Blood Gas

Systematic Approach

1. 1
   Check the pH — Acidosis (<7.35) or Alkalosis (>7.45)?
2. 2
   Check the PaCO2 — Respiratory cause? High CO2 = respiratory acidosis. Low CO2 = respiratory alkalosis.
3. 3
   Check the HCO3/BE — Metabolic cause? Low HCO3 = metabolic acidosis. High HCO3 = metabolic alkalosis.
4. 4
   Compensation? — Is the other system trying to compensate?
5. 5
   Check PaO2 — Hypoxaemia (<10 kPa on arterial)? Type 1 vs Type 2 respiratory failure?
6. 6
   Check Lactate — Elevated (>2 mmol/L)? Tissue hypoperfusion?

Respiratory Failure