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Arterial blood gas analysis

Last updated: November 22, 2019


Arterial blood gas (ABG) analysis is a test regularly performed to measure oxygen saturation, carbon dioxide, and bicarbonate blood levels. It provides quick assessment of gas exchange processes and acid-base balance. Pulse oximetry is a non-invasive and quick way of measuring the oxygen saturation of peripheral arterial hemoglobin. The test relies on the fact that oxygenated and deoxygenated hemoglobin absorb different wavelengths of light. Physiological levels of oxygen saturation are generally above 95%.These tests provide vital information about a patient that is especially important in emergency and intensive care settings.

Arterial blood gas analysis

  • Measured parameters
  • Reference ranges
    • PaCO2: 35–45 mm Hg
    • pH: 7.35–7.45
    • HCO3-: 21 to 27 mEq/L
    • Base excess: -2 to +3 mmol/L
    • Resting PaO2 > 80 mm Hg is considered normal.
  • Procedure:
    • A modified Allen test must be performed before the radial artery is punctured to assess collateral circulation in the hand.
      1. Manual pressure below the wrist is applied to both arteries, the hand is elevated, and the patient is asked to clench their fist for about 30 seconds to induce transient ischemia, leading to pallor of the hand.
      2. When the pressure is released from the ulnar artery, the patient's hand rapidly returns to normal color if collateral circulation is present.
      3. Interpretation: The test result is normal if the patient's hand rapidly returns to normal color. The test is negative and considered pathological if the patient's hand remains at least partially pale.
    • Arterial blood can be drawn from radial arteries or an indwelling arterial catheter.
  • Interpretation
    • Hypoxemic respiratory failure (type 1 respiratory failure): PaO2
    • Hypercapnic respiratory failure (type 2 respiratory failure): PaCO2 and PaO2
    • See also “Diagnostics” in acid-base disorders.


Mixed oxygen venous saturation


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