Cannula

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A cannula (plural cannulae) is a flexible tube which when inserted into the body is used either to withdraw fluid or insert medication. Cannulae normally come with a trocar (a sharp pointed needle) attached which allows puncture of the body to get into the intended space. Intravenous cannulae are the most common in hospital 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 a hospital setting, a nasal cannula is a piece of plastic tubing which runs under the nose and is used to administer oxygen.

It is also used in laboratory chemistry to transfer a liquid between flasks without exposing it to the atmosphere.

In general aviation, a cannula refers to a piece of plastic tubing which 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.

A cannula is also used in an emergency procedure to relieve pressure and bloating in cattle due most commonly to their accidentally grazing wilted legume or legume-dominant pastures, particularly alfalfa, ladino, and red and white clover [1].

Cannulae are sometimes used in body piercing and for inserting hooks for suspensions.

They are also a component used in the insertion of the Verichip.

Complications may arise in the vein as a result of the cannulation procedure, the 4 main groups of complication are:

• hematoma: a collection of blood. 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 as you remove 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. Such things can go on to lodge in an artery, blocking circulation to the corresponding area. To avoid air embolus, make sure that there is no air in the system. To avoid a thromboembolism use a smaller cannula. Avoid the catheter breaking by never reinserting the needle.
• 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 you use.