Final answer:
The nurse's first action should be to encourage the client with pneumonia to cough and deep breathe to clear secretions and maintain airway patency.
Step-by-step explanation:
If a nurse is caring for a client who has pneumonia and is coughing up secretions, the first action they should take is to encourage the client to cough and deep breathe. This is because using the airway, breathing, circulation approach to client care, the priority is to maintain the client's airway, and by encouraging them to cough and deep breathe, it helps clear secretions and preserve airway patency. While it might also be important to obtain the client's temperature, encourage them to increase oral fluids, and provide chest percussion, these actions follow after ensuring that the airway is clear.