Arterial blood gases





Interpretation

The Resuscitation Council (UK) advocate a 5 step approach to arterial blood gas interpretation.

1. How is the patient?

2. Is the patient hypoxaemic?
  • the Pa02 on air should be >10 kPa

3. Is the patient acidaemic (pH <7.35) or alkalaemic (pH >7.45)

4. Respiratory component: What has happened to the PaCO2?
  • PaCO2 > 6.0 kPa suggests a respiratory acidosis (or respiratory compensation for a metabolic alkalosis)
  • PaCO2 < 4.7 kPa suggests a respiratory alkalosis (or respiratory compensation for a metabolic acidosis)

5. Metabolic component: What is the bicarbonate level/base excess?
  • bicarbonate < 22 mmol/l (or a base excess < - 2mmol/l) suggests a metabolic acidosis (or renal compensation for a respiratory alkalosis)
  • bicarbonate > 26 mmol/l (or a base excess > + 2mmol/l) suggests a metabolic alkalosis (or renal compensation for a respiratory acidosis)

ROME

Respiratory = Opposite
  • low pH + high PaCO2 i.e. acidosis, or
  • high pH + low PaCO2 i.e. alkalosis

Metabolic = Equal
  • low pH + low bicarbonate i.e. acidosis, or
  • high pH + high bicarbonate i.e. akalosis