Final answer:
When a protruding umbilical cord is detected during the delivery of twins and the fetal heart rate is low, the nurse's immediate action should be to elevate the presenting part using two gloved fingers to relieve potential cord compression.
Step-by-step explanation:
You are working with a patient who is attempting vaginal delivery of 37-week twins. After the successful delivery of the first twin, a loop of umbilical cord protrudes at the vaginal opening, and the fetal heart tracing reveals a heart rate in the 60s. The most appropriate immediate action by the nurse is to elevate the presenting part using two gloved fingers. This action can help relieve pressure on the cord, which could be causing the decreased heart rate due to umbilical cord compression, and potentially prevent further complications until medical assistance can intervene.