Lactate
Strong ion. pKa 3.9 so completely dissociated at pH 7.4
70% metabolised in liver to pyruvate where most converted by gluconeogenesis to glucose. Small amount converted to acetylCoA and then on to CO2 and H2O
30% converted to pyruvate in mitochondrial rich tissue then to acetylCoA and CO2 + H20
<5% excreted directly from kidneys
Increased production
Hypoxia
Increased glycolysis (catecholamines)
Alanine formation (protein breakdown in critical illness)
Inhibition of pyruvate dehydrogenase (sepsis)
Decreased clearance
Hepatic metabolism
- Failure of any cause
Mitochondria rich tissue metabolism
- Hypoxia/shock
Renal excretion
- Usually <5% excreted by kidneys. Can rise if increased lactate.
Exogenous sources
Lactate containing solutions (CSL, RRT solutions).
Under most circumstances the lactate in CSL will be metabolized as rapidly as it is infused since normal lactate clearance can reach 200mmol/hr - see ketoacidosis for more detailed info on the effect of CSL infusions.
Classification
Type A - hypoperfusion
Type B - failure of metabolism