Catheterization (from Greek "kathiemai" meaning "let down" is a use of a catheter (i.e. thin, usually flexible tube), that can be inserted in the body to Tx diseases or perform a surgical procedure. Indwelling catheter is a catheter that is left inside the body, either temporarily or permanently. Permcath is a permanently inserted catheter. Catheters can be inserted into a body cavity, duct or vessel.

French scale (aka French gauge, Fr) is used to measure the size of a catheter. The French size is 3 times the diameter in millimeters. Thus, a round catheter of 1Fr has a diameter of 1/3mm. Based on the formula that C=pi.d, because the multiplier 3 is close to pi (3.142), the catheter's circumference in mm is only slightly greater (4.7%) than the French size. An increasing French size correpsondence to a larger external diameter.

• Allow drainage
• Administration of fluids or gases
• Access by surgical instruments
• Perform a wide variety of other tasks depending on the type of catheter

• Cardiovascular:
  • Central venous catheter (CVC, aka central line), a catheter in a large vein (internal jugular vein, subclavian/axillary vein, or femoral vein), used to administer drugs/fluids, obtain blood tests, and measure central venous pressure
• Urological:
  • Urinary catheterization
• GI
• Neurovascular
• Ophthalmic

• Urinary catheter
• Needle gauge size