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