Final answer:
When a nurse finds a reddened area of skin on an immobile client, the best practice is to document and monitor the area, not to apply heat or massage it, to prevent further tissue damage.
Step-by-step explanation:
Upon finding a reddened area of skin on a client who is immobile, the appropriate action for a nurse to take is to document the finding and continue monitoring for changes. The reddened area could be an early indicator of a pressure ulcer, which is a concern for patients who are not able to move regularly. It is important not to apply heat or massage the area, as these actions could potentially cause more damage to compromised skin. Massaging the area, in particular, can lead to further tissue breakdown.