Obesity Hypoventilation Syndrome

Obesity hypoventilation syndrome is a state where obese people fail to breathe deeply enough or rapidly enough. This results in high carbon dioxide (CO2) levels in the blood and low oxygen (02) levels in the blood. It is also called as Pickwickian syndrome.

Most of the people suffering from this syndrome usually stop breathing for a short period during the sleeping time. It is called Obstructive Sleep Apnea. Hence this results in sleepiness throughout the day and partial awakenings at the night time. 


This syndrome causes strain on the heart, that eventually leads to a few symptoms like leg swelling, heart failure and even some other symptoms. Effective treatment is possible through weight loss, it is also possible to reduce these symptoms by positive airway pressure by nocturnal ventilation or even any other related treatments.

OHS (Obesity Hypoventilation Syndrome) defined as the mix combination of hypoxemia (low levels of O2 in the blood), hypoventilation (shallow breathing). Also the combination of hypercapnia (high CO2 levels in the blood), obesity (BMI more than 30kg/m2). Hypercapnia seen during the day time and hypoxemia is seen during the night time of sleep.


The exact cause is unknown. Some researchers believe that OHS caused due to a brain’s control defect over the breathing process. Excess muscles formation against the chest wall makes the person harder to breath quickly and to breath deeply. This results in high levels of carbon dioxide and low levels of oxygen.

Signs and symptoms

  • Obstructive sleep apnea
  • Snoring
  • Cessation of breath (night time)
  • Excessive daytime sleepiness
  • High levels of carbon dioxide
  • Drowsiness
  • Depression and hypertension
  • Headache
  • Edema
  • Chest pain
  • Cor pulmonale ( Condition due to a mismatch in ventilation-perfusion excessive strain given on the heart in the right side. Causes failure of the right-sided heart)


OHS (Obesity Hypoventilation Syndrome) is a type of sleep-disordered breathing disorder. The first type of OHS is obstructive sleep apnea, this occurs for 6 or more episodes of hypopnea, apnea per hour during sleep. The second type of OHS is due to ‘sleep hypoventilation syndrome’. This shows an increase in the level of carbon dioxide by 1.3 kPa after sleep. But even when compared with awake measurements it also with drops in oxygen level overnight without simultaneous hypopnea or apnea. 10% of people suffer from the second type of OHS while the rest 90% of people suffer from the first type of OHS.


There is still confusion about developing obesity hypoventilation syndrome (OHS) as some people develop it and some do not. Initially, breathing becomes hard because adipose tissues obstruct the chest muscle’s normal movement and chest wall becomes less compliant. Also leads to less effective diaphragm movement, fatigue respiratory muscles and due to excessive tissue in the neck and head area causes impaired airflow in and out of the lungs.

Hence, people suffering from OHS requires to expend high energy for effective breathing. All these factors together will lead to inadequate removal of CO2 from the blood circulation, sleep-disordered breathing.

Leptin hormone levels are high in obese people, secreted by adipose tissues and increases ventilation in normal circumstances. These effects reduced in people suffering from OHS. Furthermore, due to sleep apnea, nighttime acidosis leads to retention of alkalies (bicarbonates) by the kidneys. This helps in normalizing the blood acidity. However, bicarbonate alkalies will stay longer in the bloodstream and further hypercapnia leads to acidosis and ventilatory response reduces.

Hypoxic pulmonary vasoconstriction caused due to low oxygen level tightens small blood vessels of the lung which creates an optimal blood distribution. When the oxygen level is persistently low it causes chronic vasoconstriction it leads to high pressure no the pulmonary artery, which puts a strain on the right ventricle of the heart.

Remodeling of the right ventricle becomes distended and also removal of blood from veins is less. In this case, hydrostatic pressure raised results in accumulation of fluids in the skin and in severe issues fluids accumulated in the abdominal cavity and liver.

In blood low level of oxygen leads to the release of erythropoietin, erythropoiesis activation and RBC (Red Blood Cells) production in the increased level. This will result in increased red blood cells abnormally called polycythemia.


Few criteria prior to OHS diagnosis:

  • Arterial blood gas measurement determines arterial carbon dioxide levels over 6.0kPa or 45mmHg.
  • BMI (Body Mass Index) should be over 30 kg/m2.
  • Hypoventilation with no alternative explanation such as obstructive lung disease, kyphoscoliosis (chest wall disease), usage of narcotics, neuromuscular disease or hypothyroidism.

Various tests are essential for confirmation if OHS detected. An initial test determined by the elevation of carbon dioxide levels in the blood. This performed by the arterial blood gas measurements, involves withdrawing samples of blood from an artery, mainly from the radial artery. Since complicated to perform in some people it is also suggested to measure bicarbonate levels in the blood as a screening test. If the bicarbonate level elevated, then the next step would be measuring blood gases. Other tests performed such as electrocardiography, spirometry, lung medical imaging (CAT scan, CT scan or X-ray) and echocardiography.


For people suffering from OHS, losing weight is the main initial treatment. This is possible through exercise, diet, weight loss surgery or with medication. These help in improving the symptoms and to resolve the CO2 level. Losing weight is always time-consuming and always cannot have successful results. Weight loss surgery such a bariatric surgery is mostly avoided due to severe complications. But when there are no other options which are effective then bariatric surgery becomes the option.

If significant symptoms are seen and tried with nighttime PAP (Positive Airway Pressure) treatment, then this involves a machine to support breathing.

Various forms of PAP are available but with the uncertain ideal strategy. Some medications used to correct abnormalities underlying or improve breathing but again with uncertain benefits. OHS patient has cared as an outpatient basis, some show severe abnormalities like blood acidity. Some show a high level of CO2 causing unconsciousness some deteriorate suddenly. Occasionally, admission with intubation, mechanical ventilation and intense care unit is very essential. Otherwise, sometimes ‘bi-level’ PAP (Positive Airway Pressure) is usually required to stabilize patients with conventional treatment.




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