The “Gauge” System for the Medical Use

Abstract

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.Table 1: Dimensions of Medical NeedlesTable 2: Gauge and Corresponding Sizes of Intravascular CathetersWonsik Ahn, MD Jae-Hyon Bahk, MD Young-Jin Lim, MD