A straight multisample needle is typically 1 to 1.5 inches (2.5 to 3.8 cm) in length and the gauge ranges from 20 to 22. Multisample needles are the standard choice for routine venipuncture in a patient with normal, healthy veins.Click to see full answer. In this manner, what size needle is typically used in venipuncture for adults?While the size can vary, most needle sizes are 21 to 23 gauge. If a person uses the smaller-sized needles (such as 25 to 27 gauge), blood is more likely to get destroyed (hemolyze) or clot due to the smaller-sized needle.Likewise, what is the determining factor when selecting the appropriate needle size for your blood draw? Determining Needle Size The first number in front of the letter G indicates the gauge of the needle. The higher this number is, the thinner the needle. The second number indicates the length of the needle in inches. Also Know, what kind of veins are syringes used for? Syringe – syringes are used to collect blood from patients with small or fragile veins. Another tool that can be used in these situations is a butterfly needle.Which is bigger 18 or 20 gauge needle?18 Gauge: This size allows you to do most tasks that the 16 gauge can, but it large and more painful to the patient. 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.