Which oxygen delivery device typically lacks an oxygen reservoir?

• A. Nasal cannula.
• B. Venturi mask.
• C. Simple face mask.
• D. Non-rebreather mask.

Answer: (B)

Understanding how oxygen delivery devices provide gas is key: some use a reservoir bag that stores oxygen for inhalation, while others deliver oxygen without a dedicated bag and rely on flow or entrainment to mix with room air.

A Venturi mask is designed to deliver a precise, fixed FiO2 by forcing oxygen through a specific valve that entrains ambient air through side ports. There is no separate reservoir bag attached to this device, so the gas delivered to the patient isn’t stored in a bag before inhalation. This is why it’s described as lacking an oxygen reservoir—the concentration comes from the valve and entrainment, not from a stored supply.

In contrast, a non-rebreather mask uses a reservoir bag to hold high-concentration oxygen for inhalation, which is why it clearly has a reservoir. Nasal cannulas and simple face masks don’t rely on a reservoir for delivering oxygen, but they don’t provide the same kind of fixed, precise FiO2 as the Venturi mask, making the Venturi mask the best match for “lacks an oxygen reservoir” in this context.