Figure 615

Ninety-five percent confidence intervals for metabolic acidosis. Metabolic acidosis is the acid-base disturbance initiated by a decrease in plasma bicarbonate concentration ([HCO3]). The resultant acidemia stimulates alveolar ventilation and leads to the secondary hypocapnia characteristic of the disorder. Extensive observations in humans encompassing a wide range of stable metabolic acidosis indicate a roughly linear relationship between the steady-state decrease in plasma bicarbonate concentration and the associated decrement in arterial carbon dioxide tension (PaCO2). The slope of the steady state APaCO2 versus A[HCO3] relationship has been estimated as approximately 1.2 mm Hg per mEq/L decrease in plasma bicarbonate concentration. Such empiric observations have been used for construction of 95% confidence intervals for graded degrees of metabolic acidosis, represented by the area in color in the acid-base template. The black ellipse near the center of the figure indicates the normal range for the acid-base parameters [3]. Assuming a steady state is present, values falling within the area in color are consistent with but not diagnostic of simple metabolic acidosis. Acid-base values falling outside the area in color denote the presence of a mixed acid-base disturbance [4]. [H+] — hydrogen ion concentration.

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