Final answer:
The nurse should initially pinch the lower portion of the nose for 10 minutes when dealing with a nosebleed, as this helps control the bleeding by compressing the blood vessels.
Step-by-step explanation:
The first action a nurse should take when a patient develops a nosebleed is to pinch the lower portion of the nose for 10 minutes. This initial step is crucial for stopping the blood flow by compressing the blood vessels. While other actions, such as preparing for cauterization or applying ice compresses, can be part of the treatment protocol, the immediate response should focus on controlling the bleeding. If the nosebleed is severe or does not respond to simple measures, further medical intervention may be necessary.