Primary rise in HCO₃ → alkalaemia. Chloride-responsive vs unresponsive.
Compensation
- • Expected PaCO₂ rise ≈ 0.7 × ΔHCO₃ (max ~55 mmHg)
Chloride-responsive (Urinary Cl⁻ <20)
- • Vomiting / NG suction
- • Diuretics (loop, thiazide)
- • Post-hypercapnia
- • Cystic fibrosis
Chloride-resistant (Urinary Cl⁻ >20)
- • Primary hyperaldosteronism
- • Cushing's, exogenous steroids
- • Bartter, Gitelman syndromes
- • Severe hypokalaemia
Treatment
- • Chloride-responsive: 0.9% NaCl + KCl
- • Resistant: treat underlying endocrine cause + spironolactone
- • Severe (pH >7.55): acetazolamide; rare HCl infusion via central line
