3. Acid Base Management Flashcards
venous CO2 normal value
24-30 mEq/L
(CO2 + HCO3-)
arterial CO2 normal value
22-26 mEq/L
(HCO3-)
PaCO2 normal
35-45 mmHg
PvCO2 normal
40-50 mmHg
PvCO2 is normally _______ compared to PaCO2
PvCO2 is 5 mmHg higher than PaCO2
if a pt is poorly perfused, what happens to the PvCO2:PaCO2 gradient
increases
PaO2 of atmosphere normal
160 mmHg (sea level)
PaO2 normal value
70-100 mmHg
what happens to PaO2 as you age?
it decreases
PvO2 normal value
30-40 mmHg
CaO2 normal value
16-20 mL/dL
CvO2 normal value
12-16 mL/dL
DO2
total delivery of O2 per minute
DO2 normal
1000 mL of O2 delivered per minute
normal Hb
15 g/dL
normal SaO2
93-98%
normal CO
5 L/min
mvO2 normal
60-80%
(up to 90%)
ScvO2 normal
70-75%
difference between PAO2 and PaO2
A-a gradient
A-a gradient: room air
5-15 mmHg
A-a gradient: elderly
15-25 mmHg
A-a gradient: 100% FiO2
10-110 mmHg
normal MV
7-8 L/min
Va =
2/3 of MV
Vd =
1/3 of MV
VCO2
200 mL/min
what happens to VCO2 under GA
decreased by up to 60%
VO2: normothermic adult
250 mL/min
VO2: infants
6-8 mL/kg/min
VO2: adults
3-4 mL/kg/min
pH
7.35-7.45
%MetHB on ABG
<2%
%COHb on ABG
<3%
HCO3-/PaCO2 ratio
20:1
PaO2/Fio2 ratio
480
Anion Gap
8-16 mEq/L
Base Excess
-2.0 - 2.0 mEq/L
serum lactate concentration
< 2 mmol/L
lactic acidosis
serum lactate > 5 mmol/L
Vt
volume of air expired in 1 breath
including dead space
MV
total volume of air breathed in 1 min
including dead space
MV =
MV = RR*Vt
Vd
volume of dead space in 1 breath
Vd: pulmonary dz
> 1/3 of Vt
Vd/Vt
amount of dead space ventilation that occurs in 1 min
Vd/Vt =
Vd/Vt = Vd*RR
alveolar volume
amount of air in 1 breath that reaches the alveoli and participates in gas exchange
alveolar volume =
alveolar vol = Vt - Vd
Va
amount of air in 1 min that reaches the alveoli and participates in gas exchange
Va =
Va = (Vt - Vd) *RR
blood gas: technically
gas under ordinary conditions
dissolved in our blood
blood gas: clinically
collection of values that may include actual blood gases but also include other values
ABG measures (6)
- pH
- PaCO2
- HCO3-
- PaO2
- SaO2
- Base excess
ABG additional values (6)
- Hb/Hct
- K+
- Glu
- Ca2+
- COHb
- MetHb
3 forms of CO2 in the body
- PaCO2
- HCO3- (plasma)
- HCO3- (Hb-bound)
PaCO2 accounts for ________ of all CO2
5-10%
HCO3- in plasma accounts for _______
60-65%
HCO3- bound to Hb accounts fo
30%
HCO3- total in body
90-95% of all CO2
lechatlier principle: drive RIGHT
incr CO2
or
decr HCO3-
lechatlier principle: drive LEFT
decr CO2
or
incr HCO3-
acids drive reaction
RIGHT
acids ____ H+
incr H+ ions
bases drive reaction
LEFT
bases ____ H+
decr H+ ions
respiratory acidosis cause
hypoventilation
incr PaCO2
respiratory acidosis diagnosis
low pH
high PaCO2
respiratory alkalosis cause
hyperventilation
decr PaCO2
respiratory alkalosis diagnosis
high pH
low PaCO2
metabolic acidosis cause
decr HCO3-
metabolic acidosis diagnosis
low pH
low HCO3-
metabolic alkalosis cause
incr HCO3-
metabolic alkalosis diagnosis
high pH
high HCO3-
pH is determine by
HCO3- to PaCO2 ratio
acidosis SE (6)
- decr contractility
- decr catecholamine response
- decr coag / incr bleeding
- incr PVR
- incr risk of Vfib
- incr plasma K+
alkalosis SE (6)
- shifts O2-Hb LEFT
- incr SVR
- cerebral vasoconstriction
- decr pVR
- decr plasma K+
pH ~
pH ~ HCO3- / PaCO2
base excess: technically
amount of acid or base needed to return the blood to pH 7.4 and PaCO2 to 40 mmHg
base excess: clinically
tells us if pt has too much or too little base in the blood
normal Base excess
-2 to 2 mmol/L
base excess > 2mmol/L
too much base
metabolic alkalosis
base excess < -2 mmol/L
not enough base
metabolic acidosis
what indicates metabolic acid/base status
base excess
what indicates respiratory acid/base status
PaCO2
PaCO2 should be _______ to EtCO2
PaCO2 should be 3-5 mmhg higher than EtCO2
if PaCo2 is significantly higher than EtCO2, then what might that suggest?
- lung disease
- hypotension
- low CO
PaCO2 =
PaCO2 = [(VCO2)*0.863]/Va
PaCO2 is proportional to
VCO2
PaCO2 is inversely proportional to
Va
with each subsequent minute of apnea
CO2 will increase exponentially
venous labs names
BMP
Chem 7
Electrolyte panel
venous sample includes which form of CO2
CO2
HCO3-
tCO2
venous CO2 (CO2 + HCO3-)
normal Venous CO2/HCO3-
24-30 mEq/L
normal arterial HCO3-
22-26 mEq/L
PAO2
partial pressure of O2 in the alveoli
PAO2 is determined by
FiO2
barometric pressure
PAO2 is minimally effected by
minute venilation
incr barometric pressure causes _____ FiO2
incr FiO2
can you measure PAO2
no - you can calculate it
PaO2
partial pressure of O2 dissolved in the arteries
PaO2 is what % of total body O2
1.5%
what determines PaO2
PAO2
PaO2 is not affected by
[Hb]
SaO2
CarboxyHb
MetHb
CyanoHb
normal PaO2 on room ari
80-100 mmHg
PaO2 estimate
5*FiO2
how to measure PaO2
blood sample
SaO2
% of Hb saturate w/O2
SaO2 measured
blood sample
pulse ox
SaO2 represents what % if total body O2
98.5%
what is SaO2 primarily determined by
PaO2
effect of CarboxyHb and MetHb on SaO2
decreases SaO2
right shift
Hb bind less tightly
left shift
Hb bind more tightly
right shift causes
acidosis
hypercarbia
hyperthermia
anemia
incr 2,3-DPG
left shift causes
alkalosis
hypocarbia
hypthermia
carboxyhb
methb
supp O2 effect on PAO2
incr PAO2
== incr PaO2
== incr SaO2
calculating PAO2 allows for assessment of
lung function
A-a gradient
PAO2 compared to PaO2
normal A-a gradient
5-15 mmhg
wide A-a gradient
> 15 mmHg
wide A-a gradient indicates
impaired gas exchange
or
increased R-L pulm shunting
normal A-a gradient indicates
normal lung function
equation used to calculat PAO2
alveolar gas equation
PAO2 =
PAO2 = PiO2 - (1.2)(PaCO2)
== PAO2 = (FiO2)(Pb-WVP) - 1.2*PaCO2
== PAO2 = (FiO2*713) - 1.2*PaCO2
(sea level)
primary determinant of PAO2
FiO2
PAO2 estimation
PAO2 ~ 102 - [age/3]
normal PaO2/FiO2 ratio
> 400
does PaO2/FiO2 vary with supp O2
nope
ALI PaO2/FiO2
< 300
ARDS PaO2/FiO2
< 200
CaO2 =
CaO2 = SaO2Hb1.34 + PaO2*0.003
what factors contribute to total arterial O2 content
PaO2
SaO2
Hb
which has a greater effect on CaO2: SaO2 or Hb
equal effect
which has a greater effect on CaO2: SaO2 or PaO2
SaO2
CvO2 =
CvO2 = (SvO2)Hb1.34 + PvO2*0.003
normal SvO2
70-75%
(draw off central line)
VO2 =
VO2 = CO(CaO2-CvO2)10
DO2
delivery of O2
amount of O2 available to tissue perfusion per minute
DO2 =
DO2 = CaO2CO10
DO2 is mostly dependent on
SaO2 and Hb
DO2 is minimally dependent on
PaO2
DO2 units
mL/min
hyper/hypoventilation refer to
CO2 removal not respiratory rate
hypoxia
impaired O2 perfusion
hypoxemia
decr in blood O2 content (CaO2)
hypoxemia hypoxia
hypoxia due to reduced arterial O2 saturation (SaO2)
anemic hypoxia
hypoxia due to decr [Hb] which leads to decr total O2 content in blood (CaO2)
normal SaO2
anemic hypoxia SaO2
normal
ischemic hypoxia
hypoxia due to decr blood flow to the tissues
causes of ischemic hypoxia
low CO
hypovolemia
severe vasoconstriction
etc
histotoxic/cytotoxic hypoxia
hypoxia due to inability of tissues to take up or use the O2 from the bloodstream
normal blood content
normal O2 delivery
causes of histotoxic/cytotoxic hypoxia
cyanide poisoning
carbon monixide posioning
methemoglobinemia
septic shock
impaired mitochondrial function
what happens to cerebral blood flow in hypoxic pt?
cerebral blood flow increases to deliver more O2 to brain
what pts should hypoxia be avoided in?
pts w/closed head injury
pts w/increased ICP
below what PaO2 does cerebral BF increase rapidly?
60 mmHg
Bohr effect
O2 being displaced from Hb as PaCO2 increases
Haldane effect
CO2 being displaced from Hb as O2 concentration increases
what Hb is more affinitive for CO2
deoxy Hb in peripheral veins
what Hb is less affinitive for CO2
oxy Hb in pulm capillaries
respiratory acidosis
incr PaCO2
respiratory acidosis diagnosis
low pH
high PaCO2
respiratory acidosis compensation
kidneys reabsorb HCO3- causing
1) incr HCO3-
2) incr pH
3) incr PaCO2
respiratory acidosis treatment
incr pt MV
respiratory alkalosis
decr PaCO2
respiratory alkalosis diagnosis
high pH
low PaCO2
respiratory alkalosis compensation
kidnesy excrete HCO3- causing
1) decr HCO3-
2) decr pH
3) decr PaCO2
respiratory alkalosis treatment
decr MV
metabolic acidosis
decr HCO3-k
metabolic acidosis diagnosis
low pH
low HCO3-
metabolic acidosis compensation
pt hyperventilates causing
1) decr PaCO2
2) incr pH
3) decr HCO3-
metabolic acidosis treatment
give bicarb
bicarb dosing
0.3weightbase excess
metabolic alkalosis
incr HCO3-
metabolic alkalosis diagnosis
high pH
high HCO3-
metabolic alkalosis compensation
pt hypoventilates causing
1) incr PaCO2
2) decr pH
3) incr HCO3-
metabolic alkalosis treatment
reverse the cause
normal PaCO2
40 mmHg
normal HCO3-
24 mEq/L
in respiratory acidosis, for each 10 mmHg increase in PaCO2: acute HCO3- effects
HCO3- incr 1 mEq/L (acute)
in respiratory acidosis, for each 10 mmHg increase in PaCO2: chronic HCO3- effects
HCO3- incr 4 mEq/L (chronic)
in respiratory alkalosis, for each 10 mmHg decrease in PaCO2: acute HCO3- effects
HCO3- decr 2 mEq/L
in respiratory alkalosis, for each 10 mmHg decrease in PaCO2: chronic HCO3- effects
HCO3- decr 4 mEq/L
in metabolic acidosis, PaCO2 should
PaCO2 should decrease 1.2x the HCO3- decrease
in metabolic alkalosis, PaCO2 should
PaCO2 should increase 0.7x the HCO3- increase
if pt has a respiratory distrubance, the body adjusts
HCO3-
if pt has metabolic disturbance, the body adjusts
PaCO2
routinely measured cations
Na+
K+
routinely measured anions
HCO3-
Cl-
plasma charge
neutral
“anion gap”
difference in the number of measured cations and measured anions
2 ways to calculated AG
- AG = measured Cat - measured anions
- AG= unmeasured anions - unmeasured cations
AG =
AG = (Na+ + K+) - (HCO3 + Cl-)
what can be omitted from AG equaation
K+
(relatively small)
AG ==
AG = Na+ - (HCO3- + Cl-)
normal AG
12 +/- 4 mEq/L
anion gap increases if (4)
- # measured cations incr
- # measured anions decr
- # unmeasured anions incr
- # unmeasured cations decr
anion gap decreases if (4)
- # measured cations decr
- # measured anions incr
- # unmeasured anions decr
- # unmeasured cations incr
why is anion gap useful
helps with differential diagnosis of disease states
lactic acidosis anion gap
high (widen) anion gap acidosis
lactic acid breaks down into
lactate
H+
why does lactic acidosis incr anion gap?
- incr unmeasured anions (lactate)
- decr measured anions (HCO3- binding H+)
excess NaCl
hyperchloremic
acidotic
start losing base
normal anion gap acidosis (2)
- direct loss of HCO3-
- incr [Cl-]
common cause of direct HCO3- loss
GI (diarrhea)
renal dysfunction
common cause of hyperchloremic metabolic acidosis
excess 0.9% N/S
low anion gap acidosis
low anion gap alkalosis
hypoalbuminemia
loss of albumin (-)
retention of HCO3-/Cl-
DKA pts most likely have
T1D
what causes DKA
lack of insulin
what does lack of insulin cause
cells break down fats in order to create sugar
== produced ketone bodies
are ketone bodies acids or bases
acids
what happens when blood sugar gets too high
kidneys cant keep up with filtration
– sugar spills into renal tubules
– incr osmotic diuresis
– hypovolemia
what should we give with insulin
K+
DKA symptoms
- hyperkalemia
- acidosis
- hypovolemia
- K+ disturbnaces
- Na+ disturbances
- hyperosmlarity
hyponatremia is seen in what amount of pts with DKA
2/3
DKA: K+ disturbance
hyperkalemia most common
DKA: Na+ disturbance
hyponatremia most common
DKA treatment
- admin insulin
- K+ infusion
- add glu w/insulin infusion
- give bicarb
- fluid resuscitation
when do you give insulin
K+ > 3.3 mEq/L
what should you correct prior to starting insulin therapy?
correct K+ level
when should you start adding glu to insulin infusion
glu = 250-300 mg/dL
glucose insulin infusion dosing
1 unit insulin per 5g glu
(5 units insulin per amp D50)
how much fluid is lost in DKA
6-9L
how much fluid should be replaced in DKA
total volume of loss within 24-36 hrs
how much fluid is given in DKA resucitation during the first 8-12 hrs
50% of volume
which fluid for DKA resuscitation?
crystalloid
- NS more popular than LR due to hyponatremia
air in blood sample: CO2 diffusion
CO2 diffuse OUT of blood INTO air
air in blood sample PaCO2
falsely lowerd PaCO2 reading
pt on 100% O2
air in blood: O2 diffusion
O2 diffuse OUT of blood INTO air
- pt on 100% O2*
air in blood PaO2
falsely lowerd PaO2 reading
pt on room air
air in blood: O2 diffusion
O2 diffuse OUR of air INTO blood
pt on room air
air in blood: PaO2
falsely elecated PaO2
blood samples colder than 37C
wil be warmed
blood samples warmer than 37C
will be cooled
what happens to PaO2 and PaCO2 when blood is warmed
PaO2 Incr
PaCO2 incr
what happens to PaO2 and PaCO2 when blood is cooled
PaO2 decr
PaCO2 decr
cold blood samples have
falsely elevated PaO2/PaCO2
warm blood samples have
falsely lowered PaO2/PaCO2
pregnancy PaO2
increases
(due to incr MV)
pregnancy pH
increases
(due to incr MV and resp alkalosis)
pregnancy HCO3-
decreases
neonate pH
lower
(7.2)
neonate PaO2
lower
50-80 mmHg
neonate PaCO2
normal
35-45 mmhg
