ABG Interpretation Guide
Stepwise interpretation of arterial blood gas. Identifies primary acid-base disorder and degree of compensation.
Score interpretation
pH, PaCO₂ and HCO₃⁻ within normal range (pH 7.35–7.45, PaCO₂ 4.7–6.0 kPa, HCO₃⁻ 22–26 mmol/L).
→ No acid-base disturbance. Assess oxygenation separately (PaO₂ >10 kPa on room air = normal).
Low pH with raised PaCO₂ — respiratory acidosis. Assess for compensation (raised HCO₃ in chronic).
→ Identify cause: COPD exacerbation, acute respiratory failure, sedation, chest wall disorder. NIV if appropriate. Target PaCO₂ 5.5–6.5 kPa in chronic CO2 retainers.
Low pH with low HCO₃⁻ — metabolic acidosis. Calculate anion gap. Check for respiratory compensation.
→ Identify cause using MUDPILES (methanol, uraemia, DKA, propylene glycol, INH, lactic acidosis, ethylene glycol, salicylates). Treat underlying cause.
High pH with low PaCO₂ — respiratory alkalosis.
→ Identify cause: anxiety, pain, sepsis, PE, CNS disorder, pregnancy, salicylate toxicity. Treat underlying cause.
High pH with raised HCO₃⁻ — metabolic alkalosis.
→ Identify cause: vomiting, diuretics, hypokalaemia, Bartter syndrome. Chloride-responsive vs resistant. Saline/KCl replacement.
Interpretation bands for the ABG Interpretation. Apply clinical judgement and local guidance.
References
- Kellum JA. Determinants of blood pH in health and disease. Crit Care. 2000;4(1):6-14.
- Berend K et al. Physiological approach to assessment of acid-base disturbances. N Engl J Med. 2014;371(15):1434-1445.
Related
Curated clinical cross-links plus same-class fallbacks.
- AIR Score for Appendicitis · Diagnostic
- Spontaneous Bacterial Peritonitis (SBP) Diagnosis · Diagnostic
- Modified Alvarado Score (MANTRELS) for Appendicitis · Diagnostic
- New Orleans Head CT Decision Rule · Diagnostic
- MS Phenotype Classification (McDonald / Phenotype) · Diagnostic
- CHALICE Rule for Childhood Head Injury · Diagnostic
- Noradrenaline (Norepinephrine) · Vasopressor (Alpha-1 and Beta-1 Agonist)
- Tranexamic Acid (ICU/Trauma/Surgical) · Antifibrinolytic
- Doxapram hydrochloride · Respiratory stimulant
- Trimetazidine · Metabolic Anti-Anginal
- Selexipag · Pulmonary Arterial Hypertension
- Macitentan · Pulmonary Arterial Hypertension
- Difficult Airway Algorithm (DAS) · DAS 2015; Royal College of Anaesthetists
- Major Haemorrhage Protocol · NICE NG24; UK MHP guidelines
- New-Onset Atrial Fibrillation · ESC 2020 AF Guidelines; NICE NG196
- Hypertensive Emergency · ESC/ESH 2018 Hypertension Guidelines; NICE NG136
- Bradycardia Management · Resuscitation Council UK ABCDE; ESC 2021 Pacing Guidelines
- Ventricular Tachycardia / Fibrillation · Resuscitation Council UK ACLS; ESC 2022 Ventricular Arrhythmia Guidelines
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.