EM · ABG interpretation (approach)
Arterial blood gas interpretation — the systematic emergency department approach
Also known as ABG interpretation · Blood gas analysis · Acid-base interpretation · Arterial blood gas
The systematic approach to the arterial blood gas for the emergency medicine trainee — the six values (pH, PaO2, PaCO2, HCO3, base excess, lactate), the respiratory-versus-metabolic rule (pH and PaCO2 move opposite in respiratory disorders, together in metabolic), the compensation formulas (Winter's, the respiratory rules), the anion gap Na minus Cl plus HCO3, the delta-delta for mixed disorders, and the venous-versus-arterial comparison. Includes the gas-driven drug doses — bicarbonate for severe acidaemia on BICAR-ICU terms, insulin 0.1 units per kg per hour for DKA, fomepizole for toxic alcohol. ACEM-primary, globally tagged.
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10 MCQs with explanations
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Meet the patient
A 72-year-old with severe COPD arrives drowsy, with purulent sputum and a respiratory rate of 30. The blood gas comes back: pH 7.10, PaCO2 10.6 kPa, HCO3 18, lactate 5.2. The registrar calls it "a respiratory acidosis" and reaches for non-invasive ventilation.[3]
That label is half-right and it is the half the system exists to catch. Run the six steps and you find two disorders — a respiratory acidosis AND a high-anion-gap metabolic acidosis from the lactate — and the management of each is different. Pattern recognition misses the second one; a system does not. That is the whole point of this topic.[3]
You have read the opening of this topic. The complete unit — every section and its primary-source references — is part of the Emergency Medicine fellowship atlas.
References17Show ledgerHide ledger
- [1]Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis Ann Intern Med, 1967.PMID 6016545
- [2]Adrogué HJ, Madias NE. Management of life-threatening acid-base disorders. First of two parts N Engl J Med, 1998.PMID 9414329
- [3]Berend K, de Vries APJ, Gans ROB. Physiological approach to assessment of acid-base disturbances N Engl J Med, 2014.PMID 25295502
- [4]Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine Clin J Am Soc Nephrol, 2007.PMID 17699401
- [5]Kraut JA, Madias NE. Lactic acidosis N Engl J Med, 2014.PMID 25494270
- [6]Kitabchi AE, Umpierrez GE, Miles JM, Fisher JN. Hyperglycemic crises in adult patients with diabetes Diabetes Care, 2009.PMID 19564476
- [7]Jaber S, Paugam C, Futier E, et al. Sodium bicarbonate therapy for patients with severe metabolic acidaemia in the intensive care unit (BICAR-ICU): a multicentre, open-label, randomised controlled, phase 3 trial Lancet, 2018.PMID 29910040
- [8]Middleton P, Kelly AM, Brown J, Robertson M. Agreement between arterial and central venous values for pH, bicarbonate, base excess, and lactate Emerg Med J, 2006.PMID 16858095
- [9]Jansen TC, van Bommel J, Schoonderbeek FJ, et al. Early lactate-guided therapy in intensive care unit patients: a multicenter, open-label, randomized controlled trial Am J Respir Crit Care Med, 2010.PMID 20463176
- [10]Narins RG, Emmett M Simple and mixed acid-base disorders: a practical approach Medicine (Baltimore), 1980.PMID 6774200
- [11]Wrenn K. The delta gap: an approach to mixed acid-base disorders Ann Emerg Med, 1990.PMID 2240729
- [12]Bass ME, Paavola N, Kiser TH, et al. Evaluation of insulin infusion rates for the treatment of diabetic ketoacidosis in the emergency department J Biosci Med, 2022.PMID 35386489
- [13]Barceloux DG, Krenzelok EP, Olson K, Watson W. American Academy of Clinical Toxicology practice guidelines on the treatment of ethylene glycol poisoning J Toxicol Clin Toxicol, 1999.PMID 10497633
- [14]Marano M, et al. Evaluation of the expected ventilatory response to metabolic acidosis in chronic hemodialysis patients Hemodial Int, 2018.PMID 28834137
- [15]Brent J, McMartin K, Phillips S, Aaron C, Kulig K. Fomepizole for the treatment of methanol poisoning N Engl J Med, 2001.PMID 11172179
- [16]Brent J, McMartin K, Phillips S, et al. Fomepizole for the treatment of ethylene glycol poisoning N Engl J Med, 1999.PMID 10080845
- [17]Taylor ZC, Carroll VG, Parker HG. Proximal tubule dysfunction secondary to salicylate intoxication Glob Pediatr Health, 2022.PMID 35224141