3.3.1 Hypoxia Flashcards
What is the pathway for O2 through the body?
What are the normal sea level gas values for alveolar air, veins, and arteries?
What is an example of low inspired PO2
High altitude (due to the drop in barometric pressure)
Are are the effects of high altitude on PIO2, PAO2, PaO2, PvO2, CaO2?
In a high altitude scenario, how can you calculate PAO2 with normal ventilation?
If ventilation is normal, you can assume that the PACO2 will be fourty. Then, you plug it into the following equation:
PAO2 = 60 - (40 * 1.2) = 12 mm Hg
Once you know the PAO2, how can you find the SaO2 and CaO2?
The ODC (with O2 content and O2 saturation)
What pathway will lead to hyperventilation due to the reduced PaO2?
Peripheral (Central does not respond to PaO2)
For a given PIO2, a decrease in PACO2 will result in what change in PAO2?
Increase in PAO2
If you hyperventilate at a high altitude and blow your PACO2 down to 20, what will be the PAO2?
PAO2 = 60 - (20 *1.2) = 36 mm Hg
In addition to blowing off CO2, what will aid in increasing the oxygen delivery to the tissues?
The alkalosis as a result of decreased CO2 will shift the ODC in such a way that Hb will saturate better at lower PO2 levels.
What CV factor increases O2 tissue delivery in altitude hypoxia?
Q, cardiac output
In what scenario could PIO2 be normal but PAO2 be low?
Hypoventilation
Hypoventilation results in an increase in which alveolar gas value? decrease in what?
Increase PACO2
Decrease PAO2
In long term hypoventilation, how will a person compensate for the resulting respiratory acidosis?
Metabolically, they will retain HCO3 to shift the pH up towards 7.4
What would cause a person to have low PaO2 depite a normal PAO2
Inefficient gas exchange; diffusion impairment (Increased thickness or decreased surface area)
How long does it typically take blood to equilibrate with alveolar air? Explain how changes in DLCO would alter the diffusion curve.
~1/4 to 1/3 of capillary transit time.
A large difference between PAO2 and PaO2 is often the result of what?
Shunt, Low VA/Q
Describe how to find PaO2 on the ODC in a patient who is experiencing shunting.
Average of the oxygen content b/t the blood that gets oxygenated and the blood that doesn’t
How do shunt units typically affect PaCO2?
Typically a relatively small increase in PaCO2 (ie from a normal of 40 to 43)
If PAO2, PaO2, and CaO2 are all normal, what could lead to a low VO2.
Reduced Q (cardiogenic or hemorrhagic shock)
How will the body compensate to maintain VO2 despite a reduced Q?
Increase oxygen extraction resulting in an increased C(a-v)O2 and lower CvO2
What condition
