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Lactic Acidosis

By

James L. Lewis III

, MD, Brookwood Baptist Health and Saint Vincent’s Ascension Health, Birmingham

Last full review/revision Jul 2021| Content last modified Jul 2021
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Lactic acidosis is a high anion gap metabolic acidosis Metabolic Acidosis Metabolic acidosis is primary reduction in bicarbonate (HCO3−), typically with compensatory reduction in carbon dioxide partial pressure (Pco2); pH may be markedly low or slightly subnormal... read more due to elevated blood lactate. Lactic acidosis results from overproduction of lactate, decreased metabolism of lactate, or both.

Lactate is a normal byproduct of glucose and amino acid metabolism. There are 2 main types of lactic acidosis:

  • Type A lactic acidosis

  • Type B lactic acidosis

D-Lactic acidosis (D-lactate encephalopathy) is an unusual form of lactic acidosis.

Type A lactic acidosis

Type B lactic acidosis

Type B lactic acidosis occurs in states of normal global tissue perfusion (and hence ATP production) and is less ominous.

Causes include local tissue hypoxia (eg, as with vigorous muscle use during exertion, seizures, hypothermic shivering), certain systemic and congenital conditions, cancer, and ingestion of certain drugs or toxins (see table Causes of Metabolic Acidosis Causes of Metabolic Acidosis Metabolic acidosis is primary reduction in bicarbonate (HCO3−), typically with compensatory reduction in carbon dioxide partial pressure (Pco2); pH may be markedly low or slightly subnormal... read more ). Drugs include the nucleoside reverse transcriptase inhibitors and the biguanides phenformin and, less so, metformin; although phenformin has been removed from the market in most of the world, it is still available from China (including as a component of some Chinese proprietary medicines). Metabolism may be decreased due to hepatic insufficiency or thiamin deficiency.

D-Lactic acidosis

D-Lactic acidosis is an unusual form of lactic acidosis in which D-lactic acid, the product of bacterial carbohydrate metabolism in the colon of patients with jejunoileal bypass or intestinal resection, is systemically absorbed. It persists in circulation because human lactate dehydrogenase can metabolize only L-lactate.

Symptoms and Signs

Symptoms and signs of lactic acidosis are dominated by those of the underlying disorder (eg, shock in Type A, toxin ingestion in Type B). Neurologic symptoms, including confusion, ataxia, and slurred speech, occur after a high-carbohydrate ingestion and are characteristic of D-lactic acidosis.

Diagnosis

  • Arterial blood gas (ABG) and serum electrolyte measurements

  • Anion gap and delta gap calculated

  • Blood lactate level

ABG values in types A and B lactic acidosis are as for other metabolic acidoses Diagnosis Metabolic acidosis is primary reduction in bicarbonate (HCO3−), typically with compensatory reduction in carbon dioxide partial pressure (Pco2); pH may be markedly low or slightly subnormal... read more . Diagnosis requires blood pH < 7.35 and lactate > 45 to 54 mg/dL (> 5 to 6 mmol/L). Less extreme lactate and pH changes are referred to as hyperlacticemia.

In D-lactic acidosis, the anion gap is lower than expected for the decrease in bicarbonate (HCO3), and there may be a urinary osmolar gap (difference between calculated and measured urine osmolarity). Typical laboratory lactate assays are not sensitive to D-lactate. Specific D-lactate levels are available and sometimes needed to clarify the cause of acidosis in patients with multiple potential causes including bowel problems.

Treatment

  • Treatment of cause

Treatment of the cause is paramount. In treating inadequate tissue perfusion, pressors should be omitted when possible because they may worsen tissue ischemia. Bicarbonate is potentially dangerous in high anion gap acidosis but may be considered when pH is < 7.00, with a target pH of ≤ 7.10.

In D-lactic acidosis, treatment is IV fluids, restriction of carbohydrates, and sometimes oral antibiotics (eg, metronidazole) for short bowel syndrome and bicarbonate for severe acidosis.

Key Points

  • There are 2 main types of lactic acidosis, type A and type B; type A is more serious because it is caused by ischemia.

  • Diagnosis requires blood pH < 7.35 and serum lactate levels > 45 to 54 mg/dL (> 5 to 6 mmol/L).

  • Avoid pressors when possible for types A and B lactic acidosis because they worsen tissue ischemia.

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