A single lactate in a patient with suspected infection tells you less than the direction of travel. A raised initial value has many causes — a seizure, salbutamol, metformin, alcohol, a tourniquet held too long, adrenaline given ten minutes earlier — and a normal one does not exclude serious sepsis, particularly in a patient with liver disease or an early presentation.
Repeat it at two to four hours after starting treatment. Falling lactate with improving perfusion is the finding that supports staying the course; a lactate that has not moved despite fluid and antibiotics is the finding that should change the plan — reassess the source, reconsider the diagnosis, and escalate rather than repeat the same intervention.
Two traps are worth naming. Venous and arterial lactate differ enough to matter when the value sits near a decision threshold, so compare like with like. And lactate clearance is a marker, not a target: chasing the number with more fluid in a patient who is already wet does harm, which is why perfusion, urine output and mental state have to be read alongside it.
- Repeat lactate at two to four hours — the trend carries the information, not the single value
- A normal initial lactate does not exclude sepsis, especially early or in liver disease
- Check for non-hypoperfusion causes: seizure, salbutamol, adrenaline, metformin, alcohol
- Compare venous with venous and arterial with arterial when the value is near a threshold
- A lactate that will not fall means reassess the source, not give more fluid by reflex
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