VQ ratios and expired gases - exam 3 Flashcards
Normal V/Q ratio
4200 mL air/5000 mL blood = 0.80
If there is an issue with ventilation, PO2 will be ___ and PCO2 will be ___
PO2 40 mmHg, PCO2 45mmHg - match the blood gases coming into the pulmonary artery (same as blood leaving the alveoli - no gas exchange)
If there is an issue with perfusion, PO2 will be ___ and PCO2 will be ___
PO2 150 mmHg, PCO2 0 mmHg - same as inspired air
If there is an issue with ventilation, the V/Q ratio will ________
decrease
If there is an issue with perfusion, the V/Q ratio will ________
increase
The upper and lower limits of the V/Q ratio are _____
infinity and zero
a way to describe blood flow through a non-ventilated alveolus is a _______
shunt
a way to describe ventilation through an unperfused alveolus is _______
dead space
an area with more perfusion would have what changes to O2 and CO2?
lower oxygen, higher CO2
an area with more ventilation would have what changes to O2 and CO2?
higher oxygen, lower CO2
The base of the lung has _____ ventilation and ____ blood flow compared to the apex of the lung
more and more
at the base of the lung, ventilation is _____ than blood flow
less
at the apex of the lung, ventilation is _____ than blood flow
more
between blood flow and ventilation, which has greater regional differences?
blood flow
the top of the lung compared to the bottom CO2 vs O2
base - lower O2, higher CO2
top - higher O2, lower CO2
Compare the effects of age on V/Q ratios
younger (22 yoa) - good V/Q matching
older (44 yoa) - poorer V/Q ratios; higher blood flow and lower ventilation
Anesthesia results in what change to the V/Q ratio?
atelectasis/dead space - dec ventilation
What can resolve the negative changes of anesthesia to V/Q matching?
PEEP
describe LaPlace’s Law
ventilation will be uneven: air will move to the alveoli with more air/less pressure (move from smaller to larger spheres) until the larger alveoli is 80-90% full
When is LaPlace’s law applicable?
Unhealthy patients - don’t have surfactant
How does surfactant affect LaPlace’s law?
surfactant is less spread out with less air in an alveolus, resulting in a higher concentration of surfactant to surface area, dec surface tension, corrects LaPlace’s law - healthy patients
anatomic dead space is usually _____ mL
150 mL or 1 mL/lb of ideal body weight
mixed expired gas is…?
a collection of the entire expired breath; including alveolar air and dead space air
What are the normal values of oxygen, CO2, nitrogen, and water of mixed expired air?
PEO2: 115-120 mmHg
PECO2: 27-28 mmHg
PEN2: 566 mmHg
PEH2O: 47 mmHg
If there is dead space in the lungs, mixed expired air will have what change?
dec PECO2
How is PECO2 calculated?
- Determine the partial pressure of the gas (40/760 = 5.3%)
- Multiply by volume (5.3% * 350 mL = 18.42)
- volume of CO2/total volume = new concentration of gas (18.42/500 = 3.7%)
- new concentration of gas * total pressure = PECO2 (3.7%*760 = 28 mmHg)
