Fouty- Arterial Blood Gas Flashcards
resp. alkalosis?
resp. acidosis?
3 main things arterial blood gases provide info on:
pH
adequacy of ventilation (PCO2)
adequacy of oxygenation (PaO2)
how to calculate P(A-a)O2 gradient
alveolar gas equation (PAO2)-PaO2 measured
_____ is directly related to alveolar ventilation
arterial CO2
Henderson-Hasselbach equation
pH=pKa + log (HCO3-)/s x PCO2
s in HH equation is what
solubility of CO2
normal pH in people (range)
7.36-7.44
normal solubility of CO2
0.03
PCO2 (lung or kidney)
lung
HCO3- (lung or kidney)
kidney
decrease in HCO3- and PCO2 stays the same
uncompensated metabolic acidosis
HCO3- increased and PCO2 remains the same
uncompensated metabolic alkalosis
increase in PCO2 and HCO3- the same
uncompensated respiratory acidosis
what decreases when PCO2 is increased
alveolar ventilation
decrease in PCO2 and HCO3- hasn’t changed
uncompensated respiratory alkalosis
2 things that make pH alkalinic
less PCO2
more HCO3-
2 things that make pH acidotic
decrease in HCO3-
increase in PCO2
____ and ____ are pathologic processes in which the values for acid and base are out of the normal range
acidosis and alkalosis
____compensation is fast
respiratory compensation
___ compensation is slow
metabolic
decreased HCO3-, and then decrease PCO2
compensated metabolic acidosis
causes of metabolic acidosis
seizure
DKA
severe diarrhea
in compensated metabolic acidosis, does the pH go back to normal due to increased alveolar ventilation
no, it gets it back into normal range but not all the way normal
cause of increase PCO2
hypoventilation
too much morphine
increase in PCO2 (respiratory acidosis), in 3-5 days, kidneys will compensate by what
increasing HCO3- (kidneys get pH back to normal)
Acidemia and alkalemia denote that the process has resulted in an abnormal pH. This frequently indicates that the initial acid-base abnormality is _________
uncompensated or inadequately compensated
blood pH>/= 7.45
alkalemia
denotes a blood pH </= 7.35
acidemia
body handles acidemia better than what
alkalemia
acute change of PaCO2 of 10 mmHg leads to pH change of ____
0.08
if PaCO2 is down, what is increased
alveolar ventilation
if PaCO2 is increased, what is decreased
alveolar ventilation
main way CO2 is carried from tissues to lungs
HCO3-
PCO2 correlates linearly w/ _____ content over human range
CO2
normal range of PaCO2
38-42 mmHg
normal range of HCO3
22-26 meq/L
PaCO2</= 35 mmHg
primary respiratory alkalosis
PaCO2>/= 45 mmHg
primary respiratory acidosis
HCO3- >/=28 meq/L
primary metabolic alkalosis
HCO3- </= 22 meq/L
primary metabolic acidosis
uncompensated respiratory acidosis
if PaCO2 changes by 10, HCO3- changes by ____
1
change in pH is directly a result of change in ____
PaCO2
uncompensated respiratory alkalosis
primary respiratory alkalosis and primary metabolic alkalosis
primary metabolic acidosis
hyperventilation is PaCO2 < ____
36 mmHg
compensation for metabolic acidosis
hyperventilation
Winter’s formula used for what
to check is there is adequate compensation for metabolic acidosis
Winter’s formula:
PaCO2= 1.5HCO3 + 8 +/- 2
for normal respiratory compensation, pH does not return to _____
normal range
point of compensation
to keep us from dying acutely from metabolic acidosis while physician tries to correct it
- lactic acidosis
- ketoacidosis
- toxic ingestions
- loss of HCO3
- severe diarrhea
causes of metabolic acidosis
primary respiratory alkalosis w/ metabolic compensation
primary metabolic acidosis with some respiratory compensation (went from 40 to 30)
reasons for metabolic acidosis with inadequate respiratory compensation (can’t blow out CO2 like they should)
neuromuscular weakness w/ severe diarrhea
ILD
narcotics
if this person was well yesterday and this is their ABG
metabolic acidosis
this ABG has occurred over weeks
metabolic compensation
aspirin toxicity
respiratory alkalosis w/ metabolic acidosis
long standing asbestos exposure
induced lung disease w/ respiratory alkalosis w/ metabolic compensation
if it’s an acute event, what doesn’t have time to kick in
metabolic compensation
If they can’t blow down CO2 enough, means they have underlying reason/weakness and cant generate _____to blow CO2 down
alveolar ventilation
lactic acidosis
ketoacidosis
renal failure
diarrhea
aspirin
common causes of primary metabolic acidosis
vomiting
diuretics
hypokalemia
excessive tums
hyperaldosteronism
causes of primary metabolic alkalosis
retain arterial CO2
hypoventilation
ILD
neurologic injuries
aspirin intoxication
hypoxia
causes of primary respiratory alkalosis
Takes time (48-72 hours minimum) for compensation
excretion of HCO3 by kidney
ILD
chest wall disease
neuromuscular disease
opiate use
causes of primary respiratory acidosis
how to compensate for respiratory acidosis
retain HCO3-
respiratory compensation for metabolic acidosis— fast, but ____
incomplete
metabolic compensation for respiratory acidosis—–slow, but ______
more complete
inadequate tissue oxygen
hypoxia
low arterial oxygen tension (PaO2)
less than 80 mmHg
hypoxemia
low arterial oxygen saturation (SaO2)
less than 90%
desaturation
will widen A-a gradient and lead to hypoxemia
low V/Q and shunt
alveolar gas equation
PAO2= (Pb - PH2O) x FiO2 - PaCO2/R
best estimate to low V/Q mismatch
P(A-a) gradient
normal A-a gradient
10-12
5 main causes of hypoxemia (PaO2<80 mmHg)
altitude
hypoventilation
diffusion
low V/Q mismatch
shunt
extreme exercise or extreme altitude (doesn’t occur very often in clinical medicine)
as the blood passes through the capillary in the alveolar interface, there is not complete equilibration b/t alveoli and the blood going past it
diffusion as cause of hypoxemia
normal A-a O2 gradient w/ hypoxemia
altitude
hypoventilation
increased A-a gradient w/ hypoxemia
diffusion
low V/Q mismatch
shunt
___ and ___ contribute to arterial hypoxemia
shunt and low V/Q
shunt
low V/Q
responds to 100% oxygen
low V/Q (not shunt)
How you get carboxyHb and methemoglobin
co-oximeter
failure to excrete CO2
hypercapneic (ventilatory) respiratory failure
inability to oxygenate
hypoxic respiratory failure
minute ventilation decreased or dead space increased
respiratory failure
