What is iv cannula ideal needle size?

I bet your professor can help you with this one.

I like a 13 when trochanting sheep.

The Importance of Selecting the Right Gauge

The reason it’s important to use the right gauge is because some nursing procedures can only be done with a particular sized needle. For example, if you have a patient who needs to have his or her blood drawn, you’ll want to go with a gauge large enough to do it. Otherwise, you may end up having to re-stick them with the properly sized gauge. This can cause the patient frustration and pain.

Therefore, whenever you start an IV on a patient, you want to ask yourself what type of procedures your patient will be having while in your care. Here are some common uses for the different gauge sizes, generally speaking. (NOTE: Always follow the protocols set forth by your employer or Board of Nursing when selecting gauge size).

16 Gauge: This size is mostly used in the ICU or surgery areas. This large size enables many different procedures to be performed, such as blood administration, rapid fluid administration, and so forth.
18 Gauge: This size allows you to do most tasks that the 16 gauge can, but it large and more painful to the patient. Some of the common uses include administering blood, pushing fluids rapidly, etc. You can use this for CT PE Protocols or other testing that requires large IV sizes.
20 Gauge: You may be able to push blood* through this size if you can’t use an 18 gauge, but always check your employer’s protocol. This size is better for patients with smaller veins.
22 Gauge: This small size is good for when patient’s won’t need an IV long and aren’t critically ill. You usually can’t administer blood* due to it’s small size, however, some hospital protocols allow for 22 G usage if necessary.
24 Gauge: This size is used for pediatrics and is usually only used as a last resort as an IV in the adult population.