CaO2

Question 1

What is the alveolar oxygen equation?

Ie. P_AO^₂

Answer 1

(F_iO₂ x [P_atm – P_H2O]) - (P_aCO₂/R)

Question 2

What is the PAO2 when:

F_iO₂ = 1

= 0.6

=0.5

=0.21

Answer 2

600 mmHg

378

300

100

Question 3

What is the shorcut way of calculating P_AO₂?

Answer 3

(F_iO₂ * 5) * 100

Question 4

On RA (room air), what is the equation for determining A-a gradient?

Answer 4

<= 4 + age/4

Question 5

What information does the A-a gradient provide?

Answer 5

The A-a gradient allows us to assess the efficiency of gas exchange at the alveolar – capillary membrane.

Question 6

What is a shunt?

Answer 6

Lung is perfused by not being ventilated.

Question 7

What accounts for the normal A-a difference?

Answer 7

Thebesian, bronchial, and pleural veins bypass the lungs.

Question 8

What is the ideal ratio for V/Q?

Answer 8

Ideally the ratio is 1.

When the ratio varies much from 1, hypoxemia can result.

Question 9

What is the definition of a dead space lung?

Answer 9

= ventilation > perfusion

Question 10

What is the definition of a shunt lung?

Answer 10

= perfusion > ventilation

Question 11

Shunt or deadspace?

Atelectasis?
Lateral positioning?
Right Mainstem intubation?
Bronchospasm?
Low cardiac output/hypotension?

Answer 11

Shunt

Shunt

Shunt

Shunt

Deadspace

Question 12

Why would the A-a gradient be abnormal?

Answer 12

Diffusion abnormality from diseased lungs for example.

There is inefficient O2 exhange between the alveoli and the bloodstream.

Question 13

What is HPV?

Answer 13

Hypoxic Pulmonary Vasoconstriction

The area is not being ventilation, but is being perfused. It takes about 10 minutes to redirect blood flow away from hypoxic areas.

Question 14

As the FiO2 gets higher, the 4+ age/4 equation no longer holds true. The normal A-a gradient must also increase. True or false?

Answer 14

True

Question 15

Ratio of PaO2/FiO2 should be 300 – 500. True or false?

Answer 15

True

Note: A value of < 250 indicates a clinically significant gas exchange problem.

Question 16

What does C_aO₂ comprise of?

Answer 16

O2 content can be thought of as the sum of the two means of oxygen transport in the blood:

O2 carried on Hemoglobin (contributes most to CaO2) and O2 carried dissolved in the blood (PaO2).

Question 17

What is the C_aO₂ equation?

Units = (mL O2/dL)

Answer 17

Hgb (1.34 mL O₂/g Hgb) * % sat + .003 (P_aO₂)

Note: .003 is coeff. of blood solubility.

Question 18

PaO2 contributes little to oxygen in C_aO₂ calculation. It is mainly used for assessing pulmonary gas exchange. True or false?

Answer 18

True

Question 19

Once oxygen molecules chemically bind to hemoglobin they no longer exert any pressure. True or false?

Answer 19

True

Question 20

What is D_AO₂ (dissociation) formula?

Answer 20

C_aO₂ * cardiac output

Question 21

What can right shift the Hb dissociation curve? (2)

Answer 21

pH

temperature