Catheter size

The size of vascular catheters is determined by the outside diameter of the catheter. 

There are two measures of catheter size: the gauge size and the “French” size

The gauge size

1. the higher the gauge size, the smaller the outside diameter

2. However,

there is no fixed relationship between gauge size and outside diameter.

3. the only way to determine the actual outside diameter of a

catheter is to consult the manufacturer

4. Gauge sizes are typically used for peripheral catheters, and for the infusion channels of multi-lumen catheters

5. 20 g ≈ 1mm

The Gauge size

The French size

1. accurate

   1 French = 0.33 mm

    2 French = 0.66 mm

2. most vascular catheters are between 4 French (1.3)and 10 French (3.3) in size. 

3. French sizes are typically used for multi-lumen catheters and for large-bore single lumen catheters (like introducer sheaths)

The French size