Shunt (medical)
From Wikipedia, the free encyclopedia
In medicine, a shunt is a hole or passage which moves, or allows movement of, fluid from one part of the body to another. The term may describe either congenital or acquired shunts; and acquired shunts (sometimes referred to as iatrogenic shunts) may be either biological or mechanical.
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[edit] Cardiac shunt
Cardiac shunts may be described as right-to-left, left-to-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic. The direction may be controlled by left and/or right heart pressure, a biological or artificial valve, or both. The presence of a shunt may also affect left and/or right heart pressure either beneficially or detrimentally.
[edit] Congenital
The most common congenital heart defects (CHDs) which cause shunting are the atrial septal defect (ASD), ventricular septal defect (VSD), patent ductus arteriosus (PDA), and patent foramen ovale (PFO). In isolation, these defects may be asymptomatic, or they may produce symptoms which can range from mild to severe, and which can either be acute or have delayed onset. However, these shunts are often present in combination with other defects; in these cases, they may still be asymptomatic, mild or severe, acute or delayed, but they may also work to counteract the negative symptoms caused by another defect (as with d-Transposition of the great arteries).
[edit] Acquired
[edit] Biological
Some acquired shunts are modifications of congenital ones: a balloon septostomy can enlarge a foramen ovale (if performed on a newborn), PFO or ASD; or prostaglandin can be administered to a newborn to prevent the ductus arteriosus from closing. Biological tissues may also be used to construct artificial passages.
[edit] Mechanical
Mechanical shunts are used in some cases of CHD to control blood flow or blood pressure. One example is the modern version of the Blalock-Taussig shunt.
[edit] Cerebral shunt
In cases of hydrocephalus, a one-way valve is used to drain excess cerebrospinal fluid from the brain and carry it to other parts of the body. This valve usually sits outside the skull, but beneath the skin, somewhere behind the ear.
Although a shunt generally works well, it may stop working if it disconnects, becomes blocked, or it is outgrown. If this happens the cerebrospinal fluid will begin to accumulate again and a number of physical symptoms will develop such as listlessness, headaches, irritability, light sensitivity, sound sensitivity, nausea, vomiting, dizziness, vertigo, migraines, some extremely serious, like seizures.
The shunt failure rate is also relatively high and it is not uncommon for patients to have multiple shunt revisions within their lifetime.
The diagnosis of cerebro-spinal buildup is complex and requires expertise.
[edit] Spitz-Holter
A common pediatric shunt is the Spitz-Holter shunt. It is a tiny one-way valve that releases controlled amounts of CSF from the brain to the heart. Spitz refers to the American neurosurgeon Eugene B. Spitz. Holter refers to the designer of the valve, John Holter, who was unable to save his son Casey from hydrocephalus, but his design, the Spitz-Holter valve/shunt, has helped millions around the world since the late 1950s.
[edit] Pulmonary shunt
Pulmonary shunts exist when there is normal perfusion to an alveolus, but ventilation fails to supply the perfused region. This will lead to a situation where the blood supply leaving a shunted area of the lung will have lower levels of oxygen and higher levels of carbon dioxide (i.e., the normal gas exchange doesn't occur).
[edit] Portosystemic shunt
A portosystemic shunt (PSS), also known as a liver shunt, is a bypass of the liver by the body's circulatory system. It can be either a congenital or acquired condition. Congenital PSS is an uncommon condition in dogs and cats, found mainly in small dog breeds such as Miniature Schnauzers and Yorkshire Terriers, and in cats such as Persians, Himalayans, and mix breeds. Acquired PSS is also uncommon and is found in older dogs with liver disease causing portal hypertension, especially cirrhosis.
[edit] See also
- Shunt in electronics
- Shunt resistors in ammeters
