Final answer:
The immediate action a nurse should take when noting a protruding umbilical cord is to place the patient in the knee-chest position to alleviate pressure on the cord and prevent fetal circulatory compromise.
Step-by-step explanation:
The question asks about the immediate action a nurse should take when a protruding umbilical cord is observed from the vagina. The correct response is to place the patient in the knee-chest position. This is critical because a protruding umbilical cord can lead to a cord prolapse, which is an obstetric emergency that can compromise fetal circulation due to pressure on the cord. Placing the patient in a knee-chest position helps relieve pressure on the cord until medical intervention can be performed. Notifying the charge nurse and monitoring the intensity of contractions are also important steps, but they do not take precedence over repositioning the patient to alleviate pressure on the umbilical cord.