Lactate is one of the most useful and most misunderstood markers in critical care.
An elevated lactate is associated with worse outcomes across shock states. A falling lactate can be reassuring.
But lactate is not a pure oxygen debt meter.
Lactate may rise from tissue hypoperfusion and anaerobic metabolism. That is the classic teaching.
But lactate can also rise from adrenergic stimulation, beta-agonists, seizures, liver dysfunction, mitochondrial impairment, severe work of breathing, epinephrine, and impaired clearance.