• Blood tests are used to check electrolyte levels typically showing a low plasma bicarbonate (<22 mmol/L). Lactate levels in the blood are continuously monitored.
• Arterial blood gases usually show a metabolic acidosis (pH <7.35 with low or normal pCO2). In the absence of obvious acidic toxins or ketone bodies, the situation points to lactic acidosis. The anion gap will be elevated in lactic acidosis. The anion gap should be calculated as below:
  • The anion gap is the difference between the sum of the cations (sodium plus potassium) and the anions (chloride plus bicarbonate),
    • ([Na mmol/L] + [K mmol/L]) − ([Cl mmol/L] + [HCO3 mmol/L]).

• Anion gap is also elevated in chronic kidney disease and other organic acidoses, ketoacidosis, and some drug induced acidoses.

• Keep in mind that clinically significant hyperlactataemia can occur in the absence of a raised anion gap.

• Samples for lactate estimation should be taken from arterial or mixed central venous sites, since peripheral values may reflect local rather than systemic concentrations.
• Further investigations aimed at detecting the underlying cause should be requested as thought necessary. Blood, urine and other cultures are useful for detecting occult septic causes.
• References

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