Adult patient post cardiac arrest.

What is the acid-base disorder?

Mixed Metabolic & Respiratory Acidosis

• pH : acidaemia
• PCO₂ :
• respiratory acidosis
• if acute, HCO₃^- should be ≈ 28 mmol/L
• if chronic, HCO₃^- should be ≈ 36 mmol/L
• causes of ventilatory failure
• HCO₃^- : metabolic acidosis
• PO₂ : hypoxaemia (adult on RA)
• PO₂ + 1.25*PCO₂ ≈ 133 : patient not on supplemental O₂

Mixed acidosis - causes:

• cardiac arrest
• DKA & coma
• metabolic acidosis (any cause) & respiratory disease
• septic shock & acute lung injury

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