B4-055 Hypoxia Flashcards
some inefficiency of gas exchange in a normal healthy lung is due to
2
- heterogeneity of VA/Q distribution
- small veno-arterial shunt
units with a VA/Q higher than ideal have a higher […] and lower […]
higher PO2
lower CO2
units with a lower VA/Q than ideal have a lower […] and a higher […]
lower PO2
higher PCO2
under normal conditions, the V/Q ratio of the lung is
around 1
ventilation per unit volume is greatest at the […] of the lung
base
progressively smaller toward apex
perfusion is greatest at the […] of the lung
base
changes in VA/Q are lowest at the […] of the lung and increase toward the […]
base
apex
at the top of the lung
VA/Q:
PCO2:
PO2:
VA/Q: high
PCO2: low
PO2: high
at the bottom of the lung
VA/Q:
PCO2:
PO2:
VA/Q: low
PCO2: increased
PO2: decreased
alveolar ventilation will be […] in areas of low compliance
low
alveolar ventilation will be […] in areas of high compliance
high
alveolar ventilation will be […] in areas of low resistance
high
alveolar ventilation will be […] in areas of high resistance
low
for any given PaCO2, the PECO2 will be
lower
due to volume from dead space
the PECO is diluted about 1/3 compared to
PaCO2
normal VD/VT
.25-.35
when VD/VT > 0.6, patients are
ventilated
cannot maintain ventilation
low PaO2
without much increase in CO2
increased dead space
VD/VT > 0.3
increased dead space
shunt unit produce a […] in arterial PO2
large decrease
venous blood mixed with arterial blood, mixing PO2
does increased PIO2 or hyperventiliation increase PaO2 significantly?
no
shunt
shunt units produce a […] in PaCO2
small increase
ineffective at raising PaO2, but effective in lowering PaCO2
hyperventilation
VD/VE >0.35
increased dead space
A-aPO2 > 10 mmHG
shunt
low PaO2 is sensed by
peripheral chemoreceptors
when PAO2-PaO2 is greater than 5-10, you have
diffusion impairment
increased thickness or decreased surface area for gas exchange
- produce a large decrease in arterial PO2
- produce relatively small increase in arterial CO2
shunt units
normal PAO2, PaO2, CaO2
Low Q
cardiogenic shock
PaO2 of 40 mmHg
CaO2 is 15 ml/dl
acute or chronic hypoxia
acute hypoxia
normal PaO2
90-95
normal CaO2
20 ml/dl
at a PaO2 of 40, we would expect an O2 content of
15 ml/dl
75% saturation
is PaO2 is 40 mmHg but O2 content is normal,
acute or chronic
chronic
long term compensation (increased Hb)
PaCO2 is 60 mmHg
pH is 7.36
acute or chronic hypoxia?
chronic
pH is normal despite high PaCO2
compensated respiratory acidosis
each 10 mmHg increase in PaCO2 will decrease pH by […] in the short term
0.08 units
PaO2 is 40 mmHg
CaO2 is 19.2 ml/dl
acute or chronic hypoxia
chronic
PaO2 is low, but CaO2 is normal
compensation
PaCO2 is 20 mmHg
pH is 7.56
acute or chronic
acute
PaCO2 decreased by 20, so expected pH increase is .16
non compensated
alveolar ventilation is only defined by a change in
PaCO2
:)
.
if Hb is greater than 15 g/dL
chronic hypoxia
if pH is what would be predicted based on an acute change in PaCO2
non-compensated
0.08 change in pH for every
10 mmHg change in PaCO2
PaCO2 > 40 mmHg
hypoventilation
PaCO2 < 40 mmHg
hyperventilation
PAO2 - PaO2 should be
5-10 mmHg
normal dead space
.25-.35
if PAO2 - PaO2 is greater than 5-10, what does this mean?
something besides a change in ventilation is also happening
could be diffusion issue, shunt unit
primarily drive low PaO2
shunt units
normal PECO2
30
under normal conditions with a normal CO, the difference in systemic arterial and venous O2 content is
5 ml O2/dl
- arterial O2 content is normal
- venous O2 content is markedly decreased
what does this indicate?
decreased flow to systemic organs
hypovolumic shock
- arterial PO2 is 40 mmHg
- arterial O2 content is 15 ml/dl
what would this indicate?
acute hypoxia
obstruction of large bronchus
how does anemia affect arterial O2 content,PaO2, and arterial blood content?
CaO2: decreased
PaO2: normal
arterial blood O2: decreased
how does hypoventilation affect PaCO2 and PaO2?
PaCO2: increased
PaO2: decreased
