Final answer:
The nurse's first action should be to assess the client's respiratory status when dealing with a high pressure alarm on a mechanical ventilator, as it is essential for determining the cause and deciding on further interventions.
Step-by-step explanation:
When caring for a client with emphysema who is on mechanical ventilation and appears anxious and restless, and the high pressure alarm is sounding, the first action a nurse should take is to assess the client's respiratory status. This is crucial for determining the cause of the alarm and the patient's discomfort. It may be due to a variety of factors such as a disconnection, obstruction, or the patient's respiratory efforts against the ventilator. Only after a thorough assessment, appropriate interventions such as adjusting the ventilator settings, administering medications, or contacting the healthcare provider can be carried out effectively.