Pulmonology
Alveolar Gas Equation (PAO₂)
Calculates the ideal partial pressure of oxygen in the alveoli.
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Parameters
Alveolar Gas Equation (PAO₂) Result
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Formula
PAO₂ = (Patm - 47) × FiO₂ - (PaCO₂ / 0.8)Clinical Pearls
Fundamental for differentiating causes of hypoxemia. If a patient is hypoxemic but the A-a gradient is normal, the cause is either hypoventilation or high altitude.
Limitations
Assumes a constant Respiratory Quotient (RQ) of 0.8, which may vary depending on the patient's diet and metabolic state. Assumes normal body temperature (PH2O = 47).