Final answer:
The first action a nurse should take when a client becomes unresponsive upon delivery of the placenta is to determine respiratory function. This ensures adherence to the ABC emergency protocol, prioritizing the client's airway and breathing.
Step-by-step explanation:
When a client becomes unresponsive upon delivery of the placenta, the nurse should first determine respiratory function. This primary assessment is crucial because it addresses airway and breathing, which are critical components of the ABC (Airway, Breathing, Circulation) protocol in emergency care. Ensuring that the patient is able to breathe is paramount before moving on to other interventions such as increasing the IV fluid rate, accessing emergency medications, or collecting blood samples for further analysis.