A cannula is a small flexible tube that is inserted into the body, typically into a vein or artery, to administer medications or fluids, withdraw blood, or help maintain an open airway. Cannulas are commonly used in medical settings and are an essential part of many procedures and treatments.
Types of Cannulas
Intravenous Cannula
The most common type of cannula is an intravenous (IV) cannula. An IV cannula is a small, flexible tube that is inserted into a vein using a needle. Once properly placed, the needle is removed leaving just the hollow plastic cannula in the vein. IV cannulas allow nurses and doctors to administer medications, fluids, blood products and perform blood draws through the cannula rather than repeatedly inserting needles into the vein.
There are different sizes of IV cannulas ranging from 22 gauge for smaller veins to 24 gauge for veins that are more fragile. The size and length are chosen based on the intended vein and purpose. IV cannulas can remain in place for hours or even days, allowing for repeated access to the vein without additional needle sticks.
Arterial Cannula
Sometimes known as an arterial line, an arterial cannula is inserted into an artery rather than a vein. They are thinner and more flexible than IV cannulas given the smaller size of arteries. Arterial cannulas are commonly placed in the radial, femoral or dorsalis pedis arteries to monitor blood pressure, obtain blood gas samples and other lab tests. Like IV cannulas, arterial cannulas remain in place to allow repeated access without recurrent needle insertion.
Tracheostomy Cannula
A tracheostomy cannula is a small flexible tube inserted through a surgically created opening in the neck called a tracheostomy. It allows access to the trachea or windpipe to help maintain an open airway. Tracheostomy cannulas come in different sizes based on the patient's age and trachea size. They are secured to the skin around the tracheostomy site to hold them in proper position.
Inserting a Cannula
All cannulas follow the basic principle of insertion through a needle which is then removed, leaving the cannula in place. However, there are some key steps and techniques involved:
Selecting a Proper Site
Proper vein or artery selection is important for successful cannula placement. Visible, palpable veins near the bend of the elbow or the back of the hand are commonly used. The skin around the insertion site must be cleaned and prepped.
Inserting the Needle
Using an aseptic technique, the healthcare provider will insert the needle attached to the cannula at a 10-15 degree angle into the selected vein or artery. For veins, gentle pressure or a tourniquet may help the vein engorge and become more visible near the surface.
Advancing the Cannula
Once blood return is seen in the needle, indicating proper placement in the vessel, the cannula is advanced off the needle until only the tubing portion remains in the vessel. The needle is then withdrawn.
Securing and Dressing
Adhesive dressings, tape or securement devices are used to hold the cannula securely in place and provide a barrier at the insertion site. Dressings are usually changed every few days to watch for signs of infection or complication.
Potential Complications
While generally safe, cannula insertion does carry some risks, especially if not placed properly. Common minor complications include bleeding, bruising, infection and inflammation at the insertion site. More serious risks include accidental arterial puncture, air embolism, nerve damage or collapsed vein. Always following aseptic technique and proper insertion methods can help minimize complications. Patients are also monitored closely for any issues after cannula placement.
Uses and Benefits of Cannulation
Access to Vessels
The main advantage of cannulas is that they provide stable vascular access without needing repeated needle sticks. This makes them essential for administering ongoing IV fluids and medications or drawing repeated blood samples through a single site.
Less Painful than Needles
Once inserted, cannulas cause much less pain than inserting new needles each time access is needed. This improves the patient experience of any procedure or treatment requiring vascular access.
