Asthma and COPD Q 20

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The nurse reviews the ABG values of a client. The results indicate respiratory acidosis. Which of the following values would indicate that this acid-base imbalance exists?

  

     A. pH of 7.48

     B. PCO2 of 32 mm Hg

     C. pH of 7.30

     D. HCO3- of 20 mEq/L

    

    

Correct Answer: C. pH of 7.30

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In respiratory acidosis, the ABG will show an elevated PCO2 (>45 mmHg), elevated HCO3- (>30 mmHg), and decreased pH (<7.35). The respiratory acidosis can be further classified as acute or chronic based on the relative increase in HCO3- with respect to PCO2. In cases of acute respiratory acidosis, HCO3- will have increased by one mEq/L for every ten mmHg increase in PCO2 over a few minutes.

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Option A: In respiratory acidosis, the slight increase in bicarbonate serves as a buffer for the increase in H+ ions, which helps minimize the drop in pH. The increase in hydrogen ions inevitably causes a decrease in pH, which is the mechanism behind respiratory acidosis.

Option B: In a state of hypoventilation, the body produces more CO2 than it can eliminate, causing a net retention of CO2. The increased CO2 is what leads to an increase in hydrogen ions and a slight increase in bicarbonate, as seen by a right shift in the following equilibrium reaction of carbon dioxide.

Option D: The buffer system created by carbon dioxide consists of the following three molecules in equilibrium: CO2, H2CO3-, and HCO3-. When H+ is high, HCO3- buffers the low pH. When OH- is high, H2CO3 buffers the high pH. In respiratory acidosis, the slight increase in bicarbonate serves as a buffer for the increase in H+ ions, which helps minimize the drop in pH.

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