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SOURCE

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Source: Devlin JW, Matzke GR. Acid–base disorders. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM., eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146062232. Accessed March 6, 2017.

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DEFINITION

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  • Acid–base disorder characterized by a decrease in pH as the result of a primary decrease in serum bicarbonate (HCO3) concentrations.

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ETIOLOGY

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  • Decreased HCO3 results from many clinical situations (Table 1).

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Table Graphic Jump Location
TABLE 1.Common Causes of Metabolic Acidosis
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PATHOPHYSIOLOGY

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  • Metabolic acid–base disorders are caused by changes in (HCO3).

    • Metabolic acidosis is characterized a decrease in serum HCO3 concentrations resulting from.

      • Consumption of HCO3

      • Addition of organic acid to extracellular fluid (eg, lactic acid and ketoacids)

      • Loss of HCO3 stores (eg, diarrhea, biliary drainage)

      • Accumulation of endogenous acids due to impaired renal function (eg, phosphates and sulfates)

    • Serum anion gap (SAG) can be used to determine the cause of metabolic acidosis (Table 1), calculated as follows:

      SAG = [Na+] − [Cl] − [HCO3]

      • Normal anion gap is ~9 mEq/L (9 mmol/L), with range of 3–11 mEq/L (311 mmol/L)

  • Primary compensatory mechanism: increase carbon dioxide excretion by increasing the respiratory rate, resulting in a decreased PaCO2.

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RISK FACTORS

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  • Common chronic diseases and use of medications (Table 5.1)

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CLINICAL PRESENTATION

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  • Relatively asymptomatic if acidosis acute and mild.

    • Cardiovascular, respiratory, and central nervous systems can be affected with severe metabolic acidemia (pH <7.15–7.2).

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SIGNS AND SYMPTOMS

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