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A catheter sheath is a plastic tube of larger diameter than an intravenous catheter, used in the process of introducing the catheter to limit pain and increase accuracy. Companies may package sheaths with catheters, and it is also possible to purchase them as standalone items. Like other tools intended for medical procedures where the skin will be broken, the sheath is sterile to reduce the risks of infection and inflammation. It is a single-use medical device.
In a classic example of how a doctor might use a catheter sheath, in a cardiac catheterization lab, a doctor will insert a guide wire through the femoral artery, using medical imaging studies to make sure the wire is in the right place. The doctor will then slip on a catheter sheath, a short tube that secures access to the artery. Once the sheath is in place, the doctor can insert the catheter and push it up to the heart to perform the procedure.
Catheter insertion can be painful. There are nerve endings around the insertion site, and patients may experience discomfort as the doctor guides the device in. Catheter sheaths eliminate this problem by preventing the catheter from coming into contact with the nerves. Once it enters the blood vessel, the patient shouldn't feel it, as blood vessels do not have internal nerves. The sheath also prevents problems like slipping a catheter into the wrong blood vessel, or losing venous access by accidentally jerking on the catheter. Sheaths are useful for guiding catheters into position and holding them there.
After a procedure, the doctor may leave the catheter sheath in place, typically taped down. In the event of an emergency, the doctor has rapid venous access through the sheath and does not have to wait to place a catheter. This can be critical in a patient with hemodynamic instability, as low blood pressure makes it extremely hard to place a catheter correctly on the first try. If the doctor can't access a vein quickly enough, a patient may not be able to receive lifesaving medications.
Catheter sheath construction usually involves nonreactive materials to address concerns about allergies. Placement of the sheath is usually uncomfortable, but once it is in place, the patient shouldn't experience additional discomfort. Patients who notice sharp, twinging pain or feelings of pressure around the catheter insertion site should tell a doctor or nurse, as it may be a sign of a problem.