High anion gapmetabolic acidosis is a form of metabolic acidosis characterized by a high anion gap. Metabolic acidosis occurs when the body produces too much acid, or when the kidneys are not removing enough acid from the body. Several types of metabolic acidosis occur, grouped by their influence on the anion gap. The anion gap can be increased due to relatively low levels of cations other than sodium and potassium. An anion gap is usually considered to be high if it is over 12 mEq/L. High anion gap metabolic acidosis is typically caused by acid produced by the body. More rarely, it may be caused by ingesting methanol or overdosing on aspirin. The Delta Ratio is a formula that can be used to assess elevated anion gap metabolic acidosis and to evaluate whether mixed acid base disorder is present. The list of agents that cause high anion gap metabolic acidosis is similar to but broader than the list of agents that cause a serum osmolal gap.
Causes
The most common causes of high anion gap metabolic acidosis are: ketoacidosis, lactic acidosis, kidney failure, and toxic ingestions. Ketoacidosis can occur as a complication of type Idiabetes mellitus, but can occur due to other disorders, such as chronic alcoholism and undernutrition. In these conditions, excessive free fatty acid metabolism results in the production of ketoacids, acetoacetic acid, and beta-hydroxybutyrate. Lactic acidosis results from excess formation and decreased metabolism of lactate, which occurs during states of anaerobic metabolism. It is the most common cause of metabolic acidosis in hospitalized patients. The most serious form occurs during various states of shock, due to episodes of decreased liver perfusion. Kidney failure results in decreased acid excretion and increased bicarbonate excretion. Toxins that result in acidic metabolites may trigger lactic acidosis. Rhabdomyolysis, a muscle-wasting disease, is a rare cause of metabolic acidosis.
Mnemonics
Various mnemonics are used to assist clinicians in the detection and diagnosis of conditions that may result in high anion gap metabolic acidosis: The newer 2008 mnemonic "GOLD MARK" was proposed in The Lancet reflecting current causes of anion gap metabolic acidosis:
G — glycols
O — oxoproline, a metabolite of paracetamol / acetaminophen
L — L-lactate, the chemical responsible for lactic acidosis
Another frequently used mnemonic is KULT. This is the most useful as lactate / ketones and the uraemia are the most common causes and the toxins are vanishingly rare as a cause unless you work in a toxicology centre. ACEGIFTS is the mnemonic for the toxins .
The mnemonic for the toxins is ACE GIFTs: Aspirin, Cyanide, Ethanolic ketosis, Glycols , Isoniazid, Ferrous iron, Toluene], salicylates]. Most of these cause a lactic acidosis.
