How to Survive the ICU - Arterial Blood Gass
 Arterial Blood Gas PreviousNoteHomeNext
Arterial Blood Gass

  Arterial Blood Gas reveals information on:
    Oxygen and Carbon Dioxide Exchange
    Acid-base status

  A true arterial blood gas gives you three data points:
    PaO2- Partial pressure oxygen: 60-90 mm Hg
    PaCO2- Partial pressure carbon dioxide: 36-44 mmHg
    pH -normal 7.35-7.45

  These values are derived from the measured values above:
    HCO3- 22-26 meq/L: Calculated from the Henderson-Hasselbach equation.
    Base deficit

  How is a arterial blood gas obtained?

    Sample is obtained from an artery using a "blood gas" syringe coated with heparin.
    All air bubbles are removed and a cap placed on syringe.
    Best if run within 15 minutes.
    Place on ice if it will be longer than 15 minutes.


  Oxygen and Carbon Dioxide Exchange Problems:

  Hypoxemia: PaO2 <60 mm Hg.

  Possible causes:
  1. Hypoventilation
  2. Pulmonary Disorder-Shunt.
  3. Do2/Vo2 imbalance: Oxygen delivered to the tissues is not
      being extracted.
  4. Alveolar-arterial oxygen gradient. (A-a gradient)

    A-a Gradient = PA02- Pa02
      PAO2 = 713 mm Hg x Fi02 - PaCO2/ 0.8
      Increased gradient: Shunt
      Normal gradient: Hypoventilation usually

   Hypercapnia:Elevated partial pressure of CO2 in blood.
   Possible causes:
   1. Hypoventilation
   2. Increased CO2 production
   3. Increased dead space ventilation.

    Acid-base derangements:
    Consider these values
        pH     PCO2     HCO3-

    Alkalosis pH > 7.45
       Metabolic if PaCO2 is increased
       Respiratory if PaCO2 is decreased from

    Acidosis pH-<7.35
       Metabolic if PaCO2 is decreased
       Respiratory if PaCO2 is increased due to
    Types of Metabolic Acidosis:  Gap or Non-gap
     The anion gap is an acid-base parameter that helps
     determine which type of acidosis is present,
    Anion Gap=
    (Na+ + K+) - (HCO3- + Cl- )
     Increased Gap =
       >11 meq/L indicates lactic/diabetic acidosis
    Normal Gap =
       3-11 meq/ L and indicates HCO3- losing acidosis

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Copyright © 2004, University of California San Diego, School of Medicine