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Generally, cannulas are made of plastic or metal. Plastic devices need to be designed in a way that minimizes reflections from telescopes, whether they are transparent or opaque. Metal and plastic are combined to make reusable and disposable trocars. Disposable trocars have a two-edged blade at the tip of their blade, which penetrates the abdominal wall and cuts the tissue as they pass. The sharp tip of most disposable plastic trocars is withdrawn immediately after they pass through the abdominal wall to reduce the chances of visceral injury. There are different sizes and diameters of trocars and cannulas depending on the instrument for which they are used. Cannulas vary in diameter from 3 to 30 mm; the most common sizes are 5 and 10 mm. A metal trocar has different types of tips depending on the surgeon's experience, such as pyramidal tips, eccentric tips, conical tips, and blunt tips.

In cannulas, air seals allow instruments to move in and out without losing the pneumoperitoneum. They can be oblique, transverse, or piston-style.

A trumpet type valve provides excellent seals during instrument passage, but it is not as practical as some of the other valves. These valves can be manually or automatically retractable during instrument passage. This may explain why they are less commonly used in advanced laparoscopic procedures because they require both hands during instrument insertion. Whatever the diameter of the instrument used, the flexible valves will limit carbon dioxide leakage during work.

Sharp trocars, even though they look dangerous, are actually safer than blunt ones because they require less force to enter the abdominal cavity and there is a lower chance of an inadvertent forceful entry of the trocar. A cannula's marked exterior diameter differs from its interior usable diameter. The cannula ends are either straight or oblique. An oblique tip is felt to facilitate the passage of the trocar through the abdominal wall. A trocar and a cannula should be held properly in the hand so that the head of the trocar rests near the eminence, the middle finger rests over the gas outlet, and the index finger rests over the sharp end.

 

Read more: https://www.kangjimd.com/the-use-of-laparoscopic-trocars-and-cannulas-for-laparoscopic-surgery.html