Final answer:
After a bone marrow aspiration, it is important for the nurse to apply a sterile dressing to the site.
Step-by-step explanation:
After a bone marrow aspiration from the left posterior iliac crest, it is important for the nurse to apply a sterile 2-inch gauze dressing to the site (option b). This helps in preventing infections and provides a protective covering for the wound. Elevating the head of the bed to 45 degrees (option a) is not necessary after the procedure. Using a half-inch sterile gauze to pack the wound (option c) is not recommended as it may cause further damage. Having the patient lie on the left side for 1 hour (option d) is not necessary after a bone marrow aspiration.