Causes of Hypoxemia

Question 1

P-F ratio

Answer 1

PaO₂/F_IO₂

Question 2

What does a large A-a ratio indicate?

Answer 2

pathology of gas exchange in the lun

Question 3

causes of low PaO₂

Answer 3

ambient hypoxia

diffusion impairment

hypoventilation

low V/Q

shunt

Question 4

ambient hypoxia

Answer 4

low Pb (altitude)

low F_IO2

Question 5

What are the responsibe hypoxemias?

Answer 5

ambient hypoxia

diffusion impairment

hypoventilation

ventilation/perfusion inequality

Question 6

refractory hypoxemia

Answer 6

arterial hypoxemia that does not significantly improve when F_IO₂ is increased

Question 7

ambient hypoxia

Answer 7

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

lower inspired PO₂, alveolar PO₂, and arterial PO₂

Question 8

diffusion problem

Answer 8

not a problem in healthy lung

thickened “respiratory membrane” through fibrosis

increased diffusion distance - emphysema

generally responsive to an increase in F_IO₂

Question 9

alveolar hypoventilation

Answer 9

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

Question 10

situations that cause hypoventilation

Answer 10

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)

Question 11

causes of anatomic shunts

Answer 11

bronchial and thesbian circulations - a very small amount

ventricular or atrial septal defects

patent ductus arteriosus

Question 12

capillary shunting

Answer 12

zero V/Q (unventilated alveoli or atelectasis)

refractory to increased F_IO₂

Question 13

What is the normal Q_s/Q_t ratio?

Answer 13

<7%

Question 14

low ventilation-perfusion ratio

Answer 14

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

Question 15

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

Answer 15

Question 16

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

Answer 16

decreases

caused by gravity and regional lung differences in ventilation and perfusion

Question 17

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

Answer 17

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

Question 18

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

Answer 18

a is the situation in a normal alveolus

b is decreased compliance

c is increased resistance

Question 19

compensation fo V/Q maldistribution

Answer 19

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

local hypocapnia causes bronchoconstriction, reducing ventilation of that alveolar unit

Question 20

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

Answer 20

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

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

Question 21

conditions which have elevated A-aPO₂ gradients

Answer 21

diffusion impairment

V/Q maldistribution

shunt

Question 22

conditions where the A-a gradient is not elevated

Answer 22

ambient hypoxia

hypoventilation

Question 23

PEEP

Answer 23

positive end expiratory pressure

can be used to prevent alveolar collapse

Question 24

absorption atelectasis

Answer 24

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

Question 25

What is O₂ saturation at a PO₂ of 27 mmHg?

Answer 25

50%

Question 26

What is O2 saturation at a PO2 of 40 mmHg?

Answer 26

75%

Question 27

What is O2 saturation at a PO2 of 60 mmHg?

Answer 27

90%

Question 28

What is O2 saturation at a PO2 of 80 mmHg?

Answer 28

95%

Question 29

What is O2 saturation at a PO2 of 100 mmHg?

Answer 29

97.5%

Question 30

What is the PO2 at this concentration:

50%

Answer 30

What is O₂ saturation at a PO₂ of 27 mmHg?

Question 31

What is the PO2 at this concentration:

75%

Answer 31

What is O2 saturation at a PO2 of 40 mmHg?

Question 32

What is the PO2 at this concentration:

90%

Answer 32

What is O2 saturation at a PO2 of 60 mmHg?

Question 33

What is the PO2 at this concentration:

95%

Answer 33

What is O2 saturation at a PO2 of 80 mmHg?

Question 34

What is the PO2 at this concentration:

97.5%

Answer 34

What is O2 saturation at a PO2 of 100 mmHg?