When selecting a catheter size it is important to consider the patient's body type, the procedure to be performed, and the potential risks involved. While catheter sizing depends on these and other variables, a good general rule is to select the smallest possible catheter that will work in the given procedure. Most physicians use a French 14-gauge, or 0.184 inches (about 4.7 mm), for adult males and a French 12- to 16-gauge, or 0.158 to 0.21 inches (about 4 to 5.3 mm), for adult females.
If there is a concern of excessive fluid flow, or of sediment such as blood clots, passing through the catheter, then the catheter should be slightly larger to accommodate these possibilities. These risks are often associated with urinary catheterization, or the use of a catheter to withdraw urine from the bladder. Problematic issues may also arise during some blood transfusions.
When selecting a catheter for a blood transfusion, the primary consideration should be the size of the patient's vein. Recent scientific developments have affected the sizing standards for blood transfusion catheters. While an 18-gauge, or a catheter measuring 0.234 inches (about 5.94 mm), used to be the standard, the development of short peripheral catheters with smaller but stronger walls made it possible to use a smaller size for a larger fluid flow. Now, physicians recommend that an 18- or 20-gauge, measuring 0.26 inches (about 6.6 mm), should only be used for large and rapid blood transfusions, such as in a trauma case.
Catheter length is dependent on the patient's body type and the intended procedure. A larger patient with greater body mass might need a longer catheter tube than a smaller patient with less body mass. Additionally, a male will need a longer urinary catheter than a female. Typically, urinary catheters for men are 16 inches (about 40 cm) long, while those for women are only about 6 inches (15 cm) long. In all cases, however, the following should be considered: a shorter catheter tube allows for a faster draw of fluid; a longer tube creates more resistance to the flow of fluid. For increased efficiency, a shorter catheter is recommended when possible.
In addition to choosing a catheter size, it is important to select a catheter made from material that will be safe with the fluids and body types involved in the procedure. Most catheters are made from silicone or polyurethane, which softens when warmed. Polyurethane is tougher, permitting the catheter wall to be thinner and the internal diameter larger than those made from silicone. For these reasons, using a polyurethane catheter can improve efficiency and reduce the risk of irritation to the body.
Catheterization of any part of the body is a delicate process. While minor irritation to the affected area is normal, anything more intense or extensive should be treated. Urinary tract infections due to prolonged catheterization are the most common infections among inpatients in hospitals. For this reason, close monitoring of catheterized patients is highly recommended for hospital staff. Self-catheterization is not recommended.