Suctioning is an invasive procedure that should only be performed when necessary and with great precision by a trained healthcare professional.
If the suction catheter is too small, it may not adequately clear secretions in the airways. This may require more passes of the suction catheter, which increases the chances of mechanical trauma to the tracheal mucosa.
A suction catheter that is too large carries its own set of risks. The use of a large suction catheter can lead to hypoxia because of the decreased oxygen supply to the lungs. In some cases, suctioning can lead to atelectasis (partial or complete collapse of the lung).
Large suction catheters also increase the risk of injury due to greater contact with the tracheal and bronchial walls.