V/Q Relationships and Causes of Hypoxemia

Question 1

what number classifies a hypoxemia

Answer 1

• PaO2 < 80 mmHg

Question 2

tracing the path of PO2 as it successively drops

Answer 2

• atmosphere
• alveoli
• arterial blood
• systemic capillary
• mitochondria

Question 3

why is there a small degree of normal shunt

Answer 3

• due to bronchial circulation and thebesian veins

Question 4

how to calculate the expected A-a O2 difference

Answer 4

age/4 + 4

Question 5

causes of normal A-a difference

Answer 5

• diffusion barrier in the lung
• anatomical shunt (bronchial circulation and thebesian veins)
• V/Q inequality that increases with age

Question 6

causes of hypoxemia

Answer 6

• low PiO2
• hypoventilation
• diffusion impairment
• shunt
• V/Q mismatch

Question 7

what happens to your PAO2 as you go up in elevation

Answer 7

• it decreases

Question 8

if CO2 production is constant and ventilation is halved, what will happen to PACO2 and PaCO2

Answer 8

• it will double

Question 9

if CO2 production is constant and PaCO2 is not elevated, is the patient hyperventilating

Answer 9

• no

Question 10

what rectifies hypoxemia due to hypoventilation

Answer 10

• supplemental O2

Question 11

what is the A-a O2 gradient in hypoventilation

Answer 11

• normal

Question 12

equilibration reserve is reduced when the diffusion barrier is

Answer 12

• thickened

Question 13

diffusion impairment due to which conditions

Answer 13

• pumonary edema

- fibrosis

Question 14

treatment of diffusion impairment

result

Answer 14

• O2 therapy

- increases the driving force

Question 15

abnormal intrapulmonary shunt

Answer 15

• blood goes through lung without being exposed to alveolar ventilation

Question 16

abnormal extra pulmonary shunt

Answer 16

• right to left cardiac shunt

Question 17

what do obstructed airways create

what happens

Answer 17

• physiological shunt

- alveolar capillaries cannot become oxygenated

Question 18

why would the PCO2 be normal in an anatomic shunt

Answer 18

• ventilation of the good part of the lung twice as much

Question 19

how can we test for an anatomic shunt

Answer 19

• lack of response to O2 therapy

Question 20

tiny drop in O2 content in a shunt results in _______ in PaCO2

Answer 20

• big drop

Question 21

where does the extra oxygen go if we add it in a patient with an anatomical shunt

what happens if the shunt is small

and if the shunt is big

Answer 21

• small amount dissolves into blood
• the dissolved oxygen can resaturate the deoxygenated hemoglobin
• it won’t be able to re-saturate all that deoxygenated hemoglobin

Question 22

why doesn’t O2 content drop too much during a small anatomic shunt

Answer 22

• the hemoglobin from the well ventilated alveoli is already saturated

Question 23

most important cause of hypoxemia

Answer 23

• V/Q mismatch

Question 24

compliance of the upper portion of the lung

Answer 24

• low compliance

Question 25

ventilation of the upper portion of the lung blood flow V/Q ratio

Answer 25

- low ventilation - but LOWER blood flow - high V/Q ratio

Question 26

PAO2 of upper portion of lung

Answer 26

- higher PAO2

Question 27

compliance of lower portion of the lung

Answer 27

- high compliance

Question 28

ventilation of lower portion of lung blood flow of lower portion of the lung V/Q ratio

Answer 28

- high ventilation - HIGHER blood flow - lower V/Q

Question 29

PAO2 of lower lung

Answer 29

- lower PAO2

Question 30

what causes the normal A-a gradient that exists in the body

Answer 30

- normal V/Q mismatching

Question 31

blocked ventilation is also called

Answer 31

- shunt

Question 32

blocked perfusion is also called

Answer 32

- alveolar dead space

Question 33

do patients with emphysema have decrease ventilation or perfusion? why?

Answer 33

- decreased perfusion | - have lost capillaries in their walls

Question 34

do patients with chronic bronchitis have decreased ventilation or perfusion? why?

Answer 34

- decreased ventilation | - small airways are blocked

Question 35

will patients with partially obstructed airways in V/Q mismatch respond to O2 therapy

Answer 35

- yes

Question 36

changes in V/Q during exercise

Answer 36

- (HIGH V/Q RATIO) - increased cardiac output - increased ventilation (but much higher ventilation)

Question 37

comparison of V/Q in exercises versus V/Q in disease

Answer 37

- in exercise, both V and Q increase | - in disease either/both V or/and Q decrease

Question 38

V/Q mismatch effect on A-a difference

Answer 38

- increases

Question 39

disease that cause V/Q mismatch

Answer 39

- chronic bronchitis - asthma - cystic fibrosis

Question 40

physiologic shunt effect on A-a difference

Answer 40

- increase

Question 41

will hypoventilation respond to O2 therapy

Answer 41

- yes, but O2 therapy may not solve the underlying problem

Question 42

diffusion impairment effect on A-a difference

Answer 42

- increases

Question 43

intracardiac right to left shunt effect on A-a difference

Answer 43

- increases

Question 44

reduced partial O2 content (anemia, CO poisoning) effect on A-a difference why

Answer 44

- normal | - partial pressures are unaffected

Question 45

anemia response to O2 therapy why

Answer 45

- low | - you need to increase hemoglobin

Question 46

will dead space respond to O2 therapy

Answer 46

- yes