The woman is placed in the lithotomy position and assists throughout the process by pushing. A suction cup is placed onto the head of the baby and the suction draws the skin from the scalp into the cup. Correct placement of the cup directly over the flexion point, about 3 cm anterior from the occipital (posterior) fontanelle, is critical to the success of a VE. Ventouse devices have handles to allow for traction. When the baby's head is delivered, the device is detached, allowing the birthing attendant and the mother to complete the delivery of the baby. For proper use of the ventouse, the maternal cervix has to be fully dilated, the head engaged in the birth canal, and the head position known. If the ventouse attempt fails, it may be necessary to deliver the infant by forceps or cesarean section.
There are several indications to use a ventouse to aid delivery:
Prolonged second stage of labor
Foetal distress in the second stage of labor, generally indicated by changes in the foetal heart-rate (usually measured on a CTG)
Maternal illness where prolonged "bearing down" or pushing efforts would be risky (e.g. cardiac conditions, blood pressure, aneurysm, glaucoma). If these conditions are known about before the birth, or are severe, then an elective cesarean section may be performed.