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16 Cards in this Set
- Front
- Back
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1.How is the A-a gradient formed?
What blood has the highest PaO2? What blood has a lower PaO2? |
Shunted blood creates a difference between PAO2 and PaO2
(Alveolar - arterial) Blood in the end pulmonary capillary veins (alveolar veins) Blood in the peripheral arteries |
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2. Why does blood in the peripheral arteries have a lower PaO2?
Where is blood shunted? What is this "shunted blood" termed? |
Blood PaO2 has become diluted w/ blood which has undergone incomplete or no gas exchange
Shunted around the gas exchange portions of the lungs Termed "venous admixture" |
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3. What three sources does venous admixture arise from?
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1. Intrapulmonary shunts
2. Alveoli w/ impaired diffusion **alveolar-capillary block 3. Anatomical shunts -include thesbian vessels and blood from bronchial veins |
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4. Where would intrapulmonary shunts be?
What could intrapulmonary shunts be due to? |
In areas of lung w/ abnormal V/Q ratios
Lung pathologies that include large lung areas w/ low V/Q ratio |
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5. In lungs w/ no pathology what are the principle sources of shunted blood due to anatomy?
What else can anatomical shungs be due to? |
Thebesian vessels and bronchial vessels
Congenital abnormalities 1. Pulmonary arterial-venous fistulae 2. Incomplete fetal development -patent ductus arteriosis -paten foramen ovale |
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6. What does adding blood which has been poorly ventilated or not ventilated at all to ventilated blood due?
(two things) Bottom line how doe PaO2 and PAO2 compare? How does blood ejected from aorta compare to the alveoli? |
1. Creates the A-a gradient
2. Changes the PaO2 PaO2 of pulmonary venous blood is less than PAO2 Blood ejected from aorta has a lower O2 tension than the alveoli **creates the A-a gradient |
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7. What does the size of the A-a gradient depend upon?
(two things) How is venous admixture normally? What is the A-a gradient as a result? In pathologies how can venous admixture and thus A-a gradients be? |
Volume and origin of venous admixture
Normally is 2% of the CO A-a O2 gradient of 4-10 mm Hg Venous admixture may be 40% to 50% of CO resulting in A-a gradient of 70 mm Hg |
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8. How does venous admixture PaCO2 compare to the alveoli?
Why is venous admixture near the mean alveolar PACO2? |
It is higher but is near the mean alveolar PACO2
1. CO2 is readily diffusable 2. Volume of venous admixture is usually small 3. CO2 dissociation curve is linear and steep 4. Alveoli w/ high V/Q ratios can compensate for avleoli w/ low V/Q ratios |
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9. What happens to PaCO2 if a gradient does develop for CO2?
Does this affect O2 content? |
PaCO2 is lowered to normal levels by compenstoary mechanisms
Does not increase O2 content |
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10. What are the results of a significant A-a gradient?
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1. PaCO2 is nearly normal
2. PaO2 is not |
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11. What does the shunt equation assume?
What is the Qs/Qt ratio? What is a normal Qs/Qt ratio? |
Assumes any shunt is an absolute shunt
Shunt blood flow to total blood flow 2-3% is normal |
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12. When is the A-a gradient not increased?
When is the A-a gradient widened? (during three things) |
During hypoventilation or at high altitude
1. Diffusion defects 2. V/Q defects 3. Right to left shunts |
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13. What is beneficial in patients w/ diffusion or V/Q pathologies?
Is this beneficial in patients w/ intrapulmonary shunts? Is this beneficial in patients w/ right to left shunts? |
Supplemental O2
Is somewhat beneficial in patients w/ intrapulmonary shunts Not beneficial in patients w/ right to left shunts |
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14. In patients w/ right to left shunts what happens to patients breathing 100% O2?
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Size of A-a gradient can become huge
***"shunted" blood has no chance of ever being aerated |
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15. What happens to PO2 from the alveoli to the venous return?
How is the efficiency by which the respiratory apparatus can successfully ventilate the venous return measured? |
Progressive fall in PO2
Magnitude of the changes of the arterial blood gasses **measuring efficiency of output **one analogy is that of filter |
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16. What does arterial PaO2 and PaCO2 result from?
Four things... |
1. Ventilation
2. Diffusion 3. V/Q matching 4. Shunting |
