Gas Transport

Question 1

What are normal values PaCO2, PaO2 and PaH2O in the alveoli?

Answer 1

PaO2 - 100mmHg
PaCO2 - 40mmHg
PaH2O - 47mmHg

Question 2

What is the alveolar gas equation?

Answer 2

PAO2 = PiO2 - (PaCO2/RQ)

Question 3

What is Respiratory Quotient (RQ)?

Answer 3

Its the number of CO2 molecules produced depending on what your diet consists of, usually it’s assumed to be 0.8
High carb diet, high RQ

Question 4

Your PAO2 would decrease or increase when you moved from Galveston to the Rockies? Why?

Answer 4

It would be lower since the barometric pressure would be lower in the rockies.
think PiO2=(PB-PH2O) x FiO2
and
*PAO2=PiO2 - (PaCO2/RQ)

Question 5

What are the normal ranges for the Alveolar-arterial O2 gradient?

Answer 5

Normally <15mmHg
increase with age up to 20-30mmHg
PaO2 range 60-100mmHg

Question 6

How much oxygen is extracted from the Hemoglobin?

Answer 6

25%

Question 7

What is the A-a gradient?

Answer 7

measure of difference between alveolar concentration of oxygen and arterial concentration of oxygen. PAO2-PaO2

Question 8

What an abnormal A-a gradient indicate?

Answer 8

Defect in diffusion, V/Q mismatch, or right-to-left shunt

Question 9

What is a right-to-left shunt?

Answer 9

its the shunting of blood from the right side of the heart to the left side of the heart, not allowing gas exchange in the lungs

Question 10

How can a V/Q mismatch happen?

Answer 10

it can happen atelectasis or too much ventilation in the alveoli

Question 11

What is Mixed Venous Tension

Answer 11

when you extract too much oxygen from the tissue, without enough time for the tissues to compensate for the loss

Question 12

How can Mixed Venous Tension occur?

Answer 12

Decreased Cardiac Output
High consumption of O2
Loss of hemoglobin

Question 13

What is hypoxemia (hypoxia)?

Answer 13

when there is not enough oxygen in the arterial blood stream or it’s lower than 60mmHg of oxgyen

Question 14

What are the 2 categories of hypoxia?

Answer 14

Either its hypoxia wit ha normal A-a gradient or increased A-a gradient

Question 15

Reasons for hypoxia with a normal A-a gradient?

Answer 15

1) Low inspired O2

2) Hypoventilation

Question 16

Reasons for hypoxia with an increased A-a gradient?

Answer 16

1) V/Q mismatch
2) shunt
3) abnormal diffusion

Question 17

What can be a cause of low inspired O2, the reason the A-a gradient is still normal and treatment for low inspired O2?

Answer 17

• Low oxygen concentration in elevated areas (space or mountains)
• the A-a gradient will be normal since the alveoli O2 concentration is low, then the arterial oxygen concentration becomes low
• treatment is just giving more oxygen to the patient

Question 18

What does it mean: 
V/Q=infinity
V/Q>1
V/Q<1
V/Q=0

Answer 18

• dead space ventilation
• normal V/Q
• Low lung at end expiration
• shunt

Question 19

what is the pulmonary response to hypoxia?

Answer 19

Hypoxic pulmonary vasoconstriction occurs. This is when alveolar oxygen content drops to a certain level, the vascular tone in the arteries supplying that alveoli gas goes up, then an increase in resistance going to that alveoli or it helps shunt blood away from that particular alveoli.

Question 20

How can you improve V/Q mismatch?

Answer 20

You use ways to increase oxygenation, increase PEEP or increase FiO2

Question 21

What is the equation for minute ventilation?

Answer 21

MV=RRxTV

Question 22

What are the 3 categories in the Distribution in Ventilation?

Answer 22

• Physiologic dead space (bronchiole)
• Anatomic dead space (larynx, trachea, bronchus)
• Alveolar ventilation (alveoli)

Question 23

Around which rib would we find the best ventilation?

Answer 23

rib #3