Final answer:
The first action a nurse should take when a COPD patient complains of shortness of breath while in the supine position is to help the patient into a semi-Fowler's position to ease their breathing.
Step-by-step explanation:
If a patient with chronic obstructive pulmonary disease (COPD) complains of shortness of breath while receiving oxygen at 2 L/min in a supine position, the first action a nurse should take is to assist the patient to a semi-Fowler's position. This position involves the patient sitting at a 30 to 45-degree angle, which can make breathing easier and improve lung expansion. It is more effective and immediate than adjusting the oxygen flow, performing tracheal suctioning, or reporting to a healthcare provider, which may be subsequent steps depending on the patient's response.