ICU · Renal and metabolic
Acute severe metabolic acidosis: approach, anion gap, and lactate
Also known as Metabolic acidosis · High anion gap metabolic acidosis · HAGMA · Lactic acidosis · Normal anion gap acidosis · NAGMA · Delta gap · Cohen-Woods lactic acidosis · Toxic alcohol poisoning · Diabetic ketoacidosis
Metabolic acidosis (pH <7.35, HCO3 <22, low/normal PaCO2 compensatory) is ubiquitous in ICU. SYSTEMATIC approach: (1) Is it metabolic acidosis? (2) Calculate ANION GAP: Na − (Cl + HCO3); normal 8-12. (3) HIGH anion gap (HAGMA — 12): lactate (sepsis, shock, metformin), ketones (DKA, alcoholic, starvation), toxins (methanol, ethylene glycol, salicylates, paraldehyde), renal failure (uraemic acids). Mnemonic: MUDPILES / GOLDMARK. (4) NORMAL anion gap (NAGMA): GI bicarbonate loss (diarrhoea), renal tubular acidosis, acetazolamide, ureteroenteric fistula, hyperalimentation. (5) DELTA GAP / delta-delta: assess for concurrent disorders (e.g., metabolic alkalosis from vomiting + HAGMA). (6) Treat CAUSE — bicarbonate generally NOT indicated (unle…
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Target exams
Red flags
- pH <7.1 → cardiac dysfunction, vasopressor resistance — consider bicarbonate
- HIGH anion gap (>12) → MUDPILES/GOLDMARK: lactate, ketones, toxins, renal failure
- Lactate >4 + not clearing → sepsis/shock — mortality rises
- Bicarbonate generally NOT indicated except pH <7.1 + unstable, TCA overdose, hyperkalaemia
- Propylene glycol toxicity from lorazepam/diazepam/etomidate infusions → HAGMA + high osmolar gap
- Salicylate toxicity — avoid intubation if possible; hypoventilation worsens CNS toxicity
- Give thiamine BEFORE dextrose in suspected alcoholic ketoacidosis (Wernicke prevention)
Meet the patient
Constructed exam vignette (values chosen to demonstrate severe HAGMA): a 64-year-old man with community-acquired pneumonia is on norepinephrine 0.35 microgram/kg/min and is breathing 32 deep breaths a minute. His ABG shows pH 7.10, PaCO2 24, HCO3 8, and lactate 9.6; sodium is 138, chloride 102, and albumin 21.[1]
The single question for the next hour is the anion gap. High gap sends you hunting for lactate, ketones, a toxin, or renal failure. Normal gap sends you hunting for diarrhoea, RTA, or acetazolamide. The answer changes the management.[1]
References19ShowHide
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- [12]Fenves AZ, Kirkpatrick HM 3rd, Patel VV, et al. Increased anion gap metabolic acidosis as a result of 5-oxoproline (pyroglutamic acid): a role for acetaminophen. Clinical journal of the American Society of Nephrology, 2006.PMID 17699243
- [13]Wilson KC, Reardon C, Theodore AC, Farber HW. Propylene glycol toxicity: a severe iatrogenic illness in ICU patients receiving IV benzodiazepines. Chest, 2005.PMID 16162774
- [14]Barceloux DG, Krenzelok EP, Olson K, Watson W. American Academy of Clinical Toxicology Practice Guidelines on the Treatment of Ethylene Glycol Poisoning. Ad Hoc Committee. Journal of toxicology. Clinical toxicology, 1999.PMID 10497633
- [15]Barceloux DG, Bond GR, Krenzelok EP, Cooper H, Vale JA. American Academy of Clinical Toxicology practice guidelines on the treatment of methanol poisoning. Journal of toxicology clinical toxicology, 2002.PMID 12216995
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- [17]Hoste EA, Colpaert K, Vanholder RC, et al. Sodium bicarbonate versus THAM in ICU patients with mild metabolic acidosis. Journal of nephrology, 2005.PMID 16013019
- [18]Rehman MZ, Melamed M, Harris A, et al. Urinary ammonium in clinical medicine: direct measurement and the urine anion gap and osmolar gap. Advances in kidney disease and health, 2023.PMID 36868734
- [19]Medina E, Ariceta G, Batlle D Primary distal renal tubular acidosis: toward an optimal correction of metabolic acidosis. Clinical journal of the American Society of Nephrology, 2024.PMID 38967973