Final answer:
The immediate concern would be a tension pneumothorax.
Step-by-step explanation:
Based on the patient's history of COPD, absent breath sounds on the left side, and sudden onset of shortness of breath, the immediate concern would be a tension pneumothorax. A tension pneumothorax occurs when air accumulates in the pleural space, causing compression of the lung and displacement of the mediastinum. This can lead to severe respiratory distress and can be life-threatening.