Final answer:
The first action the nurse should take is to administer O2 via a high-flow mask to immediately address the patient's respiratory distress and low oxygen saturation.
Step-by-step explanation:
The nurse in the Emergency Department (ED) should prioritize the airway and breathing of the patient presenting with absent breath sounds in the left lower lobe and symptoms indicative of respiratory distress. The most immediate action to take is C. Administer O2 via a high-flow mask. This intervention helps to address hypoxemia and improve the patient’s oxygen saturation (SaO2), which is essential for the patient's tissue perfusion and overall stability. Thereafter, the other interventions listed may be necessary, such as obtaining a Chest X-ray (CXR), preparing for chest tube insertion if a pneumothorax is suspected, or initiating IV access for possible fluid therapy and medication administration.