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Methods of Anesthesia > Acid/Base > Flashcards

Acid/Base Flashcards

1
Q

5 main things measured in ABG

A
  1. pH
  2. HCO3-
  3. Base excess
  4. PaCO2
  5. PaO2
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2
Q

Additional potential labs in an ABG

A
  1. Hb/Hct
  2. K+
  3. Glucose
  4. Ca++
  5. COHb
  6. MetHb
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3
Q

What is the technical term definition for base excess?

A

The amount of acid or base needed (at 100% SaO2 and 37 C) to return

  1. Blood pH to 7.4
  2. PaCO2 to 40 mmHg
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4
Q

Clinical definition of base excess

A
  • ABG value that reveals if the pt has too much or not enough base in blood
  • Refers to metabolic acid base status
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5
Q

Refers to pt’s respiratory acid/base status

A

PaCO2

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6
Q

Normal base excess

A

-2 to 2 mmol/L

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7
Q

Negative base excess

A

> -2 mmol/L

  • deficit of base in body
  • metabolic acidosis
  • treated with bicarb
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8
Q

Positive base excess

A

> 2 mmol/L

  • metabolic alkalosis
  • treated by reversing cause of alkalosis
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9
Q

High H+ concentration causes a (high/low) pH

A

Low pH (acidic)

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10
Q

Low H+ concentration causes a (high/low) pH

A

High pH (alkalotic)

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11
Q

Normal pH range

A

7.35-7.45

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12
Q

What determines pH?

A

The HCO3- to PaCO2 ratio

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13
Q

Consequences of acidosis

A
  1. Decreases cardiac contractility
  2. Decreases response to catecholamines
  3. Impairs coagulation and increases bleeding
  4. Increases PVR
  5. Lowers the vfib threshold (makes vfib more likely)
  6. Increases plasma K+ concentration (K+ exits cells)
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14
Q

Consequences of alkalosis

A
  1. Shifts oxyhemoglobin dissociation curve to the left
  2. Increases SVR
  3. Cerebral vasoconstriction
  4. Decreases PVR
  5. Decreases plasma K+ concentration (K+ enters cells)
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15
Q

Normal venous CO2

A

24-30 mEq/L

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16
Q

Normal arterial HCO3-

A

22-26 mEq/L

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17
Q

Normal PaCO2

A

35-45 mmHg

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18
Q

Normal PvCO2

A

40-50 mmHg

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19
Q

The PvCO2 to PaCO2 gradient increases if ____

A

the patient is poorly perfused

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20
Q

Normal PaO2 of the atmosphere at sea level

A

160 mmHg

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21
Q

Normal PaO2 in arterial blood

A

70-100 mmHg

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22
Q

PaO2 in arterial blood decreases ____

A

with age

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23
Q

normal PvO2

A

30-40 mmHg

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24
Q

Normal CaO2

A

16-20 mL/dL

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25
Q

Normal CvO2

A

12-16 mL/dL

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26
Q

Normal DO2

A

1000 mL of oxygen delivered per minute

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27
Q

Normal DO2 assumes what?

A

Normal Hgb, normal SaO2, normal CO

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28
Q

Normal mvO2

A
  • 60-80% in awake patients

- Up to 90% on 100% FiO2

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29
Q

Normal SaO2

A

93-98%

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30
Q

Normal ScvO2

A

70-75%

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31
Q

Normal A-a gradient on room air

A

5-15 mmHg

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32
Q

Normal A-a gradient in elderly patients

A

15-25 mmHg

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33
Q

Normal A-a gradient on 100% FiO2

A

10-110 mmHg

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34
Q

Normal minute ventilation

A

7-8 L/min

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35
Q

Normal Va (alveolar ventilation)

A

2/3 of minute ventilation in a healthy patient

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36
Q

Normal dead space ventilation (Vd)

A

1/3 of minute ventilation in a healthy patient

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37
Q

Normal VCO2

A

200 mL/min

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38
Q

How much is VCO2 decreased under GA?

A

By up to 60%

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39
Q

Normal VO2 (oxygen consumption)

A
  • 250 mL/min for a normothermic, 70kg adult
  • 6-8 mL/kg/min in infants
  • 3-4 mL/kg/min in adults
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40
Q

Normal %MetHb on ABG

A

<2%

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41
Q

Normal %COHb on ABG

A

<3%

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42
Q

Normal HCO3-/PaCO2 ratio

A

20:1

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43
Q

Normal PaO2/FiO2 ratio

A

480

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44
Q

Normal anion gap

A

8-16 mEq/L

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45
Q

Normal serum lactate concentration

A

<2 mmol/L

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46
Q

Lactic acidosis value

A

serum lactate >5 mmol/L

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47
Q

Total arterial oxygen content equation

A

CaO2= (SaO2)(Hb)(1.34) + (PaO2)(0.003)

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48
Q

Purpose of CaO2 equation

A
  1. PaO2 only makes up a small portion of total oxygen content in the arteries (1.5%)
  2. SaO2 and Hb are the primary determinants of CaO2
  3. SaO2 and Hb concentration have the same effect on CaO2
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49
Q

Percentage of O2 in the body bound to hemoglobin (SaO2)

A

98.5%

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50
Q

Percentage of O2 in the body dissolved in plasma (PaO2)

A

1.5%

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51
Q

What changes does CO poisoning have on SaO2 and PaO2

A

Lowers SaO2
Lowers CaO2
No change on PaO2

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52
Q

Equation for CvO2

A

CvO2= (SvO2)(Hb)(1.34) + (PvO2)(0.003)

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53
Q

Normal SvO2

A

Same as ScvO2, 70-75%

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54
Q

How is ScvO2 measured?

A

Venous sample off a central line

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55
Q

What is the Fick equation?

A

VO2 mL/min = (CO)(CaO2-CvO2)(10)

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56
Q

How do you calculate CO with the Fick equation?

A

CO L/min = VO2/ [(CaO2-CvO2)(10)]

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57
Q

What are the units for cardiac output with the Fick equation?

A

L/min

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58
Q

What are the units for VO2 with the Fick equation?

A

mL/min

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59
Q

Delivery of oxygen equation

A

DO2= (CaO2)(cardiac output)(10)

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60
Q

What does DO2 represent?

A

The amount of oxygen available for tissue perfusion

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61
Q

The tissue perfusion/delivery of oxygen is mostly dependent on

A

SaO2 and Hb concentration

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62
Q

What 3 things determines the pressure of inspired oxygen (PiO2)?

A
  1. FiO2
  2. Pressure of air in atmosphere
  3. Water vapor pressure
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63
Q

PiO2 equation

A

PiO2 = (FiO2)(barometric pressure-water vapor pressure)

PiO2= (FiO2)(713)

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64
Q

Alveolar gas equation (PAO2)

A

PAO2 = PiO2 - (1.2)(PaCO2)
or
PAO2 = (FiO2)(713)-(1.2)(PaCO2) for FiO2 <60%

PAO2 = (FiO2)(713)-(PaCO2) for FiO2 >60%

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65
Q

For each L/min on NC, the FiO2 ___

A

Increases 4%

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66
Q

Estimation for PAO2

A

PAO2 = 102 - (Age/3)

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67
Q

Volume of air that is expired in one breath, including dead space volume

A

Tidal volume

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68
Q

Total volume of air that we breathe in one minute, including dead space

A

Minute ventilation

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69
Q

Minute ventilation equation

A

=RR(Vt)

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70
Q

Normal dead space

A

1/3 of pt’s tidal volume

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71
Q

Dead space in a pt with pulmonary disease

A

more than 1/3 of tidal volume

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72
Q

Equation for dead space ventilation

A

=Vd(RR) or

=(PaCO2-EtCO2)/PaCO2

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73
Q

The amount of dead space a patient has is proportional to

A

the difference in PaCO2 and EtCO2

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74
Q

Amount of air in one breath that actually reaches the alveoli and participates in gas exchange

A

Alveolar volume

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75
Q

Alveolar volume equation

A

Vt-Vd

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76
Q

The amount of air in one minute that actually reaches the alveoli and participates in gas exchange

A

Alveolar ventilation

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77
Q

Equation for alveolar ventilation

A

VA= (Vt-Vd)(RR)

78
Q

PaCO2 equation

A

=(VCO2*0.863)/VA

79
Q

With the PaCO2 equation, if alveolar ventilation is low, PaCO2 will be…

A

High

80
Q

With the PaCO2 equation, if CO2 production is high, PaCO2 will be….

A

High

81
Q

What are the units for VCO2?

A

mL/min

82
Q

What are the units for VA?

A

L/min

83
Q

What is the main determinant of pH?

A

The ratio of HCO3- to PaCO2

84
Q

If you increase the amount of HCO3- or decrease the amount of PaCO2, pH will…

A

Increase

85
Q

If you decrease the amount of HCO3- or increase the amount of PaCO2, the pH will…

A

Decrease

86
Q

How is it possible for pH to be normal even if HCO3- and PaCO2 are abnormal?

A

If they are abnormal by the same percentage

87
Q

pH decreases ~0.1 unit per 10 mmHg (increase/decrease) in PaCO2

A

Increase

88
Q

pH increases ~0.1 unit per 10 mmHg (increase/decrease) in PaCO2

A

Decrease

89
Q

Normal A-a gradient

A

5-15 mmHg

90
Q

A larger difference in PAO2 and PaO2 indicates ___

A

lung disease

91
Q

The A-a gradient will increase with:

A
  1. Impaired gas exchange (COPD)
  2. Age
  3. Supplemental oxygen (FiO2 100% A-a gradient can be 10-110mmHg)
  4. R to L intracardiac shunting
92
Q

Disadvantages to the A-a gradient

A
  1. Anesthetist has to calculate PAO2

2. Can vary greatly in patients who are breathing supplemental oxygen

93
Q

Normal PaO2/FiO2 ratio

A

> 400
or
if the PaO2 is close to 5x the patient’s FiO2

94
Q

What does a lower value from the PaO2/FiO2 ratio suggest?

A

A higher degree of lung disease

95
Q

A PaO2/FiO2 ratio of <300 indicates ___

A

Acute lung injury

96
Q

A PaO2/FiO2 ratio of <200 indicates ___

A

ARDS

97
Q

Advantages to the PaO2/FiO2 ratio

A
  1. Don’t have to calculate PAO2

2. The PaO2/FiO2 ratio doesn’t vary as much as the A-a gradient does with supplemental oxygen administration

98
Q

What is the maximum value attainable by adding the values obtained for SaO2, %COHb and %MetHb from a single blood sample?

A

100%

99
Q

If the PaCO2 and FiO2 of a patient both increase by 50% what is most likely to happen to their PAO2?

A

It will increase

100
Q

If both barometric pressure and the PaCO2 of a patient fall by half, what is most likely to happen to their PAO2?

A

Decrease

101
Q

If a patient’s Hb decreases by half, what will happen with her PaO2, SaO2 and CaO2?

A

PaO2 and SaO2 are unchanged, CaO2 is reduced

102
Q

What is least likely to change the PAO2 of a patient?

A

SaO2

103
Q

Conversion of CO2 and HCO3- is made possible by what enzyme?

A

Carbonic anhydrase enzyme

104
Q

What are the 3 forms of CO2 in the body?

A
  1. PaCO2 (5-10%)
  2. HCO3- dissolved in plasma (60-65%)
  3. HCO3- that is attached to hemoglobin (30%)
105
Q

Normal HCO3- to PaCO2 ratio

A

20:1

106
Q

Other names for venous labs

A

BMP
Venous chem 7
Electrolyte panel

107
Q

Lab values in the venous labs

A
  1. Na+ ~135
  2. Cl- ~102
  3. BUN
  4. K+ ~4
  5. HCO3- ~24-30
  6. Cr
  7. Glucose ~70-100
108
Q

Why is the venous CO2 listed as HCO3- or CO2?

A

It includes both forms of CO2

-HCO3- dissolved in the veins and CO2 dissolved in the veins

109
Q

Normal value for venous CO2/HCO3-

A

24-30 mEq/L

110
Q

Normal arterial HCO3- value

A

22-26 mEq/L

111
Q

Is calculated and refers to the concentration of CO2 in arterial blood

A

HCO3-

112
Q

Is measured and refers to the partial pressure of CO2 in the arterial blood

A

CO2 (PaCO2)

113
Q

If HCO3- and PaCO2 double from their normal baseline values, what is most likely to happen to the patient’s pH?

A

Stays the same

114
Q

What does the Henderson-Hasselbalch equation predict will happen if a patient’s PaCO2 increases from 40-60 mmHg?

A

the pH will fall

115
Q

If the initial PaCO2 is 30 mmHg and the alveolar ventilation drops by 1L/min, the CO2 only changes by

A

4 mmHg

116
Q

If the initial PaCO2 is 68 mmHg and the alveolar ventilation drops by 1L/min, the CO2 changes by

A

24 mmHg

117
Q

The (higher/lower) the initial PaCO2, the less it changes for a given change in minute ventilation

A

Lower

118
Q

Refers to oxygen being displaced from hemoglobin as PaCO2 increases

A

Bohr effect

119
Q

Refers to CO2 being displaced from hemoglobin as oxygen concentration increases

A

Haldane effect

120
Q

Dexoygenated hemoglobin is (more/less) affinitive for CO2

A

More

121
Q

Oxygenated hemoglobin is (more/less) affinitive for CO2

A

Less

122
Q

Degree of pulmonary shunt in all humans

A

up to 3%

123
Q

Refers to any decrease in blood oxygen content

A

Hypoxemia

124
Q

Why does pH decrease in respiratory acidosis?

A
  1. The number of H+ ions increases

2. PaCO2 increases by a greater percentage

125
Q

Diagnosis of respiratory acidosis

A
  1. Low pH

2. High PaCO2

126
Q

Body’s compensation for respiratory acidosis

A

Kidneys reabsorb HCO3-

but then PaCO2 increases even more

127
Q

Treatment for respiratory acidosis

A

Increase minute ventilation and lower PaCO2

128
Q

Diagnosis of respiratory alkalosis

A
  1. High pH

2. Low PaCO2

129
Q

Body’s compensation for respiratory alkalosis

A

Kidneys excrete HCO3-

but then PaCO2 decreases more

130
Q

Treatment for respiratory alkalosis

A

Lower minute ventilation and raise PaCO2

131
Q

Causes of metabolic acidosis

A
  1. Direct, actual, physical loss of HCO3- (diarrhea)

2. Increase in acid and lowers HCO3- indirectly (lactic acidosis, diabetic ketoacidosis)

132
Q

Diagnosis of metabolic acidosis

A
  1. Low pH

2. Low HCO3-

133
Q

Body’s compensation for metabolic acidosis

A

Increasing ventilation and lowering PaCO2

but lowers HCO3- even more

134
Q

Treatment for metabolic acidosis

A

Give bicarb

135
Q

Sodium bicarb dose

A

(0.3)(kg)(base excess)

136
Q

Causes of metabolic alkalosis

A
  1. Direct loss of acid (H+) from the body (vomiting, diuretics, gastric drainage, bowel obstruction)
  2. Build up of HCO3- in the body (massive blood transfusion)
137
Q

Diagnosis of metabolic alkalosis

A
  1. High pH

2. High HCO3-

138
Q

Body’s compensation for metabolic alkalosis

A

Decreasing ventilation and increasing PaCO2

but increases HCO3- more

139
Q

Treatment for metabolic alkalosis

A

Reverse what is causing it

140
Q

For each 10 mmHg increase in PaCO2, HCO3- will increase by ____ if acute

A

1 mEq/L

141
Q

For each 10 mmHg increase in PaCO2, HCO3- will ______ if chronic

A

Increase by 4 mEq/L

142
Q

For each 10 mmHg decrease in PaCO2, HCO3- should ____ if acute

A

decrease 2mEq/L

143
Q

For each 10 mmHg decrease in PaCO2, HCO3- should ____ if chronic

A

Decrease 4 mEq/L

144
Q

During metabolic acidosis, PaCO2 should decrease ___ the HCO3- decrease

A

1.2x

145
Q

During metabolic alkalosis, PaCO2 should increase ____ the HCO3- increase

A

0.7x

146
Q

Occurs when cells receive too little oxygen (hypoxia)

A

Lactic acidosis

147
Q

Inadequate oxygen delivery to the tissues

A

Type A

148
Q

Adequate oxygen delivery, but the tissues cannot use the oxygen normally

A

Type B

149
Q

Causes of lactic acidosis

A
  1. Sepsis
  2. Shock/inadequate cardiac output/perfusion
  3. Hepatic failure
  4. Exercise
150
Q

Treatment of lactic acidosis

A
  1. Restore normal pH

2. Improve tissue oxygenation (perfusion) with fluids and/or vasopressors

151
Q

Cations in the body

A
  1. Na+
  2. K+
  3. Ca++
  4. Mg++
  5. H+
152
Q

Anions in the body

A
  1. HCO3-
  2. Cl-
  3. Lactate
  4. Proteins
  5. Phosphates
153
Q

Measured cations

A

Na+, K+

154
Q

Measured anions

A

Cl-, HCO3-

155
Q

Unmeasured cations

A

Mg++, Ca++, H+

156
Q

Unmeasured anions

A

Lactic acid, phosphates, sulfates, protein

157
Q

The difference in the number of measured cations and measured anions

A

Anion gap

158
Q

Anion gap equations

A

Measured cations - measured anions
or
unmeasured anions - unmeasured cations

159
Q

Normal anion gap (without K+)

A

12 +/- 4 mEq/L

160
Q

Causes anion gap to increase

A
  1. Inc in measured cations
  2. Dec in measured anions
  3. Unmeasured anions inc
  4. Unmeasured cations dec
161
Q

Causes anion gap to decrease

A
  1. Measured cations dec
  2. Measured anions inc
  3. Unmeasured anions dec
  4. Unmeasured cations inc
162
Q

When is an elevated anion gap most commonly observed?

A

When there is an increase in unmeasured anions (lactate)

163
Q

Why does the anion gap increase if both unmeasured anion and unmeasured cation increase?

A

H+ doesn’t technically increase because it binds HCO3-

  1. An increase in the number of unmeasured anions
  2. A decrease in the number of measured anions
164
Q

What is a normal anion gap caused by?

A

A direct loss of HCO3-

-Can happen with GI loss or renal dysfunction

165
Q

Why does a normal anion gap not increase with the loss of HCO3-?

A

It is typically replaced by a chloride ion

166
Q

What anion gap is seen with hyperchloremic metabolic acidosis

A

A normal anion gap

167
Q

Causes of a low anion gap

A
  • Hypoalbuminemia (w/liver failure)

- Results in retention of chloride and bicarb

168
Q

What is the acid/base status of a patient with
pH = 7.25
PaCO2 = 36
HCO3- = 14

A

Uncompensated metabolic acidosis

169
Q

What is the acid/base status of a patient with
pH= 7.29
PaCO2=60
HCO3-=29

A

Compensated respiratory acidosis

170
Q

What is the acid/base status of a patient with
pH= 7.36
PaCO2=28
HCO3- = 16

A

Compensated Metabolic Acidosis

171
Q

What is the acid/base status of a patient with
pH=7.53
PaCO2= 42
HCO3- = 34

A

Uncompensated Metabolic Alkalosis

172
Q

What is the acid/base status of a patient with
pH= 7.37
PaCO2 = 37
HCO3- = 24

A

Normal

173
Q

What is acid/base status of a patient with
pH= 7.25
PaCO2 = 24
HCO3- = 14

A

Compensated Metabolic Acidosis

174
Q

How does DKA happen?

A
  1. Type 1 diabetics have a lack of insulin
  2. Cells of the body become starved
  3. Body breaks down lipids in an effort to create sugar
  4. Fat breakdown produces acidic ketone bodies
  5. Sugar in the blood spills into renal tubules causing profound osmotic diuresis
  6. Diuresis can lead to hypovolemia and electrolyte abnormalities in addition to acidosis
175
Q

DKA symptoms

A
  1. Hyperglycemia
  2. Acidosis
  3. Hypovolemia
  4. Potassium disturbances
  5. Sodium disturbances
  6. Hyperosmolarity
176
Q

DKA treatment

A
  1. Administer insulin to feed the cells and reverse ketone production if K+ >3.3 mEq/L
  2. Fix the acidosis by administering bicarb
  3. Treat hypovolemia
  4. Prevent insulin induced hypokalemia
177
Q

When should glucose be added to the insulin infusion during DKA treatment, and why?

A

Once glucose gets to 250-300 mg/dL, add glucose to keep the level above that until the acidosis is corrected

178
Q

Dosing for the glucose insulin infusion

A

5 units of insulin per amp of D50 (2.5-5g glucose per unit of insulin)

179
Q

Average fluid loss during DKA

A

6-9 L

180
Q

Fluid resuscitation goal during DKA

A

Within 24-36 hours with 50% of resuscitation fluid being administered during the first 8-12 hours with NS

181
Q

How do you prevent insulin induced hypokalemia?

A
  • Administer a potassium drip as necessary

- Correct K+ prior to starting insulin

182
Q

Significance of DKA with children

A
  • Children may be dehydrated but have high serum osmolality caused by hyperglycemia
  • Rapid administration of crystalloid solution and reduction in serum osmolality may contribute to risk of cerebral edema
183
Q

Fluid administration of children w/DKA

A
  • Initial bolus of isotonic crystalloid 10-20 mL/kg over 1-2 hours
  • If pt is in hypotensive shock, default to more aggressive bolus fluids for shock
  • Isotonic saline IV then 0.45% NaCl based on corrected serum sodium concentration to help move water into intracellular compartment
184
Q

What would happen with CO2 if air got into your ABG?

A

CO2 would diffuse out of the blood and into the air, causing a falsely lowered PaCO2 reading

185
Q

What would happen with O2 if air got into your ABG for a patient on room air?

A

Oxygen would diffuse out of the air and into the blood, causing a falsely elevated PaO2 reading

186
Q

What would happen with PaO2 if air got into your ABG for a patient on 100% oxygen?

A

Oxygen would diffuse out of the blood and into the air, causing a falsely lowered PaO2 reading

187
Q

How does the ABG get corrected if air gets into the blood sample?

A

Tell the lab the pt’s FiO2

188
Q

What is the effect of warming blood on ABG readings?

A

PaO2 and PaCO2 will increase, causing falsely elevated readings

189
Q

What is the effect of cooling blood on ABG readings?

A

PaO2 and PaCO2 will decrease, causing falsely reduced readings

190
Q

How do you correct for warming/cooling ABGs?

A

Tell the lab the pts temeprature when sending the sample

Methods of Anesthesia (20 decks)

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