Cannula

Cannula, a tube used for evacuating fluids in certain surgical operations. It is commonly associated with a trochar, that is, a perforating instrument, closely fitting the cannula and admitting of withdrawal from it when the puncture has been made. By means of a trochar and a cannula ascitic fluid is drawn off from the peritoneal cavity, hydrocele sacs are tapped and the fluid contents of cysts are evacuated; sometimes the cannula is connected with an aspirating apparatus, as in the removal of fluid from the pleural cavity. The tracheotomy cannula is a tube of suitable shape inserted into the trachea to procure ready access of air to the lungs in cases of laryngeal obstruction.