A cannula (; Latin meaning 'little reed'; plural or ) is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the inner or outer surfaces of a trocar needle thus extending the effective needle length by at least half the length of the original needle. Its size mainly ranges from 14 to 24 gauge. Different-sized cannula have different colours as coded. Decannulation is the permanent removal of a cannula (extubation), especially of a tracheostomy cannula, once a physician determines it is no longer needed for breathing. Medicine Cannulas normally come with a trocar inside. The trocar is a needle, which punctures the body in order to get into the intended space. Many types of cannulas exist: Intravenous cannulas are the most common in hospital use. A variety of cannulas are used to establish cardiopulmonary bypass in cardiac surgery. A 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. Insertion of the venous cannula is a painful procedure that can lead to anxiety and stress. Use of a vapocoolant (cold spray) immediately before cannulation reduces pain during the procedure, without increasing the difficulty of cannulation. 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. The 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. It can cause