Compensation-for-Acid-Base-Disorders

(NEJM 2014;371:1434)

Respiratory: hyper/hypoventilation alters PaCO2 to counteract 1° metabolic process Renal: excretion/retention of H+/HCO3– to counteract 1° respiratory process Respiratory compensation occurs in mins-hrs; renal compensation takes days

Compensation never fully corrects pH; if pH normal, consider mixed disorder

Metabolic acidosis

• ↓ PaCO2 = 1.2 × ΔHCO3
• or PaCO2 = (1.5 × HCO3) + 8 ± 2 (Winters’ formula)
• (also, PaCO2 ≈ last 2 digits of pH)

Metabolic alkalosis

• ↑ PaCO2 = 0.7 × ΔHCO3
• or PaCO2 = 0.7 (HCO3–24) + 40 ± 2 or HCO3 + 15

Acute respiratory acidosis

• ↑ HCO3 = 0.1 × ΔPaCO2
• (also, ↓ pH = 0.008 × ΔPaCO2)
• e.g. pCO2 60  delta HCO3 = +2

Chronic respiratory acidosis

• ↑ HCO3 = 0.35 × ΔPaCO2 = 每增十上升三到四
• (also, ↓ pH = 0.003 × ΔPaCO2)
• e.g. pCO2 60  delta HCO3 = +7

Acute respiratory alkalosis

• ↓ HCO3 = 0.2 × ΔPaCO2
• (also, ↑ pH = 0.008 × ΔPaCO2)
• e.g. PCO2 = 20  delta HCO3 = -4

Chronic respiratory alkalosis

• ↓ HCO3 = 0.4 × ΔPaCO2
• e.g. PCO2 = 20  delta HCO3 = -8