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alveolar-arteriolar (Aa) oxygen gradient

Normal range: 1) FiO2 of 21%: 5-25 mm Hg 2) FiO2 of 100%: < 150 mm Hg Interpretation: Calculated: [FiO2 [(0.2* x barometric pressure - PH2O*) - PaCO2#)] - PaO2 * fraction of O2 in air & water vapor pressure, respectively # alveolar pressure of CO2 (generally 40-45 mm Hg) For room air FiO2 (0.2 x barometric pressure - PH2O) generally assumed to be 150. Thus Aa gradient (room air): 150 - PaCO2 - PaO2 In the elderly, paO2 is generally less than that in younger patients. (see paO2) Increases: - hypoxemia - excluding hypoventilation

General

general chemistry test

References

  1. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 578
  2. Current Pocket Reference 1997 Pharmacopoeia & Medical Notes, Shepherd/Whalen Specialty Cards, Norman OK, 1997