The nurse is caring for a client with adult respiratory distress syndrome (ARDS). What is the most likely laboratory finding in the early stages of this disease ？（）
A．Increased carboxyhemoglobin.
B．Decreased partial pressure of arterial oxygen (PaO2).
C．Increased partial pressure of arterial carbon dioxide (PaCO2).
D．Decreased bicarbonate (HCO3-).
参考答案：B
解析：
Decreased PaO2 indicates hypoxemia, which is a universal finding in ARDS. The PaO2 level is low early in the disease due to hyperventilation and then elevates later in the disease due to fatigue and worsening clinical status. The HCO3- level may be low in ARDS and is related to reduced tissue oxygenation. The carboxyhemoglobin level will be increased in a client with an inhalation injury, which commonly progresses into ARDS. This isn't a common cause of ARDS.