Acid-base and ABG

High anion gap metabolic acidosis

Reviewed Nov 2026·4 references
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Lactate, ketones, uraemia and toxins cause most HAGMA. Measure lactate, ketones, creatinine, glucose and serum osmolality; an osmolal gap > 10-20 points to toxic alcohols. Treat the cause; bicarbonate only for selected severe cases.

At the bedside

Timed steps
  1. 1

    First line

    Test

    Lactate, blood ketones (beta-hydroxybutyrate), glucose, urea/creatinine, CK, paracetamol and salicylate levels, serum osmolality.

  2. 2

    GOLDMARK

    Causes

    Glycols, Oxoproline (paracetamol), L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis (diabetic, alcoholic, starvation).

  3. 3

    Toxic alcohols

    Osmolal gap

    Measured − calculated osmolality (2Na + glucose/18 + urea/2.8 in mg/dL units, or 2Na + glucose + urea in mmol/L). Gap > 10-20 with HAGMA: methanol or ethylene glycol until proven otherwise.

  4. 4

    Cause first

    Treat

    Lactate: perfusion, sepsis, thiamine; DKA: insulin/fluids; uraemia: dialysis; methanol/EG: fomepizole or ethanol + haemodialysis.

  5. 5

    Selected

    Bicarbonate

    pH ≤ 7.20 with moderate-severe AKI (AKIN 2-3): bicarbonate to pH ≥ 7.30 reduced dialysis need and mortality in that subgroup (BICAR-ICU). Not routine for lactic acidosis.

Severe acidaemia with AKI

Sodium bicarbonate

IV
Dose
4.2% 125-250 mL over 30 min, repeat to pH ≥ 7.30 (max 1 L/24 h) – BICAR-ICU
Worked example
Deficit 70 kg, HCO3- 8 → target 16: 0.5 × 70 × 8 = 280 mmol; give ~140 mmol then re-check

Suspected deficiency

Thiamine

IV
Dose
200-500 mg

Methanol / ethylene glycol

Fomepizole / ethanol

IV
Dose
15 mg/kg load, then 10 mg/kg every 12 h
Red flag · call your senior now
HAGMA + visual blurring after illicit liquor: methanol (Indian hooch tragedies) → ethanol/fomepizole + urgent dialysis.
Red flag
HAGMA with normal lactate and ketones in a patient on paracetamol (malnourished, sepsis): 5-oxoproline.
Pitfall
Treating lactic acidosis with bicarbonate alone (no outcome benefit; worsens intracellular acidosis).
Pitfall
Euglycaemic DKA on SGLT2 inhibitors (glucose < 250 mg/dL).
Pearl
Alcoholic ketoacidosis: often normal glucose, mixed alkalosis from vomiting; treat with dextrose, thiamine and fluids, not insulin.

Calculators for this topic

Osmolal gap

Measured − calculated osmolality. Raised in toxic alcohol poisoning.

Calculated serum osmolality (Indian units)

2 × Na + glucose (mg/dL)/18 + urea (mg/dL)/6. Uses blood urea, as reported by most Indian labs.

Albumin-corrected anion gap

AG + 2.5 × (4.0 − albumin g/dL).

References

  1. 1

    Kraut JA, Madias NE. Metabolic acidosis: pathophysiology, diagnosis and management. Nat Rev Nephrol. 2010;6(5):274-285

  2. 2

    Kraut JA, Madias NE. Lactic acidosis. N Engl J Med. 2014;371(24):2309-2319

  3. 3

    Kraut JA, Kurtz I. Toxic alcohol ingestions: clinical features, diagnosis, and management. Clin J Am Soc Nephrol. 2008;3(1):208-225

  4. 4

    Jaber S, Paugam C, Futier E, et al. Sodium bicarbonate therapy for patients with severe metabolic acidaemia in the intensive care unit (BICAR-ICU). Lancet. 2018;392(10141):31-40

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Normal anion gap (hyperchloraemic) metabolic acidosis

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