What is the significance of an anion gap of 20 in a 20-month-old child with vomiting?

From the Guidelines

The immediate management of a 20-month-old child with vomiting and an anion gap of 20 should focus on rehydration with oral rehydration solution (ORS), as recommended by the 2017 Infectious Diseases Society of America clinical practice guidelines 1. The child's symptoms suggest metabolic acidosis, likely due to dehydration and ketosis.

• The anion gap of 20 is elevated, indicating the presence of unmeasured anions in the bloodstream.
• The child's vomiting is a significant concern, as it can lead to further dehydration and electrolyte imbalances.
• According to the 2017 IDSA guidelines, reduced ORS is recommended as the first-line therapy for mild to moderate dehydration in infants, children, and adults with acute diarrhea from any cause 1.
• The guidelines also recommend nasogastric administration of ORS in infants, children, and adults with moderate dehydration who cannot tolerate oral intake 1.
• In this case, the child's anion gap and vomiting suggest that rehydration with ORS is the most appropriate initial management strategy.
• Electrolytes, glucose, and acid-base status should be monitored closely, and ondansetron (0.15 mg/kg) can be given to control vomiting.
• The underlying cause of the child's symptoms needs investigation, with common possibilities including gastroenteritis, diabetic ketoacidosis, toxic ingestion, or inborn errors of metabolism.
• Blood glucose should be checked immediately to rule out diabetic ketoacidosis, and urine ketones, complete blood count, comprehensive metabolic panel, and possibly ammonia levels should be obtained 1.

From the Research

Anion Gap Interpretation

• The anion gap is a mathematical construct that compares the blood sodium concentration with the sum of the chloride and bicarbonate concentrations 2.
• It is used to divide metabolic acidoses into two categories: high anion gap metabolic acidosis (HAGMA) and hyperchloremic metabolic acidosis 2.
• A normal anion gap reference interval is between 7 to 18 mmol/L with a median of 13 mmol/L in healthy adults 3.

Clinical Significance of Anion Gap in Vomiting

• Vomiting can lead to severe dehydration and metabolic acidosis with an elevated anion gap, as seen in a case of cow milk protein allergy (CMPA) in a neonate 4.
• Metabolic acidosis with an elevated anion gap can present with nausea, vomiting, and changes in mental status, and possible causes include ketoacidosis, certain toxic ingestions, renal failure, and lactic acidosis 5.

Limitations of Anion Gap Calculation

• The serum anion gap has limitations in evaluating acid-base disorders, including a wide range of normal values and the effect of perturbations other than changes in acid-base balance 6.
• The type of retained anion can affect the magnitude of the increase in anion gap relative to change in serum bicarbonate, being greater with lactic acidosis compared with ketoacidosis 6.

Anion Gap of 20 in a 20-month-old with Vomiting

• An anion gap of 20 is slightly above the normal reference interval of 7 to 18 mmol/L 3.
• In the context of vomiting, an elevated anion gap may indicate metabolic acidosis, and possible causes should be investigated, including CMPA, ketoacidosis, and renal failure 4, 5.