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Analysis of blood gas can be a daunting task. However, it is still one of the most useful laboratory tests in managing respiratory and metabolic disorders. Busy medical students have struggled ineffectively with Hasselbach’s modification of the Henderson equation, been torn between the Copenhagen and the Boston schools of thought; and lately, been confronted with the radically different strong-ion approach.
In modern medical practice, the health provider’s time is precious: it is crucial to retain focus on those aspects of clinical medicine that are of key importance. Adoption of an algorithm-based approach in the study of topics that are hard to understand (particularly those that are rooted in clinical physiology) can be extremely advantageous. Handbook of Blood Gas/Acid-Base Interpretation, 2nd edition, is organized in a logical sequence of flow charts that introduce concepts and gradually build upon them. This approach facilitates understanding and retention of the subject matter. Medical students, residents, nurses, and practitioners of respiratory and intensive care will find it possible to quickly grasp the principles underlying respiratory and acid-base physiology, and apply them effectively in clinical decision making.
Contents
1 Gas Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 The Respiratory Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Rhythmicity of the Respiratory Centre . . . . . . . . . . . . . . . . . . . . 4
1.3 The Thoracic Neural Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Chemoreceptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 The Central Chemoreceptors and the Alpha-Stat Hypothesis . . . 7
1.6 Peripheral Chemoreceptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.7 Chemoreceptors in Hypoxia . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.8 Response of the Respiratory Centre to Hypoxemia . . . . . . . . . . . 10
1.9 Respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.10 Partial Pressure of a Mixture of Gases. . . . . . . . . . . . . . . . . . . . . 12
1.10.1 Atmospheric Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.10.2 Gas Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.11 Partial Pressure of a Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.12 The Fractional Concentration of a Gas (Fgas) . . . . . . . . . . . . . . . 14
1.13 Diffusion of Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.14 Henry’s Law and the Solubility of a Gas in Liquid . . . . . . . . . . . 16
1.15 Inhaled Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.16 The O2 Cascade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.17 PaO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.18 The Modified Alveolar Gas Equation . . . . . . . . . . . . . . . . . . . . . 21
1.19 The Determinants of the Alveolar Gas Equation . . . . . . . . . . . . . 22
1.20 The Respiratory Quotient (RQ) in the Alveolar
Air Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.21 FIO2, PAO2, PaO2 and CaO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.22 DO2, CaO2, SpO2, PaO2 and FIO2 . . . . . . . . . . . . . . . . . . . . . . . . 25
1.23 O2 Content: An Illustrative Example . . . . . . . . . . . . . . . . . . . . . . 26
1.24 Mechanisms of Hypoxemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1.25 Processes Dependent Upon Ventilation . . . . . . . . . . . . . . . . . . . . 28
1.26 Defining Hypercapnia (Elevated CO2) . . . . . . . . . . . . . . . . . . . . . 29
1.27 Factors That Determine PaCO2 Levels . . . . . . . . . . . . . . . . . . . . 30
1.28 Relationship Between CO2 Production and Elimination . . . . . . . 31
1.29 Exercise, CO2 Production and PaCO2 . . . . . . . . . . . . . . . . . . . . . 32
1.30 Dead Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.31 Minute Ventilation and Alveolar Ventilation . . . . . . . . . . . . . . . . 34
1.32 The Determinants of the PaCO2 . . . . . . . . . . . . . . . . . . . . . . . . . . 35
1.33 Alveolar Ventilation in Health and Disease . . . . . . . . . . . . . . . . . 36
1.34 Hypoventilation and PaCO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
1.35 The Causes of Hypoventilation . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.36 Blood Gases in Hypoventilation . . . . . . . . . . . . . . . . . . . . . . . . . 39
1.37 Decreased CO2 Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
1.37.1 Summary: Conditions That Can Result
in Hypercapnia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
1.38 V/Q Mismatch: A Hypothetical Model . . . . . . . . . . . . . . . . . . . . 41
1.39 V/Q Mismatch and Shunt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.40 Quantifying Hypoxemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
1.41 Compensation for Regional V/Q Inequalities . . . . . . . . . . . . . . . 44
1.42 Alveolo-Arterial Diffusion of Oxygen (A-aDO2) . . . . . . . . . . . . 45
1.43 A-aDO2 is Difficult to Predict on Intermediate
Levels of FIO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
1.44 Defects of Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
1.45 Determinants of Diffusion: DLCO . . . . . . . . . . . . . . . . . . . . . . . . . 48
1.46 Timing the ABG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
1.47 A-aDO2 Helps in Differentiating Between
the Different Mechanisms of Hypoxemia . . . . . . . . . . . . . . . . . . 50
2 The Non-Invasive Monitoring of Blood Oxygen
and Carbon Dioxide Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.1 The Structure and Function of Haemoglobin . . . . . . . . . . . . . . . 53
2.2 Co-operativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.3 The Bohr Effect and the Haldane Effect . . . . . . . . . . . . . . . . . . . 55
2.4 Oxygenated and Non-oxygenated Hemoglobin . . . . . . . . . . . . . . 56
2.5 PaO2 and the Oxy-hemoglobin Dissociation Curve . . . . . . . . . . . 57
2.6 Monitoring of Blood Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.6.1 Invasive O2 Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.6.2 The Non-invasive Monitoring of Blood Gases. . . . . . . . 58
2.7 Principles of Pulse Oximetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2.8 Spectrophotometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.9 Optical Plethysmography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.10 Types of Pulse Oximeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.11 Pulse Oximetry and PaO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
2.12 P50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.13 Shifts in the Oxy-hemoglobin Dissociation Curve . . . . . . . . . . . 65
2.14 Oxygen Saturation (SpO2) in Anemia
and Skin Pigmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
2.15 Oxygen Saturation (SpO2) in Abnormal Forms
of Hemoglobin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.16 Mechanisms of Hypoxemia in Methemoglobinemia . . . . . . . . . . 68
2.17 Methemoglobinemias: Classification . . . . . . . . . . . . . . . . . . . . . . 69
2.18 Sulfhemoglobinemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
2.19 Carbon Monoxide (CO) Poisoning . . . . . . . . . . . . . . . . . . . . . . . 71
2.20 Saturation Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
2.21 Sources of Error While Measuring SpO2 . . . . . . . . . . . . . . . . . . . 73
2.22 Point of Care (POC) Cartridges . . . . . . . . . . . . . . . . . . . . . . . . . . 75
2.23 Capnography and Capnometry . . . . . . . . . . . . . . . . . . . . . . . . . . 76
2.24 The Capnographic Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
2.25 Main-Stream and Side-Stream Capnometers . . . . . . . . . . . . . . . . 78
2.26 PEtCO2 (EtCO2): A Surrogate for PaCO2 . . . . . . . . . . . . . . . . . . . 79
2.27 Factors Affecting PetCO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
2.28 Causes of Increased PaCO2-PEtCO2 Difference . . . . . . . . . . . . . . 81
2.29 Bohr’s Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
2.30 Application of Bohr’s Equation . . . . . . . . . . . . . . . . . . . . . . . . . . 83
2.31 Variations in EtCO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2.32 False-Positive and False-Negative Capnography . . . . . . . . . . . . . 85
2.33 Capnography and Cardiac Output . . . . . . . . . . . . . . . . . . . . . . . . 86
2.34 Capnography as a Guide to Successful Resuscitation . . . . . . . . . 87
2.35 Capnography in Respiratory Disease . . . . . . . . . . . . . . . . . . . . . . 88
2.36 Esophageal Intubation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
2.37 Capnography in Tube Disconnection and Cuff Rupture . . . . . . . 91
2.37.1 Biphasic Capnograph . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3 Acids and Bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.1 Intracellular and Extracellular pH . . . . . . . . . . . . . . . . . . . . . . . . 96
3.2 pH Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3.3 Surrogate Measurement of Intracellular pH . . . . . . . . . . . . . . . . 98
3.4 Preferential Permeability of the Cell Membrane . . . . . . . . . . . . . 99
3.5 Ionization and Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
3.6 The Reason Why Substances Need to Be Ionized . . . . . . . . . . . . 101
3.7 The Exceptions to the Rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
3.8 The Hydrogen Ion (H+, Proton) . . . . . . . . . . . . . . . . . . . . . . . . . . 103
3.9 Intracellular pH Is Regulated Within a Narrow Range . . . . . . . . 104
3.10 A Narrow Range of pH Does Not Mean
a Small Range of the H+ Concentration . . . . . . . . . . . . . . . . . . . . 105
3.11 The Earliest Concept of an Acid . . . . . . . . . . . . . . . . . . . . . . . . . 106
3.12 Arrhenius’s Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
3.13 Bronsted-Lowry Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
3.14 Lewis’ Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
3.15 The Usanovich Theory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
3.16 Summary of Definitions of Acids and Bases . . . . . . . . . . . . . . . . 110
3.17 Stewart’s Physico-Chemical Approach . . . . . . . . . . . . . . . . . . . . 111
3.18 The Dissociation of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
3.19 Electrolytes, Non-electrolytes and Ions . . . . . . . . . . . . . . . . . . . . 113
3.20 Strong Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
3.21 Stewart’s Determinants of the Acid Base Status . . . . . . . . . . . . . 115
3.22 Apparent and Effective Strong Ion Difference . . . . . . . . . . . . . . 116
3.23 Strong Ion Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
3.24 Major Regulators of Independent Variables . . . . . . . . . . . . . . . . 118
3.25 Fourth Order Polynomial Equation . . . . . . . . . . . . . . . . . . . . . . . 119
3.26 The Workings of Stewart’s Approach . . . . . . . . . . . . . . . . . . . . . 121
4 Buffer Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
4.1 Generation of Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
4.2 Disposal of Volatile Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
4.3 Disposal of Fixed Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.4 Buffer Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
4.5 Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
4.6 Mechanisms for the Homeostasis of Hydrogen Ions . . . . . . . . . . 129
4.7 Intracellular Buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
4.8 Alkali Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
4.9 Buffer Systems of the Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.10 Transcellular Ion Shifts with Acute Acid Loading . . . . . . . . . . . 133
4.11 Time-Frame of Compensatory Responses
to Acute Acid Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
4.12 Quantifying Buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
4.13 Buffering in Respiratory Acidosis . . . . . . . . . . . . . . . . . . . . . . . . 136
4.14 Regeneration of the Buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
4.15 Buffering in Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
4.16 Site Buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
4.17 Isohydric Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
4.18 Base–Buffering by the Bicarbonate Buffer System . . . . . . . . . . . 140
4.19 Bone Buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
4.20 Role of the Liver in Acid–Base Homeostasis . . . . . . . . . . . . . . . 142
5 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
5.1 Hydrogen Ion Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
5.2 Definitions of the Ad-hoc Committee of New York
Academy of Sciences, 1965 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
5.3 Acidosis and Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
5.4 The Law of Mass Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
5.5 Dissociation Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
5.6 pK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
5.7 The Buffering Capacity of Acids . . . . . . . . . . . . . . . . . . . . . . . . . 150
5.7.1 Buffering Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
5.8 The Modified Henderson-Hasselbach Equation . . . . . . . . . . . . . 151
5.9 The Difficulty in Handling Small Numbers . . . . . . . . . . . . . . . . . 153
5.10 The Puissance Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
5.11 Why pH? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
5.12 Relationship Between pH and H+ . . . . . . . . . . . . . . . . . . . . . . . . 156
5.13 Disadvantages of Using a Logarithmic Scale . . . . . . . . . . . . . . . 157
5.14 pH in Relation to pK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
5.15 Is the Carbonic Acid System an Ideal Buffer System? . . . . . . . . 159
5.16 The Bicarbonate Buffer System Is Open Ended . . . . . . . . . . . . . 160
5.17 Importance of Alveolar Ventilation to the
Bicarbonate Buffer System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
5.18 Difference Between the Bicarbonate and
Non-bicarbonate Buffer Systems . . . . . . . . . . . . . . . . . . . . . . . . . 162
5.19 Measuring and Calculated Bicarbonate . . . . . . . . . . . . . . . . . . . . 163
6 Acidosis and Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
6.1 Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
6.2 Coexistence of Acid Base Disorders . . . . . . . . . . . . . . . . . . . . . . 167
6.3 Conditions in Which pH Can Be Normal . . . . . . . . . . . . . . . . . . 168
6.4 The Acid Base Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
7 Respiratory Acidosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
7.1 Respiratory Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
7.2 The Causes of Respiratory Acidosis . . . . . . . . . . . . . . . . . . . . . . 173
7.3 Acute Respiratory Acidosis: Clinical Effects . . . . . . . . . . . . . . . 174
7.4 Effect of Acute Respiratory Acidosis on the
Oxy-hemoglobin Dissociation Curve . . . . . . . . . . . . . . . . . . . . . 175
7.5 Buffers in Acute Respiratory Acidosis . . . . . . . . . . . . . . . . . . . . 176
7.6 Respiratory Acidosis: Mechanisms
for Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
7.7 Compensation for Respiratory Acidosis . . . . . . . . . . . . . . . . . . . 177
7.8 Post-hypercapnic Metabolic Alkalosis . . . . . . . . . . . . . . . . . . . . 178
7.9 Acute on Chronic Respiratory Acidosis . . . . . . . . . . . . . . . . . . . 179
7.10 Respiratory Acidosis: Acute or Chronic? . . . . . . . . . . . . . . . . . . 180
8 Respiratory Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
8.1 Respiratory Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
8.2 Electrolyte Shifts in Acute Respiratory Alkalosis . . . . . . . . . . . . 183
8.3 Causes of Respiratory Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . 184
8.4 Miscellaneous Mechanisms of Respiratory Alkalosis . . . . . . . . . 185
8.5 Compensation for Respiratory Alkalosis . . . . . . . . . . . . . . . . . . . 187
8.6 Clinical Features of Acute Respiratory Alkalosis . . . . . . . . . . . . 188
9 Metabolic Acidosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
9.1 The Pathogenesis of Metabolic Acidosis . . . . . . . . . . . . . . . . . . . 191
9.2 The pH, PCO2 and Base Excess: Relationships . . . . . . . . . . . . . . 192
9.3 The Law of Electroneutrality and the Anion Gap . . . . . . . . . . . . 193
9.4 Electrolytes and the Anion Gap . . . . . . . . . . . . . . . . . . . . . . . . . . 194
9.5 Electrolytes That Influence the Anion Gap . . . . . . . . . . . . . . . . . 195
9.6 The Derivation of the Anion Gap . . . . . . . . . . . . . . . . . . . . . . . . 196
9.7 Calculation of the Anion Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
9.8 Causes of a Wide-Anion-Gap Metabolic Acidosis . . . . . . . . . . . 198
9.9 The Corrected Anion Gap (AGc) . . . . . . . . . . . . . . . . . . . . . . . . . 199
9.10 Clues to the Presence of Metabolic Acidosis . . . . . . . . . . . . . . . 200
9.11 Normal Anion-Gap Metabolic Acidosis . . . . . . . . . . . . . . . . . . . 201
9.12 Pathogenesis of Normal-Anion Gap Metabolic Acidosis . . . . . . 202
9.13 Negative Anion Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
9.14 Systemic Consequences of Metabolic Acidosis . . . . . . . . . . . . . 204
9.15 Other Systemic Consequences of Metabolic Acidosis . . . . . . . . 205
9.16 Hyperkalemia and Hypokalemia in Metabolic Acidosis . . . . . . . 207
9.17 Compensatory Response to Metabolic Acidosis . . . . . . . . . . . . . 208
9.18 Compensation for Metabolic Acidosis . . . . . . . . . . . . . . . . . . . . 209
9.19 Total CO2 (TCO2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
9.20 Altered Bicarbonate Is Not Specific
for a Metabolic Derangement . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
9.21 Actual Bicarbonate and Standard Bicarbonate . . . . . . . . . . . . . . 212
9.22 Relationship Between ABC and SBC . . . . . . . . . . . . . . . . . . . . . 213
9.23 Buffer Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
9.24 Base Excess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
9.25 Ketosis and Ketoacidosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
9.26 Acidosis in Untreated Diabetic Ketoacidosis . . . . . . . . . . . . . . . 217
9.27 Acidosis in Diabetic Ketoacidosis Under Treatment . . . . . . . . . . 218
9.28 Renal Mechanisms of Acidosis . . . . . . . . . . . . . . . . . . . . . . . . . . 219
9.29 l-Lactic Acidosis and d-Lactic Acidosis . . . . . . . . . . . . . . . . . . . 220
9.30 Diagnosis of Specific Etiologies of Wide Anion
Gap Metabolic Acidosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
9.31 Pitfalls in the Diagnosis of Lactic Acidosis . . . . . . . . . . . . . . . . . 223
9.32 Renal Tubular Acidosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
9.33 Distal RTA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
9.34 Mechanisms in Miscellaneous Causes of Normal
Anion Gap Metabolic Acidosis . . . . . . . . . . . . . . . . . . . . . . . . . . 226
9.35 Toxin Ingestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
9.36 Bicarbonate Gap (the Delta Ratio) . . . . . . . . . . . . . . . . . . . . . . . 228
9.37 Urinary Anion Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
9.38 Utility of the Urinary Anion Gap . . . . . . . . . . . . . . . . . . . . . . . . . 230
9.39 Osmoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
9.40 Osmolarity and Osmolality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
9.41 Osmolar Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
9.42 Abnormal Low Molecular Weight Circulating Solutes . . . . . . . . 234
9.43 Conditions That Can Create an Osmolar Gap . . . . . . . . . . . . . . . 235
Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
10 Metabolic Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
10.1 Etiology of Metabolic Alkalosis . . . . . . . . . . . . . . . . . . . . . . . . . 238
10.2 Pathways Leading to Metabolic Alkalosis . . . . . . . . . . . . . . . . . . 239
10.3 Maintenance Factors for Metabolic Alkalosis . . . . . . . . . . . . . . . 240
10.4 Maintenance Factors for Metabolic Alkalosis:
Volume Contraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
10.5 Maintenance Factors for Metabolic Alkalosis:
Dyselectrolytemias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
10.6 Compensation for Metabolic Alkalosis . . . . . . . . . . . . . . . . . . . . 243
10.7 Urinary Sodium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
10.8 Diagnostic Utility of Urinary Chloride (1) . . . . . . . . . . . . . . . . . 245
10.9 The Diagnostic Utility of Urinary Chloride (2) . . . . . . . . . . . . . . 246
10.10 Diagnostic Utility of Urinary Chloride (3) . . . . . . . . . . . . . . . . . 247
10.11 Some Special Causes of Metabolic Alkalosis . . . . . . . . . . . . . . . 248
10.12 Metabolic Alkalosis Can Result in Hypoxemia . . . . . . . . . . . . . . 250
10.13 Metabolic Alkalosis and the Respiratory Drive . . . . . . . . . . . . . . 251
11 The Analysis of Blood Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
11.1 Normal Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
11.1.1 Venous Blood Gas (VBG) as a Surrogate
for ABG Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
11.2 Step 1: Authentication of Data . . . . . . . . . . . . . . . . . . . . . . . . . . 255
11.3 Step 2: Characterization of the Acid-Base Disturbance . . . . . . . 256
11.4 Step 3: Calculation of the Expected Compensation . . . . . . . . . . 257
11.5 The Alpha-Numeric (a-1) Mnemonic . . . . . . . . . . . . . . . . . . . . . 258
11.6 The Metabolic Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
11.7 The Respiratory Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
11.8 Step 4: The ‘Bottom Line’: Clinical Correlation . . . . . . . . . . . . . 261
11.8.1 Clinical Conditions Associated with Simple
Acid-Base Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
11.8.2 Mixed Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
11.9 Acid-Base Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
12 Factors Modifying the Accuracy of ABG Results . . . . . . . . . . . . . . . . 267
12.1 Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
12.2 Accuracy of Blood Gas Values . . . . . . . . . . . . . . . . . . . . . . . . . . 269
12.3 The Effects of Metabolizing Blood Cells . . . . . . . . . . . . . . . . . . 270
12.4 Leucocyte Larceny . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
12.5 The Effect of an Air Bubble in the Syringe . . . . . . . . . . . . . . . . . 272
12.6 Effect of Over-Heparization of the Syringe . . . . . . . . . . . . . . . . . 273
12.7 The Effect of Temperature on the Inhaled Gas Mixture . . . . . . . 274
12.8 Effect of Pyrexia (Hyperthermia) on Blood Gases . . . . . . . . . . . 275
12.9 Effect of Hypothermia on Blood Gases . . . . . . . . . . . . . . . . . . . . 276
12.10 Plastic and Glass Syringes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
13 Case Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
13.1 Patient A: A 34 year-old man with Metabolic Encephalopathy . . . . 281
13.2 Patient B: A 40 year-old man with Breathlessness . . . . . . . . . . . 282
13.3 Patient C: A 50 year-old woman with Hypoxemia . . . . . . . . . . . 283
13.4 Patient D: A 20 year-old woman with Breathlessness . . . . . . . . . 284
13.5 Patient E: A 35 year-old man with
Non-resolving Pneumonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
13.6 Patient F: A 60 year-old man with Cardiogenic
Pulmonary Edema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
13.7 Patient G: A 72 year-old Drowsy COPD Patient . . . . . . . . . . . . . 287
13.8 Patient H: A 30 year-old man with Epileptic Seizures . . . . . . . . 289
13.9 Patient I: An Elderly Male with Opiate
Induced Respiratory Depression . . . . . . . . . . . . . . . . . . . . . . . . . 291
13.10 Patient J: A 73 year-old man with Congestive
Cardiac Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
13.11 Patient K: A 20 year-old woman with a Normal X-ray . . . . . . . . 295
13.12 Patient L: A 22 year-old man with a Head Injury . . . . . . . . . . . . 297
13.13 Patient M: A 72 year-old man with Bronchopneumonia . . . . . . . 299
13.14 Patient N: A 70 year-old woman with
a Cerebrovascular Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
13.15 Patient O: A 60 year-old man with COPD
and Cor Pulmonale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
13.16 Patient P: A 70 year-old smoker with Acute Exacerbation
of Chronic Bronchitis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
13.17 Patient Q: A 50 year-old man with Hematemesis . . . . . . . . . . . . 307
13.18 Patient R: A 68 year-old man with an Acute Abdomen . . . . . . . 309
13.19 Patient S: A young woman with Gastroenteritis
and Dehydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
13.20 Patient T: A 50 year-old woman with Paralytic Ileus . . . . . . . . . 313
13.21 Patient U: An 80 year-old woman with Extreme Weakness . . . . 315
13.22 Patient V: A 50 year-old man with Diarrhea . . . . . . . . . . . . . . . . 317
13.23 Patient W: A 68 year-old woman with
Congestive Cardiac Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
13.24 Patient X: An 82 year-old woman with
Diabetic Ketoacidosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
13.25 Patient Y: A 50 year-old male in Cardiac Arrest . . . . . . . . . . . . . 323
13.26 Patient Z: A 50 year-old Diabetic with Cellulitis . . . . . . . . . . . . 325
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
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