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Apex 1 - 2 Respiratory II: Physiology (24) > A-a Gradient > Flashcards

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1

The difference between alveolar oxygen (PAO2) and arterial oxygen (PaO2) is called:

A-a gradient

 

2

By relating partial pressure of oxygen inside the alveolus to the partial pressure of oxygen in the arterial circulation, it helps us diagnose the cause of: 

Hypoxemia

3

By relating partial pressure of oxygen inside the alveolus to the partial pressure of oxygen in the arterial circulation, it helps us diagnose the cause of hypoxemia by indicating the amount of

Venous admixture

4

When breathing room air, the normal A-a difference is

less than 15 mmHg

5

When breathing room air, the normal A-a difference is less than 15 mmHg. Why is this?

Some deoxygenated blood is delivered to the left heart

6

Which veins bypass the alveolar-capillary interface and deliver deoxygenated blood to the left heart, causing a normal A-a difference of less than 15 mmHg when breathing room air?

Thebesian, Bronchiolar, and Pleural veins

7

When breathing room air, the normal A-a difference is less than 15 mmHg. Why is this? The Thebesian, bronchiolar, and pleural veins bypass the alveolar-capillary interface and deliver deoxygenated blood to the left heart. This accounts for:

A. a very small anatomic Dead space

B. a very small physiologic Shunt

B. a very small physiologic Shunt

8

Let's compare 2 hypothetical patients: one that has normal lungs and another that has V/Q mismatch.

The healthy patient breathing room air has a PAO2 of 105 mmHg, PaO2 of 95 mmHg, and an A-a difference of:

10 mmHg

(105 -95 = 10)

9

Let's compare 2 hypothetical patients: one that has normal lungs and another that has V/Q mismatch.

The patient with V/Q mismatch has a PAO2 of 313 mmHg, PaO2 of 95 mmHg, and an A-a difference of:

218 mmHg

(313 - 95 = 218)

10

Let's compare 2 hypothetical patients: one that has normal lungs and another that has V/Q mismatch.

The patient with V/Q mismatch has a PAO2 of 313 mmHg, PaO2 of 95 mmHg, and an A-a difference of 218 mmHg.

This wide variation between PAO2 and PaO2 implies a significant degree of which physiologic abnormalities?

Shunt

V/ Q mismatch

Diffusion defect across the alveolar-capillary membrane

11

The A-a gradient is increased by:

Aging,

Vasodilators,

Right-to-left shunt,

Diffusion limitation

12

Why is the A-a gradient increased with aging?

Increased Closing capacity relative to FRC

13

How is the A-a gradient increased by vasodilators?

Decreased hypoxic pulmonary vasoconstriction

14

Which Right-to-left shunts increase the A-a gradient?

Atelectasis

Pneumonia

Bronchial intubation

Intracardiac defect

15

Which Diffusion limitation increases the A-a gradient?

Alveolo-capillary thickening

(hinders O2 diffusion)

16

In the context of Normal A-a Gradient, what are possible causes of Hypoxemia?

Reduced FiO2

Hypoventilation

17

Explanation of Reduced Fi02

Not enough 02 in inspired gas

18

Can Reduced Fi0 2  be Fixed With Supplemental Oxygen?

Yes

19

Hypoventilation can be described as:

Inadequate air transfer in and out of lungs

20

Can Hypoventilation be Fixed With Supplemental Oxygen?

Yes

21

In the context of Increased A-a Gradient, Hypoxemia can be caused by:

Diffusion Limitation

V/Q Mismatch

Shunt

22

Diffusion Limitation can be described as:

Capillary thickening that hinders 02 diffusion

23

Can Diffusion Limitation be Fixed With Supplemental Oxygen?

Yes

24

V/Q Mismatch can be described as:

Poor matching of V and Q

25

Can V/Q Mismatch be Fixed With Supplemental Oxygen?

Yes

26

Shunt can be described as:

Pulmonary blood bypassing alveoli

27

In the context of Normal and increased A-a gradient, what is the only cause of hypoxemia that CANNOT be Fixed With Supplemental Oxygen?

Shunt

28

Why can't we fix shunt with supplemental oxygen?

No way for 02 to access the pulmonary capillary

All of the other causes allow 02 to transfer between the alveolus and the pulmonary capillary.

29

How is the A-a gradient calculated?

A-a  Gradient   PA02  - Pa02

30

What's the relationship between the A-a gradient and the Estimation of % Shunt?

Shunt increases by 1%

for every 20 mmHg of A-a gradient