Overview
Recognise a raised-anion-gap metabolic acidosis, identify lactate and other unmeasured acids, and reverse tissue hypoperfusion or toxic and metabolic causes before severe acidemia compounds organ failure.
The anion gap is a bookkeeping estimate of negatively charged substances not routinely measured. When lactate, ketone bodies, uraemic acids or toxin metabolites accumulate, bicarbonate falls as it buffers hydrogen ions and the gap usually rises. Hypoalbuminaemia lowers the baseline gap, while chloride-rich fluid can add a simultaneous normal-gap acidosis. A patient may therefore have several processes at once.
Lactate production is not synonymous with anaerobic death. Adrenergic stimulation, seizures and high-dose beta-2 agonists can raise lactate despite adequate global oxygen delivery, whereas poor clearance in liver dysfunction prolongs it. The dangerous question is not merely why the value is high but whether shock, local ischaemia, sepsis, poisoning, DKA or organ failure is continuing.
The central decision is whether the physiology demands immediate resuscitation, whether a time-critical source such as sepsis, bowel ischaemia or toxic exposure needs definitive action, and whether the calculated gap reveals another acid when lactate does not explain the bicarbonate fall. Serial clinical response is more informative than repeatedly measuring lactate without changing treatment.