Which of the following needle gauges has the largest lumen?

The needle gauge system is a standard used to classify the size of needles. This system operates inversely; smaller gauge numbers indicate larger needle diameters. Therefore, a 16-gauge needle has the largest lumen among the options provided. A larger lumen allows for a greater flow of fluids, which is particularly beneficial for tasks such as drawing blood or administering large volumes of medications quickly.

The other gauges offered—18, 19, and 20—are progressively smaller in diameter compared to a 16-gauge, leading to narrower lumens. Each gauge serves specific purposes where a larger lumen may not be necessary, such as for smaller volume injections or providing a more controlled flow in certain situations. Thus, the 16-gauge needle is the appropriate choice for situations requiring maximal flow capacity.