Investigating the Vacuum Extractors of Biomedical Devices of Different Materials and Pressures on the Fetal Head during Delivery

Abstract

Operative delivery requires the use of a vacuum extractor; obstetricians can choose the appropriate vacuum extractor to make the delivery process smoother and safer. However, there is no biomechanical literature focused on the imposed effects of a vacuum extractor prepared with different materials and vacuum pressure on the fetal head during the process of delivery. Therefore, we first established and performed the finite element analytical model to explore the influences of vacuum extractors manufactured from different materials on the fetal head under various extractive pressures. The model of the vacuum extractor was designed as a hemispherical shape, and the material of the vacuum extractor was composed of silicone rubber and stainless steel for comparison. Four different vacuum pressures (500 cm H2O, 600 cm H2O, 700 cm H2O, and 800 cm H2O) were applied as the factors for investigation. The reaction force on the fetal head, von Mises stress of vacuum extractor, and von Mises stress on the skull of fetal head were measured and analyzed to evaluate the effects. The results revealed that subtle divergent influences of different vacuum pressures were observed, and the stainless-steel vacuum extractor induced a larger reaction force (358.04–361.37 N), accompanied with stress (13.547–13.675 MPa), on the fetal head than non-metallic or relatively softer materials. The results provide a reliable basis for selecting proper vacuum extractor during operative delivery to avoid obstetrical complications, such as scalp scratch, cephalohematoma and even intracerebral hemorrhage.

Investigating the Effects of Different Sizes of Silicone Rubber Vacuum Extractors during the Course of Delivery on the Fetal Head: A Finite Element Analysis Study

“…These study results were similar to the trends of previous studies even though previous researchers used metallic vacuum extractors and not flexible materials for examination [11]. In addition, previous studies have shown that metal vacuum extractors (358.04-361.37 N) exert more force than non-metal ones (12.229-15.064 N) [10]. When the force of attraction is greater than 135 N, such conditions may increase the risk of sphincter injury in the mother and scalp injury in the baby [28].…”

“…In order to assess the effects of different vacuum extractor sizes, we separately used vacuum extractors to act on a flat surface, hemispherical ball, and infant head model. The infant head model was mainly based on a previous study, and a geometric appearance of infant's scalp and skull was constructed based on the anatomical model of neonatal heads [10,19]. For flat surface, hemispherical ball, and fetal head models, two layered structures were used, which were 1 mm-thick scalp and 2 mm-thick skull.…”

“…However, silicone rubber vacuum extractors cause less injury to the infant head compared to the metallic vacuum extractors [9]. The selection of an appropriate vacuum extractor can provide a reliable basis for avoiding obstetric complications such as scalp wound, head hematoma, and even cerebral hemorrhage [10]. In addition, there are different vacuum extractor sizes indicated for different clinical situations.…”

“…Researchers also analyzed the angle of obstetrical forceps and the study results showed that a larger curve angle of the forceps blades can decrease the stress and pressure on the neck of the newborn; however, it may lead to rotation toward the posterior side [19]. A previous study also employed finite element analysis to observe the biomechanical effects of vacuum extractors on fetal heads [10]. In addition, finite element analysis has been employed to study the biomechanical effects of vacuum extractors in correct and incorrect positions [20].…”