Blood Gas Analysis Flashcards
what value is considered hypoxemic
PaO2 < 80 mmHg
what value is considered severely hypoxemic
PaO2 < 60 mmHg
what are the causes of hypoxemia
- low PaO2 (low PIO2 or hypoventilation)
- decreased gas exchange (increased venous admixture from V/Q mismatch, R to L shunt, diffusion defects)
are mucus membranes a good indicator of oxygenation
NO - does not turn cyanotic until PaO2 = 40 mmHg or less (severe hypoxemia)
can have PaO2 = 40-80 and still have pink mucus membranes
how does PCV affect cyanosis
anemia: decreases the PaO2 at which the animal becomes cyanotic (PaO2 < 40 mmHg)
polycythemia: increases the PaO2 at which the animal becomes cyanotic (PaO2 > 40 mmHg)
what is the most accurate measure of oxygenation
PaO2
what are two methods you can use to determine the cause of hypoxemia on a patient breathing room air
A-a gradient
120 rule
what are two methods you can use to determine the cause of hypoxemia on a patient breathing supplemental O2
5x rule
P/F ratio
can venous samples be used to assess oxygenation
NO
A-a gradient
PAO2 - PaO2
PAO2: calculate from alveolar gas equation
PaO2: measured on arterial blood gas
normal A-a gradient
< 15 mmHg
cause of hypoxemia with a normal A-a gradient
low PaO2:
1. hypoventilation - assess PaCO2 on blood gas
2. low PIO2 - unlikely on room air
cause of hypoxemia with an increased A-a gradient
increased venous admixture
1. V/Q mismatch
2. R to L shunt
3. Diffusion defect
120 rule
PaO2 + PaCO2
if > 120 mmHg: normal A-a gradient
if < 120 mmHg: increased venous admixture
5x rule
expected PaO2 = 5 x FIO2% of supplemental O2
If on 100% O2 –> expect PaO2 = 500 mmHg
If PaO2 < 500 mmHg –> indicates decreased lung function
