Final answer:
A licensed practical nurse (PN) can obtain vital signs after the infusion of blood or blood products has begun, under the direct supervision of a registered nurse.
Step-by-step explanation:
When administering blood or blood products the task that can be assigned to a licensed practical nurse (PN) under the direct supervision of a registered nurse is obtaining vital signs after the infusion has begun. Tasks like the initiation of the blood product, assessment of the client's condition prior to blood administration, and evaluation of the client's response after receiving the blood product typically fall under the responsibilities of a registered nurse or higher-level practitioner.
The PN's role may involve supporting activities, such as taking and reporting patient vital signs, which is crucial in monitoring the patient during the treatment to ensure their safety.