If reservoir bag is not kept inflated during use, what risk increases?

• A. Hypoxemia occurs
• B. Ventilator dyssynchrony
• C. Rebreathing CO2 occurs
• D. Mask becomes discolored

Answer: (C)

When using a reservoir bag with an oxygen delivery mask, keeping the bag inflated ensures a pocket of high-concentration oxygen is available for each inhalation and prevents inhaling exhaled air. If the bag is not kept inflated, the patient may draw in air that contains CO2 from previous breaths, leading to rebreathing of CO2. This raises the CO2 level in the blood (hypercapnia) and can worsen ventilation or cause respiratory acidosis, especially in patients with limited ventilatory reserve. While a deflated bag can also reduce the amount of fresh oxygen reaching the patient, the immediate and defining risk here is rebreathing CO2. Ventilator dyssynchrony is related to mechanical ventilation timing, and mask discoloration has no clinical significance.