ICU · renal-metabolic

Systematic Arterial Blood Gas Interpretation — Comprehensive

Also known as Blood gas interpretation · ABG analysis · Acid-base interpretation · Anion gap · GOLDMARK · Delta gap · A-a gradient · Osmolar gap · Compensation equations

Systematic arterial blood gas (ABG) interpretation — the 10-step approach to analysing every ABG in ICU. Step 1: pH (acidosis <7.35, alkalosis 7.45). Step 2: PaCO2 (respiratory — high = acidosis, low = alkalosis). Step 3: HCO3 (metabolic — low = acidosis, high = alkalosis). Step 4: Determine primary disorder (pH direction matches primary disorder). Step 5: Check compensation (expected PaCO2 for metabolic, expected HCO3 for respiratory — if compensation is INADEQUATE → mixed disorder). Step 6: A-a gradient (PAO2 - PaO2 — elevated = V/Q mismatch/shunt/diffusion). Step 7: Anion gap (Na - Cl - HCO3, albumin-corrected — elevated = unmeasured anions [GOLDMARK: Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis]). Step 8: Delta gap (Wrenn: ΔAG − ΔHCO3 — over +6 additional metabolic alkalosis; under −6 additional hyperchloraemic acidosis). Step 9: Osmolar gap (measured − calculated — elevated = toxic alcohols). Step 10: Lactate (Shapiro: ≥4.0 mmol/L in ED infection → 28.4% in-hospital mortality vs 4.9% when 0–2.5). Common ICU patterns: sepsis (metabolic acidosis + respiratory alkalosis), COPD (respiratory acidosis + metabolic compensation), DKA (high AG metabolic acidosis + respiratory compensation), renal failure (high AG + non-AG metabolic acidosis).

Checked against its sources on 3 Sept 2026