Final answer:
The nurse should complete an incident report if the client experiences decreased blood pressure after receiving ceftazidime.
Step-by-step explanation:
The nurse should identify decreased blood pressure as an indication to complete an incident report after administering ceftazidime to a client with a severe penicillin allergy. A severe decrease in blood pressure can be a sign of an allergic reaction, known as anaphylaxis, which can be life-threatening. It is important for the nurse to document this incident in an incident report to ensure that appropriate actions are taken to address the situation.