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Chapter: Paediatrics: Inherited metabolic disease

Paediatrics: Metabolic syndromes: metabolic acidosis

The emergency care of acid–base problems.

Metabolic syndromes: metabolic acidosis

 

The emergency care of acid–base problems.

Metabolic acidosis may occur as a result of:

   Abnormal loss of bicarbonate.

 

   Abnormal accumulation of hydrogen ions in association with a non-volatile organic anion.

 

These two states can be differentiated by calculating the anion gap (i.e. the difference between plasma [Na+] and the sum of plasma [Cl] and [HCO3 ]). The normal anion gap is 10–15mmol/L.

 

Abnormal bicarbonate loss

 

When metabolic acidosis is due to bicarbonate loss from either the gut or kidney:

   The anion gap is normal.

 

   Hyperchloraemia is usually present.

 

To distinguish bicarbonate loss from the gut or from the kidney:

   A history of diarrhoea will distinguish between hyperchloraemia due to GI losses from that due to renal tubular losses.

   Urine net charge (UNC), calculated as [Na++ K+] – [Cl], is used to estimate urine ammonium (NH4+) when there is no accumulated organic acid. A negative UNC implies the presence of adequate or increased urinary ammonium; therefore the acidosis results from abnormal GI loss of bicarbonate. (Note: Urine ammonium is low in renal tubular disorders.)

 

IMDs associated with RTA include—galactosaemia; hereditary fructose intolerance; hepatorenal tyrosinaemia; cystinosis; glycogen storage disease I; Fanconi–Bickel syndrome; congenital lactic acidosis; Wilson disease; vita-min D dependency; osteopetrosis with RTA; Lowe syndrome.

 

Accumulation of organic anion

 

When metabolic acidosis is due to accumulated organic anion:

   It is associated with failure to thrive.

 

   Tachypnoea may be present.

 

   s hypoglycaemia leads to a neurological syndrome.

 

   Organic anion may lead to distinct smell of sweat or urine.

 

   The anion gap is raised.

 

The causes include the following:

   Lactic acidosis: pyruvate accumulation (e.g. pyruvate dehydrogenase deficiency, pyruvate carboxylase deficiency, multiple carboxylase deficiency); NADH accumulation (e.g. defect of mitochondrial electron chain).

 

   Ketoacidosis: s to IMD (e.g. maple syrup urine disease, organic acido-pathies, glycogen storage disease, disorders of gluconeogenesis; rare p disorders of ketone utilization, e.g. B-ketothiolase deficiency, succinyl-CoA: 3-ketoacid transferase deficiency.

Organic aciduria: a large spectrum of disorders.

 

 

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Paediatrics: Inherited metabolic disease : Paediatrics: Metabolic syndromes: metabolic acidosis |


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