What is the alveolar oxygen equation?
(FiO2 x [Patm – PH2O]) - (PaCO2/R)
What is the PAO2 when:
FiO2 = 1
What is the shorcut way of calculating PAO2?
(FiO2 * 5) * 100
On RA (room air), what is the equation for determining A-a gradient?
<= 4 + age/4
What information does the A-a gradient provide?
The A-a gradient allows us to assess the efficiency of gas exchange at the alveolar – capillary membrane.
What is a shunt?
Lung is perfused by not being ventilated.
What accounts for the normal A-a difference?
Thebesian, bronchial, and pleural veins bypass the lungs.
What is the ideal ratio for V/Q?
Ideally the ratio is 1.
When the ratio varies much from 1, hypoxemia can result.
What is the definition of a dead space lung?
= ventilation > perfusion
What is the definition of a shunt lung?
= perfusion > ventilation
Shunt or deadspace?
Right Mainstem intubation?
Low cardiac output/hypotension?
Why would the A-a gradient be abnormal?
Diffusion abnormality from diseased lungs for example.
There is inefficient O2 exhange between the alveoli and the bloodstream.
What is HPV?
Hypoxic Pulmonary Vasoconstriction
The area is not being ventilation, but is being perfused. It takes about 10 minutes to redirect blood flow away from hypoxic areas.
As the FiO2 gets higher, the 4+ age/4 equation no longer holds true. The normal A-a gradient must also increase. True or false?
Ratio of PaO2/FiO2 should be 300 – 500. True or false?
Note: A value of < 250 indicates a clinically significant gas exchange problem.
What does CaO2 comprise of?
O2 content can be thought of as the sum of the two means of oxygen transport in the blood:
O2 carried on Hemoglobin (contributes most to CaO2) and O2 carried dissolved in the blood (PaO2).
What is the CaO2 equation?
Units = (mL O2/dL)
Hgb (1.34 mL O2/g Hgb) * % sat + .003 (PaO2)
Note: .003 is coeff. of blood solubility.
PaO2 contributes little to oxygen in CaO2 calculation. It is mainly used for assessing pulmonary gas exchange. True or false?
Once oxygen molecules chemically bind to hemoglobin they no longer exert any pressure. True or false?
What is DAO2 (dissociation) formula?
CaO2 * cardiac output
What can right shift the Hb dissociation curve? (2)