Causes of Hypoxemia Flashcards Preview

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Flashcards in Causes of Hypoxemia Deck (34):
1

P-F ratio

PaO2/FIO2

2

What does a large A-a ratio indicate?

pathology of gas exchange in the lun

3

causes of low PaO2

ambient hypoxia

diffusion impairment

hypoventilation

low V/Q

shunt

4

ambient hypoxia

low Pb (altitude)

low FIO2

5

What are the responsibe hypoxemias?

ambient hypoxia

diffusion impairment

hypoventilation

ventilation/perfusion inequality

6

refractory hypoxemia

arterial hypoxemia that does not significantly improve when FIO2 is increased

7

ambient hypoxia

results from low barometric pressure (high altitiude) or breathing low concentrations of oxygen in inspired gas

lower inspired PO2, alveolar PO2, and arterial PO2

8

diffusion problem

not a problem in healthy lung

thickened "respiratory membrane" through fibrosis

increased diffusion distance - emphysema

generally responsive to an increase in FIO2

9

alveolar hypoventilation

with normal gas exchange, hypoventilation can decrease alveolar and therefore arterial PO2

hallmark is elevated PaCO2 and hypercapnia

inspired oxygen readily reverses the hypoxemia but has no direct effect on the hypercapnia

10

situations that cause hypoventilation

low lung compliance

depression of the brainstem respiratory oscillator

inadequate ventilator settings

muscle paralysis or fatigue including neurological disorders (myasthenia gravis)

high airway resistance (asthma)

11

causes of anatomic shunts

bronchial and thesbian circulations - a very small amount

ventricular or atrial septal defects

patent ductus arteriosus

12

capillary shunting

zero V/Q (unventilated alveoli or atelectasis)

refractory to increased FIO2

 

13

What is the normal Qs/Qt ratio?

<7%

14

low ventilation-perfusion ratio

high V/Q states don't compensate for regions of low V/Q because of the non-linear hemoglobin dissociation curve

the level of PaO2 will be lower and PaCO2 will be higher in alveoli with less ventilation-perfusion ratios

15

effecto of V/Q ratio on Pc'O2 and Pc'CO2

16

How does V/Q change from the top of the lung to the bottom of the lung?

decreases

caused by gravity and regional lung differences in ventilation and perfusion

17

does gravity have more of an effect on ventilation or perfusion?

it has more of an effect on perfusion

as a result, the V/Q ratio progressively declines as one moves from the top to the base of the lungs

18

Describe the time/volume relationship during inspiration and expiration for a normal alveolus, reduced compliance, and increased resistance

a is the situation in a normal alveolus

b is decreased compliance

c is increased resistance

19

compensation fo V/Q maldistribution

local hypoxia and hypercapnia cause vasoconstriction, limiting perfusion to that alveolar unit

local hypocapnia causes bronchoconstriction, reducing ventilation of that alveolar unit

20

What happens when V/Q is at 0? at infinity?

if V/Q = 0, it is an effective shunt

if V/Q = infinity, it is alveolar dead space

21

conditions which have elevated A-aPO2 gradients

diffusion impairment

V/Q maldistribution

shunt

22

conditions where the A-a gradient is not elevated

ambient hypoxia

hypoventilation

23

PEEP

positive end expiratory pressure

can be used to prevent alveolar collapse

24

absorption atelectasis

in alveolar units that become plugged after being vilated wth 100% oxygen, there is a continualgradient for the transfer of oxygen from the alveolus to the pulmonary capillary bed

since the alveolus has been blocked off form the major pathways, nothing comes it replace the oxygen moving into the blood and the alveolus will soon collapse

25

What is O2 saturation at a PO2 of 27 mmHg?

50%

26

What is O2 saturation at a PO2 of 40 mmHg?

75%

27

What is O2 saturation at a PO2 of 60 mmHg?

90%

28

What is O2 saturation at a PO2 of 80 mmHg?

95%

29

What is O2 saturation at a PO2 of 100 mmHg?

97.5%

30

50%

What is O2 saturation at a PO2 of 27 mmHg?

31

75%

What is O2 saturation at a PO2 of 40 mmHg?

32

90%

What is O2 saturation at a PO2 of 60 mmHg?

33

95%

What is O2 saturation at a PO2 of 80 mmHg?

34

97.5%

What is O2 saturation at a PO2 of 100 mmHg?