Obstetrics Simplified - Diaa
Vacuum Extraction (Ventouse)
It is traction of the foetal head by a created negative pressure through
a cup applied to the head.
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
- 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.
The main difference between vacuum extractors lies in the 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.
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.
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
and less scalp abrasions.
Disadvantage: It slips more than the metal cup but with less scalp injuries.
- 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.
- Moderate or severe cephalopelvic disproportion.
- Other presentations than vertex.
- Premature infants.
- Intact membranes.
- 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
- 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.
- Scalp lacerations.
- Rarely, intracranial haemorrhage.
- Vaginal and cervical lacerations.
- Annular detachment of the cervix, cervical incompetence and
may be future prolapse if used with incompletely dilated cervix.
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Edited by Aldo Campana,