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1

Imagine a patient that has a PaO2 of 100 mm Hg. How do you know if this is good or bad? The alveolar gas equation provides the context to make this assessment.

What does the alveolar gas equation tell us regarding the alveolus?

Partial pressure of oxygen in the alveolus

2

What's the formula for the alveolar gas equation?

Alveolar oxygen

 Alveolar oxygen

= FiO2 x (Pb - PH2O) - (PaCO2 / RQ)

FiO2 Fraction of inspired oxygen

Pb Barometric pressure

PH20 Humidity of inhaled gas (assumed to be 47 mmHg)

RQ Respiratory quotient (assumed to be 0.8- detailed below)

3

The alveolar gas equation illustrates several very important points. What are two immediate consequences of Hypoventilation?

 

Hypercarbia

an

Hypoxemia

4

True or False

Supplemental oxygen can easily reverse both hypoxemia and hypercarbia

False

Supplemental oxygen can easily reverse hypoxemia, however, it does nothing to reverse hypercarbia

5

True or False

Hypercarbia can go undetected in the patient breathing supplemental oxygen

True

Hypercarbia can go undetected in the patient breathing supplemental oxygen

6

The alveolar gas equation is used to determine which important physiologic value inside the alveolus?

Partial pressure of oxygen

7

The Alveolar Gas Equation tells us the maximal ----- that can be achieved at a given Fi02

PA02

8

The Alveolar Gas Equation tells us the maximal PA02 that can be achieved at a given Fi02. It also gives us a context for evaluating ____

PaO2

9

True or False

FiO2 is always higher than the partial pressure of oxygen in the alveolus (PA02)

True

FiO2 is always higher than the partial pressure of oxygen in the alveolus (PA02)

FiO2 > PAO2

10

True or False

Inspired air becomes 100% humidified as it moves towards the alveoli

True

Inspired air becomes 100% humidified as it moves towards the alveoli

11

Inspired air becomes 100% humidified as it moves towards the alveoli. How does this water affect oxygen concentration?

Takes up space and dilutes the oxygen concentration

12

What's the composition of inspired air?

lots of oxygen and no carbon dioxide

(O2 >> CO2)

13

What's the composition of expired air?

a little oxygen and lots of carbon dioxide

(CO2 > O2)

14

How does the mixing of inspired and expired air affect the concentration of oxygen going towards the alveoli?

It dilutes the concentration of oxygen going towards the alveoli

15

What are the two main reasons why FiO2 is always higher than the partial pressure of oxygen in the alveolus (PA02)?

(FiO2 > PAO2)

Humidification of inspired air

dilutes its oxygen concentration

Mixing of inspired and expired air

dilutes the concentration of oxygen going towards the alveoli

(FiO2 > PAO2)

16

If Alveolar oxygen (PAO2)

PAO2 = FiO2 x (Pb - PH2O) - (PaCO2 / RQ),

changes in which variables influence the final concentration of oxygen in the alveolus. 

FiO2,

Barometric pressure (Pb),

PaCO2, or the

Respiratory quotient (RQ)

17

If

Alveolar oxygen = FiO2 x (Pb - PH2O) - (PaCO2 / RQ), How can we increase PAO2 as well as PaO2?

 

Supplemental oxygen

18

True or False

Supplemental oxygen can increase PAO2 as well as PaO2 and also treat the cause of hypoventilation

 

False

Supplemental oxygen only masks hypoventilation and will not treat the cause.

19

Calculate the normal PAO2

PAO2 = FiO2 x (Pb - PH2O) - (PaCO2 / RQ)

PAO2 = 0.21 x (760 - 47) - (35/0.8) = 105.98 mmHg

20

A patient is breathing room air at sea level. The arterial blood gas reveals a Pa02 of 60 mmHg and a PaC02 of 70 mmHg. Calculate the patient's alveolar oxygen concentration (Enter your answer in mmHg and round to the nearest whole number)

PAO2 = ?

PAO2 = FiO2 x (Pb - PH2O) - (PaCO2 / RQ)

We know these: Pa02 of 60 mmHg, PaC02 of 70 mmHg, FiO2 room air: 0.21, Pb: 760 mmHg, 

PH2O: 47, RQ: 0.8

PAO2 = 0.21 x (760 - 47) - (70 / 0.8) = 62.23 mmHg

PAO2 = 62 mmHg

21

The patient in the previous question has a PaO2 of 60 mmHg, what can be said about his A-a gradient?

A-a gradient is  normal

(more on this in the next question)

PAO2 = 62 mmHg

PaO2 = 60 mmHg

22

A patient is breathing room air at sea level. The arterial blood gas reveals a Pa02 of 60 mmHg and a PaC02 of 70 mmHg. The patient's calculated alveolar oxygen concentration PAO2 was 62 mmHg, what happens If we increase the FiO2 to 40%?

PAO2 = ?

PAO2 = FiO2 x (Pb - PH2O) - (PaCO2 / RQ)

We know these: Pa02 of 60 mmHg, PaC02 of 70 mmHg, FiO2: 0.40, Pb: 760 mmHg, 

PH2O: 47, RQ: 0.8

PAO2 = 0.40 x (760 - 47) - (70 / 0.8) = 197.7 mmHg

 

23

A patient is breathing room air at sea level. The arterial blood gas reveals a Pa02 of 60 mmHg and a PaC02 of 70 mmHg. By increasing the Fi02 to 40%, we fixed the hypoxemia but not the ---

Hypercarbia

24

What is the most appropriate intervention which would remedy both hypoxemia and hypercarbia?

Increased alveolar ventilation

25

What's the average CO2 production per minute?

200 mL/min

26

What's the average O2 consumption per minute?

250 mL/min

27

The ratio "CO2 production / O2 consumption" is called:

Respiratory Quotient (RQ)

28

What's the normal value of Respiratory Quotient (RQ)?

(CO2 production / O2 consumption)

=

(200 mL/min) / (250 mL/min)

=

0.8

29

How does overfeeding affect Respiratory Quotient (RQ)?

RQ > 1

30

An RQ > 1 suggests which metabolic process?

Lipogenesis