A primigravida client at 36-weeks gestation is admitted to the labor and delivery unit because her membranes ruptured 30 minutes ago. Initial assessment indicates a 2 cm cervical dilatation, 50% effaced, -2 station, vertex presentation, greenish-colored amniotic fluid, and contractions occurring every 3 to 5 minutes, with a decrease in fetal heart rate after the last four contraction peaks. Which action should the nurse implement first?