Acid Base Management Flashcards
1
Q
technical definition of blood gas
A
gas under ordinary conditions
dissolved to some extent into our blood
2
Q
clinical definition of blood gas
A
test that measures actual gases (PaO2, PaCO2) but includes values that aren’t blood gases
3
Q
5 main things in arterial blood gas
A
pH HCO3- base excess PaCO2 PaO2
4
Q
additional things that can be added to ABGs
A
Hb/Hct K Glucose Calcium Carboxyhemoglobin Methemoglobin
5
Q
technical definition of base excess
A
amount of acid or base needed (at 100% SaO2 and 37C) to return:
pH to 7.4
PaCO2 to 40mmHg
6
Q
clinical definition of base excess
A
ABG value that reveals if the pt has too much or not enough base
7
Q
What type of base status does base excess refer to?
A
metabolic acid base status
8
Q
normal base excess
A
-2 to 2 mmol/L
9
Q
negative base excess
A
< -2 mmol/L
not enough base
metabolic acidosis
10
Q
treatment for negative base excess?
A
bicarb
11
Q
positive base excess
A
> 2mmol/L
too much base
metabolic alkalosis
12
Q
how do you treat metabolic alkalosis
A
reversing the cause of alkalosis
13
Q
what is pH defined as
A
H+ concentration
14
Q
what is pH determined by?
A
HCO3-/PaCO2
15
Q
normal pH range
A
7.35-7.45
16
Q
pH >7.45
A
alkalosis
17
Q
pH<7.35
A
acidosis
18
Q
6 consequences of acidosis
A
decrease cardiac contractility decreases response to catecholamines impairs coagulation and increases bleeding increases PVR lowers vfib threshold increases plasma K concentration
19
Q
why does acidosis increase K concentration in the plasma?
A
H+ enters cells and K+ leaves cells
20
Q
5 consequences of alkalosis
A
shifts oxyhemoglobin curve to left increases SVR cerebral vasoconstriction decreases PVR decreases plasma K concentration
21
Q
venous measurement CO2
A
24-30mEq/L
22
Q
arterial measurement HCO3-
A
22-26mEq/L
23
Q
PaCO2
A
35-45mmHg
24
Q
PvCO2
A
40-50mmHg
~5 higher than PaCO2
25
when does the PvCO2 to PaCO2 gradient increase
pt is poorly perfused
26
PaO2 of atmosphere
~160mmHg
27
PaO2
70-100mmHg
| decreases with age
28
PvO2
30-40mmHg
29
CaO2
16-20mL/dL
30
CvO2
12-16mL/dL
31
SmvO2
60-80% in awake pts
32
SaO2
93-98%
33
use a decimal or percent for SaO2 in the equation?
decimal
34
on room air what is the A-a gradient
5-15mmHg
35
in elderly pts what does the A-a gradient increase to
15-25mmHg
36
on 100% FiO2 what can the A-a gradient be as high as?
10-110mmHg
37
minute ventilation
7-8L/min
38
Va
alveolar ventilation
| 2/3 minute ventilation
39
what is tissue perfusion primarily depended on?
SaO2
| PaO2 has little effect on tissue perfusion
40
VCO2
CO2 production
| 200mL/min
41
how much is VCO2 decreased by with GA
60%
42
VO2
oxygen consumption
| 250mL/min (normothermic 70kg)
43
%MetHb normal
<2%
44
%COHb normal
<3%
45
HCO3-/PaCO2 ratio
20:1
| abnormal ratio always leads to abnormal pH
46
PaO2/FiO2 ratio
480
47
Anion Gap
8-16mEq/L
48
Lances simple PiO2 equation
PiO2= (FiO2)(713)
49
serum lactate concentration
<2mmol/L
50
lactic acidosis
serum lactate >5mmol/L
51
CaO2 Equation
(SaO2)(Hb)(1.34)+(PaO2)(0.003)
52
what % of oxygen is bound to Hb?
98.5%
53
what % of oxygen is dissolved in plasma?
1.5%
54
T/F PaO2 makes up a large portion of the total oxygen content in the arteries.
False
| it makes up a small portion
55
what is the primary determinant of CaO2?
SaO2
56
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
57
what are the units for 1.34 in the CaO2 equation?
mL O2/ 1g Hb
| varrying capacity of Hb
58
use a decimal or percent for SaO2 in the equation?
decimal
59
CvO2 equation
(SvO2)(Hb)(1.34)+(PvO2)(0.003)
60
fick equation
VO2= (Cardiac Output)(CaO2-CvO2)(10)
61
units for the fick equation answer
mL/min
62
DO2
amount of oxygen available for tissue perfusion per minute
63
DO2 equation
DO2= (CaO2)(Cardiac Output)
64
what is tissue perfusion primarily depended on?
SaO2
| PaO2 has little effect on tissue perfusion
65
PiO2 definition
pressure of inspired oxygen
66
3 things that determine PiO2
FiO2
pressure in the atmosphere
water vapor pressure
67
equation alveolar volume
Vt-Vd
68
if atmospheric pressure increasees then PiO2 _____?
increases
69
as water vapor pressure in the air increases PiO2 _____?
decreases
70
PiO2 equation
PiO2= (FiO2)(Barometric Pressure -Water Vapor Pressure)
71
sea level barometric pressure
760
72
sea level water vapor pressure
47
73
Lances simple PiO2 equation
PiO2= (FiO2)(713)
74
PAO2 equations
(PiO2)- (1.2)(PaCO2)
OR
(FiO2)(713)- (1.2)(PaCO2)
75
what changes about the PAO2 equation if the FiO2 is >60%?
leave out the 1.2
NEW=
(FiO2)(713)-(PaCO2)
76
if PaCO2 decreases what does that do to PAO2?
increases
| exact mechanism unknown
77
is it possible to have a normal pH with abnormal bicarb and PaCO2 levels?
yes
78
PAO2 estimation
PAO2= 102- (age/3)
79
Vt
tidal volume
| air expired in one breath
80
does Vt include dead space volume?
yes
81
MV
minute ventilation
| total volume of air that we breath in 1 min
82
does MV include dead space?
yes
83
MV equation
RR*Vt
84
Vd
volume of dead space in one breath
85
what amount of the Vt is dead space?
1/3
86
in a pt with pulm disease what amount of Vt is dead space?
>1/3
87
PaO2/FiO2 <200 indicates what?
ARDS
| acute respiratory distress syndrome
88
Vd/Vt=
(Vd)(RR)
89
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
90
what is the amount of dead space proportional to?
difference in PaCO2 and etCO2
91
Alveolar Volume
amount of air in one breath that actually reaches the alveoli and participates in gas exchange
92
equation alveolar volume
Vt-Vd
93
VA
alveolar ventilation
| amount of air in one min that participates in gas exchange
94
equation for VA
VA= (Vt-Vd)(RR)
95
PaCO2 equation
(VCO2mL/min)(0.863)/ VA L/min
96
if alveolar ventilation is low then PaCO2 will be?
high
97
if CO2 production is high then PaCO2 will be?
high
98
what can high levels of CO2 cause?
acidosis
99
what can low levels of CO2 cause?
alkalosis
100
clinical henderson hasselbalch equation
pH= HCO3-/PaCO2
101
is it possible to have an abnormal pH with normal bicarb and PaCO2 levels?
no
102
what % of CO2 is in the form of HCO3-?
90-95%
103
what is the A-a gradient
difference between the PAO2 and PaO2
104
what does an increase in A-a gradient indicate?
lung disease
105
A-a gradient will increase with
impaired gas exchange (COPD)
age
supplemental oxygen
right to left intracardiac shunting
106
disadvantages to A-a gradient
anesthetist must calculate PAO2
| varies greatly in ppl breathing supplemental O2
107
alternative to A-a gradient
PaO2/FiO2
108
normal PaO2/FiO2 ratio?
>400
109
in health pts the PaO2 is ~ ___ greater than FiO2
5x
110
the lower number we get for the PaO2/FiO2 ratio indicates what?
higher degree of lung disease
111
PaO2/FiO2 <300 indicates what?
ALI
| acute lung injury
112
PaO2/FiO2 <200 indicates what?
ARDS
| acute respiratory distress syndrome
113
advantages to PaO2/FiO2 ratio
anesthetist doesnt have to calculate PAO2
| this ratio doesnt vary as much with people on supplemental O2
114
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
115
What is the maximum value attainable by adding the values obtained for SaO2, %COHb, and %MetHb from a single blood sample?
100%
116
If the PaCO2 and FiO2 of a patient both increase by 50%, what is most likely to happen to their PAO2?
increase
117
If both barometric pressure and the PaCO2 of a patient fall by half, what is most likely to happen to their PAO2?
decrease
118
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
119
```
Which of the following is least likely to change the PAO2 of a patient?
SaO2
PaCO2
Barometric pressure
FiO2
```
SaO2
120
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
121
when is CaO2 reduced?
anemia
carbon monoxide poisoning
V/Q mismatch
high altitude
122
what converts CO2 to H2CO3?
carbonic anhydrase
123
what are the 3 forms of CO2 in the body?
PaCO2 (dissolved in plasma)
HCO3- (dissolved in plasma)
HCO3- (attached to Hb)
124
what % of CO2 is dissolved in the plasma?
5-10%
125
what % of CO2 is in HCO3- form in the plasma?
60-65%
126
what % of CO2 is in HCO3- form attached to Hb?
~30%
127
what % of CO2 is in the form of HCO3-?
90-95%
128
what can venous labs be called?
BMP (basic metabolic panel)
venous chem 7
electrolyte panel
129
what is venous CO2 listed as?
CO2 or HCO3-
130
what forms of CO2 are included in venous labs?
```
CO2 form (dissolved)
HCO3- form (dissolved)
```
131
venous HCO3- normal value
24-30mEq/L
132
what is arterial CO2 listed as? why?
HCO3-
| because it only includes the HCO3- form and omits the PaCO2 form
133
arterial HCO3- normal value
22-26mEq/L
134
If HCO3- and PaCO2 double from their normal baseline values, what is most likely to happen to the patient’s pH?
stays the same
135
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
136
bohr effect
oxygen being displaced from Hb as PaCO2 rises (right shift of curve)
137
Haldane effect
CO2 being displaced from Hb as oxygen concentration increases
138
is oxygenated or deoxygenated blood more affinitive for CO2?
deoxygenated
139
what % of shunt do normal humans have?
3%
140
what does hyper and hypoventilation refer to? respiratory rate or CO2 removal?
CO2 removal
141
hypoxia
impaired oxygen perfusion
142
hypoxemia
decrease in the blood oxygen content (CaO2)
143
can someone be hypoxemic but not hypoxic?
yes if they have increased cardiac output to compensate for low blood oxygen content
144
respiratory acidosis
increase in PaCO2 concentration
145
what way does respiratory acidosis shift the lechatliers equation?
to the right
146
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)
147
diagnosis of resp acidosis
low pH
| high PaCO2
148
problem with resp acidosis
too much H+ ions
149
compensation for resp acidosis
kidney reabsorb HCO3-
150
what is the problem with the compensation of resp acidosis?
kidneys reabsorbing HCO3- will increase PaCO2 even more
151
why don't we treat resp acidosis with bicarb?
because it will ultimately raise the PaCO2
152
treatment for resp acidosis
increase minute ventilation and lower PaCO2
153
resp alkalosis
decrease in PaCO2
154
what way does respiratory alkalosis shift the lechatliers equation?
to the left
155
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
156
diagnosis of resp alkalosis
high pH
| low PaCO2
157
problem with resp alkalosis
too few H+ ions
158
compensation for resp alkalosis
kidneys excrete more bicarb
159
problem with the compensation for resp alkalosis
kidneys excreting HCO3- will cause the PaCO2 to decrease more
160
treatment for resp alkalosis
lower the minute ventilation and raise PaCO2
161
metabolic acidosis
decrease in bicarb concentration
162
what can cause a decrease in bicarb
direct physical loss of bicarb
| increase in acid that lowers the HCO3- indirectly
163
what are examples of two indirect ways to cause metabolic acidosis
lactic acidosis
| DKA
164
why pH decreases in metabolic acidosis
1- H+ increases
| 2- HCO3- decreases and decreases the HCO3-/PaCO2 ration and lowers pH
165
diagnosis of metabolic acidosis
low pH
| low HCO3-
166
the problem with metabolic acidosis
too much H+ ion
167
compensation for metabolic acidosis
lungs increase ventilation and lower the PaCO2
168
problem with the compensation for metabolic acidosis
it will lower PaCO2 but by doing that it will also lower the HCO3-
169
treatment for metabolic acidosis
give bicarb
170
sodium bicarb dose
(0.3)(kg)(base excess)
171
A 50kg patient has a base excess of -3. What is the dose of bicarb recommended to correct the base excess?
45mEq
172
metabolic alkalosis
increase in bicarb
173
two possible mechanisms for metabolic alkalosis
1-actual physical increase in HCO3-
| 2- decrease in the H+ causing indirect increase in HCO3-
174
what are ways to cause direct loss of acid?
vomiting
diuretics
gastric drainage
175
when would you have buildup of HCO3- in the body
massive blood transfusion
| citrate preservative is converted to HCO3-
176
T/F massive blood transfusion can cause metabolic alkalosis
true
177
why pH increase in metabolic alkalosis
1- H+ decreases
| 2- HCO3- increases the HCO3-/PaCO2 ratio and increases pH
178
diagnosis of metabolic alkalosis
high pH
| high HCO3-
179
the problem with metabolic alkalosis
too few H+ ions
180
compensation for metabolic alkalosis
lungs will decrease their minute ventilation (hypovent) and increase the PaCO2 and decrease the pH
181
problem with the compensation for metabolic alkalosis
it will also increase the HCO3- and that is what caused the problem in the first place
182
treatment for metabolic alkalosis
try to reverse whats causing it
| example: zofran if they have had a lot of N/V
183
normal lactate concentration
<2mmol/L
184
lactic acidosis serum lactate concentration
>5mmol/L`
185
when does lactic acidosis occur?
when cells receive too little oxygen
186
type a lactic acidosis
inadequate oxygen delivery to tissues
187
type b lactic acidosis
adequate oxygen delivery,
| tissues cannot use the oxygen normally
188
causes of lactic acidosis 4
1-sepsis
2-shock/ inadequate perfusion
3-hepatic failure
4-exercise
189
treatment of lactic acidosis 2
1- restore normal pH
| 2- improve tissue oxygenation (perfusion) with fluids and pressors
190
cations in our body
```
Na+
K+
Ca2+
Mg2+
H+
etc
```
191
anions in our body
```
HCO3-
Cl-
Lactate
Proteins (albumin)
Phosphates
```
192
measured cations
Na
| K
193
measured anions
Cl-
| HCO3-
194
Na normal values
135-145 mEq/L
195
K normal values
3.5-4.5 mEq/L
196
Cl- normal values
96-106 mEq/L
197
HCO3- normal values venous
24-30 mEq/L
198
in theory should a pt have more anions or cations?
they should be electrically neutral
| equal number of both
199
anion gap definition
difference between the number of measured cations and the number of measured anions
200
two ways to calculate the anion gap
```
AG= measured cations- measured anions
AG= unmeasured anions- unmeasured cations
```
201
Anion gap equation from our venous lab values
anion gap= (Na+K)-(HCO3- + Cl-)
| K+ is usually omitted bc it is so small
202
anion gab normal value (without K)
12 +/- 4 mEq/L
203
anion gap will increase if=
measured cations goes up
measured anions goes down
unmeasured anions goes up
unmeasured cations goes down
204
anion gap will decrease if=
measured cations decreases
measured anions increases
unmeasured anions decreases
unmeasured cations increases
205
elevated/WIDE anion gap is most commonly observed when?
there has been an increase in the number of unmeasured anions
206
what are unmeasured anions considered?
acids bc they dissociate from H+ and increase the H+ ion concentration
207
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-)
208
normal anion gap is caused by what?
direct loss of HCO3-
| GI loss or renal dysfunction
209
why doesnt the gap increase when there is direct loss of HCO3-?
it is replaced by Cl-
210
hyperchloremic metabolic acidosis
acidosis with an increase in Cl- concentration
211
does hyperchloremic metabolic acidosis have a normal or abnormal anion gap?
normal
212
common cause of hyperchloremic metabolic acidosis
excess 0.9% N/S administration
213
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-
214
low anion gap cause
hypoalbuminemia (liver failure) bc albumin is neg charged protein
215
why does the anion gap decrease with hypoalbuminemia?
bc you are losing unmeasured anions and increases measured anions (Cl- and HCO3-)
216
3 steps to diagnosing acid base status
1- acidosis or alkalosis? via pH
2- respiratory (PaCO2) or metabolic (HCO3-)?
3- compensated or uncompensated?
217
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
218
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
219
DKA symptoms
```
hyperglycemia
acidosis
hypovolemia
electrolyte disturbances
hyperosmolarity
```
220
can DKA cause hyper or hypokalemia?
```
acute= hyperkalemia (from acidosis)
chronic= hypokalemia (from diuresis)
```
221
hyperosmolarity symptoms
```
cell shrinkage
cerebral edema
altered consciousness
increased blood viscosity
thrombosis
```
222
DKA treatment 4
1 insulin (reverse ketone production)
2 fix acidosis (bicarb as needed)
3 treat hypovolemia
4- prevent hypokalemia
223
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
224
glucose insulin infusion=
5g glucose added to each unit of insulin
| 1 amp dextrose per 5 units insulin
225
how to treat the hypovolemia
large bore IVS
agressive fluid admin
a line
226
how to prevent insulin induced hypokalemia
potassium chloride drip as necessary
227
what is in the ABG synringe already?
air and anticoagulant
228
PaCO2 in the air
0.3 mmHg
229
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
230
PaO2 of blood on 100% FiO2
500mmHg
231
PaO2 of blood on room air
100mmHg
232
PaO2 in the air at sea level
160 mmHg
233
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
234
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
235
What do we tell the lab when sending a ABG?
the FiO2
| the pts temp
236
if blood is cold what does that do for the solubility of CO2 and O2?
increases
237
if the blood is warm what does that do for the solubility of CO2 and O2?
decreases
| think boiling water
238
what temp are blood samples measured at?
37C
239
what happens if the pts blood is not 37C
it will be warmed or cooled prior to measurement
240
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
241
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
