A patient suspected of being hypoxemic can be quickly evaluated and the likely cause surmised.
Questions:
(1) Is the pO2 < 80 mm Hg?
(2) Is the Alveolar-arterial oxygen difference (AaDO2) increased?
(3) Is the pCO2 increased?
(4) Does oxygen therapy correct the problem?
If the pO2 is >= 80 mm Hg, adequate oxygenation is present.
If the pO2 is < 80 mm Hg and the alveolar-arterial oxygen difference is not increased, then hypoventilation (increased pCO2) or low inspired oxygen concentration (normal or low pCO2) is suspected.
|
Age in Years |
Upper Limit of Normal AaDO2 in mm Hg |
|
< 40 |
10 |
|
40-50 |
15 |
|
50-59 |
20 |
|
60-69 |
25 |
|
>= 70 |
30 |
If the pO2 is < 80 mm Hg, the alveolar-arterial oxygen difference is increased and oxygen therapy does not correct the problem, suspect shunt (normal pCO2) or impaired diffusion (increased pCO2).
If the pO2 is < 80 mm Hg, the alveolar-arterial oxygen difference is increased and oxygen therapy does correct the problem, suspect ventilation-to-perfusion mismatch.
|
Pathophysiologic Process |
Alveolar-Arterial Oxygen Difference |
Response to Oxygen Therapy |
|
hypoventilation or low inspired oxygen concentration |
normal |
increased pO2 |
|
ventilation-to-perfusion mismatch |
increased |
increased pO2 |
|
right-to-left shunt or impaired diffusion |
increased |
no or minimal increase in pO2 |
Purpose: To evaluate a patient with hypoxemia .
Specialty: Pulmonology
Objective: other testing, criteria for diagnosis
ICD-10: J96.9,
