ABG interpretation

Question 1

What are the 5 steps of ABG interpretation recommended by the Resuscitation Council (UK)?

Answer 1

Assess the patient clinically first; check for hypoxaemia (PaO₂ >10 kPa on air); determine if the pH shows acidaemia (<7.35) or alkalaemia (>7.45); assess the respiratory component (PaCO₂ >6.0 kPa = respiratory acidosis, <4.7 kPa = respiratory alkalosis); assess the metabolic component (HCO₃⁻ <22 = metabolic acidosis, >26 = metabolic alkalosis).

Question 2

What PaO₂ value indicates hypoxaemia on room air?

Answer 2

PaO₂ <10 kPa on room air indicates hypoxaemia.

Question 3

What pH values define acidaemia and alkalaemia?

Answer 3

pH <7.35 indicates acidaemia and pH >7.45 indicates alkalaemia.

Question 4

What does a PaCO₂ >6.0 kPa indicate?

Answer 4

A raised PaCO₂ >6.0 kPa indicates respiratory acidosis or respiratory compensation for a metabolic alkalosis.

Question 5

What does a PaCO₂ <4.7 kPa indicate?

Answer 5

A low PaCO₂ <4.7 kPa indicates respiratory alkalosis or respiratory compensation for a metabolic acidosis.

Question 6

What bicarbonate level suggests metabolic acidosis?

Answer 6

HCO₃⁻ <22 mmol/L (or base excess < –2 mmol/L) suggests metabolic acidosis.

Question 7

What bicarbonate level suggests metabolic alkalosis?

Answer 7

HCO₃⁻ >26 mmol/L (or base excess > +2 mmol/L) suggests metabolic alkalosis.

Question 8

What does the mnemonic ROME stand for?

Answer 8

ROME (Respiratory Opposite: pH and PaCO₂ move in opposite directions; Metabolic Equal: pH and HCO₃⁻ move in the same direction).

Question 9

How does ROME help classify respiratory disorders on ABG?

Answer 9

Respiratory acidosis = low pH + high PaCO₂; respiratory alkalosis = high pH + low PaCO₂.

Question 10

How does ROME help classify metabolic disorders on ABG?

Answer 10

Metabolic acidosis = low pH + low HCO₃⁻; metabolic alkalosis = high pH + high HCO₃⁻.