Causes of Lactic Acidosis
Lactic acidosis results from either increased lactate production (most commonly from tissue hypoxia and anaerobic metabolism) or decreased lactate clearance (from liver or kidney dysfunction), with the most critical distinction being Type A (tissue hypoxia) versus Type B (no tissue hypoxia) mechanisms 1, 2.
Type A Lactic Acidosis: Tissue Hypoxia/Hypoperfusion
This is the most common and life-threatening category, occurring when oxygen delivery fails to meet metabolic demand:
- Shock states: Septic, cardiogenic, hypovolemic, or hemorrhagic shock 2, 3
- Severe hypoxemia: Respiratory failure, severe pneumonia
- Circulatory failure: Cardiac arrest, severe heart failure
- Regional ischemia: Mesenteric ischemia, limb ischemia
- Severe anemia: Impaired oxygen-carrying capacity
- Carbon monoxide or cyanide poisoning: Blocks cellular oxygen utilization 2
Clinical Pearl: In sepsis, lactic acidosis is not purely from tissue hypoxia—epinephrine-induced aerobic glycolysis also contributes significantly, meaning lactate can remain elevated even with adequate tissue perfusion 4.
Type B Lactic Acidosis: No Tissue Hypoxia
This occurs when tissue oxygenation is maintained but lactate accumulates through other mechanisms:
Medications (Critical to Recognize)
Metformin: Risk dramatically increases with renal impairment (eGFR <30 mL/min/1.73 m²), sepsis, hypoxia, shock, or liver failure. In COVID-19 patients, metformin increased lactic acidosis risk 4.5-fold, particularly with higher doses and worse kidney function 5
Nucleoside Reverse Transcriptase Inhibitors (NRTIs): Stavudine and didanosine carry the highest risk through mitochondrial DNA polymerase γ inhibition, causing mitochondrial dysfunction. Risk factors include female sex, obesity, pregnancy (especially late-stage), and prolonged NRTI use 6, 7, 6. The incidence has decreased as abacavir and tenofovir replaced older NRTIs 8
Metabolic and Organ Dysfunction
- Liver failure: Impairs lactate clearance through reduced gluconeogenesis and oxidation 2
- Renal failure: Kidneys contribute to lactate removal; severe dysfunction impairs clearance 2
- Thiamine deficiency: Inhibits pyruvate dehydrogenase, blocking lactate oxidation 6, 2
- Diabetic ketoacidosis: Can present with concomitant type B lactic acidosis 9
Other Causes
- Malignancies: Particularly hematologic malignancies with high tumor burden 9, 2
- Grand mal seizures: Massive muscle activity generates lactate 9
- Alcohol abuse: Impairs lactate metabolism 9
- Congenital enzyme deficiencies: Rare metabolic disorders 9
Critical Diagnostic Considerations
When evaluating lactic acidosis, measure lactate properly using prechilled fluoride-oxalate tubes, transported immediately on ice, processed within 4 hours, collected without tourniquet or fist-clenching 6.
Lactate interpretation:
- 2-5 mmol/L: Elevated, correlate with symptoms
5 mmol/L: Abnormal
10 mmol/L: Life-threatening 6
Check for increased anion gap (Na − [Cl+CO₂] >16), though hypoalbuminemia may mask this 3. Monitor serum bicarbonate and electrolytes every 3 months in high-risk patients 6.
Common Pitfalls
Don't assume all lactic acidosis in sepsis means inadequate resuscitation—aerobic glycolysis from catecholamine surge contributes independently 4
Metformin must be stopped immediately in patients with acute kidney injury, sepsis, hypoxia, shock, or before contrast procedures in those with eGFR <60 mL/min/1.73 m² 5
NRTI-associated lactic acidosis presents insidiously with nonspecific GI symptoms (nausea, vomiting, abdominal pain), weakness, dyspnea, and hepatomegaly weeks before severe decompensation 6
Bicarbonate therapy does not improve hemodynamics or mortality in hypoperfusion-induced lactic acidemia with pH ≥7.15 and should not be routinely used 10