Final answer:
The nurse should complete an incident report if the client experiences a decreased blood pressure after receiving ceftazidime due to a severe penicillin allergy.
Step-by-step explanation:
The nurse should identify a decreased blood pressure (option C) as an indication to complete an incident report. When a severe penicillin allergy occurs, the administration of ceftazidime, which is a cephalosporin antibiotic, can cause a hypersensitivity reaction leading to anaphylaxis. Anaphylaxis is a severe allergic reaction that can result in a drop in blood pressure. It is important for the nurse to document this adverse event by completing an incident report, as it is a serious patient safety issue.