What is obesity hypoventilation syndrome?
Obesity hypoventilation syndrome (OHS) is breathing disorder affects mainly obese patient, which cause hypoxemia. Hypoxemia means a deficiency in oxygen and enhancement of carbon-di-oxide level in the circulating blood. Alternatively, obesity hypoventilation syndrome is also known as Pickwickian syndrome. 
Breathing consist of two mechanism – inspiration (oxygen intake) and expiration (carbon-di-oxide exhalation). In a normal individual, during inspiration alveoli in the lungs become filled up with oxygen, which is take in through the nasal cavity and traveled via windpipe. The gaseous exchange occur in the surrounded blood capillaries present around the air alveoli and blood collect oxygen and carbon dioxide moves to air sacs to get back to the environment via windpipe and nasal cavity. 
In some obese patient, the adequate rate of breathing is not followed and cause insufficient oxygen intake. The resultant of this cause improper gaseous exchange and blood contains less amount of oxygen (hypoxemia) and more amount of carbon dioxide (hypoventilation). The pathophysiological condition which may cause obesity hypoventilation syndrome are
- Respiratory muscle myopathic condition disrupts normal breathing
- A higher degree of central adiposity (more fat distribution) causes cephalic dislocation of the diaphragm and leads to incompetent mechanical action.
- More central fat distribution also causes reduction of lung volumes
- The combination of above-mentioned factors increases the breathing effort. In addition, most of the patient having obesity hypoventilation syndrome are suffering from upper airway obstruction, including snoring and witnessed apneas. 
Signs & Symptoms
The precise sign of the OHS is a lower level of PaO2 and higher level PaCO2 at daytime, which influence increased the proportion of sleep duration (SpO2 < 90%) at the daytime. Obesity hypoventilation syndrome specifically develops in obese individual means the measured BMI should be more than or equal to 35kg/m2. The individual with this BMI usually has the tendency to feel sleepiness at daytime and also has neurocognitive function impairment.
The chronic suffering from Obesity hypoventilation syndrome causes the following symptoms:
- Disturbed sleep
- Early morning headache
- Reduced recital
- Lack of concentration
- Memory impairment
- Learning difficulty
Worse the condition leads to pulmonary hypertension and cardiac failure at right-sided and these may follow with symptoms like exertion due to labored breathing (dyspnea) and fluid accumulation (edema) at lower limb. [4,5]
The proper cause is yet not discovered. According to the belief of clinicians, brain unable to control breathing. chest wall becomes compressed due to excessive weight and difficult to take a deep breath and also maintain the proper rate of breath. This leads to blood is not contains sufficient amount of oxygen, whereas the amount of carbon dioxide is increased. 
The following sequential diagnostic methods are followed to diagnose the OHS:
- Symptomatic analysis: Detail information about the symptoms are discussed during consultation with the doctor, including sleep pattern, body mass index (BMI) evaluation, determining oxygen and carbon dioxide levels.
- Height and weight measurements are required to calculate BMI. Clinically it is accepted that 30 or more than 30 BMI denotes obesity.
- Blood test is required to evaluate oxygen and carbon dioxide levels in blood
- A pulse oximeter is a medical device which attached to the finger, which can measure the oxygen level in blood but does not detect carbon dioxide level. Though the pulse oximetry is non-invasive technique, but not provide an accurate result in comparison with a blood test.
- Chest X-ray also conducted for determining the underlying cause of breathing difficulty.
- Polysomnography is the diagnostic test for studying sleep. This test is required to perform in case of sleep apnea. 
The available treatment approaches for OHS can be broadly divided into two categories:
- Medical therapy
- Surgical intervention
Medical therapies are non-invasive techniques and include continuous positive airway pressure (PAP) therapy. In positive airway pressure, a mask is tightly fitted around the nose and mouth to maintain continuous positive airway pressure. This technique is applied for sleep disturbance arise for breathing difficulty and also provide a better result for nocturnal gaseous exchange.
This is applied for a patient who cannot tolerate continuous positive airway pressure (PAP) therapy due to wearing of mask cause difficulty. In this process, one channel is made through the neck for breathing, though this option is not applicable for long-term management.
- Oxygen therapy is also provided for positive airway pressure
The most effective treatment for OHS is Bariatric surgery. This surgical intervention attains more significant degrees of weight loss and continues this loss over longer periods.
Untreated OHS can cause hollowing complications :
- Edema or fluid accumulation in lower extremities
- In pulmonary arteries, pressure becomes increased and causes pulmonary hypertension
- Right-sided cardiac chambers fail to function and the condition is termed as Cor pulmonale
- Production of red blood cells is increased in body tissue and the condition is known as secondary erythrocytosis. 
- What Is Obesity Hypoventilation Syndrome?; National Heart, Lung and Blood Institute; Retrieve from: https://www.nhlbi.nih.gov/health/health-topics/topics/ohs
- Amanda J. Piper and Ronald R. Grunstein “Obesity Hypoventilation Syndrome”, American Journal of Respiratory and Critical Care Medicine, Vol. 183, No. 3 (2011), pp. 292-298.
- doi: 10.1164/rccm.201008-1280CI; Retrieve from:http://www.atsjournals.org/doi/full/10.1164/rccm.201008-1280CI#.WBKz2tV97IU
- Laila Al Dabal, Ahmed S. BaHammam; Obesity hypoventilation syndrome; Ann Thorac Med. 2009 Apr-Jun; 4(2): 41–49.doi: 10.4103/1817-1737.49411; Retrieve from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2700483/,
- What Are the Signs and Symptoms of Obesity Hypoventilation Syndrome? National Heart, Lung and Blood Institute; Retrieve from:http://www.nhlbi.nih.gov/health/health-topics/topics/ohs/signs
- Obesity hypoventilation syndrome (OHS); MedlinePlus; Retrieve from: https://medlineplus.gov/ency/article/000085.htm
- Obesity Hypoventilation Syndrome; American Thoracic Society; Retrieve from: https://www.thoracic.org/patients/patient-resources/resources/obesity-hypoventilation-syndrome.pdf