Why is tube suction catheter size included in the calculation sheet?

• A. To determine appropriate suction catheter size relative to the endotracheal tube
• B. To estimate oxygen consumption
• C. To assess blood glucose
• D. To measure heart rate

Answer: (A)

The main idea is to choose a suction catheter size that fits safely inside the endotracheal tube to allow effective suctioning without compromising the airway or ventilation. When suctioning an intubated patient, the catheter travels through the endotracheal tube, so if it’s too large, it can occupy too much of the lumen, increase airway resistance, impair ventilation during suction, and risk mucosal injury. If it’s too small, suctioning may be ineffective and require repeated passes, with more time the patient may desaturate. Using a calculation sheet helps clinicians standardize this choice, typically recommending a catheter diameter about half the inner diameter of the endotracheal tube (sometimes up to two-thirds depending on protocol). For example, a 4.0 mm endotracheal tube would commonly use about a 2.0 mm suction catheter. The other options aren’t related to suction catheter sizing—they pertain to different physiologic measurements (oxygen consumption, blood glucose, heart rate) that aren’t determined by the catheter size used for airway suctioning.