Blow By at 10 L/min delivers how much oxygen?

• A. More than 50% O2
• B. About 40% O2
• C. 100% O2
• D. Less than 30% O2

Answer: (D)

Blow-by delivers oxygen by streaming it near the face, but there’s no seal to keep the gas from mixing with room air. Because the oxygen quickly mixes with surrounding air before it can be inhaled, the amount that actually reaches the lungs is fairly low. Even with a relatively high flow like 10 L/min, most of the gas escapes and dilutes, so the inspired oxygen fraction stays well below higher percentages. That’s why a blow-by setup at this flow typically provides less than 30% oxygen. If you need a higher, more reliable oxygen concentration, a properly sealed delivery method (like a nasal cannula at an appropriate flow or a mask) is used.