Gastrointestinal System Disorders Q 259

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Your patient’s ABG reveals an acidic pH, an acidic CO2, and a normal bicarbonate level. Which of the following indicates this acid-base disturbance?

  

    A. Respiratory acidosis

    B. Respiratory alkalosis

    C. Metabolic acidosis

    D. Metabolic alkalosis

    

    

Correct Answer: A. Respiratory acidosis

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A pH of 7.35 indicates acidosis, as does an acidic CO2 and bicarbonate. The primary disturbance of elevated arterial PCO2 is the decreased ratio of arterial bicarbonate to arterial PCO2, which leads to a lowering of the pH. In the presence of alveolar hypoventilation, 2 features commonly are seen are respiratory acidosis and hypercapnia. To compensate for the disturbance in the balance between carbon dioxide and bicarbonate (HCO3-), the kidneys begin to excrete more acid in the forms of hydrogen and ammonium and reabsorb more base in the form of bicarbonate. See also: 8-Step Guide to ABG Analysis: Tic-Tac-Toe Method

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Option B: Respiratory alkalosis is 1 of the 4 basic classifications of blood pH imbalances. Normal human physiological pH is 7.35 to 7.45. A decrease in pH below this range is acidosis, an increase above this range is alkalosis. Respiratory alkalosis is by definition a disease state where the body’s pH is elevated to greater than 7.45 secondary to some respiratory or pulmonary process.

Option C: Determining the type of metabolic acidosis can help clinicians narrow down the cause of the disturbance. Acidemia refers to a pH less than the normal range of 7.35 to 7.45. In addition, metabolic acidosis requires a bicarbonate value less than 24 mEq/L. Further classification of metabolic acidosis is based on the presence or absence of an anion gap, or concentration of unmeasured serum anions.

Option D: HCO3 functions as an alkalotic substance. CO2 functions as an acidic substance. Therefore, increases in HCO3 or decreases in CO2 will make blood more alkalotic. The opposite is also true where decreases in HCO3 or an increase in CO2 will make blood more acidic. CO2 levels are physiologically regulated by the pulmonary system through respiration, whereas the HCO3 levels are regulated through the renal system with reabsorption rates. Therefore, metabolic alkalosis is an increase in serum HCO3.

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