Vent and perfusion Flashcards
most common cause of hypoxemia
V/Q mismatch
define vent.
amount of air into lungs, L/min
define perf.
amount of blood to lungs, L/min
define hypoxemia
low art. O2
define hypercapnia
high art. CO2
define shunt
blood that passes the lung
what is idea V/Q ratio
1
what is normal alveolar and arterial pO2
100 and 90 torr
define SaO2
% of Hb saturated with O2
5 causes of arterial hypoxemia
- low inspired O2
- hypoventilation
- poor diffusion
- shunt
- V<Q
cause of low inspred O2
altitude and poor anethesia
what is regional hypoventilation
part of lung not getting air - like a peanut in the lung
how will poor diffusion affect paO2 and paCO2
O2 - low
CO2 - will be normal or even low, because not affected by diffusion
what will happen to CO2 and O2 if the is low V/Q in one region
local hypercapnea, but normal global capnea, both local and global hypoxemia
what will happen if give more O2 is v/Q is low
will improve if can reach regional area
what are 3 causes of shunts?
- within the lung (pneumonia)
- intracardiac
- physiological - bronch arts. and veins
3 characteristics of a shunt
- doesn’t improve with 100% O2
- does not increase pCO2 - breathe faster
- global hyperventialtion - to decrease CO2
what is it called when V>Q?
dead space - a region with no perfusion
what is most important in V/Q
the ratio, not absolute values
where in the lung does most ventilation and perfusion occur?
at the base
how does the V/Q ratio change as go from bottom to top of lung?
goes up
how does the lung improve gas exchnage during excercise
perfuses more apical lung portions
what is PAO2 calculation
PA02 = PiO2 - (1.25xPaCO2)
what is normal A-a gradient
10-15
when do we need to calculate the A-a gradient
only when pCO2 is abnormal - is pCO2 is normal, we know there is a mismatch problem
how does the lung react to V<Q?
arteries constrict to decrease perfusion
what does pulmonary hypertension cause?
cor pulmonale - heart disease caused by lung
