the normal serum lactate range is up to 2 mmol/L (18 mg/dL)
raised serum lactate > 4 mmol is often used as a marker for severe sepsis or localised ischaemia such as bowel or limb ischaemia and its use in at risk patients helps to detect occult severe sepsis or bowel ischaemia earlier
high levels of serum lactate is associated with “lactic acidosis” which is one of the types of metabolic acidosis
Physiology
lactate is metabolized in the liver either by gluconeogenesis or oxidation with both reactions consuming a hydrogen ion
lactic acid / lactate is produced when the amount of pyruvate exceeds the capacity of the Krebs cycle and is converted to lactate anaerobically at a rate higher than it can be metabolised - this may occur due to a range of mechanisms:
increased pyruvate production through the beta-2 adrenergic stress response which increases glycogenolysis and glucose production
reduced capacity of Krebs cycle:
relative thiamine deficiency
decreased activity of pyruvate dehydrogenase (this may be due to cytokine activity during a stress response)
cellular hypoxia
reduced hepatic metabolism of lactate
Aetiology of raised serum lactate levels and "lactic acidosis"
traditional classification of lactic acidosis states
extremely severe global cellular impaired oxygenation where the cellular oxygen delivery falls below the global anaerobic threshold of adults which is about 4mls/kg/min and equates to a cardiac index of just over 1 L/minM2 and Hb of around 4g/dl and this level generally only is reached in pre-terminal states