Evidence-based acid–base interpretation for emergency medicine. 6-step systematic ABG analysis with guideline-referenced management.
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5
Delta-Delta Ratio
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Δ/Δ = 0.68 — HAGMA + concurrent Normal AG Metabolic Acidosis
Using demo sepsis scenario (pH 7.21, HCO₃⁻ 11, corrected AG 27.5):
Δ/Δ = (27.5 − 12) / (24 − 11) = 0.68 → <1 indicates a hidden concurrent normal AG metabolic acidosis in addition to the HAGMA.
This suggests an additional process such as RTA, diarrhoea, or saline excess.
Management must address both components simultaneously.
Ref: Kaplan LJ, Kellum JA. Crit Care Med 2004;32(2):465–9
6
Oxygenation + Management · Sepsis
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Elevated A-a gradient — V/Q mismatch or shunt
Immediate Actions (SSC 2021):
▸ IV crystalloid 30 mL/kg bolus if MAP <65 mmHg or lactate ≥4 mmol/L
▸ Blood cultures ×2 before antibiotics; broad-spectrum within 1h
▸ Norepinephrine 0.01–0.5 mcg/kg/min as first-line vasopressor
Acid-Base: NaHCO₃ NOT recommended if pH ≥7.15
If pH <7.15 with AKI: consider NaHCO₃ 100–200 mEq IV over 4h
Differential: Septic shock, Lactic acidosis Type A, ARDS, AKI
Ref: Evans L et al. SSC 2021; Jaber S et al. Lancet 2018