A cannula (from Latin "little reed"; plural cannulae) or canula is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of data. In simple terms, a cannula can surround the inner or outer surfaces of a trocar needle thus extending needle approach to a vein by half or more of the length of the introducer.
Intravenous cannulae are the most common in hospital use. A variety of cannulae are used to establish cardiopulmonary bypass in cardiac surgery. Nasal cannula is a piece of plastic tubing that runs under the nose and is used to administer oxygen.
Intravenous (IV) cannulation 
A venous cannula is inserted into a vein, primarily for the administration of intravenous fluids, for obtaining blood samples and for administering medicines. An arterial cannula is inserted into an artery, commonly the radial artery, and is used during major operations and in critical care areas to measure beat-to-beat blood pressure and to draw repeated blood samples.
Complications may arise in the vein as a result of the cannulation procedure, the four main groups of complication are:
- hematoma: a collection of blood, which can result from failure to puncture the vein when the cannula is inserted or when the cannula is removed. Selection of an appropriate vein and gently applying pressure slightly above the insertion point on removal of the cannula may prevent this.
- infiltration: when infusate enters the subcutaneous tissue instead of the vein. To prevent this, a cannula with accurate trim distances may be used. It is essential to fix the cannula in place firmly.
- embolism: this can be caused by air, a thrombus, or fragment of a catheter breaking off and entering the venous system. Possibly even causing a Pulmonary Embolism. Air emboli can be avoided by making sure that there is no air in the system. A thromboembolism can be avoided by using a smaller cannula.
- phlebitis: an inflammation of the vein resulting from mechanical or chemical irritation or from an infection. Phlebitis can be avoided by carefully choosing the site for cannulation and by checking the type of infusate used.
Nasal cannulation and oral-nasal cannulation 
A nasal cannula or an oral–nasal cannula consists of a flexible tube, usually with multiple short, open-ended branches for comfortable insertion into the nostrils and/or mouth, and may be used for the delivery of a gas (such as pure oxygen), a gas mixture (as, for example, during anesthesia), or to measure airflow into and out of the nose and/or mouth.
Tracheotomy tube 
The removal of a tracheotomy tube is referred to as decannulation.
Veterinary use 
A cannula is also used in an emergency procedure to relieve pressure and bloating in cattle and sheep due most commonly to their accidentally grazing wilted legume or legume-dominant pastures, particularly alfalfa, ladino, and red and white clover.
They are also a component used in the insertion of the Verichip.
Aesthetic Medicine & Anti-ageing 
In Aesthetic medicine, a Blunt-tip microcannula (also called smooth tip microcannula, Blunt tipped cannula or simply blunt needle) is a small tube, with an edge that is not sharp, designed for atraumatic intradermal injections of fluids. Depending on the size of the inter diameter, it can be used either for fat transfer, or for the injection of fillers, like Hyaluronic Acid, Collagen, poly-L-lactic acid, CaHA, etc. The advantage of using these cannulas is that they are less painful, have less risk of bruising, and have a better safety profile. An intravascular injection is near impossible with the cannulas making the risk of blindness when injecting around the eye much safer. Skin necrosis risk is also lowered. 
As of January 2012, the Dermasculpt microcannula is the sole blunt-tipped, flexible cannula approved by the FDA for use in the United States for use with soft tissue fillers.
Body piercing 
Cannulae are used in body piercing when using a standard IV needle (usually between 18GA and 12GA, although may be as large as 0GA, in which case the procedure is known as dermal punching and uses a biopsy punch without a cannula), and for inserting hooks for suspensions.
During piercing, the fistula is created by inserting the needle. The needle is then removed, leaving the cannula in place, which is sometimes trimmed down. The cannula is then removed and sterile jewelry is inserted into the fistula simultaneously, in order to minimise trauma to the fresh fistula caused by insertion of blunt-ended jewelry.
Non-medical use 
In biological research, a push-pull cannula, which both withdraws and injects fluid, can be used to determine the effect of a certain chemical on a specific cell. The push part of the cannula is filled with a physiological solution plus the chemical of interest and is then injected slowly into the local cellular environment of a cell. The pull cannula then draws liquid from the extracellular medium, thus measuring the cellular response to the chemical of interest. This technique is especially used for neuroscience.
In general aviation, a cannula refers to a piece of plastic tubing that runs under the nose and is used to administer oxygen in non-pressurized aircraft flying above 10,000 feet above sea level in Canada and above 12,500 feet above sea level in the United States.
In synthetic chemistry, a cannula refers to a piece of stainless steel or plastic tubing used to transfer liquids or gases from one vessel to another without exposure to air. See more at Cannula transfer.
See also 
- Children with Tracheostomies Resource Guide, by Marilyn K. Kertoy, page 15 (Google book search)
- Dorland's Illustrated Medical Dictionary
- Vita Needle - Typical Cannula Points
- Morris, Linda; Sherif Afifi, M. Sherif Afifi (2010-02-19). Tracheostomies: The Complete Guide. Springer Publishing Company. p. 311. ISBN 978-0-8261-0517-2.
- Diseases of the Ruminant Forestomach : Bloat, Merck Veterinary Manual
- http://jddonline.com/articles/dermatology/1696Use of Blunt Tipped Cannulas for Soft Tissue Fillers. Journal of Drugs in Dermatology. 2012-01-15. p. 70.