No History

What is the acid-base disorder?

Hypoxaemia & Metabolic Acidosis - Partially Compensated

• PO₂ + 1.25*PCO₂ ≈ 60 : large A-aO₂ gradient - even if on RA
• pH : acidaemia
• HCO₃^- : metabolic (mild)
• PCO₂ : should be 29 mmHg, ∴ respiratory component
• * equally called 'mixed metabolic & respiratory acidosis'
  however, 1° metabolic with failure of resp compensation more likely
• aetiology → any cause of metabolic acidosis with ventilatory compromise
• septicaemia (esp. respiratory)
• cardiac arrest
• trauma
• coma
• renal failure

ABG Correction Factors

1. Metabolic Acidosis:
• PCO₂ : last 2 digits of pH ≥ 7.10
• HCO₃^- : for each 10 mmol/L fall → ↓ PCO₂ ≈ 12 mmHg
2. Metabolic Alkalosis:
• PCO₂ : last 2 digits of pH ≤ 7.60
• HCO₃^- : for each 10 mmol/L rise → ↑ PCO₂ ≈ 7 mmHg
• *least well compensated due to hypoxaemia 2° hypoventilation
3. Respiratory Acidosis:
• Acute : for each 10 mmHg PCO₂ rise → ↑ HCO₃^- ≈ 1-2 mmol/L
• Chronic : for each 10 mmHg PCO₂ rise → ↑ HCO₃^- ≈ 4 mmol/L
4. Respiratory Alkalosis:
• PCO₂ : for each 10 mmHg fall → ↓ HCO₃^- ≈ 2.5 mmol/L