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Respiratory Exam 1 > V/Q Relationships and Causes of Hypoxemia > Flashcards

V/Q Relationships and Causes of Hypoxemia Flashcards

1
Q

what number classifies a hypoxemia

A
  • PaO2 < 80 mmHg
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2
Q

tracing the path of PO2 as it successively drops

A
  • atmosphere
  • alveoli
  • arterial blood
  • systemic capillary
  • mitochondria
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3
Q

why is there a small degree of normal shunt

A
  • due to bronchial circulation and thebesian veins
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4
Q

how to calculate the expected A-a O2 difference

A

age/4 + 4

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5
Q

causes of normal A-a difference

A
  • diffusion barrier in the lung
  • anatomical shunt (bronchial circulation and thebesian veins)
  • V/Q inequality that increases with age
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6
Q

causes of hypoxemia

A
  • low PiO2
  • hypoventilation
  • diffusion impairment
  • shunt
  • V/Q mismatch
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7
Q

what happens to your PAO2 as you go up in elevation

A
  • it decreases
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8
Q

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

A
  • it will double
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9
Q

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

A
  • no
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10
Q

what rectifies hypoxemia due to hypoventilation

A
  • supplemental O2
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11
Q

what is the A-a O2 gradient in hypoventilation

A
  • normal
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12
Q

equilibration reserve is reduced when the diffusion barrier is

A
  • thickened
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13
Q

diffusion impairment due to which conditions

A
  • pumonary edema

- fibrosis

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14
Q

treatment of diffusion impairment

result

A
  • O2 therapy

- increases the driving force

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15
Q

abnormal intrapulmonary shunt

A
  • blood goes through lung without being exposed to alveolar ventilation
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16
Q

abnormal extra pulmonary shunt

A
  • right to left cardiac shunt
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17
Q

what do obstructed airways create

what happens

A
  • physiological shunt

- alveolar capillaries cannot become oxygenated

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18
Q

why would the PCO2 be normal in an anatomic shunt

A
  • ventilation of the good part of the lung twice as much
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19
Q

how can we test for an anatomic shunt

A
  • lack of response to O2 therapy
20
Q

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

A
  • big drop
21
Q

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

A
  • 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
22
Q

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

A
  • the hemoglobin from the well ventilated alveoli is already saturated
23
Q

most important cause of hypoxemia

A
  • V/Q mismatch
24
Q

compliance of the upper portion of the lung

A
  • low compliance
25
Q

ventilation of the upper portion of the lung

blood flow

V/Q ratio

A
  • low ventilation
  • but LOWER blood flow
  • high V/Q ratio
26
Q

PAO2 of upper portion of lung

A
  • higher PAO2
27
Q

compliance of lower portion of the lung

A
  • high compliance
28
Q

ventilation of lower portion of lung

blood flow of lower portion of the lung

V/Q ratio

A
  • high ventilation
  • HIGHER blood flow
  • lower V/Q
29
Q

PAO2 of lower lung

A
  • lower PAO2
30
Q

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

A
  • normal V/Q mismatching
31
Q

blocked ventilation is also called

A
  • shunt
32
Q

blocked perfusion is also called

A
  • alveolar dead space
33
Q

do patients with emphysema have decrease ventilation or perfusion?

why?

A
  • decreased perfusion

- have lost capillaries in their walls

34
Q

do patients with chronic bronchitis have decreased ventilation or perfusion?

why?

A
  • decreased ventilation

- small airways are blocked

35
Q

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

A
  • yes
36
Q

changes in V/Q during exercise

A
  • (HIGH V/Q RATIO)
  • increased cardiac output
  • increased ventilation (but much higher ventilation)
37
Q

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

A
  • in exercise, both V and Q increase

- in disease either/both V or/and Q decrease

38
Q

V/Q mismatch effect on A-a difference

A
  • increases
39
Q

disease that cause V/Q mismatch

A
  • chronic bronchitis
  • asthma
  • cystic fibrosis
40
Q

physiologic shunt effect on A-a difference

A
  • increase
41
Q

will hypoventilation respond to O2 therapy

A
  • yes, but O2 therapy may not solve the underlying problem
42
Q

diffusion impairment effect on A-a difference

A
  • increases
43
Q

intracardiac right to left shunt effect on A-a difference

A
  • increases
44
Q

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

why

A
  • normal

- partial pressures are unaffected

45
Q

anemia response to O2 therapy

why

A
  • low

- you need to increase hemoglobin

46
Q

will dead space respond to O2 therapy

A
  • yes

Respiratory Exam 1 (27 decks)

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