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Assisted Vaginal Delivery – Vacuum
The Vacuum Extractor – Historical Context
The use of the vacuum extractor in high-income countries has increased, so that a majority of assisted vaginal deliveries globally are now performed using this instrument as opposed to the obstetric forceps. The vacuum principle was probably first applied with use of a cupping-glass to treat depressed skull fractures in infants and adults. The first attempted obstetrical application was in 1705 by James Yonge, surgeon to the Naval Hospital in Plymouth, England. He was unsuccessful in his attempts to deliver a fetus “by a cupping-glass fixt to the scalp with an air pump,” a concept developed further by Simpson in the 19th century. who used an “air tractor” with more success ( Fig. 17.1 ).
In the 1950s, Tage Malmström of Sweden developed the metal extractor that is still widely used globally. The English obstetrician Geoffrey Bird (1922–2001), emphasized the importance of accurate cup placement over the flexion point. He separated the traction from the suction port and moved the latter to insert in the lateral margin, producing the ‘posterior cup’. The posterior cup facilitates placement over the flexion point in occipitoposterior (OP) positions associated with head deflexion.
In the 1970s, softer cups reduced superficial scalp trauma but were associated with a much higher failure rate compared with metal cups (25% vs <5%). Harder plastic cups are now used, with the Kiwi OmniCup, developed by Aldo Vacca in Australia, being the most common.
Background
In the second half of the 20th century, obstetricians moved from using forceps to vacuum extraction for the majority of assisted vaginal deliveries. Vacuum-assisted delivery is relatively easy to perform and teach. It can be used to manage prolonged second stage of labour, to achieve timely delivery in case of fetal distress in the second stage and to avoid maternal effort in the presence of severe cardiopulmonary conditions. Vacuum is also a good option in mid-pelvic rotational births. In recent years, vacuum-assisted deliveries (and particularly those involving rotation) have been increasingly replaced by emergency second stage caesarean section (CS) which is associated with higher rates of adverse maternal and perinatal outcome. Retaining skills in vacuum-assisted delivery is essential to turn this tide, and may be achieved by regular training on mannequins and appropriate supervision of trainees by experienced operators.
Vacuum-assisted delivery does have a lower risk of maternal vaginal and perineal trauma compared with forceps. In addition, it can often be performed successfully with local infiltration or pudendal block, without the need for neuraxial blockade. Since premature infants are at higher risk of cephalhaematoma, neonatal jaundice, and intracranial and subgaleal haemorrhage, forceps is preferred over vacuum below a gestational age of 34 weeks.
There are many variations in manufacturing material and cup shape with a paucity of data as to the optimal type to use for vacuum extraction. In essence the same principles apply to all types of vacuum extractors with regard to technique in use. The metal cup of the Malmström device has an elevated connector that holds both vacuum tubing and traction chain. The elevated insertion makes it more prone to slipping off when traction is not applied perpendicular to the cup surface. The ‘O’Neil’ metal cup overcomes this problem by having the traction chain linked to a nylon loop with a separate suction connector. The loop is attached to the edges of a rotating disc on the top of the cup. If traction moves away from the perpendicular, the chain moves along the nylon loop, resulting in the traction force applied to all edges of the cup remaining equal, thus reducing the risk of detachment. The ‘Bird’ metal cup also has separate connectors, and the variant for OP position has the tubing attached to the side of the cup enabling deep sacral insertion to achieve placement as near to the flexion point as possible for rotational birth. With the traction chain attached directly to the cup without elevation, higher traction force can be achieved, even with deviation from the perpendicular.
Alternatives to metal cups include cone or bell-shaped cups made of silastic (‘softcup’) or moulded flexible plastic. With these cups, only low traction force is possible and there is a much higher chance of failure. Placing these cups on the flexion point in deflexed positions is difficult, either because of the size of the instrument or lack of flexibility in the stem. In our opinion, these cups are best used for low cavity or outlet births with the head in an occipitoanterior (OA) position. The Kiwi OmniCup is made from hard plastic and is a disposable handheld instrument with a centrally placed suction/traction tube and an integrated hand-pump/handle. The thinner suction tube fits into a groove on the upper surface of the cup allowing deeper insertion in deflexed OP positions. The OmniCup can be used for both rotational and nonrotational births with the fetal head in all positions. The high failure rates found in early randomized trials seem to imply that the Kiwi cup, although effective, requires experience and careful technique to prevent ‘pop-offs’. Based on our experience, we recommend that the largest metal cup available should be considered for mid-cavity rotational deliveries which are at or just below the level of the ischial spines. Larger cups are less likely to detach. An ‘OP metal cup’ may be required if there is significant deflexion at mid-cavity level, although in experience hands a Kiwi Omnicup can still be used effectively.
Both metal and rigid plastic cups have an ‘in-curved’ margin. Thus, the peripheral margin of the cup attached to the fetal scalp has a narrower diameter than the upper curved margin and this produces the ‘chignon’ on the fetal scalp. This reduces the risk of cup detachment and adds to the effective diameter of the cup.
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