Primary fall in HCO₃ → acidaemia. Categorise by anion gap.
Compensation
- • Expected PaCO₂ = 1.5 × HCO₃ + 8 ± 2 (Winters)
- • If actual PaCO₂ > expected → coexisting respiratory acidosis
- • If actual PaCO₂ < expected → coexisting respiratory alkalosis
HAGMA (↑ anion gap) — MUDPILES
- • Methanol
- • Uraemia
- • DKA / starvation / alcoholic ketoacidosis
- • Paraldehyde, Propylene glycol
- • Iron, Isoniazid
- • Lactic acidosis (sepsis, ischaemia, metformin)
- • Ethylene glycol
- • Salicylates
NAGMA — HARDUPS
- • Hyperalimentation (TPN)
- • Acetazolamide / Addison's
- • RTA
- • Diarrhoea
- • Ureteroenteric fistula
- • Pancreatic fistula
- • Saline (chloride-rich)
Delta gap (HAGMA)
- • ΔAG = measured AG − 12; ΔHCO₃ = 24 − measured HCO₃
- • Ratio <1 = concurrent NAGMA; >2 = concurrent metabolic alkalosis
