Modelling Medical Device Sizes: Encoding Ureteral Access Sheaths in a Product Catalogue

#healthtech #database #ecommerce #datamodeling

If you build catalogue, ERP or e-commerce systems for medical device companies, you will meet products whose "size" is not one number. Ureteral access sheaths are a good example.

Two diameters and a length

A sheath is labelled like 12/14 Fr, 45 cm:

12 Fr: inner diameter (the working channel for a scope)
14 Fr: outer diameter (what sits in the patient)
45 cm: working length

French units convert simply: mm = Fr / 3. So 12/14 Fr is roughly 4.0 / 4.7 mm.

A simple data model

Storing the size as a single string makes filtering painful. Split it into fields instead:

{
  "product_type": "ureteral_access_sheath",
  "inner_fr": 12,
  "outer_fr": 14,
  "length_cm": 45,
  "coating": "hydrophilic",
  "sterile": true,
  "single_use": true
}

Now the UI can offer filters such as "inner diameter at least 11 Fr" or "length 35 to 46 cm", and you can validate that outer_fr > inner_fr on import.

Compatibility rules

Real buyers search by the instrument they own. A useful rule is: show sheaths where inner_fr is greater than the scope's outer diameter, so there is space for fluid to drain. Store scope diameters in a separate table and join on that rule rather than hard-coding pairs.

Labels and SKUs

Generate the SKU and the pack label from the fields, not by hand, for example UAS-12-14-45. This keeps printed labels, barcodes and the website in sync and avoids the classic error of a 35 cm product shipped in a 45 cm box.

Import validation

Supplier price lists rarely follow one format. Some write 12/14Fr, others 12-14 F or Fr 12/14. A small parser with a regex such as (\d+(?:\.\d)?)\s*[/-]\s*(\d+(?:\.\d)?) handles most variants. Reject rows where the outer value is not larger than the inner one, and flag lengths outside a sensible range, for example 15 to 70 cm, for manual review instead of importing them silently.

Search and SEO

Buyers search with phrases like "12/14 access sheath 45 cm". Generate product titles from the fields in one consistent pattern, and include both the Fr value and the millimetre conversion in the description. Structured data with additionalProperty for each dimension also helps search engines understand the product.

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