Gas exchange Flashcards
What two things does PaO2 depend on?
PAO2 and architecture of the lungs
What are the 2 main categories for causation of hypoxemia?
not enough O2 getting into the alveoli
not enough O2 transferred into the capillary blood
How can you get not enough O2 getting into the alveoli?
low atmospheric pressure (PIO2) or pure hypoventilation
How can you get not enough o2 transferred into the capillary blood?
a) ventilation-perfusion mismatch
b) right-to-left shunting
c) diffusion defects
(architechure of the lung not performing well)
PaO2 will always be (blank) than PAO2
less
(blank) is a cause of hypoxemia and results in a decrease in PaO2 in responseto a decrease in PAO2.
hypoventilation
Can you have a normal A-a interval but be hypoventilating?
yes! (they go down, but down together)
pure hypoventilation causes (blank)
hypoxemia
If you are undergoing hypoventilation what will happen to your PaO2 and your PAO2?
your PaO2 will go down due to a drop in PAO2
what are the main problems of hypoventilation?
acidemia and hypercarbia; hypoxemia less of a problem
one cause for hypoxemia is pure (blank)
hypoventilation
Give three examples for the cause of hypovnetilation with normal lungs and no disease
- depression of respiratory center via morphine or barbituates
- diseases of the respiratory muscles- muscular dystrophy
- extreme obesity
why do you have an P(A-a)O2 differnce in a normal people?
because lungs dont work perfectly and because there is some ‘wasted’ blood (ie not all blood gets fully oxygenated.
Why do you get wasted blood?
cuz of anatomic shunts and low region v/q ratios
What is an anatomic shunt?
it is the entry of blood into the systemic arterial system without going through ventilated areas of lungs
But PAO2 > PaO2 if there is any (blank)
anatomic shunt.
The mixing of unoxygenated blood with oxygenated blood is known as (blank)
venous admixture
VA (alveolar ventilation) is about the same as the (blank)rate.
pulmonary blood flow
v/q ratio is typically (blank)
1
Gas exchange depends critically on the proper matching of ventilation (V) and perfusion (Q)
Therefore gas exchange problems have to do with abnormal (blank)
V/Q ratios
What is happening if:
v/q=0?
v/q=1?
v/q= infinity
shunt (ventilation is totally absent) normal ideal (ventilation is perfectly matched to perfusion) Dead space (perfusion is totally absent)
Main reason for the V/Q differences between the apex and the base of the lung is (blank).
gravity
Towards the apex of the lung the v/q ratio tends to be (blank). Towards the base, the v/q ration tends to be (blank)
higher
lower
What is the equation for total wasted blood (physiological shunt)?
Physiological shunt=anatomic shunt + low V/Q regions
What is the equation for physiological dead space/ total wasted air?
physiological dead space=anatomic dead space + alveolar dead space
Is it normal to have anatomic shunts and anataomic dead space?
yes
Is it normal to have low v/q regions and alveolar dead space?
yes
A normal A-a difference of (blank) results from gravitational effects on V/Q and on anatomic shunting
10-15
V/Q mismatch among different alveoli is clinically relevant.
-A large V/Q dispersion causes an (blank)
P(A-a)O2 difference
(blank) is all about mixing blood of different O2 concentrations and different volumes
V/Q mismatch
What is the differences in PAO2, PACO2 and V/q ratio at the apex and base of the lung?
increase V/q, increased PAO2 and decreased PACO2 at the apex
Decreased V/q ratio,decreased PAO2, and increased PACO2 at the base
When the V/Q of two different units are not the same, this is called a (blank)
mismatch.
PaO2 and SaO2 are (blank) proportional
directly
what is the oxygen content equation?
CaO2=Hb X 1.34 X SaO2/100
If the Hb is the same for mixed samples, then the CaO2 will be (blank) to the SaO2
proportional
(blank) is key variable in understanding V/Q mismatch.
SaO2
Hyperoxemic will effect your O2 content a lot or a little? how about hypoxemic?
little, a lot
Mixing two volumes of blood with different PO2 concentrations will have a Po2 concentration in the blood that is the mean of what concentrations? Can you use the mean of the two PO2 concentrations?
CaO2 or SaO2
no
If you have a shunted arterial, can the other arterial make up for it?
no it cannot, you will get hypoxemia
Due to the flat shape of the oxygen binding curve, the resulting PO2 after mixing is (blank) than the mean PO2
lower
Mixing unequal volumes (Q) of blood with different PO2 results in a flow-weighted average of (blank)
SaO2
If you have a v/q of zero what does this mean
you have a shunt
Can supplemental O2 rescue effects of perfused but not ventilated region?
NO
Can supplemental oxygen rescue effects of V/Q mismatch?
yes
What is the ideal V/Q ratio?
1
If you have a v/q ratio of less than 1 what happens?
If you have a v/q ratio of greater than 1 what happens?
you will get a decrease alveolar oxygen and increase in PACO2
Increase PAO2 and decrease PACO2
if there is a v/q mismatch between 2 alveoli, which one will win?
the hypoxemic one
V/Q mismatching is a major clinical reason for (blank)
hypoxemia
When you have a v/q mismatch what happens to your A-a difference?
it gets larger than normal
When you have a v/q mismatch what does it reflect?
an intrinsic lung problem and gas exchange problem
(blank) is the most important cause of gas exchange abnormalities in most lung diseases.
V/Q mismatch
If you have increased PaCO2, hypoventilation, and a abnormal PAO2 and PaO2 interval whats happening?
hypoventilation plus another mechanism
If PaCO2 isn’t increased, you have abnormal PaO2-PAO2 interval, and have a Po2 that is correctable with O2 what do you have?
V/Q mismatch (airway disease, interstitial lung disease, alveolar disease, pulmonary vascular disease)
If PaCO2 isn’t increased, you have abnormal PaO2-PAO2 interval, and have a Po2 that is not correctable with O2 what do you have?
Shunt (alveolar collaspe, intraalveolar filling, intracardiac shunt, vascular shunt within lungs)
Although V/Q mismatching can influence PaCO2, this effect is often overcome by an increase in (blank).
minute ventilation
As long as there is sufficient (blank), PaCO2 will be unaffected by the degrees of V/Q mismatch that routinely lead to hypoxemia.
alveolar ventilation
What are the mechanisms for hypoxemia?
- decrease in PIO2 (high altitude, poor ventilator)
- pure hypoventilation
- v/q mismatch
- shunt
Increased (blank) can compensate for low V/Q units. Total ventilation (VE) must (blank) for this compensation
ventilation
increase
Where is ventilation and blood flow the highest, at the top or bottom of lung?
at the bottom of lung
Different (blank) may have widely differing amounts of ventilation and perfusion.
alveoli
In normal gas exchange, there is matching of (blank) for each alveolar unit
ventilation and perfusion
Alveoli with increased perfusion also have increased (blank)
Alveoli with decreased perfusion also have decreased (blank)
ventilation
ventilation
What are these symptoms of
Impaired judgment
Motor incoordination
Clinical picture closely resembling that of acute alcoholism
acute hypoxia
What are these symptoms of: Fatigue, drowsiness Apathy Inattentiveness Delayed reaction time Reduced work capacity
long-standing hypoxia
What is this?
Lower than normal PaO2 for a person’s age
Low CaO2
hypoxemia
What do you use to determine hypoxemia?
ABG (PaO2,PaCO2) PAO2 and P(A-a) O2 difference
