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Metabolic acidosis is a condition characterized by decreased blood pH due to either excess acid production, impaired acid excretion, or bicarbonate loss. It results in compensatory hyperventilation and can be classified as high anion gap or normal anion gap acidosis based on unmeasured anions.
The condition occurs through four main mechanisms: increased acid production (ketoacids, lactic acid), decreased acid excretion (renal failure), bicarbonate loss (diarrhea, renal tubular acidosis), or dilutional acidosis from rapid saline infusion. The body compensates through respiratory alkalosis (hyperventilation) and renal bicarbonate retention, though these mechanisms may be insufficient in severe cases.
Diagnosis involves arterial blood gas analysis showing pH <7.35 with low bicarbonate, and calculating the anion gap to determine etiology. High anion gap causes include diabetic ketoacidosis, lactic acidosis, and toxin ingestion, while normal anion gap causes include diarrhea and renal tubular acidosis. Treatment focuses on addressing the underlying cause while carefully correcting severe acidemia with bicarbonate when pH <7.1.