72yo male with CAL on diuretics.

What is the acid-base disorder?

Mixed Respiratory Acidosis & Metabolic Alkalosis

• pH : normal
• PCO₂:
• respiratory acidosis
• if only disorder, HCO₃^- should be ≈ 40 mmol/L
• causes of respiratory failure
• HCO₃^-:
• added metabolic alkalosis
• if only disorder, PCO₂ should be ≈ 55 mmHg
• PO₂ + 1.25*PCO₂ ≈ 165 : patient on supplemental O₂

Therefore, likely mixed metabolic alkalosis 2° to diuretic use in setting of chronic respiratory acidosis from CAL

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