Progressive Care Nursing Certification (PCCN) Practice Exam

What is the primary cause of hypoxemia?

1. Hypoventilation

2. Abnormal respiratory rhythm

3. Ventilation-perfusion (V/Q) mismatch

4. Decreased ventilation

The correct answer is: Ventilation-perfusion (V/Q) mismatch

The primary cause of hypoxemia is commonly attributed to ventilation-perfusion (V/Q) mismatch. This refers to a situation where air does not reach the alveoli (ventilation) in an adequate manner, or where the blood flow (perfusion) to these areas of the lung is inadequate. In a healthy respiratory system, there is a direct correlation between ventilation and perfusion, ensuring that oxygen can effectively diffuse into the bloodstream. When there is a mismatch, such as in conditions like pulmonary embolism or certain types of pneumonia, some areas of the lung may receive either too little air for the amount of blood flowing through them or vice versa. This imbalance leads to a decrease in the amount of oxygen that gets into the blood, resulting in hypoxemia. Hypoventilation and decreased ventilation can contribute to hypoxemia, but they are not the primary causes. These conditions affect the overall exchange of gases in the lungs, but the more critical issue often centers around the V/Q ratio. Likewise, an abnormal respiratory rhythm can influence respiratory efficiency, yet it too is not as central to the mechanics of hypoxemia as ventilation-perfusion mismatch. Understanding this distinction is crucial for assessing patients with respiratory distress and formulating appropriate interventions.