Which is the most common cause of metabolic acidosis in clinical practice?

Explanation

## Most Common Cause of Metabolic Acidosis in Clinical Practice **Key Point:** Lactic acidosis is the most common cause of metabolic acidosis **in clinical practice**, accounting for the majority of high anion gap metabolic acidosis cases encountered in hospital and ICU settings. ### Pathophysiology of Lactic Acidosis 1. **Type A (most common):** Tissue hypoperfusion/hypoxia → anaerobic glycolysis → excess lactate production (sepsis, shock, cardiac arrest, severe anemia) 2. **Type B:** No overt tissue hypoxia — drugs (metformin, linezolid), liver failure, malignancy, mitochondrial disorders 3. **High anion gap:** Lactate accumulates as an unmeasured anion, raising the anion gap (>12 mEq/L) 4. **Rapid onset:** Can develop within hours in critically ill patients, making it the dominant cause seen by clinicians ### Frequency Comparison of Metabolic Acidosis Causes | Cause | Anion Gap Status | Frequency in Clinical Practice | Clinical Context | |-------|-----------------|-------------------------------|-----------------| | **Lactic acidosis** | High AG | **Most common overall** | Sepsis, shock, hypoxia | | DKA | High AG | Common in diabetics | Insulin deficiency | | Renal failure | High AG | Common in CKD stage 5 | Uremia | | Diarrhea | Normal AG | Common in community/pediatrics | GI bicarbonate loss | | RTA | Normal AG | Rare | Tubular dysfunction | **High-Yield:** Harrison's Principles of Internal Medicine explicitly states that **lactic acidosis is the most common cause of metabolic acidosis in clinical practice**. The phrase "in clinical practice" refers to the hospital/clinical encounter setting, where critically ill patients with sepsis, shock, and hypoxemia predominate. **Clinical Pearl:** Diarrhea is the most common cause of **normal anion gap (hyperchloremic) metabolic acidosis** in the community/general population, but when the question asks about "clinical practice" without restriction to anion gap type, lactic acidosis takes precedence due to its overwhelming prevalence in hospitalized patients. - Lactic acidosis: serum lactate >2 mmol/L (significant) or >5 mmol/L (severe) - Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻); normal 8–12 mEq/L; elevated in lactic acidosis - Urine anion gap is **positive** (impaired renal acid excretion is not the mechanism) **Mnemonic for high anion gap acidosis: MUDPILES** - **M**ethanol / **M**etformin - **U**remia - **D**KA - **P**ropylene glycol / **P**araldehyde - **I**soniazid / Iron - **L**actic acidosis ← **most common** - **E**thylene glycol - **S**alicylates [cite: Harrison's Principles of Internal Medicine, 21e, Ch. 48 — Acid-Base Disturbances]