The history and meaning of the catheter diameter "French"

In clinical practice, we often encounter 6F, 8F, and 16F tubes, but we don't know what the F stands for.

Today, I just happened to come across an article introducing this content, so I learned a little and kept it as a note.

The catheter diameter unit "French" (abbreviated as Fr or Fg) was first proposed by Joseph-Frédéric-Benoit Charrière (1803-1876), a Swiss-French surgical instrument manufacturer in the 19th century. It is a unit for measuring the outer diameter of medical devices such as catheters. This unit is mainly used to describe medical devices, especially catheters, guidewires, endotracheal tubes, etc.

The term "French" (abbreviated as Fr) is a unit of measurement for the outer diameter of circular or nearly circular devices (such as catheters or sheaths). 1 Fr=1/3mm (0.33mm). The larger the outer diameter, the larger the number in front of Fr (see the figure below).

In other words, the diameter of the catheter (mm) is equal to the French number divided by 3. Therefore, the diameter of a 9 French catheter is 9 ÷ 3 = 3 mm.

The specific formula is: Diameter (mm) = French number 3\text{Diameter (mm)} = \frac{\text{French number}}{3}Diameter (mm) = 3French number

For example, a 30 French catheter has a diameter of 10 mm.

Here is a 7 Fr triple-lumen central venous catheter (see figure below). Similarly, "7 Fr" refers to the outer diameter of the tube, which is 2.33 mm.

On the "oval" chest catheter (see figure below), "Fr" is also used to represent the size of the tube, representing the diameter of the long axis.

But there are different descriptions on vascular sheaths. For example, the "6 Fr" sheath (see figure below) refers to the diameter of the inner diameter (Figure 8), indicating the size of the device that can pass through the sheath. This is exactly the opposite of "Fr" in other cases that indicate the size of the outer diameter.