Asthma and COPD Q 38

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A client with Guillain-Barré syndrome develops respiratory acidosis as a result of reduced alveolar ventilation. Which combination of arterial blood gas (ABG) values confirms respiratory acidosis?

  

     A. pH, 5.0; PaCO2 30 mm Hg

     B. pH, 7.40; PaCO2 35 mm Hg

     C. pH, 7.35; PaCO2 40 mm Hg

     D. pH, 7.25; PaCO2 50 mm Hg

    

    

Correct Answer: D. pH, 7.25; PaCO2 50 mm Hg

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In respiratory acidosis, ABG analysis reveals an arterial pH below 7.35 and partial pressure of arterial carbon dioxide (PaCO2) above 45 mm Hg. Therefore, the combination of a pH value of 7.25 and a PaCO2 value of 50 mm Hg confirms respiratory acidosis. The primary disturbance is an elevated arterial partial pressure of carbon dioxide (pCO2) and a decreased ratio of arterial bicarbonate to arterial pCO2, which results in a decrease in the pH of the blood. Options B and C represent normal ABG values, reflecting normal gas exchange in the lungs.

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Option A: A pH value of 5.0 with a PaCO2 value of 30 mm Hg indicates respiratory alkalosis. 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 B: In acute respiratory acidosis, there is a sudden elevation of PCO2 because of failure of ventilation. This may be due to cerebrovascular accidents, use of central nervous system (CNS) depressants such as opioids, or inability to use muscles of respiration because of disorders like myasthenia gravis, muscular dystrophy or Guillain-Barre Syndrome.

Option C: On the contrary, chronic respiratory acidosis may be caused by COPD where there is a decreased responsiveness of the reflexes to states of hypoxia and hypercapnia. Other individuals who develop chronic respiratory acidosis may have fatigue of the diaphragm resulting from a muscular disorder.

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