Lactate has become the number that decides whether a patient with infection is treated as septic, and it fails in two specific directions that are worth holding in mind at the bedside.
It can be normal in real shock. Early compensated sepsis, sepsis in a patient on metformin-free regimens with preserved hepatic clearance, and above all the elderly patient whose baseline blood pressure is 160 and who is now sitting at 105 — all of these can have a lactate under 2 while being profoundly unwell. Relative hypotension against a known baseline is the finding, and it is invisible if you only read the absolute number.
It can also be raised without shock. Beta-agonists, adrenaline, alcohol, seizures, metformin, thiamine deficiency and liver disease all raise lactate. Treating that lactate with fluid is how a patient with a post-ictal level of 6 receives four litres they did not need.
Use the trend, not the value. A lactate that is not falling after resuscitation is the useful signal — more useful than the height of the first one.
- Compare the blood pressure with the patient's own baseline, not with 90 systolic.
- Repeat the lactate — the trend after two hours carries more information than the initial value.
- Ask what else could be raising it before attributing a raised lactate to hypoperfusion.
- A normal initial lactate in a patient who looks unwell is a reason to re-examine, not to downgrade.
Why it matters
Triage pathways increasingly key off a single lactate, and that number is wrong in both directions often enough to matter.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for emergency & critical care, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free