The Essential Burn Unit Handbook by Jeffrey J. Roth William B Hughes

Author:Jeffrey J. Roth,William B Hughes
Language: eng
Format: epub
Publisher: Thieme Medical Publishing Inc.
Published: 2017-04-04T04:00:00+00:00

a.

DA-aO2 is 5 to 15 mm Hg in healthy, young patients.

b.

DA-aO2 is increased in all causes of hypoxemia except hypoventilation and high altitude. It increases with age and in patients with lung diseases that cause a V/Q mismatch (i.e., shunt or diffusion abnormality). A patient with a pulmonary embolus has an increased DA-aO2, but if the patient is hyperventilating (as is often the case), the ABG may show a normal PaO2.

c.

PAO2 = Alveolar air pressure of O2. PaO2 = arterial air pressure of O2. PCO2 = Arterial air pressure of CO2. FIO2 = Fractional inspired oxygen.

d.

To determine the DA-aO2, the PaO2 in the alveoli (PAO2) is calculated first. This is the partial pressure of inspired O2 minus the partial pressure of alveolar CO2 (PACO2). The PACO2 = PaCO2/0.8. The 0.8 used in this short formula represents the respiratory quotient (CO2 produced per minute or O2 consumed per minute). The partial pressure of CO2 in the alveoli is slightly lower than in the arterial blood.

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