☰ Menu

Obstetrics Simplified - Diaa M. EI-Mowafi

Vacuum Extraction (Ventouse)

It is traction of the foetal head by a created negative pressure through a cup applied to the head.

Description

Vacuum extractor is composed of:

  • A specially designed cup with a diameter of 3, 4, 5 or 6 cm.
  • A rubber tube attaching the cup to a glass bottle with a screw in between to release the negative pressure.
  • A manometer fitted in the mouth of the glass bottle to declare the negative pressure.
  • Another rubber tube connecting the bottle to a suction piece which may be manual or electronic creating a negative pressure that should not exceed - 0.8 kg per cm2.

Types

The main difference between vacuum extractors lies in the cup.

Malmstrom cup

A metal cup to its centre attached a metal chain passed through the rubber tube. The other end of the chain is attached to a handle for traction.

Bird’s cup

The suction rubber tube is attached to the periphery of the cup while the handle of traction is attached by a separate short metal chain to the centre of the cup.

Soft cup

It is a bell-shaped 6.5 cm diameter soft cup which is made of a firm but supple silastic material.

Advantage: It produces symmetric, less cosmetically alarming caput succedaneum and less scalp abrasions.

Disadvantage: It slips more than the metal cup but with less scalp injuries.

Indications

  • The same as forceps: but it is not recommended in preterm babies and not used for the after-coming head in breech delivery.
  • During the 1st stage: The small cup 3 or 4 cm may be used in a soft, stretchable cervix of not less than 7 cm dilatation.
  • During caesarean section: It may be used to extract the foetal head through the uterine incision.

N.B. Vacuum is not an instrument for rotation of the head but it rotates spontaneously when meets the pelvic floor. Trial to rotate the head with the cup will cause it to slip.

Contraindications

  • Moderate or severe cephalopelvic disproportion.
  • Other presentations than vertex.
  • Premature infants.
  • Intact membranes.

Procedure

  • Lithotomy position.
  • Antiseptic measures for the vagina, vulva and perineum.
  • Vaginal examination to check pelvic capacity, cervical dilatation, presentation, position, station and degree of flexion of the head and that the membranes are ruptured.
  • Application of the cup: The largest cup that can easily passed is introduced sideways into the vagina by pressing it backwards against the perineum. It is then applied as near as possible to the posterior fontanelle over the mid sagittal line with its edge 3 cm from the anterior fontanelle. This position will promote flexion of the head and brings the smallest diameters of the foetal skull into the maternal passages. Be sure that there is no cervical or vaginal tissues nor the umbilical cord or a limb in complex presentation is included in the cup.
  • Creating the negative pressure: holding the cup in place, the negative pressure is gradually increased by 0.2 kg/cm2 every 1 minute until - 0.8 kg/cm2 is attained. This creates an artificial caput within the cup.
  • Traction: on the handle is made perpendicular to the cup and intermittently during uterine contractions, the direction of pull is changing as the head descends through the birth canal.
  • Release of the cup: when the head is delivered the vacuum is reduced as slowly as it was created using the screw as this diminishes the risk of scalp damage.

Bird’s safety rules for vacuum extraction:

  • The head must be completely or partially delivered with no more than 3 pulls.
  • The head is at least begin to move with the first pull.
  • The cup must not be applied more than twice.
  • Application of the cup must not exceed 20 minutes.

Advantages of Vacuum over Forceps

  • Anaesthesia is not required so it is preferred in cardiac and pulmonary patient.
  • The ventouse is not occupying a space beside the head as forceps.
  • Less compression force (0.77 kg/cm2) compared to forceps (1.3 kg/cm2) so injuries to the head is less common.
  • Less genital tract lacerations.
  • Can be applied before full cervical dilatation.
  • It can be applied on non-engaged head.

Complications

  • Foetal:
    • Cephalohaematoma.
    • Scalp lacerations.    
    • Rarely, intracranial haemorrhage.
  • Maternal:
    • Vaginal and cervical lacerations.
    • Annular detachment of the cervix, cervical incompetence and may be future prolapse if used with incompletely dilated cervix.

Links