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Metabolic Acidosis Evaluation & Management

Metabolic Acidosis Evaluation & Management: Low serum bicarbonate → Unwell or severe acidaemia: resuscitate and treat while you investigate → Confirm me...

Pathway Overview

20 steps

Algorithm Steps

20 total

  1. 01Start

    Low serum bicarbonate

    HCO3 <22 mmol/L or pH <7.35. Adults. Children: the diagnostic steps apply; treat per paediatric protocols.

  2. 02Warning

    Unwell or severe acidaemia: resuscitate and treat while you investigate

    Get senior or ICU help early. Do not wait for the full workup.

    • pH 7.20 or less, shock, confusion, high lactate or severe K+ disorder: senior or ICU review now
    • Check now: glucose, blood ketones, lactate, K+, creatinine, paracetamol and salicylate levels
    • If ventilated: keep a high minute ventilation so that respiratory compensation continues (aim pH 7.15 or more)
  3. 03Action

    Confirm metabolic acidosis with an arterial blood gas

    The arterial gas rules out respiratory alkalosis and shows mixed disorders.

    • pH <7.35 with low HCO3: metabolic acidosis
    • Low HCO3 with pH >7.45: primary respiratory alkalosis. A metabolic acidosis can coexist (for example salicylate), so still calculate the anion gap
    • Expected PaCO2 = 1.5 x HCO3 + 8 (plus or minus 2) mmHg (Winter's formula; arterial PaCO2)
    • PaCO2 above expected: also respiratory acidosis. PaCO2 below expected: also respiratory alkalosis
    • A near-normal pH does not exclude metabolic acidosis in a mixed disorder
  4. 04Action

    Calculate the anion gap and correct it for albumin

    AG = Na - (Cl + HCO3), all in mmol/L.

    • Corrected AG = AG + 0.25 x (40 - albumin in g/L)
    • Low albumin hides a high anion gap: always correct
    • Use your laboratory's reference range (some laboratories include K+). Without K+, AG >12 mmol/L is high
  5. 05Decision

    Corrected anion gap high?

    Above the laboratory reference range (about >12 mmol/L when K+ is not included).

  6. If Yes
    1. Yes (HAGMA)
    2. 06Action

      If yes: high anion gap metabolic acidosis (HAGMA)

      Causes (GOLD MARK): glycols, oxoproline, L-lactate, D-lactate, methanol, aspirin (salicylate), renal failure, ketoacidosis.

      • Blood lactate, blood ketones (beta-hydroxybutyrate) and glucose
      • Urea, creatinine, K+ and CK
      • Measured osmolality (for the osmolar gap), blood ethanol, salicylate and paracetamol levels
      • Ask about ingestion, alcohol, fasting, metformin, SGLT2 inhibitors, and paracetamol with flucloxacillin
    3. 07Action

      HAGMA: check the delta ratio for a second disorder

      Delta ratio = (AG - 12) / (24 - HCO3), using the albumin-corrected AG without K+. It is an estimate only; it varies widely between patients.

      • Less than 1: a normal anion gap acidosis is probably also present (common in DKA, at presentation or during treatment)
      • 1 to 2: HAGMA alone is likely
      • More than 2: a metabolic alkalosis (or a compensated chronic respiratory acidosis) is probably also present
    4. 08Warning

      Blood ketones raised: diabetic, alcoholic or starvation ketoacidosis

      DKA (blood ketones 3.0 mmol/L or more): follow the DKA pathway and stop any SGLT2 inhibitor. Glucose can be normal (SGLT2 inhibitor, pregnancy, low intake). Pregnancy: urgent senior and obstetric care.

      • DKA: check K+ before insulin. If K+ <3.5 mmol/L, give K+ first and delay insulin until K+ >3.5 mmol/L
      • DKA: no routine bicarbonate. Children: paediatric DKA protocol (bicarbonate increases cerebral injury risk)
      • Alcoholic ketoacidosis: IV fluids with glucose; give thiamine first where practical, but never delay glucose for hypoglycaemia
    5. 09Warning

      Lactate >2 mmol/L: lactic acidosis

      Treat the cause (perfusion, oxygen delivery, sepsis). Recheck lactate in the first hours. Metformin: stop it. Smoke inhalation: consider carbon monoxide and cyanide; severe cyanide poisoning needs hydroxocobalamin now (call 13 11 26).

      • Type A (poor perfusion or oxygen delivery): shock, sepsis, hypoxia, severe anaemia, ischaemia, seizures
      • Type B: metformin, liver failure, cancer, thiamine deficiency, beta-agonists, other drugs and toxins
      • High lactate with a possible ingestion: consider ethylene glycol (some analysers read glycolate as lactate)
    6. 10Warning

      Toxic alcohol possible: raised osmolar gap, unexplained HAGMA or ingestion

      No osmolar gap value excludes it. Call the Poisons Information Centre 13 11 26 now.

      • If toxic alcohol cannot be excluded, give an antidote (ethanol or fomepizole) without delay; toxicologist advises the dose
      • Early: high osmolar gap. Late: high anion gap with a falling or normal osmolar gap
      • Osmolar gap = measured osmolality - (2 x Na + glucose + urea), in mmol/L. Ethanol also raises it
    7. 11Action

      Other HAGMA causes: salicylate, kidney failure, pyroglutamic acid, D-lactate

      Salicylate poisoning is time-critical: call 13 11 26. IV sodium bicarbonate is advised whatever the pH, on toxicology advice; keep K+ normal.

      • Salicylate: dialysis if altered mental state, hypoxaemia needing oxygen, failing standard treatment, pH 7.20 or less, or level >6.5 mmol/L (90 mg/dL); >5.8 mmol/L (80 mg/dL) if kidney function is impaired
      • Kidney failure: high AG with raised urea and creatinine
      • Pyroglutamic acid (5-oxoproline): paracetamol, especially with flucloxacillin, sepsis, malnutrition or severe kidney impairment. Test urine 5-oxoproline; review both drugs
      • D-lactate: short bowel or bowel bypass; the standard lactate test is normal
      • Also: rhabdomyolysis, iron, isoniazid, inborn errors of metabolism
    8. 12Warning

      Before any sodium bicarbonate: check K+, ionised calcium, ventilation and volume

      Not routine (except salicylate poisoning, on toxicology advice). Not for DKA. Children: paediatric protocols. Senior or ICU decision. Do not delay dialysis or cause-specific treatment.

      • Low K+ or low ionised calcium: correct first or at the same time; bicarbonate lowers both
      • Needs PaCO2 <45 mmHg and adequate ventilation: bicarbonate adds CO2
      • Heart failure, oliguria or high Na+: risk of fluid overload and hypernatraemia
    9. 13Action

      Treat the cause; give bicarbonate or dialysis only for set indications

      Recheck the blood gas, K+ and lactate within hours.

      • ICU, pH 7.20 or less, PaCO2 <45 mmHg and moderate to severe AKI: IV sodium bicarbonate reduces the need for dialysis but not mortality
      • GI or kidney bicarbonate loss that the patient tolerates poorly: IV sodium bicarbonate
      • Salicylate poisoning: IV sodium bicarbonate whatever the pH, on toxicology advice
      • Dialysis: pH 7.15 or less with shock or AKI despite treatment; toxic alcohol with AG >20 mmol/L, pH 7.15 or less, AKI, visual loss, coma or seizures; severe salicylate or metformin poisoning
      • Bicarbonate dose and rate: see local ICU protocol or specialist advice
      • CKD: oral alkali to prevent HCO3 <18 mmol/L; avoid HCO3 above normal and watch BP, K+ and fluid
      • RTA: oral alkali (bicarbonate or citrate) and K+ as needed. Type 4: stop causative drugs and treat high K+
    10. Acute
    11. 14Outcome

      Acute cause treated: acidosis resolving

      Recheck the gas and electrolytes until normal.

    12. Chronic
    13. 15Outcome

      Chronic acidosis (CKD or RTA): ongoing follow-up

      Nephrology follow-up. Monitor HCO3 and K+.

    If No
    1. No (NAGMA)
    2. 16Action

      If no: normal anion gap (hyperchloraemic) acidosis (NAGMA)

      Look for bicarbonate loss or chloride gain first. If the cause is clear, treat it.

      • GI loss: diarrhoea, ileostomy, pancreatic or biliary drain or fistula
      • Urinary diversion into bowel (for example ileal conduit)
      • Large volumes of 0.9% sodium chloride
      • Drugs: acetazolamide, topiramate
      • Recovery phase of DKA (ketones lost in the urine)
      • Kidney: CKD or renal tubular acidosis (RTA). Check K+: low in GI loss and RTA types 1 and 2; high in type 4 RTA
    3. 17Action

      NAGMA with no clear cause: calculate the urine anion gap (UAG)

      UAG = urine Na + urine K - urine Cl. It estimates urine ammonium (acid) excretion.

      • Negative UAG: the kidneys excrete acid normally (GI or other extra-renal loss)
      • Positive or zero UAG: low acid excretion (kidney cause)
      • Misleading with urinary ketones, D-lactate or toluene (glue sniffing), or if urine Na <25 mmol/L (volume depletion)
      • Also positive in chronic respiratory alkalosis
    4. 18Decision

      Urine anion gap positive?

      Positive or zero suggests a kidney cause.

    5. If Yes
      1. Positive UAG
      2. 19Action

        Positive UAG: classify the renal tubular acidosis (RTA) by K+ and urine pH

        Get nephrology advice.

        • Distal (type 1): urine pH >5.5 despite acidaemia, low or normal K+, kidney stones. Causes: Sjogren's, SLE, amphotericin B, lithium, genetic
        • Proximal (type 2): bicarbonate wasting, urine pH <5.5 once HCO3 is low, low K+. Fanconi signs: glycosuria with normal glucose, low phosphate. Causes: myeloma, tenofovir, ifosfamide, acetazolamide
        • Type 4 (hyperkalaemic): high K+, urine pH usually <5.5. Low aldosterone effect: diabetes, ACE inhibitor, ARB, spironolactone, trimethoprim, NSAID, calcineurin inhibitor, heparin, adrenal insufficiency
        • Urinary tract obstruction can cause a hyperkalaemic distal RTA
      3. Path rejoins step 12Shared downstream outcome
      If No
      1. Negative UAG
      2. 20Action

        Negative UAG: GI or other extra-renal cause

        Treat the cause. Replace fluid and K+ as needed.

        • No GI loss found: consider proximal RTA (the UAG can be negative) and get nephrology advice
      3. Path rejoins step 12Shared downstream outcome

Guideline Source

Diagnosis and management of metabolic acidosis: guidelines from a French expert panel (Jung et al., Ann Intensive Care 2019)

DOI: 10.1186/s13613-019-0563-2View Guideline

Clinical Safety Information

Clinical Decision Support — Not a Substitute for Clinical Judgment

Individual patient factors may require deviation from these recommendations.

Known Limitations

  • Adults. Children: the diagnostic steps apply, but treat per paediatric DKA and toxicology protocols.
  • The delta ratio and the urine anion gap are estimates; mixed or complex disorders need senior review.
  • Does not replace the DKA, toxic alcohol or salicylate pathways and toxicology advice.
  • The Stewart (strong ion) method can help when the anion gap approach does not explain the result.

Contraindicated Populations

Children under 18 years: treatment steps do not apply (use paediatric protocols)

Applicable Regions

AUNZEUUSglobal

AU: Poisons Information Centre 13 11 26. Fomepizole (Antizol) is on the ARTG; IV ethanol is an alternative antidote. Laboratory units are mmol/L.

NZ: National Poisons Centre 0800 764 766.

US: US units: calculated osmolality = 2 x Na + glucose/18 + BUN/2.8 (glucose and BUN in mg/dL); corrected AG = AG + 2.5 x (4 - albumin in g/dL).

global: Uses the anion gap (Henderson-Hasselbalch) approach, as the French expert panel 2019 suggests first.

Version 2Next review: 2027-09-30

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Frequently Asked Questions

What is the Metabolic Acidosis Evaluation & Management?

The Metabolic Acidosis Evaluation & Management is a diagnostic clinical algorithm for Nephrology. It provides a structured decision tree to guide clinical decision-making, based on Diagnosis and management of metabolic acidosis: guidelines from a French expert panel (Jung et al., Ann Intensive Care 2019).

What guideline is the Metabolic Acidosis Evaluation & Management based on?

This algorithm is based on Diagnosis and management of metabolic acidosis: guidelines from a French expert panel (Jung et al., Ann Intensive Care 2019) (DOI: 10.1186/s13613-019-0563-2).

What are the limitations of the Metabolic Acidosis Evaluation & Management?

Known limitations include: Adults. Children: the diagnostic steps apply, but treat per paediatric DKA and toxicology protocols.; The delta ratio and the urine anion gap are estimates; mixed or complex disorders need senior review.; Does not replace the DKA, toxic alcohol or salicylate pathways and toxicology advice.; The Stewart (strong ion) method can help when the anion gap approach does not explain the result.. Individual patient factors may require deviation from these recommendations.

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