An engineering perspective of vacuum assisted delivery devices in obstetrics: A review

Abstract

Complications during childbirth result in the need for clinicians to use 'assisted delivery' in over 12% of cases (UK). After more than 50 years in clinical practice, vacuum assisted delivery (VAD) devices remain a mainstay in physically assisting child delivery; sometimes preferred over forceps due to their ease of use and reduced maternal morbidity. Despite their popularity and enduring track-record, VAD devices have shown little evidence of innovation or design change since their inception. In addition, evidence on the safety and functionality of VAD devices remains limited but does present opportunities for improvements to reduce adverse clinical outcomes. Consequently in this review we examine the literature and patent landscape surrounding VAD biomechanics, design evolution and performance from an engineering perspective, aiming to collate the limited but valuable information from a disparate field and provide a series of recommendations to inform future research into improved, safer, VAD systems.

Keywords: Vacuum assistive delivery; birth; maternal trauma; neonatal trauma; obstetrics; operative vaginal delivery; vacuum extraction; ventouse.

Figure 1.

Timeline of normal delivery events: (a) Foetus aligns to the bony maternal pelvis in a cephalic presentation(vertex/head first), (b) Baby progressing through the stations of delivery, (c) Baby’s head scalp is visible at the introitus, and (d) Delivery of the baby is completed where the body delivers, either spontaneously or with the healthcare professional (accoucheur) holding the foetal head, sometimes to help delivery of the shoulders. This also marks completion of the second stage of labour.

Figure 2.

Illustration of Forceps. Top: Key design features of Kielland Forceps, Bottom: Illustration of Simpson Forceps.

Figure 3.

Process steps during VAD: (a) Cup placement-A vacuum source is applied to create a chignon by manual/electric pumping after placement on the flexion point. On caption-Illustration of Malmstroem's cup placement on a foetal head, (b) Traction-Applied traction with a counter traction used to overcome resistant introitus and (c) Cup Release: VAD device is released to proceed with delivery of the head.

Figure 4.

Trauma associated with VAD: (a) Elevation of scalp after VAD, (b) Dissipation of caput succedaneum after a few hours leading to a cup mark (c) Baby head with SGH and (d) All trauma levels associated with VAD.

Figure 5.

The evolutionary track of VAD device design: (a) James Young Simpson’s ‘Air Tractor’, (b) Saleh’s rubber cup with finger grips, (c) McCahey’s designs, (d) Stillman’s design, (e) Couzigou’s ventouse eutocique, (f) Finderle’s horn VAD device, (g) Malmstroem’s VAD device proposed in 1968, and (h) Bird’s modified VAD device proposed in 1969.

Figure 6.

Evolutionary trail of modern VAD devices: (a) Metal cups, (b) Kobayashi silastic cup and (c) Single use instrumented devices-Kiwi Omni Cup©.

Figure 7.

Replotted traction experiments by Malmstroem VE60:60 mm diameter cup, VE50:50 mm diameter cup, VE40: 40 mm diameter cup. Predicted curves displays force values modelled vacuum induced multiplied by the contact cross-sectional area of cup onto scalp.

Figure 8.

Attachment of cup onto flexion point and creation of chignon.