Final answer:
For a client with a chronic lung disorder requiring 2L/min of portable oxygen, the nurse should select a nasal cannula. It provides low levels of supplemental oxygen while allowing for patient mobility and comfort. The Douglas bag method is not appropriate for clinical oxygen delivery.
Step-by-step explanation:
The nurse caring for a client with a chronic lung disorder who requires portable oxygen at a flow rate of 2L/min should select a nasal cannula as the most appropriate oxygen delivery device. The nasal cannula is a lightweight tube with two prongs for insertion into the nostrils and is suitable for patients who require low levels of supplemental oxygen. It allows for mobility and comfort while providing the necessary oxygen support. The Douglas bag method you mentioned is primarily used for measuring oxygen consumption and CO2 production during research studies or exercise testing and is not typically used for oxygen delivery in clinical settings.