A client has been in labor for 10 hours. Her contractions have become hypoactive and slowed in duration. The fetus is at 0 station, cervix is dilated 8 cm and effaced 90%. The physician orders an oxytocin (Pitocin) infusion to be started at once. The RN begins the oxytocin infusion. It is important that the RN discontinue the infusion if which one of the following occur?