The man who left us his “Ch”
The name Joseph-Frédéric-Benoît Charrière may not roll easily off the tongue, and its 19th century owner may now be largely forgotten. But although few will be aware of his full name, the first two letters of his surname still live on in the field of urology.
Of Swiss descent, Charrière lived and worked in Paris, where he was a renowned cutler and surgical instrument maker. Modern developments in surgery owe a lot to his profession, and Charrière is credited with the crossing the legs of forceps so that they open when compressed and close on release, the idea behind spring forceps. He also designed the screw-action lithotrite, an instrument that is passed through the urethra to facilitate the crushing of bladder stones.
Another of Charrière’s inventions was the “French unit” — the “Ch” number that we still use to indicate the gauge of catheters. Charrièrre’s system was a scale that rose uniformly by one French unit equivalent to 0.33mm. The size in French units is roughly equal to the circumference of the bore of the catheter in millimetres. Therefore 12Ch is 12mm in circumference, which works out to a diameter of 4mm, and 16Ch is 16mm in circumference, and so on.
Catheters had already been around for centuries when Charrière invented his scale. Apparently the ancient Egyptians made catheters from reeds and probably did not worry too much about the Ch size. The Greeks used a hollow metal tube — a katheter — inserted through the urethra into the bladder to drain urine. The word comes from kathiemai, meaning to sound with a probe.
Citation: The Pharmaceutical Journal URI: 10007275