If FiO2 is 0.21 and PB is 760 mmHg, what is PiO2?

Study for the Respiratory Therapy Test. Use flashcards and multiple choice questions, featuring hints and explanations. Prepare for your exam successfully!

Multiple Choice

If FiO2 is 0.21 and PB is 760 mmHg, what is PiO2?

Partial pressure of inspired oxygen comes from how much oxygen is in the air (FiO2) multiplied by how much pressure that air carries (PB). In many practice problems, we use the simple relation PiO2 ≈ FiO2 × PB for dry inspired gas. Here, 0.21 × 760 mmHg equals 159.6 mmHg, so the inspired oxygen pressure is about 159.6 mmHg. Note: if you account for humidity, PiO2 ≈ FiO2 × (PB − PH2O) with PH2O around 47 mmHg at body temperature, which would give roughly 149.7 mmHg. The problem's option aligns with the simpler calculation. The other numbers don’t fit: one uses the wrong unit (cmHg), another would require a different FiO2 factor, and 21 mmHg reflects a much smaller partial pressure not consistent with an FiO2 of 0.21 at 760 mmHg.

Partial pressure of inspired oxygen comes from how much oxygen is in the air (FiO2) multiplied by how much pressure that air carries (PB). In many practice problems, we use the simple relation PiO2 ≈ FiO2 × PB for dry inspired gas. Here, 0.21 × 760 mmHg equals 159.6 mmHg, so the inspired oxygen pressure is about 159.6 mmHg.

Note: if you account for humidity, PiO2 ≈ FiO2 × (PB − PH2O) with PH2O around 47 mmHg at body temperature, which would give roughly 149.7 mmHg. The problem's option aligns with the simpler calculation.

The other numbers don’t fit: one uses the wrong unit (cmHg), another would require a different FiO2 factor, and 21 mmHg reflects a much smaller partial pressure not consistent with an FiO2 of 0.21 at 760 mmHg.

More practice questions