Acid Base Management Flashcards
technical definition of blood gas
gas under ordinary conditions
dissolved to some extent into our blood
clinical definition of blood gas
test that measures actual gases (PaO2, PaCO2) but includes values that aren’t blood gases
5 main things in arterial blood gas
pH HCO3- base excess PaCO2 PaO2
additional things that can be added to ABGs
Hb/Hct K Glucose Calcium Carboxyhemoglobin Methemoglobin
technical definition of base excess
amount of acid or base needed (at 100% SaO2 and 37C) to return:
pH to 7.4
PaCO2 to 40mmHg
clinical definition of base excess
ABG value that reveals if the pt has too much or not enough base
What type of base status does base excess refer to?
metabolic acid base status
normal base excess
-2 to 2 mmol/L
negative base excess
< -2 mmol/L
not enough base
metabolic acidosis
treatment for negative base excess?
bicarb
positive base excess
> 2mmol/L
too much base
metabolic alkalosis
how do you treat metabolic alkalosis
reversing the cause of alkalosis
what is pH defined as
H+ concentration
what is pH determined by?
HCO3-/PaCO2
normal pH range
7.35-7.45
pH >7.45
alkalosis
pH<7.35
acidosis
6 consequences of acidosis
decrease cardiac contractility decreases response to catecholamines impairs coagulation and increases bleeding increases PVR lowers vfib threshold increases plasma K concentration
why does acidosis increase K concentration in the plasma?
H+ enters cells and K+ leaves cells
5 consequences of alkalosis
shifts oxyhemoglobin curve to left increases SVR cerebral vasoconstriction decreases PVR decreases plasma K concentration
venous measurement CO2
24-30mEq/L
arterial measurement HCO3-
22-26mEq/L
PaCO2
35-45mmHg
PvCO2
40-50mmHg
~5 higher than PaCO2
when does the PvCO2 to PaCO2 gradient increase
pt is poorly perfused
PaO2 of atmosphere
~160mmHg
PaO2
70-100mmHg
decreases with age
PvO2
30-40mmHg
CaO2
16-20mL/dL
CvO2
12-16mL/dL
SmvO2
60-80% in awake pts
SaO2
93-98%
use a decimal or percent for SaO2 in the equation?
decimal
on room air what is the A-a gradient
5-15mmHg
in elderly pts what does the A-a gradient increase to
15-25mmHg
on 100% FiO2 what can the A-a gradient be as high as?
10-110mmHg
minute ventilation
7-8L/min
Va
alveolar ventilation
2/3 minute ventilation
what is tissue perfusion primarily depended on?
SaO2
PaO2 has little effect on tissue perfusion
VCO2
CO2 production
200mL/min
how much is VCO2 decreased by with GA
60%
VO2
oxygen consumption
250mL/min (normothermic 70kg)
%MetHb normal
<2%
%COHb normal
<3%
HCO3-/PaCO2 ratio
20:1
abnormal ratio always leads to abnormal pH
PaO2/FiO2 ratio
480
Anion Gap
8-16mEq/L
Lances simple PiO2 equation
PiO2= (FiO2)(713)
serum lactate concentration
<2mmol/L
lactic acidosis
serum lactate >5mmol/L
CaO2 Equation
(SaO2)(Hb)(1.34)+(PaO2)(0.003)
what % of oxygen is bound to Hb?
98.5%
what % of oxygen is dissolved in plasma?
1.5%
T/F PaO2 makes up a large portion of the total oxygen content in the arteries.
False
it makes up a small portion
what is the primary determinant of CaO2?
SaO2
If SaO2 increased by 10% and Hb also increased by 10% which would have the greater effect on CaO2?
they would have the same effect
what are the units for 1.34 in the CaO2 equation?
mL O2/ 1g Hb
varrying capacity of Hb
use a decimal or percent for SaO2 in the equation?
decimal
CvO2 equation
(SvO2)(Hb)(1.34)+(PvO2)(0.003)
fick equation
VO2= (Cardiac Output)(CaO2-CvO2)(10)
units for the fick equation answer
mL/min
DO2
amount of oxygen available for tissue perfusion per minute
DO2 equation
DO2= (CaO2)(Cardiac Output)
what is tissue perfusion primarily depended on?
SaO2
PaO2 has little effect on tissue perfusion
PiO2 definition
pressure of inspired oxygen
3 things that determine PiO2
FiO2
pressure in the atmosphere
water vapor pressure
equation alveolar volume
Vt-Vd
if atmospheric pressure increasees then PiO2 _____?
increases
as water vapor pressure in the air increases PiO2 _____?
decreases
PiO2 equation
PiO2= (FiO2)(Barometric Pressure -Water Vapor Pressure)
sea level barometric pressure
760
sea level water vapor pressure
47
Lances simple PiO2 equation
PiO2= (FiO2)(713)
PAO2 equations
(PiO2)- (1.2)(PaCO2)
OR
(FiO2)(713)- (1.2)(PaCO2)
what changes about the PAO2 equation if the FiO2 is >60%?
leave out the 1.2
NEW=
(FiO2)(713)-(PaCO2)
if PaCO2 decreases what does that do to PAO2?
increases
exact mechanism unknown
is it possible to have a normal pH with abnormal bicarb and PaCO2 levels?
yes
PAO2 estimation
PAO2= 102- (age/3)
Vt
tidal volume
air expired in one breath
does Vt include dead space volume?
yes
MV
minute ventilation
total volume of air that we breath in 1 min
does MV include dead space?
yes
MV equation
RR*Vt
Vd
volume of dead space in one breath
what amount of the Vt is dead space?
1/3
in a pt with pulm disease what amount of Vt is dead space?
> 1/3
PaO2/FiO2 <200 indicates what?
ARDS
acute respiratory distress syndrome
Vd/Vt=
(Vd)(RR)
Which of the following is least likely to lower a patient’s alveolar PO2?
- Increase in altitude
- Elevated PaCO2
- A left to right intracardiac shunt
- None of the above
-A left to right intracardiac shunt
what is the amount of dead space proportional to?
difference in PaCO2 and etCO2
Alveolar Volume
amount of air in one breath that actually reaches the alveoli and participates in gas exchange
equation alveolar volume
Vt-Vd
VA
alveolar ventilation
amount of air in one min that participates in gas exchange
equation for VA
VA= (Vt-Vd)(RR)
PaCO2 equation
(VCO2mL/min)(0.863)/ VA L/min
if alveolar ventilation is low then PaCO2 will be?
high
if CO2 production is high then PaCO2 will be?
high
what can high levels of CO2 cause?
acidosis
what can low levels of CO2 cause?
alkalosis
clinical henderson hasselbalch equation
pH= HCO3-/PaCO2
is it possible to have an abnormal pH with normal bicarb and PaCO2 levels?
no
what % of CO2 is in the form of HCO3-?
90-95%
what is the A-a gradient
difference between the PAO2 and PaO2
what does an increase in A-a gradient indicate?
lung disease
A-a gradient will increase with
impaired gas exchange (COPD)
age
supplemental oxygen
right to left intracardiac shunting
disadvantages to A-a gradient
anesthetist must calculate PAO2
varies greatly in ppl breathing supplemental O2
alternative to A-a gradient
PaO2/FiO2
normal PaO2/FiO2 ratio?
> 400
in health pts the PaO2 is ~ ___ greater than FiO2
5x
the lower number we get for the PaO2/FiO2 ratio indicates what?
higher degree of lung disease
PaO2/FiO2 <300 indicates what?
ALI
acute lung injury
PaO2/FiO2 <200 indicates what?
ARDS
acute respiratory distress syndrome
advantages to PaO2/FiO2 ratio
anesthetist doesnt have to calculate PAO2
this ratio doesnt vary as much with people on supplemental O2
Which of the following is least likely to lower a patient’s alveolar PO2?
- Increase in altitude
- Elevated PaCO2
- A left to right intracardiac shunt
- None of the above
-A left to right intracardiac shunt
What is the maximum value attainable by adding the values obtained for SaO2, %COHb, and %MetHb from a single blood sample?
100%
If the PaCO2 and FiO2 of a patient both increase by 50%, what is most likely to happen to their PAO2?
increase
If both barometric pressure and the PaCO2 of a patient fall by half, what is most likely to happen to their PAO2?
decrease
At 10:00am, a patient has a PaO2 of 85mmHg, and SaO2 of 98%, and a Hb of 14g/dL. At 10:05am, she suffers a severe hemolytic reaction that suddenly leaves her with a Hb of 7g/dL. Assuming no lung disease occurs from the hemolytic reaction, what is most likely to occur with her PaO2, SaO2, and CaO2?
PaO2 unchanged, SaO2 unchanged, CaO2 reduced
Which of the following is least likely to change the PAO2 of a patient? SaO2 PaCO2 Barometric pressure FiO2
SaO2
Which of the following situations would be most likely to lower the PaO2 of a patient?
- Carbon monoxide poisoning
- Abnormal hemoglobin that holds oxygen with twice the affinity of normal hemoglobin
- Anemia
- Lung disease with intrapulmonary shunting
Lung disease with intrapulmonary shunting
when is CaO2 reduced?
anemia
carbon monoxide poisoning
V/Q mismatch
high altitude
what converts CO2 to H2CO3?
carbonic anhydrase
what are the 3 forms of CO2 in the body?
PaCO2 (dissolved in plasma)
HCO3- (dissolved in plasma)
HCO3- (attached to Hb)
what % of CO2 is dissolved in the plasma?
5-10%
what % of CO2 is in HCO3- form in the plasma?
60-65%
what % of CO2 is in HCO3- form attached to Hb?
~30%
what % of CO2 is in the form of HCO3-?
90-95%
what can venous labs be called?
BMP (basic metabolic panel)
venous chem 7
electrolyte panel
what is venous CO2 listed as?
CO2 or HCO3-
what forms of CO2 are included in venous labs?
CO2 form (dissolved) HCO3- form (dissolved)
venous HCO3- normal value
24-30mEq/L
what is arterial CO2 listed as? why?
HCO3-
because it only includes the HCO3- form and omits the PaCO2 form
arterial HCO3- normal value
22-26mEq/L
If HCO3- and PaCO2 double from their normal baseline values, what is most likely to happen to the patient’s pH?
stays the same
What does the Henderson-Hasselbalch equation predict will happen if a patient’s PaCO2 increases from 40-60mmHg?
- pH fall
- bicarb fall
- bicarb rise
- cannot determine
not enough information provided
bohr effect
oxygen being displaced from Hb as PaCO2 rises (right shift of curve)
Haldane effect
CO2 being displaced from Hb as oxygen concentration increases
is oxygenated or deoxygenated blood more affinitive for CO2?
deoxygenated
what % of shunt do normal humans have?
3%
what does hyper and hypoventilation refer to? respiratory rate or CO2 removal?
CO2 removal
hypoxia
impaired oxygen perfusion
hypoxemia
decrease in the blood oxygen content (CaO2)
can someone be hypoxemic but not hypoxic?
yes if they have increased cardiac output to compensate for low blood oxygen content
respiratory acidosis
increase in PaCO2 concentration
what way does respiratory acidosis shift the lechatliers equation?
to the right
if when you have respiratory acidosis and you shift the equation to the right and you increase H+ and HCO3- then how does the pH go down?
1-the number of H+ increases and the definition of pH is the number of H+ ions
2- PaCO2 increases by a greater percentage
(20:1 vs 21:2)
diagnosis of resp acidosis
low pH
high PaCO2
problem with resp acidosis
too much H+ ions
compensation for resp acidosis
kidney reabsorb HCO3-
what is the problem with the compensation of resp acidosis?
kidneys reabsorbing HCO3- will increase PaCO2 even more
why don’t we treat resp acidosis with bicarb?
because it will ultimately raise the PaCO2
treatment for resp acidosis
increase minute ventilation and lower PaCO2
resp alkalosis
decrease in PaCO2
what way does respiratory alkalosis shift the lechatliers equation?
to the left
if when you have respiratory alkalosis and you shift the equation to the left and you decrease H+ and HCO3- then how does the pH go up?
1- decrease in H+ is the definition of pH so it will increase
2- the PaCO2 decreased by a greater percent than bicarb
diagnosis of resp alkalosis
high pH
low PaCO2
problem with resp alkalosis
too few H+ ions
compensation for resp alkalosis
kidneys excrete more bicarb
problem with the compensation for resp alkalosis
kidneys excreting HCO3- will cause the PaCO2 to decrease more
treatment for resp alkalosis
lower the minute ventilation and raise PaCO2
metabolic acidosis
decrease in bicarb concentration
what can cause a decrease in bicarb
direct physical loss of bicarb
increase in acid that lowers the HCO3- indirectly
what are examples of two indirect ways to cause metabolic acidosis
lactic acidosis
DKA
why pH decreases in metabolic acidosis
1- H+ increases
2- HCO3- decreases and decreases the HCO3-/PaCO2 ration and lowers pH
diagnosis of metabolic acidosis
low pH
low HCO3-
the problem with metabolic acidosis
too much H+ ion
compensation for metabolic acidosis
lungs increase ventilation and lower the PaCO2
problem with the compensation for metabolic acidosis
it will lower PaCO2 but by doing that it will also lower the HCO3-
treatment for metabolic acidosis
give bicarb
sodium bicarb dose
(0.3)(kg)(base excess)
A 50kg patient has a base excess of -3. What is the dose of bicarb recommended to correct the base excess?
45mEq
metabolic alkalosis
increase in bicarb
two possible mechanisms for metabolic alkalosis
1-actual physical increase in HCO3-
2- decrease in the H+ causing indirect increase in HCO3-
what are ways to cause direct loss of acid?
vomiting
diuretics
gastric drainage
when would you have buildup of HCO3- in the body
massive blood transfusion
citrate preservative is converted to HCO3-
T/F massive blood transfusion can cause metabolic alkalosis
true
why pH increase in metabolic alkalosis
1- H+ decreases
2- HCO3- increases the HCO3-/PaCO2 ratio and increases pH
diagnosis of metabolic alkalosis
high pH
high HCO3-
the problem with metabolic alkalosis
too few H+ ions
compensation for metabolic alkalosis
lungs will decrease their minute ventilation (hypovent) and increase the PaCO2 and decrease the pH
problem with the compensation for metabolic alkalosis
it will also increase the HCO3- and that is what caused the problem in the first place
treatment for metabolic alkalosis
try to reverse whats causing it
example: zofran if they have had a lot of N/V
normal lactate concentration
<2mmol/L
lactic acidosis serum lactate concentration
> 5mmol/L`
when does lactic acidosis occur?
when cells receive too little oxygen
type a lactic acidosis
inadequate oxygen delivery to tissues
type b lactic acidosis
adequate oxygen delivery,
tissues cannot use the oxygen normally
causes of lactic acidosis 4
1-sepsis
2-shock/ inadequate perfusion
3-hepatic failure
4-exercise
treatment of lactic acidosis 2
1- restore normal pH
2- improve tissue oxygenation (perfusion) with fluids and pressors
cations in our body
Na+ K+ Ca2+ Mg2+ H+ etc
anions in our body
HCO3- Cl- Lactate Proteins (albumin) Phosphates
measured cations
Na
K
measured anions
Cl-
HCO3-
Na normal values
135-145 mEq/L
K normal values
3.5-4.5 mEq/L
Cl- normal values
96-106 mEq/L
HCO3- normal values venous
24-30 mEq/L
in theory should a pt have more anions or cations?
they should be electrically neutral
equal number of both
anion gap definition
difference between the number of measured cations and the number of measured anions
two ways to calculate the anion gap
AG= measured cations- measured anions AG= unmeasured anions- unmeasured cations
Anion gap equation from our venous lab values
anion gap= (Na+K)-(HCO3- + Cl-)
K+ is usually omitted bc it is so small
anion gab normal value (without K)
12 +/- 4 mEq/L
anion gap will increase if=
measured cations goes up
measured anions goes down
unmeasured anions goes up
unmeasured cations goes down
anion gap will decrease if=
measured cations decreases
measured anions increases
unmeasured anions decreases
unmeasured cations increases
elevated/WIDE anion gap is most commonly observed when?
there has been an increase in the number of unmeasured anions
what are unmeasured anions considered?
acids bc they dissociate from H+ and increase the H+ ion concentration
How does the anion gap increase if I’m increasing both an unmeasured anion (lactate) and an unmeasured cation (H+)? Wouldn’t the anion gap remain unchanged?
1- increase in unmeasured anions (lactate)
decrease in the measured anions (HCO3-)
normal anion gap is caused by what?
direct loss of HCO3-
GI loss or renal dysfunction
why doesnt the gap increase when there is direct loss of HCO3-?
it is replaced by Cl-
hyperchloremic metabolic acidosis
acidosis with an increase in Cl- concentration
does hyperchloremic metabolic acidosis have a normal or abnormal anion gap?
normal
common cause of hyperchloremic metabolic acidosis
excess 0.9% N/S administration
why does excess N/S admin cause hyperchloremic met acidosis?
NORMALLY- Na reabsorbs with HCO3-
but in EXCESS-
Na reabsorbs more with Cl- causing loss of HCO3-
low anion gap cause
hypoalbuminemia (liver failure) bc albumin is neg charged protein
why does the anion gap decrease with hypoalbuminemia?
bc you are losing unmeasured anions and increases measured anions (Cl- and HCO3-)
3 steps to diagnosing acid base status
1- acidosis or alkalosis? via pH
2- respiratory (PaCO2) or metabolic (HCO3-)?
3- compensated or uncompensated?
what type of diabetes do people that have DKA have?
type I-
lack of insulin= starved cells (even with high blood sugar)
starved cells= fat breakdown and ketone bodies made
DKA what happens after ketone bodies are made?
sugar in blood goes into renal tubules causing osmotic diuresis
leads to hypovolemia and electrolyte abnormalities and acidosis
DKA symptoms
hyperglycemia acidosis hypovolemia electrolyte disturbances hyperosmolarity
can DKA cause hyper or hypokalemia?
acute= hyperkalemia (from acidosis) chronic= hypokalemia (from diuresis)
hyperosmolarity symptoms
cell shrinkage cerebral edema altered consciousness increased blood viscosity thrombosis
DKA treatment 4
1 insulin (reverse ketone production)
2 fix acidosis (bicarb as needed)
3 treat hypovolemia
4- prevent hypokalemia
insulin treatment for DKA protocol
once glucose gets to 250-300mg/dL add glucose to insulin infusion to keep at that level until acidosis corrected
glucose insulin infusion=
5g glucose added to each unit of insulin
1 amp dextrose per 5 units insulin
how to treat the hypovolemia
large bore IVS
agressive fluid admin
a line
how to prevent insulin induced hypokalemia
potassium chloride drip as necessary
what is in the ABG synringe already?
air and anticoagulant
PaCO2 in the air
0.3 mmHg
Will air in the sample falsely higher or lower the PaCO2 reading? why?
lower
bc the CO2 will diffuse out of the blood and into the air
PaO2 of blood on 100% FiO2
500mmHg
PaO2 of blood on room air
100mmHg
PaO2 in the air at sea level
160 mmHg
will the air in the sample of a pt breathing room air falsely higher or lower the PaO2? why?
falsely higher
because O2 will diffuse from the air to the blood
will the air in the sample of a pt breathing 100% FiO2 falsely higher or lower the PaO2? why?
falsely lower
because O2 will diffuse from the blood to the air
What do we tell the lab when sending a ABG?
the FiO2
the pts temp
if blood is cold what does that do for the solubility of CO2 and O2?
increases
if the blood is warm what does that do for the solubility of CO2 and O2?
decreases
think boiling water
what temp are blood samples measured at?
37C
what happens if the pts blood is not 37C
it will be warmed or cooled prior to measurement
cold blood sample will be increased or decreased PaCO2 and O2 readings?
increased
bc even though the solubility is decreased bc it is warmed….
it also increases the KINETIC ENERGY and that exerts greater pressure
warm blood sample will be increased or decreased PaCO2 and O2 readings?
decreased
bc even though the solubility will be increased due to cooling….
it decreases the kinetic energy and that exerts less pressure
