Fluid & Electrolyte Q 52

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Mang Teban has a history of chronic obstructive pulmonary disease and has the following arterial blood gas results: partial pressure of oxygen (PO2), 55 mm Hg, and partial pressure of carbon dioxide (PCO2), 60 mm Hg. When attempting to improve the client’s blood gas values through improved ventilation and oxygen therapy, which is the client’s primary stimulus for breathing?

  

    A. High PCO2

    B. Low PO2

    C. Normal pH

    D. Normal bicarbonate (HCO3)

    

    

Correct Answer: B. Low PO2

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A chronically elevated PCO2 level (above 50 mmHg) is associated with inadequate response of the respiratory center to plasma carbon dioxide. The major stimulus to breathing then becomes hypoxia (low PO2). High PCO2 and normal pH and HCO3 levels would not be the primary stimulus for breathing in this client.

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Option A: The inability to fully exhale also causes elevations in carbon dioxide (CO2) levels. As the disease progresses, impairment of gas exchange is often seen. The reduction in ventilation or increase in physiologic dead space leads to CO2 retention. Pulmonary hypertension may occur due to diffuse vasoconstriction from hypoxemia.

Option C: An acid-base disturbance arises when arterial pH lies outside that range. If pH is less than 7.35 an acidosis is present, if pH is greater than 7.45 the alkalosis is present. Tight control on blood pH is achieved by a combination of blood buffers and the respiratory and renal systems which make adjustments to return pH toward its normal levels.

Option D: Acidosis can be caused by either a rise in PaCO2 or a fall in HCO3. Alkalosis can be caused by either a fall in PaCO2 or a rise in HCO3. When the primary change is in CO2 we name the disturbance respiratory, and when the primary change is in bicarbonate, we name the disturbance metabolic.

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