What suction catheter size is appropriate for a 4.0 mm ID tracheostomy tube?

• A. 4 Fr
• B. 6 Fr
• C. 8 Fr
• D. 10 Fr

Answer: (B)

Choosing suction catheter size is all about not blocking the airway while still being able to remove secretions effectively. The safer rule is to use a catheter no larger than about two-thirds of the tracheostomy tube’s inner diameter. For a tube with a 4.0 mm ID, two-thirds is roughly 2.7 mm. In practice, that emphasizes using a catheter smaller than that margin to ensure easy passage and to minimize airway obstruction during suctioning.

A 6 French catheter is about 2.0 mm in diameter, which sits well within that safe range and provides a comfortable margin for passage through the tube and around the end of the catheter. It reduces the risk of occluding the lumen or causing trauma during suctioning. While a larger size near the two-thirds limit might technically be acceptable in some measurements, the 6 Fr option is consistently safer and easier to use across measurement variations and clinical setups.

So, the appropriate size is a 6 French suction catheter.