be a precursor to hypoxia or hypoxemia — chronic, severe oxygen deprivation that causes tissue to deteriorate.

Over time, this deterioration leads to serious and even deadly emergencies like cardiopulmonary arrest (failure of the heart muscle) or respiratory failure. 

How OHS Is Different from OSA


Although the two conditions are often closely related, they’re not the same, and they’re not always linked.

Some basic facts about OHS and OSA:



OHS Symptoms

What does it feel like to have OHS? You may not notice any disruption to your sleep quality, particularly if you are not experiencing obstructive sleep apnea in addition to OHS.

However, you will likely experience some of the following:


How OHS Is Diagnosed



OHS can be tricky to diagnose because its symptoms overlap with so many other conditions.

For example, it’s not uncommon for someone who’s very obese to feel tired, short of breath, or moody. People with OHS also frequently have other conditions like asthma or diabetes, which can present with some of the same problems.

If you have the known risk factors for OHS, in combination with the above symptoms, your physician may order lab tests to confirm a diagnosis.

Known OHS risk factors include:

If your physician suspects OHS based on your medical history and the above risk factors, she may order the following tests to confirm a diagnosis. 

Your doctor may also check for an accumulation of blood or fluid in your tissue, higher-than-normal red blood cell count, high blood pressure in the lungs (pulmonary artery hypertension), and any signs of heart strain, enlargement, dysfunction, or “right-sided heart failure.”

In addition to these tests, your doctor may order an overnight polysomnography (sleep study) to check for hypoventilation, hypoxia and hypercapnia during sleep. 

During the sleep study, sleep lab technicians can also conduct a nocturnal pulse oximetry to measure your heart rate and oxygen levels. Pulse oximetry can show whether you also have obstructive sleep apnea in addition to (or in lieu of) OHS.

Treatment of OHS

Currently, the treatment approach for OHS entails two steps: 

  1. Losing weight. Obesity appears to be the main cause of OHS. To reverse or improve symptoms, you should try to return to a normal body weight with a healthy BMI. Some patients cannot achieve this goal with diet and exercise alone, especially if respiratory symptoms are too severe to allow for cardiovascular exercise. In those cases, bariatric surgery may be recommended.
  2. Complying with non-invasive ventilation (NIV), CPAP, or Bi-level PAP therapy. OHS patients without OSA may be given an NIV mask that provides assisted ventilation supplemented with oxygen. This treatment can help to normalize blood oxygen levels and prevent hypoxemia. In the case of OHS with OSA, CPAP or Bi-level PAP therapy may be more effective because the forced air pressure overcomes the soft tissue obstruction in the upper airway.

The bad news is, untreated OHS is very serious. In most cases, by the time it’s diagnosed, it’s already done enough damage to the heart and lungs to put you at a 23% risk of death over 18 months. That risk grows to 46% over 50 months. 

The good news is, diagnosing and treating OHS with PAP therapy can improve or even normalize blood CO2 levels, bringing the mortality risk down to less than 10%.

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