French catheter scale

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The French scale or French gauge system is commonly used to measure the size of a catheter. It is most often abbreviated as Fr, but can often be seen abbreviated as Fg, Ga, FR or F. It may also be abbreviated as CH or Ch (for Charrière, its inventor).

A catheter of 1 French has a diameter of ⅓ mm,[1] and therefore the diameter of a round catheter in millimeters can be determined by dividing the French size by 3:

D (mm) = Fr / 3

or

Fr = D (mm) * 3

For example, if the French size is 9, the diameter is 3 mm.

From the basic math equation C = πd, it follows that the catheter's circumference in mm is only slightly (about 4.7%) greater than the French size.

An increasing French size corresponds to a larger external diameter. This is contrary to needle-gauge size, where an increasing gauge corresponds to a smaller diameter needle.

The French size is a measure of the external diameter of a catheter (not internal drainage channel). So, for example, if a two-way catheter of 20 Fr is compared to a 20 Fr three-way catheter, they both have the same external diameter but the two-way catheter will have a larger drainage channel than the three-way. Three-way catheters accommodate an extra channel for irrigation within a similar external diameter.

The French gauge was devised by Joseph-Frédéric-Benoît Charrière, a 19th-century Parisian maker of surgical instruments, who defined the "diameter times 3" relationship.[2]

Size correspondence[edit]

French catheter scale
French
Gauge
Diameter
(mm)
Diameter
(inches)
3 1 0.039
4 1.33 0.053
5 1.67 0.066
6 2 0.079
7 2.3 0.092
8 2.7 0.105
9 3 0.118
10 3.3 0.131
11 3.7 0.144
12 4 0.158
13 4.3 0.170
14 4.7 0.184
15 5 0.197
16 5.3 0.210
17 5.7 0.223
18 6 0.236
19 6.3 0.249
20 6.7 0.263
22 7.3 0.288
24 8 0.315
26 8.7 0.341
28 9.3 0.367
30 10 0.393
32 10.7 0.419
34 11.3 0.445

See also[edit]

References[edit]

  1. ^ "1 French". Wolfram|Alpha. Retrieved 20 March 2012. 
  2. ^ Iserson, Kenneth V. (1987). "J.-F.-B. Charrière: The man behind the "French" gauge". Journal of Emergency Medicine 5 (6): 545–8. doi:10.1016/0736-4679(87)90218-6. PMID 3323304. 

External links[edit]