French catheter scale: Difference between revisions

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The French catheter scale is commonly used to measure the outside diameter of cylindrical medical instruments including catheters. In the French system, the diameter in millimeters of the catheter can be determined by dividing the French size by 3, thus an increasing French size corresponds with a larger diameter catheter. The following equations summarize the relationships:

D(mm) = F/3 or F = D(mm)*3

For example, if the French size is 9, the diameter is 3 mm. Note: the French scale is equal to the diameter in mm multiplied by THREE, not the circumference (diameter times pi) as is sometimes thought.

This is contrary to needle-gauge size, where the diameter is 1/gauge inches; thus the larger the gauge needle, the more narrow the bore of the needle. The Stubs Iron Wire Gauge system is also commonly used in a medical setting and is in fact more common for measuring needles, even though many find the Stubs system to be more confusing because the scale is non-linear and inversely proportional.

The "French Guage", as it is also known, was invented by Joseph-Frédéric-Benoît Charrière, a 19th century Parisian maker of surgical instruments, who defined the "diameter times 3" relationship.

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 [[Image:French catheter scale.gif|thumb|right|350px|Sizing scale of the French catheter system]]
-The '''French catheter scale''' is commonly used to measure the outside circumference (= pi x diameter) of cylindrical medical instruments including [[catheter]]s.  In the French system, the diameter in millimeters of the catheter can be determined by dividing the French size by Pi (Estimates of Pi are not usually adequate if one wishes to be accurate), thus an increasing French size corresponds with a larger diameter catheter.  The following equations summarize the relationships:
+The '''French catheter scale''' is commonly used to measure the outside diameter of cylindrical medical instruments including [[catheter]]s.  In the French system, the diameter in millimeters of the catheter can be determined by dividing the French size by 3, thus an increasing French size corresponds with a larger diameter catheter.  The following equations summarize the relationships:
-D = F/(3 mm) = C/pi <br>
+D(mm) = F/3    or    F = D(mm)*3
-F = C*(3 mm)/pi
+For example, if the French size is 9, the diameter is  3 mm. Note: the French scale is equal to the diameter in mm multiplied by THREE, not the circumference (diameter times pi) as is sometimes thought.
-For example, if the French size is 10, the diameter is  3.18 mm.
 This is contrary to needle-gauge size, where the diameter is 1/gauge inches; thus the larger the gauge needle, the more narrow the bore of the needle.
 The [[Stubs Iron Wire Gauge]] system is also commonly used in a medical setting and is in fact more common for measuring needles, even though many find the Stubs system to be more confusing because the scale is non-linear and inversely proportional.
+The "French Guage", as it is also known, was invented by Joseph-Frédéric-Benoît Charrière, a 19th century Parisian maker of surgical instruments, who defined the "diameter times 3" relationship.
 == See also ==