Respiratory and sleep medicine
Arterial blood gas interpretation
A six-step read of the arterial blood gas with reference ranges, the A-a gradient and P/F ratio, co-oximetry, venous versus arterial gases, sampling errors, and worked examples from COPD, salicylate and pulmonary embolism.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Read every gas in the same order: pH, primary process, compensation, anion gap, oxygenation, then the rest of the panel (lactate, electrolytes, co-oximetry).
- The A-a gradient separates hypoventilation from lung disease. The PaO2/FiO2 ratio tracks oxygenation when FiO2 changes.
- A venous gas is enough for pH, bicarbonate, lactate and potassium, and a normal venous PCO2 rules out arterial hypercapnia. It can't assess oxygenation.
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Sources
- Thoracic Society of Australia and New Zealand position statement on acute oxygen use in adults ("Swimming between the flags")AU/NZThoracic Society of Australia and New Zealand (Respirology), 2022
- Position statement for arterial blood gas samplingAU/NZAustralian and New Zealand Society of Respiratory Science (Internal Medicine Journal), 2024
- Therapeutic Guidelines: RespiratoryAU/NZTherapeutic Guidelines Limited (eTG complete), current eTG edition (version not verified)
- BTS Guideline for oxygen use in adults in healthcare and emergency settingsBritish Thoracic Society (Thorax), 2017, reaffirmed 2019 (update on target saturations in development)
- A new global definition of acute respiratory distress syndromeAmerican Journal of Respiratory and Critical Care Medicine (Matthay et al), 2024
- Byrne AL, Bennett M, Chatterji R et al. Peripheral venous and arterial blood gas analysis in adults: are they comparable? A systematic review and meta-analysis. Respirology 2014;19:168-175Respirology, 2014
- Last updated
- 14 November 2026
What changed
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