ICU SAQs · Respiratory / acid-base
Systematic interpretation of a metabolic acidosis ABG
A CICM First-Part SAQ applying a systematic ABG approach — alveolar gas equation, Winter's formula, anion gap and delta gap — to a septic patient with a high-anion-gap lactic acidosis and an additional respiratory acidosis.
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Prompt
Interpret the following arterial blood gas from a 60-year-old septic patient at sea level, using a systematic approach: pH 7.20, PaCO2 28 mmHg, PaO2 70 mmHg on room air, bicarbonate 11 mmol/L, lactate 6 mmol/L, sodium 140 mmol/L, chloride 100 mmol/L.
Question
Interpret the following arterial blood gas from a 60-year-old septic patient at sea level, using a systematic approach: pH 7.20, PaCO2 28 mmHg, PaO2 70 mmHg on room air, bicarbonate 11 mmol/L, lactate 6 mmol/L, sodium 140 mmol/L, chloride 100 mmol/L. Assume reference values of 12 mmol/L for the anion gap and 24 mmol/L for bicarbonate.[6]
References8ShowHide
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- [2]Hantzidiamantis PJ, Amaro E Physiology, Alveolar to Arterial Oxygen Gradient StatPearls [Internet], 2023.PMID 31424737
- [3]Trulock EP III Arterial Blood Gases NCBI Bookshelf / Butterworths, 1990.PMID 21250212
- [4]Marano M Evaluation of the expected ventilatory response to metabolic acidosis in chronic hemodialysis patients Hemodial Int, 2018.PMID 28834137
- [5]Wrenn K The delta (delta) gap: an approach to mixed acid-base disorders Ann Emerg Med, 1990.PMID 2240729
- [6]Kharsa A, Vashisht R, Rout P, Meseeha M Anion Gap and Non-Anion Gap Metabolic Acidosis StatPearls [Internet], 2026.PMID 28846305
- [7]Baddam S, Tubben RE Lactic Acidosis StatPearls [Internet], 2026.PMID 29262026
- [8]Rastegar A Use of the DeltaAG/DeltaHCO3- ratio in the diagnosis of mixed acid-base disorders J Am Soc Nephrol, 2007.PMID 17656477