Anion gap

Metabolic Effects. Severe metabolic acidosis with high anion gap and hyperglycemia was reported in humans after acute poisoning with endosulfan (Blanco-Coronado et al. 1992 Lo et al. 1995). In five of the six cases reported by Blanco-Coronado et al. (1992), the metabolic acidosis was corrected with gastric lavage with activated charcoal and intravenous sodium bicarbonate and diazepam. No further information regarding metabolic effects in humans after exposure to endosulfan was located. 

Chronic or large ingestions of propylene glycol have been associated with the development of hyperosmolar anion-gap metabolic acidosis, renal dysfunction, hemolysis, cardiac arrhythmias, and seizures. 

When plasma glucose drops to 250 mg/dL, decrease insulin infusion rate and continue until acidosis is corrected (i.e., anion gap closes)... 

Serum electrolytes should be monitored in patients with CKD for the development of metabolic acidosis. Metabolic acidosis in patients with CKD is generally characterized by an elevated anion gap greater than 17 mEq/L (17 mmol/L), due to the accumulation of phosphate, sulfate, and other organic anions. 

Integrate the supplemental concepts of the anion gap and the excess gap to help assess complex acid-base disturbances. 

Metabolic acidosis is characterized by a decrease in serum HC03. The anion gap is used to narrow the differential diagnosis, as this acidosis may be caused by addition of acids (increased anion gap) or loss of HC03 (normal anion gap). The compensation for metabolic acidosis is an increase in ventilation with a decrease in arterial C02. 

It is important to realize that the serum HCO, concentration may be affected by the presence of unmeasured endogenous acids (lactic acidosis or ketoacidosis). Bicarbonate will attempt to buffer these acids, resulting in a 1 mEq loss of serum HCO, for each 1 mEq of acid titrated. Because the cation side of the equation is not affected by this transaction, the loss of serum HC03 results in an increase in the calculated anion gap. Identification of an increased anion gap is very important for identifying the etiology of the acid-base disorder. The concept of the increased anion gap will be applied later in the case studies section. 

Any time an ABG is analyzed it is wise to concurrently inspect the serum chemistry values to calculate the anion gap. The body does not generate an anion gap to compensate for a primary disorder. As such, if the calculated anion gap exceeds 12 mEq/L (mmol/L) there is a primary metabolic acidosis regardless of the pH or the serum HC03 concentration. The anion gap may be artificially lowered by decreased serum albumin, multiple myeloma, lithium intoxication, or a profound increase in the serum potassium, calcium, or magnesium. 

Calculation of the anion gap also facilitates determination of the excess gap or the degree to which the calculated anion gap exceeds the normal anion gap. The excess gap is calculated as follows ... 

This patient had ingested a large quantity of aspirin resulting in the classic findings of a salicylate overdose a centrally mediated respiratory alkalosis with a concurrent anion gap metabolic acidosis. 

As previously discussed, in anion gap metabolic acidosis, the isoelectric state is maintained because unmeasured anions are present. With a normal anion gap metabolic acidosis, the isoelectric state is maintained by an increase in the measured... 

In patients with a normal anion gap metabolic acidosis it is ... 

Acid-base disturbances are common clinical problems that are not difficult to analyze if approached in a consistent manner. The pH, PaC02, and HCO, should be inspected to identify all abnormal values. This should lead to an assessment of which deviations represent the primary abnormality and which represent compensatory changes. The serum electrolytes should always be used to calculate the anion gap. In cases in which the anion gap is increased, the excess anion gap should be added back to the measured HC03 . The anion gap and the excess... 

Is the anion gap excessively large If so, does calculation of the excess gap identify another acid-base disorder ... 

Measure capillary glucose every 1-2 hours measure electrolytes (especially K+, bicarbonate, phosphate) and anion gap every 4 hours for first 24 hours. 

None unless symptoms present => Consider lactate concentrations in patients with 4- serum bicarbonate or T anion gap... 

Etoposide Blood pressure, respiratory rate, serum pH, serum bicarbonate with arterial blood gases, and evaluation of anion gap if necessary... 

The anion gap is the concentration of plasma anions not routinely measured by laboratory screening. It is useful in the evaluation of acid-base disorders. The anion gap is greater with increased plasma concentrations of endogenous species (e.g., phosphate, sulfate, lactate, and ketoacids) or exogenous species (e.g., salicylate, penicillin, ethylene glycol, ethanol, and methanol). The formulas for calculating the anion gap are as follows ... 

Tinnitus, confusion, lethargy, and seizures hyperventilation and an anion-gap metabolic acidosis... 

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