Ideal Alveolar Oxygen Tension

\[P_{AO_2}=F_{IO_2}\left(P_{atm}-P_{H_2O}\right)\]

Variables

PAO2ideal alveolar oxygen partial pressure (mmHg)

FiO2fraction of inspired oxygen

Patmatmospheric pressure (mmHg)

PH2Owater vapor pressure (mmHg)

Description

What is this formula?

The Ideal Alveolar Oxygen Tension formula estimates the maximum theoretical oxygen partial pressure available in humidified inspired gas before accounting for carbon dioxide exchange.

When to use it

Use this formula when studying inspired gas humidification, oxygen delivery, altitude physiology, or the simplified upper limit of alveolar oxygen tension.

Example

Data:

FiO2 = 0.21

Patm = 760 mmHg

PH2O = 47 mmHg

Formula:

PAO2 = FiO2(Patm − PH2O)

Substitution:

PAO2 = 0.21(760 − 47)

PAO2 = 0.21(713)

PAO2 = 149.7 mmHg

Result:

PAO2 ≈ 150 mmHg

Applications

- Respiratory physiology

- Inspired oxygen calculations

- Altitude medicine

- Oxygen therapy education

- Pulmonary gas exchange analysis

Note

This formula is a simplified theoretical estimate. It does not include the effect of alveolar carbon dioxide, so it gives a higher value than the full Alveolar Gas Equation under normal physiological conditions.