Wed3November0919PM 19

Tubes used for vascular access and drainage of body cavities are available in a range of sizes.

Which one of the following measurements is used when selecting an intravenous or intra-arterial cannula?

(Please select 1 option)

Internal diameter (mm)

Standard wire gauge (SWG) Correct

French gauge (mm)

External circumference (mm)

Cross sectional area (mm2)

Explanation

Intravenous and intra-arterial cannulae are available in standard wire gauge (SWG or G). SWG is an old imperial unit (which requires metric conversion). Cross sectional area is now a more popular size measurement for wires.

SWG refers to the number of wires that will fit into a standard hole template;

22 thin wires will fit side-by-side into this standard sized hole (each wire the diameter of a 22 gauge cannula)

14 thicker wires would fit into the same hole (each wire the diameter of a 14 gauge cannula)

Whilst diameter and therefore radius of a parallel sided tube is the most important determinant of the rate flow of a fluid it is not routinely used to compare the size of cannulae.

French gauge (FG) catheters (urinary or chest drain) are measured in terms of circumference. Double lumen tracheal tube sizes are FG. Single lumen tubes are measured according to internal diameter.

Answer Statistics

1

7%

2

50%

3

41%

4

1%

5

4%

Times answered: 251