Acid-base disorders etiology

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. 

After an acid-base disorder has been completely characterized, the patient s medical history, physical exam, and medications should be reviewed in order to establish the etiology of the given disorder. Tables 25-3 through 25-7 outline the most commonly encountered causes of the primary acid-base disorders. The therapeutic approach to each of these acid-base derangements should emphasize a search for the cause, as opposed to immediate attempts to normalize the pH. Although supportive measures to prevent the sequelae of marked acid-base abnormalities is often required, these therapies will be required indefinitely if the causative process is not also identified and corrected.7,8... 

A description of acid-base balance involves an accounting of the carbonic (H2C03, HCOh COa", and CO2) and noncar-bonic acids and conjugate bases in terms of input (intake plus metabolic production) and output (excretion plus metabolic conversion) over a given time interval. The acid-base status of the body fluids is typically assessed by measurements of total CO2 plasma pH and PCO2, because the bicarbonate/carbonic acid system is the most important buffering system of the plasma. Occasionally, measurement of total titratable acid or base, or other acid and base analytes (e.g., lactate and ammonia [NH3]) is necessary to determine the etiology of an acid-base disorder. 

Patients receiving either casein hydrolysates or fibrin hydrolysate as the nitrogen source of total parenteral nutrition rarely develop acid-base disorders. If they do, there is usually an obvious etiology for the disorder. However, with the advent of crystalline amino acid mixtures, especially NeoAminosol (an experimental preparation patterned after the free amino acid composition of Aminosol ) and to a lesser extent FreAmine, a number of patients, especially infants and young children, developed a hyperchloremic... 

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