Metabolic Acidosis (Study Outline) 1. Background Definitio…
Metabolic Acidosis (Study Outline) 1. Background Definition: A primary decrease in HCO₃⁻ with low blood pH (12 (lab dependent). High AG clues: Lactic acidosis → elevated lactate. Renal failure → ↑ BUN/Cr. DKA → elevated serum ketones, high glucose. Toxins → osmolar gap (ethanol surrogates). Normal AG (hyperchloremic) clues: RTA → urine pH abnormal patterns. Diarrhea → history of GI losses. Carbonic anhydrase inhibitors. Additional tests: Serum osmolality, ketones, lactate, toxicology screening as indicated. Urinalysis for RTA evaluation. Gold Standard: ABG and serum chemistry confirming ↓ pH, ↓ HCO₃⁻, and AG classification. 5. Management (Exam Concepts) General principles: Correct underlying cause conceptually. Monitor electrolytes (especially K⁺). Avoid nephrotoxins; adjust medication dosing. High AG causes (concept-level): DKA: manage hyperglycemia/ketosis principles. Lactic acidosis: address tissue hypoxia/shock source. Uremia: consider renal replacement therapy if severe (AEIOU). Toxins: antidotes or enhanced elimination principles (e.g., dialysis in selected toxins). Normal AG causes: Diarrheal losses: conceptual volume/electrolyte correction. Renal tubular acidosis: manage acid-base imbalance at concept level. Alkali therapy: May be used conceptually in severe acidosis (pH < severe threshold) or RTA. Monitoring: Serial ABGs, electrolytes, renal function. Dialysis indications: refractory acidosis, toxin-associated AG acidosis, recurrent hyperkalemia, or uremic complications. QUESTION A 52‑year‑old man is brought to the emergency department after being found unconscious at home. His wife reports he had been vomiting and having diarrhea for three days. On arrival his vital signs show: heart rate 110/min, respirations 28/min, blood pressure 92/60 mmHg. He appears weak and dehydrated. Laboratory tests show: Arterial blood gas: pH 7.22 (normal 7.35‑7.45), HCO₃⁻ 14 mEq/L (normal 24‑28) Serum electrolytes: Na⁺ 138 mEq/L, Cl⁻ 110 mEq/L, HCO₃⁻ 14 mEq/L BUN/Cr elevated consistent with dehydration What is the most likely acid‑base disorder and its classification? A) High‑anion‑gap metabolic acidosis due to toxin exposureB) Normal anion gap (hyperchloremic) metabolic acidosis due to gastrointestinal bicarbonate lossC) Mixed metabolic acidosis and respiratory acidosis from respiratory failureD) Normal anion gap metabolic alkalosis from vomiting