| Obesity Classification and external resources |
|
| ICD-10 |
E66.2 |
|---|---|
| ICD-9 | 278.8 |
| OMIM | 257500 |
| DiseasesDB | 32243 |
| eMedicine | ped/1627 |
| MeSH | D010845 |
The obesity hypoventilation syndrome, also known as Pickwickian syndrome, is the combination of obesity (Body mass index
It may cause dyspnea (difficulty breathing), poor sleep with daytime tiredness, leg swelling and various other symptoms. The main treatments are Weight loss
Most people with obesity hypoventilation syndrome have concurrent obstructive sleep apnea, a condition characterized by snoring, brief episodes of apnea (cessation of breathing) during the night, interrupted sleep and excessive daytime sleepiness. In OHS, sleepiness may be worsened by elevated blood levels of carbon dioxide, which causes drowsiness ("CO2 narcosis"). Other symptoms present in both conditions are depression, hypertension (high blood pressure) that is difficult to control with medication and headaches occurring in the morning.[2] Blurring of vision and visual obscurations may result from papilledema (swelling of the optic disc) in response to the raised carbon dioxide levels.[3]
The low oxygen and elevated carbon dioxide levels lead to excessive strain on the right side of the heart, known as "cor pulmonale". Symptoms of this disorder include edema (swelling) of the legs, decreased exercise tolerance, ascites (accumulation of fluid in the abdominal cavity) and exertional chest pain.[2]
If OHS is suspected, various tests are required for its confirmation. Arterial blood gas
Formal criteria for diagnosis of OHS are:[1]
Two subtypes are recognized. The first is OHS in the context of obstructive sleep apnea; this is confirmed by the occurrence of 5 or more episodes of apnea, hypopnea or respiratory-related arousals per hour (high apnea-hypopnea index) during sleep. The second is OHS primarily due to "sleep hypoventilation syndrome"; this requires a rise of CO2 levels by 10 mmHg (1.3 kPa) after sleep compared to awake measurements and overnight drops in oxygen levels without simultaneous apnea or hypopnea.[1] In many patients, both phenomena are present.[2]
Despite many studies, it is still unclear why some obese people develop hypoventilation and others do not. Impairment of lung expansion by adipose tissue means that one needs to breathe faster and deeper to still absorb sufficient amounts of oxygen and remove adequate amounts of carbon dioxide. It appears that the respiratory center (an area in the brain stem that regulates breathing) becomes relatively insensitive to normal stimuli, leading to a decreased response to low oxygen levels. While this may be the result of obstructive sleep apnea, it does not explain why some people with OHS have no features of obstruction. Recent studies postulate that there is a vicious cycle in which low oxygen levels make the respiratory center progressively more insensitive to hypoxia, impairing normal compensatory mechanisms normally in place to prevent hypercapnia. It appears that insensitivity to the hormone leptin, which is elevated in obesity, plays a role in this process, but there is no conclusive evidence that this is the case.[2]
Low oxygen levels lead to hypoxic pulmonary vasoconstriction, the tightening of small blood vessels in the lung to create an optimal distribution of blood through the lung. Persistently low oxygen levels causing chronic vasoconstriction leads to increased pressure on the pulmonary artery (pulmonary hypertension), which in turn puts strain on the right ventricle, the part of the heart that pumps blood to the lungs. The right ventricle undergoes remodeling, becomes distended and is less able to remove blood from the veins. When this is the case, raised hydrostatic pressure leads to accumulation of fluid in the skin (edema), and in more severe cases the liver and the abdominal cavity. The dysfunction of the right ventricle improves with treatment.[4]
Reduction in weight, either through a regimen of diet and exercise, medication or sometimes through bariatric surgery, has been shown to improve the symptoms of OHS and resolution of the high carbon dioxide levels. Weight loss may take a long time and is not always successful.[2]
Overnight mask ventilation with positive airway pressure may lead to an improvement in most symptoms of OHS. The type of mask ventilation depends on the underlying problem. If the main abnormality on investigations is obstructive sleep apnea, CPAP (continuous PAP) may be sufficient; this involves sleeping with a face mask connected to a machine that delivers a continuously high atmospheric pressure; this stops tissues in the mouth and throat area from collapsing and obstructing air flow.[2] If sleep hypoventilation is the predominant problem, CPAP may be insufficient, and increased pressure ("pressure support") needs to be delivered during inspiration to allow more airflow into the alveoli (the sacs of the lung where gas transport takes place). This is referred to as BIPAP ("bi-level" PAP).[2][5] In patients whose symptoms are highly disabling but are unable to tolerate CPAP or BIPAP, ventilation through a tracheostomy (opening in the windpipe) is sometimes required.[2]
Despite some initial positive reports about improvement of OHS with medroxyprogesterone,[3] this is not recommended in practice.[2]
The exact prevalence of OHS is unknown. In patients with a BMI over 35 who were admitted to hospital, 31% had elevated carbon dioxide levels. It is not known whether men or women are at greater risk. The presence of OHS is associated with an increased risk of death compared to those with obesity but no OHS (24% vs 9% over an 18 month period).[2]
The condition was first described in 1956 in a patient who, after gaining weight, became somnolent and fatigued and prone to fall asleep during the day, as well as developing edema of the legs suggesting heart failure. The authors coined the newly described condition "Pickwickian syndrome" after the character Joe from Dickens' The Posthumous Papers of the Pickwick Club (1837), who was markedly obese and tended to fall asleep uncontrollably during the day.[6]
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