To the Editor:
The size of needles and catheters is categorized by the “gauge” system. Medical references about the definition of “gauge” are not available. In the early 19th century, Peter Stubs invented the so-called “gauge” system but a definition was not included, and only an arbitrary conversion table for the iron wire existed (1). Recently, the International Organization for Standardization (ISO) published some guidelines for the dimensions of needles and catheters (Tables 1 and 2) (2–4). For the needles, ISO standards for inner and outer diameters (ID and OD) are available, but for the catheters, only OD standards are available. In addition, the needles and catheters of the same gauge appear to have different IDs and ODs. Thus, whenever we want to know the exact ID or OD of needles or catheters, e.g., combined spinal-epidural techniques, spinal needle insertion through an introducer, comparison with French system or guidewire insertion during the retrograde intubation etc., we have to refer to the manufacturer’s catalog or contact the customer representatives. We suggest that ISO should set some guidelines for IDs of catheters because it is ID that mainly determines the amount of flow through the catheter, and that all the standards should be revised to offer less variability in the ID and OD of needles and catheters.
Wonsik Ahn, MD
Jae-Hyon Bahk, MD
Young-Jin Lim, MD
1. Iserson KV. The origins of the gauge system for medical equipment. J Emerg Med 1987; 5: 45–8.
2. ISO 9626: Stainless steel needle tubing for the manufacture of medical devices, 1st ed. Geneva: International Organization for Standardization, 1991: 1–2.
3. ISO 9626: Stainless steel needle tubing for the manufacture of medical devices, Amendment 1. Geneva: International Organization for Standardization, 2001: 1–2.
4. ISO 10555-5: Sterile, single-use intravascular catheters—Part 5: Over-needle peripheral catheters, 1st ed. Geneva: International Organization for Standardization, 1996: 1–3.