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Introduction
  • Acid-base disorders are commonly seen throughout medicine 
    • acidosis results in an abnormally elevated H+ concentration in the blood (thus called acidemia)
    • alkalosis results in an abnormally decreased H+ concentration in the blood (thus called alkalemia)
  • These acid-base disorders may be caused by
    • a primary disturbance in HCO3- resulting in a metabolic acidosis or alkalosis
    • a primary disturbance in PCO2 resulting in a respiratory acidosis or alkalosis
  • Simple acid-base disorders
    • blood pH abnormalities caused by one acid base disorder
    • metabolic acidosis
      • due to a decrease in blood HCO3-
        • secondary to impaired H+ excretion, fixed H+ ingestion, or increased H+ production
          • look at "anion gap" below
    • metabolic alkalosis
      • due to an increase in blood HCO3-
        • secondary to increased HCO3- intake or loss of fixed H+
          • loop diuretics (e.g., furosemide)
          • vomiting and nasogastric tube suction
          • antacid use
          • hyperaldosteronism
          • laxative abuse
    • respiratory acidosis
      • due to an increase in PCO2
        • due to hypoventilation
          • airway obstruction (e.g., epiglottitis)
          • acute lung disease
          • chronic lung disease
          • opioids and sedatives
          • respiratory muscle weakness
    • respiratory alkalosis
      • due to a decrease in PCO2
        • due to hyperventilation
          • normal pregnancy
          • hysteria
          • hypoxemia (e.g., high altitude)
          • salicylates (early)
          • pulmonary embolism
          • pneumonia
  • Anion gap
    • under normal conditions, anions and cations are equal to each other within any body fluid compartment (e.g., plasma)
      • the major cation that is measured is Na+
      • the major anions that are measured is HCO3- and Cl-
      • because there is more Na+ than HCO3- and Cl- there are unmeasured anions that allow us to achieve electroneutrality
        • unmeasured plasma anions include plasma proteins, citrate, phosphate, and sulfate
      • anion gap = Na+ - (Cl- + HCO3-)
        • normal = 8-16 mEq/L
    • anion gap is very useful for narrowing the differential diagnosis of metabolic acidosis
      • normal anion gap metabolic acidosis (also called hyperchloremic metabolic acidosis with a normal anion gap)
        • Hyperalimentation
        • Addison's disease
        • Renal tubular acidosis
        • Diarrhea
        • Acetazolamide
        • Spironolactone
        • Saline infusion
        • mnemonic: HARDASS
      • elevated anion gap metabolic acidosis
        • Methanol (formic acid)
        • Uremia
        • Diabetic ketoacidosis
        • Propylene glycol
        • Iron tablets or isoniazid
        • Lactic acidosis
        • Ethylene glycol
        • Salicylates (late)
        • mnemonic: MUDPILES
 
 

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