How to Insert a Cannula

Preparing to Insert a Cannula

Gather your equipment. Cannulation requires some basic preparation and precaution. You will need to protect yourself from contact with the patient’s body fluids, and protect the patient from injury or infection. To begin the procedure, make sure you have the following materials: Non-sterile gloves Tourniquet Alcohol wipe or antiseptic solution (2% chlorhexidine in 70% isopropyl alcohol) Local anesthetic solution (optional) Syringe with a needle of appropriate gauge Venous access device Transparent dressing Paper tape Sharps container

Choose the correct cannula size for your patient. The larger the gauge of the needle, the higher the maximum flow rate of fluid entering into the vein. This means larger-sized needles have a smaller number, so a 14-gauge is large, while a 22-gauge is small. Choose a size that corresponds to the specific procedure but does not exceed ⅔ the size of the vessel being accessed. The size of the cannula depends on several factors, including the patient’s vein condition and the purpose of the infusion. For routine procedures, a 20 to 22-gauge cannula is often suitable for adults, while a 22 to 24-gauge cannula is suitable for children. A 14 to 16-gauge cannula is typically reserved for emergency situations, such as a rapid blood transfusion.

Explain the procedure to your patient and get informed consent. Before you begin the procedure, you must gain informed consent, which is usually verbal. Perform the following steps in order to build rapport with your patient and create a more comfortable experience: Introduce yourself to your patient. Verify your patient’s identity, including their name and date of birth. Explain the procedure to the patient and answer any questions they may have. Check if your patient has any allergies or sensitivities. If they have a latex allergy, make sure your tourniquet, gloves, and cannula are latex free.

Wash your hands and put on gloves. All medical professionals must follow the proper hygiene practices before coming into contact with a patient. To minimize the risk of your patient getting an infection, wash your hands with soap and water and wear gloves before touching them.

Use proper personal protective equipment. Using gloves will not only protect your patient, but will also protect you from exposure to bodily fluids and potentially infectious material. A single pair of non-sterile gloves will probably be sufficient for this task. Depending on your facility’s requirements, you can also wear an apron or protective eyewear when inserting an IV catheter.

Apply the tourniquet around the patient's arm. In most cases, the patient’s non-dominant arm is preferable. Place the tourniquet about 5 to 10 cm above the cannulation site, then tighten it. Other methods for locating a good vein include: Tapping on the vein to make it dilate. Asking the patient to open and close their fist. Using gravity to highlight the vein by holding the patient’s arm down. Applying mild heat to the site of the vein. If you have a difficult time finding a good vein on the arm you have selected, inspect the opposite arm. In some cases (e.g. if the patient has diabetes or a history of IV drug abuse), you may need to use an ultrasound to help you locate a good vein.

Clean the skin with an alcohol wipe or antiseptic solution. Rub the wipe or solution over the patient’s skin for at least 30 seconds, focusing on the area around the vein that will be used for cannulation. Allow the site to dry completely to prevent the risk of infection and reduce stinging.

Inserting the Needle

Insert the cannula needle at an appropriate angle. The correct angle will depend on the size of the device and the depth of the vein. If you are trying to access a small, superficial vein, use a small catheter (with a gauge of 22-24) and insert at an angle of 10° to 25°. For a deeper vein, use a larger catheter and insert at an angle of 30° to 45°. Make sure you insert the needle bevel up (with its eye facing upwards). This means that the point of the needle is down against the skin.

Advance the cannula until you achieve flashback. Hold the cannula in the front of its wings with your pointer and middle finger and in the back with your thumb. Advance it slowly into the skin until blood enters the base of the cannula. This is called a flashback, and it signals that you have entered a vein. Once flashback occurs, reduce the angle of the needle to avoid puncturing the posterior wall of the vein.

Advance the plastic piece of the cannula. The needle should now be held stationary while the plastic component of the cannula is advanced another 2 to 3 mm into the vein. The goal is to get the plastic sheath into the vein, and keep it there, while the needle is removed. Keep advancing the plastic component of the cannula until the plastic tube is fully inserted. The "hub" of the plastic component will hit the skin when it is all the way in.

Remove the tourniquet and needle, then let blood flow into the cannula. Release the tourniquet from the patient's arm, apply pressure to the vein at the top of the cannula, then remove the needle from the base of the cannula, leaving the plastic component in sight. Allow blood to flow into the base of the cannula to reduce the risk of air going into the vein if something is injected through the cannula (air embolism). Then, cap the cannula or attach test tubes or other supplies.

Recatheterize if your first attempt is unsuccessful. If you do not observe blood in the flashback chamber when you inspect the cannula, withdraw the device until it’s just below skin level and then attempt to recatheterize. Flashback may stop if you've punctured the posterior wall of the vein, or if your patient has hypotension (low blood pressure). If swelling develops at the site, remove the device and release the tourniquet, then apply direct pressure to the site for 5 minutes Do not remove the needle from the skin entirely and then reinsert it. This could result in fragmentation of the catheter and embolism in the patient. Instead, throw away the used needle in a sharps container and reattempt using a fresh needle.

Finishing the Procedure

Secure the cannula with an appropriate dressing. Using transparent dressing and tape, or a specialized dressing that comes with the cannula, secure the venous access device to the skin. Attach the cannula to the skin so that it’s comfortable for the patient but stays in place in the vein. Then, place a label over the transparent dressing with the date, time, and any other information required by your facility. You may need to tape attachments to the skin as well, such as a tube leading to another attachment point.

Inspect and clean the cannula. First, pull back on the syringe to withdraw a little blood and confirm that the cannula is still in place inside the vein. Then, flush the cannula with a saline or heparin solution. This will assure that the site is clean and that the cannula is correctly positioned within the vein. To flush the cannula, fill a syringe with 5 mL of saline, inject it into the cannula port, detach the syringe, and then close the port. If you are returning to put an injection into a cannula, flush it with saline solution again. This will assure that the cannula is still in place.

Discard any waste and document the procedure. Dispose of the needle in a sharps container to reduce the risk of a needle stick. Then, document the procedure in the appropriate set of notes. If you’re removing the cannula, place a piece of gauze on the injection site and keep it in place with medical tape or a bandage. This will assure that the patient is not bleeding after the procedure.