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Acid–Base Disorders and ABG Interpretation

ABG steps, anion gap, respiratory vs metabolic disorders, and compensation rules for ward/USMLE recall.

12 cards· by GuruOwl

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  1. 01
    Normal arterial blood gas ranges (pH, PaCO₂, HCO₃⁻)?
    pH ≈ 7.35–7.45; PaCO₂ ≈ 35–45 mmHg; HCO₃⁻ ≈ 22–26 mEq/L.
    abg
  2. 02
    How do you first classify an acid–base disorder from pH?
    pH < 7.35 = acidemia; pH > 7.45 = alkalemia; then look at PaCO₂ and HCO₃⁻ to find the primary process.
    abg
  3. 03
    What defines metabolic acidosis on ABG?
    Low pH with low HCO₃⁻ (primary). PaCO₂ falls as respiratory compensation.
    metabolic
  4. 04
    What defines respiratory acidosis on ABG?
    Low pH with high PaCO₂ (primary). HCO₃⁻ rises as renal compensation (chronic).
    respiratory
  5. 05
    What is the anion gap formula?
    AG = Na⁺ − (Cl⁻ + HCO₃⁻). Elevated AG suggests unmeasured anions (e.g., lactate, ketoacids).
    anion-gap
  6. 06
    MUDPILES causes of high anion-gap metabolic acidosis?
    Methanol; Uremia; Diabetic ketoacidosis; Propylene glycol/Paraldehyde; Iron/INH; Lactic acidosis; Ethylene glycol; Salicylates (classic mnemonic variants exist).
    anion-gap
  7. 07
    Common causes of normal anion-gap metabolic acidosis (HARDUP sketch)?
    Hyperchloremia / diarrhea / RTA / acetazolamide / ureteral diversion / pancreatic fistula — loss of HCO₃⁻ or impaired renal acid handling.
    nagma
  8. 08
    Winter’s formula is used for what?
    Expected PaCO₂ compensation in metabolic acidosis: PaCO₂ ≈ 1.5 × [HCO₃⁻] + 8 (±2).
    compensation
  9. 09
    Metabolic alkalosis with volume depletion — classic chloride-responsive causes?
    Vomiting / NG suction, diuretics — often respond to saline (urine Cl⁻ low).
    metabolic
  10. 10
    Respiratory alkalosis — common acute causes?
    Hyperventilation: anxiety/pain, PE, pneumonia, salicylate early, pregnancy, high altitude.
    respiratory
  11. 11
    What does a mixed disorder mean on ABG?
    More than one primary process; compensation formulas don’t match a single simple disorder.
    mixed
  12. 12
    In chronic respiratory acidosis, what happens to HCO₃⁻?
    Kidneys retain HCO₃⁻ over days, raising HCO₃⁻ and partially normalizing pH.
    compensation