Assessment of V/Q Flashcards
What happens in an extreme V/Q (infinity)?
all ventilation but no perfusion leading to no gas exchange
what happens when V/Q = 0
all perfusion but no ventilation leading to no gas exchange
What is the V/Q ratio in the upper lungs? (not a number but relative of ventilation vs perfusion)
High ventilation but underperfusion
What is V/Q ratio in lower lungs?
high perfusion under ventilation
What are the measurements for PaO2, PaCO2, SAT, CaO2, and CaCO2 at sea level?
PaO2= 104 PaCO2 = 40 SAT = 97.5% CaO2 = 20.7 CaCO2 = 44
What are the measurements for PaO2, PaCO2, SAT, CaO2, and CaCO2 at Denver?
PaO2 = 80 PaCO2 = 35 SAT = 95% CaO2 = 19 CaCO2 = 42
What are the 5 causes of deadspace?
rapid shallow breathing pulmonary embolism decreased CO mechanical ventilation emphysema
what is the clinical definition of a shunt?
1% of CO/ 20 torr A-a
blood passes through capillaries but does not get oxygenated
what do shunt and low V/Q contribute to?
arterial hypoxemia
arterial hypercapnia
How can you differentiate between a low V/Q and a shunt?
low V/Q responds to increased FI02 like if you put the patient on 100% oxygen the V/Q will normalize sat. A shunt does not respond to increased FIO2
What percentage of tidal volume is dead space?
1/3
What is the most commonly used mechanism to estimate V/Q mismatch?
Calculation of the A-a gradient
In a perfect V/Q mismatched world, PaO2 would be what?
78 mmHg
What does SpO2 pulse oximetry measure?
hemoglobin saturation
What are the 2 causes of a normal A-a gradient in hypoxemia?
altitude
hypoventilation
