French sizing of medical devices is not fit for purpose

The purpose of the study is to quantify the variation in the metric equivalent of French size in a range of medical devices, from various manufacturers, used in interventional radiology.

The labelling of a range of catheters, introducers, drains, balloons, stents, and endografts was examined. Products were chosen to achieve a broad range of French sizes from several manufacturers. To assess manufacturing accuracy, eight devices were selected for measurement using a laser micrometer. The external diameters of three specimens of each device were measured at centimeter intervals along the length of the device to ensure uniformity.

A total of 200 labels of interventional radiology equipment were scrutinized. The results demonstrate a wide variation in the metric equivalent of French sizing. Labelled products can vary in diameter across the product range by up to 0.79 mm. The devices selected for measurement with the non-contact laser micrometer demonstrate acceptable manufacturing consistency. The external diameter differed by 0.05 mm on average.

Our results demonstrate wide variation in the interpretation of the French scale by different manufacturers of medical devices. This has the potential to lead to problems using coaxial systems especially when the products are from different manufacturers. It is recommended that standard labelling should be employed by all manufacturers conveying specific details of the equipment. Given the wide variation in the interpretation of the French scale, our opinion is that this scale either needs to be abandoned or be strictly defined and followed.