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Handbook of Blood Gas Acid-Base Interpretation - Ashfaq Hasan
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Handbook of Blood Gas Acid-Base Interpretation - Ashfaq Hasan

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Handbook of Blood Gas Acid-Base Interpretation - Ashfaq HasanГод выпуска: 2013

Автор: Ashfaq Hasan

Жанр: Интенсивная терапия

Формат: PDF

Качество: OCR

Описание: For the uninitiated, the analysis of blood gas can be a daunting task. Hapless medical students, badly constrained for time, 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 of Peter Stewart.
I n the modern medical practice, the multi-tasking health provider's time has become precious — and his attention span short. It is therefore important to retain focus on those aspects of clinical medicine that truly matter. In the handling of those subjects rooted in clinical physiology (and therefore predictably difficult to understand), it makes perfect sense, in my opinion, to adopt an 'algorithmic' approach. A picture can say a thousand words; a well-constructed algorithm can save at least a hundred — not to say, much precious time—and make for clarity of thinking. I have personally found this method relatively painless — and easy to assimilate. The book is set out in the form of flow charts in logical sequence, introducing and gradually building upon the underlying concepts.
The goal of this book is to enable medical students, residents, nurses and respiratory care practitioners to quickly grasp the principles underlying respiratory and acid-base physiology, and to apply the concepts effectively in clinical decision making. Each of these sections, barring a few exceptions, has been designed to fit into a single powerpoint slide: this should facilitate teaching.
Over the years, many excellent books and articles have appeared on the subject. I have found the manuals by Lawrence Martin and Kerry Brandis thoroughly enjoyable as also the online tutorials of Alan Grogono and Bhavani Shankar Kodali : I have tried to incorporate into my own book, some of their energy and content.
No matter how small, a project such as this can never be accomplished without the support of well wishers and friends. I would like to acknowledge the unwavering support of my colleagues Dr. TLN Swamy and Dr. Syed Mahmood Ahmed; my assistants A. Shoba and P. Sudheer; and above all, my family who had to endure the painstaking writing of yet another manuscript.


«Handbook of Blood Gas Acid-Base Interpretation»

Gas Exchange

  • The Respiratory Centre
  • Rhythmicity of the Respiratory Centre
  • The Thoracic Neural Receptors
  • Chemoreceptors
  • The Central Chemoreceptors and the Alpha-Stat Hypothesis
  • Peripheral Chemoreceptors
  • Chemoreceptors in Hypoxia
  • Response of the Respiratory Centre to Hypoxemia
  • Respiration
  • Partial Pressure of a Mixture of Gases
    • Atmospheric Pressure
    • Gas Pressure
  • Partial Pressure of a Gas
  • The Fractional Concentration of a Gas (Fgas)
  • Diffusion of Gases
  • Henry's Law and the Solubility of a Gas in Liquid
  • Inhaled Air
  • The O2 Cascade
  • PaO2
  • The Modified Alveolar Gas Equation
  • The Determinants of the Alveolar Gas Equation
  • The Respiratory Quotient (RQ) in the Alveolar Air Equation
  • FIO2, PAO2, PaO2 and CaO2
  • DO2, CaO2, SpO2, PaO2 and FIO2
  • O2 Content: An Illustrative Example
  • Mechanisms of Hypoxemia
  • Processes Dependent Upon Ventilation
  • Defining Hypercapnia (Elevated CO2)
  • Factors That Determine PaCO2 Levels
  • Relationship Between CO2 Production and Elimination
  • Exercise, CO2 Production and PaCO2
  • Dead Space
  • Minute Ventilation and Alveolar Ventilation
  • The Determinants of the PaCO2
  • Alveolar Ventilation in Health and Disease
  • Hypoventilation and PaCO2
  • The Causes of Hypoventilation
  • Blood Gases in Hypoventilation
  • Decreased CO2Production
    • Summary: Conditions That Can Result in Hypercapnia
  • V/Q Mismatch: A Hypothetical Model
  • V/Q Mismatch and Shunt
  • Quantifying Hypoxemia
  • Compensation for Regional V/Q Inequalities
  • Alveolo-Arterial Diffusion of Oxygen (A-aDO2)
  • A-aDO2 is Difficult to Predict on Intermediate Levels of FIO2
  • Defects of Dif2fusion
  • Determinants of Diffusion: DLCO
  • Timing the ABG
  • A-aDO2 Helps in Differentiating Between the Different Mechanisms of Hypoxemia

The Non-Invasive Monitoring of Blood Oxygen and Carbon Dioxide Levels

  • The Structure and Function of Haemoglobin
  • Co-operativity
  • The Bohr Effect and the Haldane Effect
  • Oxygenated and Non-oxygenated Hemoglobin
  • PaO2 and the Oxy-hemoglobin Dissociation Curve
  • Monitoring of Blood Gases
    • Invasive O2 Monitoring
    • The Non-invasive Monitoring of Blood Gases
  • Principles of Pulse Oximetry
  • Spectrophotometry
  • Optical Plethysmography
  • Types of Pulse Oximeters
  • Pulse Oximetry and PaO2
  • P50
  • Shifts in the Oxy-hemoglobin Dissociation Curve
  • Oxygen Saturation (SpO2) in Anemia and Skin Pigmentation
  • Oxygen Saturation (SpO2) in Abnormal Forms of Hemoglobin
  • Mechanisms of Hypoxemia in Methemoglobinemia
  • Methemoglobinemias: Classification
  • Sulfhemoglobinemia
  • Carbon Monoxide (CO) Poisoning
  • Saturation Gap
  • Sources of Error While Measuring SpO2
  • Point of Care (POC) Cartridges
  • Capnography and Capnometry
  • The Capnographic Waveform
  • Main-Stream and Side-Stream Capnometers
  • PEtCO2 (EtCO2): A Surrogate for PaCO2
  • Factors Affecting PEtCO2
  • Causes of Increased' PaCO2-PEtCO2 Difference
  • Bohr's Equation
  • Application of Bohr's Equation
  • Variations in EtCO2
  • False-Positive and False-Negative Capnography
  • Capnography and Cardiac Output
  • Capnography as a Guide to Successful Resuscitation
  • Capnography in Respiratory Disease
  • Esophageal Intubation
  • Capnography in Tube Disconnection and Cuff Rupture
    • Biphasic Capnograph

Acids and Bases

  • Intracellular and Extracellular pH
  • pH Differences
  • Surrogate Measurement of Intracellular pH
  • Preferential Permeability of the Cell Membrane
  • Ionization and Permeability
  • The Reason Why Substances Need to Be Ionized
  • The Exceptions to the Rule
  • The Hydrogen Ion (H+, Proton)
  • Intracellular pH Is Regulated Within a Narrow Range
  • A Narrow Range of pH Does Not Mean a Small Range of the H+ Concentration
  • The Earliest Concept of an Acid
  • Arrhenius's Theory
  • Bronsted-Lowry Acids
  • Lewis' Approach
  • The Usanovich Theory
  • Summary of Definitions of Acids and Bases
  • Stewart's Physico-Chemical Approach
  • The Dissociation of Water
  • Electrolytes, Non-electrolytes and Ions
  • Strong Ions
  • Stewart's Determinants of the Acid Base Status
  • Apparent and Effective Strong Ion Difference
  • Strong Ion Gap
  • Major Regulators of Independent Variables
  • Fourth Order Polynomial Equation
  • The Workings of Stewart's Approach

Buffer Systems

  • Generation of Acids
  • Disposal of Volatile Acids
  • Disposal of Fixed Acids
  • Buffer Systems
  • Buffers
  • Mechanisms for the Homeostasis of Hydrogen Ions
  • Intracellular Buffering
  • Alkali Generation
  • Buffer Systems of the Body
  • Transcellular Ion Shifts with Acute Acid Loading
  • Time-Frame of Compensatory Responses to Acute Acid Loading
  • Quantifying Buffering
  • Buffering in Respiratory Acidosis
  • Regeneration of the Buffer
  • Buffering in Alkalosis
  • Site Buffering
  • Isohydric Principle
  • Base-Buffering by the Bicarbonate Buffer System
  • Bone Buffering
  • Role of the Liver in Acid-Base Homeostasis


  • Hydrogen Ion Activity
  • Definitions of the Ad-hoc Committee of New York Academy of Sciences, 1965
  • Acidosis and Alkalosis
  • The Law of Mass Action
  • Dissociation Constants
  • pK
  • The Buffering Capacity of Acids
    • Buffering Power
  • The Modified Henderson-Hasselbach Equation
  • The Difficulty in Handling Small Numbers
  • The Puissance Hydrogen
  • Why pH?
  • Relationship Between pH and H+
  • Disadvantages of Using a Logarithmic Scale
  • pH in Relation to pK
  • Is the Carbonic Acid System an Ideal Buffer System?
  • The Bicarbonate Buffer System Is Open Ended
  • Importance of Alveolar Ventilation to the Bicarbonate Buffer System
  • Difference Between the Bicarbonate and Non-bicarbonate Buffer Systems
  • Measuring and Calculated Bicarbonate

Acidosis and Alkalosis

  • Compensation
  • Coexistence of Acid Base Disorders
  • Conditions in Which pH Can Be Normal
  • The Acid Base Map

Respiratory Acidosis

  • Respiratory Failure
  • The Causes of Respiratory Acidosis
  • Acute Respiratory Acidosis: Clinical Effects
  • Effect of Acute Respiratory Acidosis on the Oxy-hemoglobin Dissociation Curve
  • Buffers in Acute Respiratory Acidosis
  • Respiratory Acidosis: Mechanisms for Compensation
  • Compensation for Respiratory Acidosis
  • Post-hypercapnic Metabolic Alkalosis
  • Acute on Chronic Respiratory Acidosis
  • Respiratory Acidosis: Acute or Chronic?

Respiratory Alkalosis

  • Respiratory Alkalosis
  • Electrolyte Shifts in Acute Respiratory Alkalosis
  • Causes of Respiratory Alkalosis
  • Miscellaneous Mechanisms of Respiratory Alkalosis
  • Compensation for Respiratory Alkalosis
  • Clinical Features of Acute Respiratory Alkalosis

Metabolic Acidosis

  • The Pathogenesis of Metabolic Acidosis
  • The pH, PCO2 and Base Excess: Relationships
  • The Law of Electroneutrality and the Anion Gap
  • Electrolytes and the Anion Gap
  • Electrolytes That Influence the Anion Gap
  • The Derivation of the Anion Gap
  • Calculation of the Anion Gap
  • Causes of a Wide-Anion-Gap Metabolic Acidosis
  • The Corrected Anion Gap (AGc)
  • Clues to the Presence of Metabolic Acidosis
  • Normal Anion-Gap Metabolic Acidosis
  • Pathogenesis of Normal-Anion Gap Metabolic Acidosis
  • Negative Anion Gap
  • Systemic Consequences of Metabolic Acidosis
  • Other Systemic Consequences of Metabolic Acidosis
  • Hyperkalemia and Hypokalemia in Metabolic Acidosis
  • Compensatory Response to Metabolic Acidosis
  • Compensation for Metabolic Acidosis
  • Total CO2 (TCO2)
  • Altered Bicarbonate Is Not Specific for a Metabolic Derangement
  • Actual Bicarbonate and Standard Bicarbonate
  • Relationship Between ABC and SBC
  • Buffer Base
  • Base Excess
  • Ketosis and Ketoacidosis
  • Acidosis in Untreated Diabetic Ketoacidosis
  • Acidosis in Diabetic Ketoacidosis Under Treatment
  • Renal Mechanisms of Acidosis
  • L-Lactic Acidosis and D-Lactic Acidosis
  • Diagnosis of Specific Etiologies of Wide Anion Gap Metabolic Acidosis
  • Pitfalls in the Diagnosis of Lactic Acidosis
  • Renal Tubular Acidosis
  • Distal RTA
  • Mechanisms in Miscellaneous Causes of Normal Anion Gap Metabolic Acidosis
  • Toxin Ingestion
  • Bicarbonate Gap (the Delta Ratio)
  • Urinary Anion Gap
  • Utility of the Urinary Anion Gap
  • Osmoles
  • Osmolarity and Osmolality
  • Osmolar Gap
  • Abnormal Low Molecular Weight Circulating Solutes
  • Conditions That Can Create an Osmolar Gap

Metabolic Alkalosis

  • Etiology of Metabolic Alkalosis
  • Pathways Leading to Metabolic Alkalosis
  • Maintenance Factors for Metabolic Alkalosis
  • Maintenance Factors for Metabolic Alkalosis: Volume Contraction
  • Maintenance Factors for Metabolic Alkalosis: Dyselectrolytemias
  • Compensation for Metabolic Alkalosis
  • Urinary Sodium
  • Diagnostic Utility of Urinary Chloride (1)
  • The Diagnostic Utility of Urinary Chloride (2)
  • Diagnostic Utility of Urinary Chloride (3)
  • Some Special Causes of Metabolic Alkalosis
  • Metabolic Alkalosis Can Result in Hypoxemia
  • Metabolic Alkalosis and the Respiratory Drive

The Analysis of Blood Gases

  • Normal Values
    • Venous Blood Gas (VBG) as a Surrogate for ABG Analysis
  • Step 1: Authentication of Data
  • Step 2: Characterization of the Acid-Base Disturbance
  • Step 3: Calculation of the Expected Compensation
  • The Alpha-Numeric (a-1) Mnemonic
  • The Metabolic Track
  • The Respiratory Track
  • Step 4: The 'Bottom Line': Clinical Correlation
    • Clinical Conditions Associated with Simple Acid-Base Disorders
    • Mixed Disorders
  • Acid-Base Maps

Factors Modifying the Accuracy of ABG Results

  • Electrodes
  • Accuracy of Blood Gas Values
  • The Effects of Metabolizing Blood Cells
  • Leucocyte Larceny
  • The Effect of an Air Bubble in the Syringe
  • Effect of Over-Heparization of the Syringe
  • The Effect of Temperature on the Inhaled Gas Mixture
  • Effect of Pyrexia (Hyperthermia) on Blood Gases
  • Effect of Hypothermia on Blood Gases
  • Plastic and Glass Syringes

Case Examples

  • Patient A: A 34 year-old man with Metabolic Encephalopathy
  • Patient B: A 40 year-old man with Breathlessness
  • Patient C: A 50 year-old woman with Hypoxemia
  • Patient D: A 20 year-old woman with Breathlessness
  • Patient E: A 35 year-old man with Non-resolving Pneumonia
  • Patient F: A 60 year-old man with Cardiogenic Pulmonary Edema
  • Patient G: A 72 year-old Drowsy COPD Patient
  • Patient H: A 30 year-old man with Epileptic Seizures
  • Patient I: An Elderly Male with Opiate Induced Respiratory Depression
  • Patient J: A 73 year-old man with Congestive Cardiac Failure
  • Patient K: A 20 year-old woman with a Normal X-ray
  • Patient L: A 22 year-old man with a Head Injury
  • Patient M: A 72 year-old man with Bronchopneumonia
  • Patient N: A 70 year-old woman with a Cerebrovascular Event
  • Patient O: A 60 year-old man with COPD and Cor Pulmonale
  • Patient P: A 70 year-old smoker with Acute Exacerbation of Chronic Bronchitis
  • Patient Q: A 50 year-old man with Hematemesis
  • Patient R: A 68 year-old man with an Acute Abdomen
  • Patient S: A young woman with Gastroenteritis and Dehydration
  • Patient T: A 50 year-old woman with Paralytic Ileus
  • Patient U: An 80 year-old woman with Extreme Weakness
  • Patient V: A 50 year-old man with Diarrhea
  • Patient W: A 68 year-old woman with Congestive Cardiac Failure
  • Patient X: An 82 year-old woman with Diabetic Ketoacidosis
  • Patient Y: A 50 year-old male in Cardiac Arrest
  • Patient Z: A 50 year-old Diabetic with Cellulitis

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