Introduction to ABGs

Cards (46)

  • What is the pH in veins?
    7.33 - 7.44
  • What is the actual HCO3- in veins?
    24 - 30
  • What is the PaCO2 in veins?
    5.3 - 6.7
  • What is the PaCO2 in alveolar gas?
    4.8
  • What is the pH in arteries?
    7.35 - 7.45
  • What is the PaCO2 in arteries?
    4.7 - 6.0
  • What is the PaCO2 in arteries?
    10 - 13
  • What is the PaO2 in alveolar gas?
    14.2
  • What is a conjugate acid?
    When a base gains a H+
  • What is the actual HCO3- in arteries?
    22 - 28
  • What is the PaO2 in veins?
    4.0 - 5.5
  • What is metabolic acidosis?
    When [HCO3-] decreased & pH decreases
  • What is Henry's Law?
    Concentration in liquid phase is proportional to partial pressure in gaseous phase
  • How are respiratory & metabolic systems involved in pH homeostasis?
    Resp
    • change in resp rate -> can change PaCO2 RAPIDLY
    • lung pathology can also change PaCO2
    Metabolic
    • kidneys regulate HCO3- levels SLOWLY
    • many pathologies can change HCO3- & other acids/bases
  • What is Type II respiratory failure?
    Failure in process of breathing (underventilation)
    = low O2 & high CO2
  • What are the steps for interpreting an ABG?
    Steps
    1. Look at oxygenation
    2. Look at pH
    3. Look at pH-PaCO2 relationship
    4. Look at bicarb
    5. Base Excess
    6. Look for compensation
  • What is respiratory acidosis?
    When CO2 increases & pH decreases
  • What is a cinjugate base?
    Particle that remains when an acid has donated a H+
  • How can you tell whether a pH is respiratory or metabolic?
    Using PaCO2 (normal= 4.7 - 6 kPa)
    If acidotic then…
    • PaCO2 > 6 = RESPIRATORY acidosis
    • PaCO2 < 4.7 = METABOLIC acidosis
    If alkalotic then…
    • PaCO2 > 6 = METABOLIC alkalosis
    • PaCO2 < 4.7 = RESPIRATORY alkalosis
  • What is Type I respiratory failure?
    Faliure of oxygenation (normal/low PaCO2 AND low O2 (PaO2 < 8kPa))
    Impaired gas exchange (V/Q mismatch) leads to increased ventilation -> indicative of something going wrong in the lungs
  • What does BE < -2 mEq/L mean?
    Low HCO3-
    = metabolic ACIDOSIS
  • Alkalosis
    pH > 7.45
  • What is Ka?
    Acid dissociation constant
    How readily acids dissociate into H+ & A-
  • Define partial pressure.
    Total pressure an individual gas would exert on its own in the same total volume at the same temperature
  • What is classed as resp failure?
    PaO2 < 8kPa
  • What is metabolic alkalosis?
    When [HCO3-] increases & pH increases
  • Acidosis
    pH < 7.35
  • What is respiratory alkalosis?
    When CO2 decreases & pH increases
  • What is the difference between actual & standard HCO3-?
    Actual HCO3- is used to assess both metabolic & respiratory causes of acid-base disturbances
    Standard HCO3- is a measure of only the metabolic component
  • What happens when there is physiological dead space? How is this compensated?
    High V/Q ratio (decreased perfusion)
    -> reduction in effective alveolar ventilation -> could lead to reduction in PaO2
    Compensation by bronchoconstriction & reduced surfactant -> helps divert air to well-perfused alveoli
  • What does a BE > 2 mEq/L mean?
    High HCO3-
    = metabolic ALKALOSIS
  • What does the body do in response to respiratory alkalosis?
    Type B intercalated cells in the kidneys secrete HCO3- into lumen -> increased [HCO3-] in urine -> decreases plasma [HCO3-] & decreases plasma pH
  • How do you find out if there is any compensation in respiratory acidosis/alkalosis?
    Respiratory ACIDOSIS
    • Normal BE = no compensation (acute)
    • High BE = compensation (chronic)
    • Low BE = mixed resp & metabolic
    Respiratory ALKALOSIS
    • Normal BE = no compensation (acute)
    • Low BE = compensation (chronic)
    • High BE = mixed resp & metabolic
  • What does the body do in response to respiratory acidosis?
    Liver produces more glutamine
    Kidney produces glutamate dehydrogemase & PECK to breakdown glutamine -> glutamine breaks down into NH4+ & HCO3-
    = increased plasma [HCO3-] & increases pH
  • What happens when there is physiological shunting? How is this compensated?
    Low V/Q ratio (decrease in ventilation)
    -> poorly oxygenated blood mixed with blood from normally ventilated side -> reduction in PaO2
    Compensation by hypoxic vasoconstriction -> helps to divert blood to well-ventilated alveoli
  • How is a stable pH maintained?
    Respiratory & metabolic systems act together to maintain stable pH
    NOTE: even for the respiratory system, pH is the priority, not CO2 or O2
  • How does hyperventilation affect PaCO2?
    Decreases
  • What is the base excess in arteries & veins?
    -2 to +2
  • Define acid.
    Proton donor
  • Define base.
    Proton acceptor