📊 Definitions
• Acidemia: blood pH <7.35
• Metabolic acidosis: primary decrease in HCO₃⁻
• Respiratory acidosis: primary increase in PCO₂
• Mixed disorders: combined abnormalities
⚡ High Anion Gap Metabolic Acidosis (MUDPILES)
• Methanol, Uremia, Diabetic ketoacidosis, Paraldehyde, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates
• Calculate anion gap = Na - (Cl + HCO₃); Normal 8-12
• Osmolar gap (measured - calculated) >10-15 suggests toxic alcohol ingestion
🩺 Normal Anion Gap Metabolic Acidosis (Hyperchloremic)
• Diarrhea (most common cause in children)
• Renal tubular acidosis (RTA): types 1 (distal), 2 (proximal), 4 (hypoaldosteronism)
• Urine AG: negative suggests normal ammonium excretion; positive suggests inadequate ammonium (RTA)
🫁 Respiratory Acidosis
• Hypoventilation: asthma, pneumonia, airway obstruction, neuromuscular (GBS, MD, botulism), CNS depression (sedatives, trauma), opioids
• Compensation: metabolic (increased HCO₃) - acute 1 mEq/L HCO₃ per 10 mmHg PCO₂; chronic 4 mEq/L
📌 Decision strategy: First determine pH, PCO₂, HCO₃ → identify primary disorder. Calculate anion gap. High AG → toxic ingestion or lactic acidosis. Normal AG → diarrheal losses or RTA. Urine AG helps differentiate GI from renal losses.