Blood Gases (Medical Students)

You are given the following investigation results (normal range in brackets):

    pH  7.12

    PaCO₂  20 mmHg (35–45 mmHg)

    HCO₃⁻  7 mmol/L (22–26 mmol/L)

    PaO₂  98 mmHg (80–100 mmHg)

    BE  −20 mmol/L (−2 to +2 mmol/L)

1. What investigation is this?

Arterial blood gas analysis / ABG

2. What is the normal range for pH?

7.35–7.45

3. Interpret these results systematically.

  • Severe acidaemia (pH 7.12)
  • Markedly reduced bicarbonate and BE → metabolic acidosis
  • Low PaCO₂ indicates respiratory compensation
  • Oxygenation is normal

4. What is the overall acid–base diagnosis?

Severe metabolic acidosis with respiratory compensation

5. Name four clinical situations in paediatrics that may present with this metabolic derangement.

  • Diabetic ketoacidosis
  • Severe gastroenteritis with dehydration
  • Septic shock / severe sepsis with lactic acidosis
  • Poisoning or toxic ingestion (e.g. salicylates, methanol, ethylene glycol)