Sanduram Flashcards
What is the alveolar gas equation?
PAO2 = FiO2 ( Pb - PH2O) - PaCO2/R
Assuming everything is normal, it becomes 150-1.25(PaCO2)
How do you calculate PIO2?
All you do is calculate the first part of the alveolar gas equation. So, FIO2 (Pb - PH2O). So normally it is 150.
What are our 3 situations where you can have a normal A-a gradient but still be hypoxemic?
What 2 situation2 Would you see large A-a gradient and hypoxemia?
1) High altitudes, fire (decreased fraction of O2), hypoventilation
2) Pneumonia, shunt
What is a normal A-a gradient?
Less then 15. However in all of the practice problems he gave us it was 5
According to the EBook, the age correction formula is age/4 +4.
What situation do you see in zone 3 vs. zone 2
In zone 3 arterial pressure will be greater than alveolar. Therefore, the capillaries will be open, there will be gas exchange and perfusion. In zone one though, the alveolar pressure is far greater than arterial ad venous, so the capillary stays shut and there is no perfusion/gas exchange.
V:Q ratio - where is it the largest/smallest
Largest in the zone 1 because you have a lot of ventilation and no perfusion. On the contrary, in zone 3 you have more perfusion than ventilation
What mechanism do we use to perform ventilation-perfusion matching?
If an alveoli is not functioning properly and therefore isn’t being ventilated properly, we constrict that capillary in order to ensure that the amount of blood that it is receiving is commensurate with the amount of ventilation. Also, you can give blood to other, better functioning, alveoli.
Main difference between VQ Mismatch And shunt?
VQ mismatch will improve with supplemental O2 because it will raise the ventilation for the already high perfusion.
Anatomic vs. physiological shunt
Anatomic. - situation where you have mixture of deoxygenated blood due to Like a septal defect.
Physiological - This would be like A situation where there is Ike a blockage in the alveoli or a diffusion defect. So like if a small piece of steak blocked the passage of air to the alveoli. The blood will come and go without being deoxygenated.
- No matter how much supplemental O2 you give this person they will not improve because there is a diffusion issue, or blockage.
Total Ventilation. =
VE =
VE = VA + VD
TOtal ventilation = alveolar ventilation + dead space ventilation
- alveolar ventilation - volume of air per minute that enters or exits the alveoli of the lung and participates in gas exchange
- dead space ventilation - volume of air per minute that enters conducting pathway and doesn’t partake in gas exchange.
2 types of dead space ventilation
Anatomic - so this would be like in the trachea or larynx
Physiologic - this would be like if you have a non-perffused alveolus.
What is the order of airflow and at what point does gas exchange occur?
NO GAS EXCHANGE: Larynx –> trachea –> bronchi –> bronchioles –>
GAS EXCHANGE: Respiratory bronchioles –> Alveolar ducts –> Alveoli
What does a large A-a gradient tell us?
The oxygen that is reaching his aveoli is not getting to the artery for whatever reason.
If a patient has pneumonia, what would you expect their CO2 levels to Be?
Can be high, low, or normal. This is because CO2 is very diffusible.
