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Blood gases and oxygenation

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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The normal range for PaO2 is 11.3-13.3 kPa. A partial pressure less than 8 kPa defines respiratory failure.

Arterial hypoxaemia is commonly due to pulmonary disease:

  • poor gas transfer:
    • type I respiratory failure
    • PaCO2 is typically low
  • hypoventilation:
    • type II respiratory failure
    • PaCO2 is typically raised

Arterial hypoxaemia may occur when the lungs are normal:

  • low inspired partial pressure of oxygen e.g. altitude
  • ventilation-perfusion mismatch
  • right to left shunts:
    • congenital heart disease
    • arteriovenous malformation of the pulmonary vessels

Measurement of the alveolar-arterial (A-a) gradient is useful in hypoxic patients and may help to distinguish hypoxaemia due to pulmonary disease from other causes of hypoxaemia.

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The content herein is provided for informational purposes and does not replace the need to apply professional clinical judgement when diagnosing or treating any medical condition. A licensed medical practitioner should be consulted for diagnosis and treatment of any and all medical conditions.

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