Causes of metabolic acidosis

increase in hydrogen ion load taken by mouth (e.g. ingestion of ammonium chloride) or by injection  

excessive loss of bicarbonate ions from the body through the gastrointestinal tract (e.g. diarrhoea, pancreatic or biliary drainage)  

increase in hydrogen ion load from endogenous sources  

decrease in the kidney s ability to excrete acid, due to carbonic anhydrase inhibitors or renal disease. 

---

Anion gap can be calculated to elucidate the cause of metabolic acidosis (T able 74-3). The anion gap is calculated as follows ... 

Lactate, pyruvate, acetoacetate (ACAC) and 3-hydroxybutyrate ( ) are intermediary metabolites that normally occur in blood and play an essential role in energy production. Their accumulation in blood is a frequent cause of metabolic acidosis in children. The determination of these metabolites in biological fluids is useful in the early detection, diagnosis and treatment follow-up of abnormalities such as those of ... 

Although there is a long list of causes of metabolic acidosis with an increased anion gap (286,287), clinical clues can help diagnosis. A case report has illustrated the acute metabolic and hemodynamic effects of ingestion of a massive load of oral citric acid. The principal findings included a metabolic acidosis accompanied by an increase in the plasma anion gap, not due to lactic acidosis, hyperkalemia, and the abrupt onset of hypotension (288). 

DeMars CS, Hollister K, Tomassoni A, Himmelfarb J, Halperin ML. Citric acid ingestion a life-threatening cause of metabolic acidosis. Ann Emerg Med 2001 38(5) 588-91. 

These unmeasured anions are generated as the result of the consumption of HCOJ by endogenous organic acids such as lactic acid, acetoacetic acid, or / -hydroxybutyric acid or from the ingestion of toxins such as methanol or ethylene glycol. The degree of elevation in the SAG is dependent on the clearance of the anion, as well as the multiple factors that influence HCOJ concentrations. Thus the SAG is a relative rather than an absolute indication of the cause of metabolic acidosis. The SAG may also be elevated in the metabolic acidosis due to renal failure, as the result of the accumulation of various organic anions, phosphates, and sulfates. 

In hyperchloremic metabolic acidosis, bicarbonate losses from the ECF are replaced by chloride and the SAG remains normal. This decrease in bicarbonate results from losses from the gastrointestinal tract, dilution of bicarbonate in the ECF space by the addition of sodium chloride solutions, or the addition of chloride-containing acids to the ECF. Common causes of metabolic acidosis with an increased or a normal SAG are listed in Table 51-5. 

Megarbane B, Bruneel F, Bedos JP, et al. 2000. Ammonium chloride poisoning a misunderstood cause of metabolic acidosis with normal anion gap. Intensive Care Med 26(12) 1869. 

The commonest causes of metabolic acidosis are renal disease, diabetic ketoacidosis and lactic acidosis. Consideration of fhe anion gap may sometime be helpful in esfablishing the cause of a metabolic acidosis. 

A brief classification of the causes of metabolic acidosis is given in section A.2. 

An example of metabolic acidosis occurring as a result of disease is uncontrolled diabetes mellitus (Table 3.4). The tissues cannot metabolize glucose properly and instead excessively metabolize fat to yield so-called ketone bodies which include aceto-acetic and beta-hydroxy-butyric acids. These are strong acids. Such acids are called non-volatile , or fixed because they cannot be blown off in the lungs as can CO2. Renal damage is another cause of metabolic acidosis as will be explained later, a normal mixed diet yields a preponderance of acid when metabolized and the urine is normally acid. When renal function is impaired, the kidney fails to excrete this metabolically-derived acid and the acid accumulates in the body. In surgical patients, a common... 

A. Some causes of metabolic acidosis Diabetes mellitus... 

---