Blood Gas Analysis Flashcards
why is precise regulation of acid/bases needed?
enzyme activity
O2 transport
chemical rxn rate
normal blood pH
7.35-7.45
acidemia
blood pH <7.35
alkalemia
blood pH >7.35
acidosis
process that lowers pH
alkalosis
process that raises pH
3 ways body regulates acids/bases
buffers
pulm excretion of CO2 (mins)
renal elim of acids (days)
buffer
substance in a solution that prevents extreme changes in pH
buffer equations
henderson hasselbach
pH = pKa + log ( [base]/[conjugate acid])
pKa
pH where acid is 50% protonated and 50% deprotonated
pKa measures
strength of acid
buffers in blood
bicarbonate
hemoglobin buffer system
protein buffer
phosphate
ammonia
bicarbonate buffer
CO2 +H2O –> H2CO8 –> H+ + HCO3-
bicarbonate rxn speed
slow
how does the body speed up the bicarbonate rxn
carbonic anhydrase
where is carbonic anhydrase located
endothelium
erythrocytes
kidneys
hgb buffer
hgb contains multiple histidines
imidizole size chains
H+ binds to rings
displaces O2
hgb buffer depends on what
the bicarb buffer to move CO2 intracellular
% of CO2 in blood
70% buffered
23% carbaminohemoglobin (not buffered)
7% CO2 dissolved in plasma (PaCO2)
bohr effect
CO2 and H+ effect Hbg affinity for O2
high CO2/low pH does what to the Hb-O2 curve
right shift
haldane effect
deoxyhemoglobin has 3.5% greater affinity for CO2 than hb
PO2 is low in venous blood
hgb carries more CO2
central chemoreceptors
respond to changes in CSF pH
H+ activates chemoreceptors
incr MV
MV increases ______ for every _____ increase in CO2
MV increases 1-4L/min for every 1 mmHg increase in PaCO2
peripheral chemoreceptros
carotid bodies
sensistive to:
PaO2
PaCO2
pH
arterial perfusion
aortic bodies nerve
vaguys
carotid bodies
glosopharyngeal
renal compensation mechanisms
reabsorption of filtere HCO3-
excretion of acids
ammonia
venous gas pH
0.03-0.04 les than arterial
venous pO2
less than PaO2
venous gas is used for
trends
temperature and solubility relationship
inversely proportional
at a lower temp ______ goes into solution
at a lower temp more gas goes into solution
alpha stat
measures all blood gases at 37F
(raise the temp of the sample)
alpha stat pH
try to keep pt at 7.4pH
pt vs alpha stat pH
pt pH is higher than the alpha stat will read
pH stat
taken at temp of pt
pH stat pH
keep pH at 7.4
drawing a pH stat from hypothermic pt
add CO2 to mx pH of 7.4
lower pH and higher CO2 improve
CV perfusion
cerebral O2
hypoventilation
increases CO2
increases H+
decreases pH
hyperventilation
decreases CO2
decreases H+
increases pH
base excess/base deficit
amount of strong acide or strong base required to return 1L of whole blood to pH of 7.4 at a PCO2 of 40 mmHg
anion gap
difference between measured cations and measured anions
anion gap equation
AG = Na+ - (Cl- + HCO3-)
normal anion gap
8-12 mEq/L
most common unmeasures anions
lactic acid
ketones
anion gap step 1
determin oxygenation status
PaO2 ~ FiO2*5
anion gap step 2
determine alkalemia or acidemia
pH
anion gap step 3
determine respiratory or metabolic
resp:
normal PacO2 = 35-45
meta:
normal HCO3- = 22-28
anion gap step 4 (respiratory origin)
acute respiratory acidosis
- pH change 0.08 for every 10 mmHg in PCO2 from 40
chronic
- pH change 0.03 for every 10mmHg in PCO2 from 40
anion gap step 5 (metabolic)
calculate anion gap
AG = Na-(Cl+HCO3)
Normal: 8-12
anion gap step 6
calculate delta gap
(AG - 12) + HCO3-
delta gap < 22: concurrent non gap
delta gap > 26: concurrent metabolic acidosis
anion gap step 7
respiratory compensation?
metabolic acidosis
- PCO2 = (0.7HCO3)+21
or
- PCO2 = (1.5HCO3)+8 (winter formula)
PCO2 > PCO2 calculated = concurrent resp acidosis
PCO2 < PCO2 calculated = concurrent resp alkalosis
