The size of the needle used for a cannula varies depending on the purpose of the cannulation and the patient's vein condition. The needle is actually just used to insert the plastic cannula into the vein, the needle is then immediately withdrawn and disposed of. Different cannula sizes are indicated by different colours.
Here's a breakdown of common cannula sizes and their typical uses, as detailed by the provided reference from Doctor Khalid's website:
| Colour | Size (Gauge) | Use |
|---|---|---|
| Blue | 22G | Suitable for patients with small or fragile veins. |
| Pink | 20G | Commonly used for routine IV fluids and drug administration, as well as blood transfusions. |
| Green | 18G | Used for blood transfusions and administering IV medications or fluids. |
| White | 17G | Used for blood transfusions and administering IV medications or fluids. |
As you can see from the table above:
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Gauge: The gauge is a measure of the needle's diameter. A higher gauge number indicates a smaller needle diameter.
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Needle Function: The needle's purpose is to allow for the insertion of the cannula. Once the cannula is correctly positioned in the vein, the needle is immediately withdrawn and disposed of. The plastic cannula, not the needle, stays in the patient's vein.
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Cannula Use: Different sizes of cannulas are needed depending on the size of the vein, and the use that the cannula is needed for. The smallest gauge cannulas (e.g., 22G) are used for patients with smaller veins where a larger needle could damage the vein. Larger gauge cannulas (e.g., 17G or 18G) may be used when larger quantities of fluid or blood need to be delivered quickly, such as in cases of blood transfusions. The 20G is a commonly used routine cannula.
