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 mild abuse results in alkalosis due to hypokalemia and the resulting shift of H+ into the cells if abuse is severe, metabolic acidosis results due to the excessive diarrhea and loss of HCO3- 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 (such as by metformin toxicity) Ethylene glycol Salicylates (late) mnemonic: MUDPILES