Final answer:
An (a) 18 gauge catheter has the largest lumen among the options listed and is suitable for administering larger volumes of IV therapy quickly or infusing viscous fluids.
Step-by-step explanation:
The nurse looking to administer IV therapy and seeking a catheter with the largest lumen should select an 18 gauge catheter. In the context of IV catheter sizes, the lower the gauge number, the larger the diameter of the catheter's lumen. Therefore, among the options provided:
- 18 gauge
- 22 gauge
- 20 gauge
- 21 gauge
18 gauge is the largest, and as such, it is capable of delivering larger volumes of fluid more quickly than the higher-gauged, smaller-lumened catheters. This is crucial in emergency situations where rapid fluid delivery is needed, or for infusing viscous fluids that a smaller gauge catheter could not accommodate as well.