Cannulas are very important in clinical settings. A cannula is a small plastic tube that can be inserted into the vein to supply fluids, medication, directly to the bloodstream. It is also used to collect blood sample from the body. Different types of cannula are available for different purposes. Three main vein positions are used for cannulation: Metacarpal, Cephalic, and Basilic.
There are many types of cannula such as nasal cannula that runs under the nose to deliver oxygen. There is also arterial cannula used mainly on the radial artery. It is used in critical conditions to draw blood, and also measures blood pressure.
For the purpose of this post, we will discuss only the different types of intravenous cannula.
Different Types of Cannula sizes
There are different types of cannula sizes in a clinical setting. They have different colors, sizes, and importantly different uses. It is good to note that the bigger the cannula size, the smaller the number.
For instance, a cannula size of 16G is larger in diameter than a cannula of the size of 22G and will have faster flow. The “G” in cannula size stands for “Birmingham gauge” This gauge is used to show the thickness, or diameter of different hypodermic needles. In this post, we will explain all the different types of the cannula by sizes, colours, and estimated flow rate of 1L/hour.
Cannula size 14G
The cannula colour is Orange. It has a flow rate of 10.3l/hr for blood (240ml/minute), 16.2l/hr for plasma, and 13.5l/hr for crystalloids. The size is 45 mm.
Uses Emergency blood transfusion, fluid replacement, surgeries, and trauma cases.
Cannula Size 16G
The 16G cannula size is Grey in colour. It has a flow rate of 7.1L/hr for blood (180ml/minute), 10.8l/hr for plasma, and 9.4l/hr for crystalloids such as 0.9% normal saline, 5% dextrose water, etc.
Uses: It is mostly used in emergency blood transfusion, intravenous fluid replacement, surgeries where rapid results are needed. The uses are similar to the 14G.
Cannula size 18G
This cannula size is Green in colour. The flow rate is 2.7l/hr for blood (90ml/minute), 4.8l/hr for plasma, and 4.1l/hr for crystalloids. It has a size of 32 mm.
Uses: It is used for blood transfusions, fluid replacement, large fluid volume, trauma cases, parenteral nutrition, and stem cell harvesting, major surgeries.
Cannula size 20G
20G cannula comes in Pink colour. It has a length of 32 mm, and a flow rate of 1.9l/hr for blood (60ml/minute), 3.2l/hr for plasma, and 2.9l/hr for crystalloids.
Uses: For transfusion of blood and intravenous fluids. It is the most commonly used cannula in clinical settings.
Cannula size 22G
The cannula is Blue in colour. It has a length of 25 mm, and a flow rate of 1.1l/hr for blood (36ml/minute), 1.9l/hr for plasma, and 1.7l/hr for crystalloid fluids.
Uses: Used in most paediatric cases, and for smaller veins for transfusion of fluids, blood. Also used in the elderly and oncology patients.
Cannula size 24G
The colour of the cannula is Yellow. It has a length of 19 mm and a flow rate of 20ml/min
Uses: Used mostly in neonates, and also children.
Important Considerations while using the cannula
It is necessary to note that cannulation can be painful. It is important to reduce the anxiety and fear in the patient. Use cold spray to reduce the pain. An expert handling is needed to avoid complications from cannulation such as extravasation (cannula entering the tissue instead of vein causing swelling), embolism, haematoma, thrombophlebitis, and artery puncturing.
To avoid infection, the small cap on the outside of the cannula should always remain closed. Use the tourniquet about 5-10 cm above the cannulation site to help you select the right vein. The cannula should always be washed with normal saline before and after administration of injection. It is recommended that the cannula should be changed after every 72 hours.
Wash your hands, and sanitize your skin with alcohol based solution. When your skin is dry, make sure you use your disposable hand gloves. The patient skin must be wiped with a 2% chlorhexidine, and 70% alcohol solution.
For more in-depth knowledge on cannulation, watch this video.