Vacuum-assisted vaginal delivery
Scott A. Paluska
Operative deliveries using forceps or a vacuum extractor represent a small but significant minority of the vaginal deliveries performed in the United States. First introduced by Simpson in 1855, the vacuum extractor was infrequently used until 1954, when Malmstrom developed the inflexible metal cup with an inverted lip, which became the springboard for modern vacuum extractors. In the 1970s, cups were made of soft, pliable rubber and, thus, were associated with fewer scalp injuries.[3,4] This softer cup also facilitated delivery of distressed infants because less time was needed to create the artificial caput succedaneum (chignon) required to establish effective delivery traction.
Currently, the vacuum extractor has replaced forceps as the instrument of choice in many European and developing countries. While physicians practicing obstetrics in the United States have begun to incorporate vacuum extraction into their practices, many physicians still fear injuring the mother or the fetus. This article reviews the role and safety of the vacuum extractor in modern obstetrics, particularly in relation to the family physician.
Vacuum Extraction vs. Forceps
The modern vacuum instrument has undergone many refinements that offer several advantages over forceps. These include a greater ease of instrument application, the absence of space-occupying blades in the pelvic outlet, and the ability to position the instrument precisely over the fetal head, rotate the fetal head without maternal soft tissue impingement and place less pressure on the fetal cranium.[5,6] Table 1 lists advantages and disadvantages of vacuum extraction compared with extraction using forceps.
Comparison of Vacuum Extractor and Forceps
Advantages of vacuum extractor over forceps
Less force applied to fetal head
Less anesthesia required
Less maternal soft tissue injury
Fewer fetal injuries
Less parental concern
Fetal head remains free to rotate
Disadvantages of vacuum extractor compared
Traction applied during contractions only
Possibly longer delivery than forceps
Small increase in cephalohematomas
Higher prevalence of neonatal jaundice
Lack of operator familiarity and experience
Difficulty in maintaining effective vacuum
Only used for term/near-term vertex infants
Placement of the cup as close as possible to the fetal occiput along the sagittal suture promotes flexion of the head (Figure 4). The cup should rest over the posterior fontanelle and should be free of surrounding vaginal rugae. A circumferential finger sweep around the cup ensures that no vaginal tissue has been included between the scalp and the cup. This precautionary step should be regularly repeated throughout the procedure.
[Figure 4 ILLUSTRATION OMITTED]
Once the cup has been secured on the fetal cranium, the operator or an assistant establishes negative pressure. This is done by increasing the vacuum’s pressure to the “yellow zone,” corresponding to 100 mm Hg (0.13 kg per [cm.sup.2]). With the next contraction, the pressure is rapidly increased to the “green zone,” corresponding to 400 to 600 mm Hg (0.54 to 0.82 kg per [cm.sup.2]). Increasing the negative force to greater than 600 mm Hg has been associated with increased risk of fetal trauma without significant obstetric benefit. Traction attempts should be intermittent and should coincide with uterine contractions and maternal pushing efforts.
The operator applies gentle traction in the direction of the pelvic axis with one hand. The thumb of the nonpulling hand can secure the cup against the fetal head while the middle and index fingers of this hand simultaneously monitor descent by pressing against the fetal head. The performance of vacuum cups markedly deteriorates with the presence of caput (chignon), and chignon expansion will be minimized if negative pressure is applied only in harmony with traction. The importance of axial traction is demonstrated by the fact that off-axis traction produces a linear decline in maximal attainable force. If the cup disengages, the fetal scalp should be examined for injury before the cup is reapplied. An inherent advantage of the vacuum extractor is that the cup usually detaches before causing fetal injury.
Between contractions, the negative pressure should be reduced to 100 mm Hg with gentle triggering of the vacuum release valve or pedal. With each subsequent contraction, the pressure is rapidly increased to 400 to 600 mm Hg, and the two-handed gentle traction is repeated unless indications to discontinue further attempts are manifest. Vacuum operators should be willing to seek other means of delivery if no clear improvement is observed in the course of descent. The system should not remain at maximum pressure for more than a total of 10 minutes. By deferring episiotomy (if indicated) until the head is almost delivered, perineal pressure against the extraction cup will help keep the cup attached to the fetal head. Once the head crowns, the extractor should be pulled upward at a 45 degree angle to the floor. As the head crosses the perineum, the negative pressure is released and the extractor cup is gently disengaged. Delivery of the head is performed in the usual manner. After delivery, the cups, tubing and filter are discarded, and the pump is cleaned before reuse.
Unfortunately, vacuum extraction can be associated with both maternal and neonatal morbidity. Studies suggest that maternal injuries incurred during vacuum delivery with soft extractor cups occur at a rate similar to that seen with spontaneous deliveries. Most maternal injuries consist of lacerations, hematomas or pudendal nerve injury. Vacuum extraction has also been associated with anal sphincter trauma and defecatory dysfunction; however, the incidence is lower than that for forceps delivery. One study showed that, overall, forceps or vacuum delivery resulted in less maternal blood loss, shorter hospital stays and decreased morbidity when compared with cesarean section.
Fetal injury sustained during vacuum extraction tends to be more significant than maternal morbidity. Minor injuries, such as scalp trauma, are seen more frequently with metal cups, which produce “cookie-cutter” lacerations in the fetal chignon. In addition, applying the vacuum over fetal scalp areas previously subjected to electrode or scalp sampling may result in increased fetal blood loss. Other minor fetal complications include hyperbilirubinemia, which is transient and rarely requires phototherapy. The superficial chignon that forms during delivery typically recedes spontaneously within one to three days without long-term sequelae.
More serious fetal complications have also been reported following vacuum extraction. One study reported moderate to severe retinal hemorrhage in 28 percent of vacuum-assisted deliveries, 18 percent of spontaneous deliveries and 13 percent of forceps-assisted deliveries. The incidence and severity of retinal hemorrhage was greater in small-for-gestational-age infants and in association with sequential use of vacuum and forceps, fetal distress and second stage of labor lasting less than 30 minutes. The retinal bleeding has no apparent association with neonatal visual deficiency, and most affected infants have a benign course free of developmental abnormalities.
Cephalohematomas, collections of blood beneath the periostea of cranial bones, have been reported in 1 to 15 percent of vacuum extraction deliveries. Such self-limited lesions may take weeks to resolve but rarely produce cranial deformity or extraosseous calcification. Since they are limited to suture lines, even large cephalohematomas pose little threat to the infant.
Vacuum-assisted delivery with both metal and soft-cup extractors has been implicated in the formation of extensive subgaleal (subaponeurotic) hematomas, which are a rare cause of significant neonatal morbidity and mortality.[20-22] Known fetal risk factors for this complication include macrosomia, cephalopelvic disproportion, primiparity, rapid extraction or prolonged labor. The potential space between the skull periosteum and the galea aponeurotica can sequester dangerous amounts of fetal blood; in one case, blood extravasation sufficient to result in neonatal hypovolemic shock was reported. Moreover, bleeding that has begun may be difficult to curtail because of a confounding coagulopathy. While subaponeurotic bleeding is not specific to vacuum-assisted delivery, its reported mortality in excess of 20 percent should alert vacuum operators to provide rapid diagnosis and supportive care with blood, fresh frozen plasma and pressure wrapping of the infant’s head.
Intraventricular, intracerebral and subdural hemorrhages have been observed following vacuum-assisted vaginal deliveries but are uncommon causes of neonatal morbidity. Some studies suggest that high-station vacuum extractions result in a greater incidence of intracranial hemorrhage. Intracranial and extracranial hemorrhages have rarely been noted simultaneously. Nonetheless, the incidence of intracranial bleeding is similar between unassisted and assisted vaginal deliveries.
Since vacuum extraction has the potential to induce a wide spectrum of maternal and neonatal injuries, it is incumbent on the operator to use good judgment and skill during the procedure. It is also important to heed the recommendation of the American College of Obstetricians and Gynecologists (ACOG) that vacuum-assisted delivery be discontinued if satisfactory progress is not made or preset delivery limits are not fulfilled.
Vacuum extraction continues to gain popularity in the United States as the availability of technical training and equipment increases. Improvements in materials and device design have facilitated the speed and safety of vacuum extractors for operative vaginal deliveries. Comfort and proficiency with modern equipment can be readily achieved by most operators in a limited time.
Physicians must be cautious in the use of a vacuum extractor and be familiar with its indications and contraindications. Avoiding vacuum extraction in cases where it is likely to fail or cause injury will minimize neonatal and maternal injuries. Operators should begin by performing basic vacuum-assisted deliveries and advance to more complex cases only after having achieved mastery of the former. As with any procedure, the potential for misuse mandates that practitioners rigorously attend to sound technique and judgment in the use of vacuum extractors.
The author thanks Barbara Apgar, M.D., M.S., and Nancy McElwain, M.A., for their time and suggestions in the preparation of the manuscript.
Figures 1 (top), 2 and 3 courtesy of PrisTech, Inc., Cucamonga, Calif. Figure 1 (bottom) courtesy of Ameda-Egnell, Cary, Ill.
REFERENCES[1.] Robinson JC. Forceps and vacuum extraction. Curr Opin Obstet Gynecol 1994;6:414-6.[2.] Malmstrom T. Vacuum extractor–an obstetrical instrument. Acta Obstet Gynecol Scand 1954;33(suppl 4):3-31.[3.] Chenoy R, Johanson RB. A randomized prospective study comparing delivery with metal and silicone rubber vacuum extractor cups. Br J Obstet Gynaecol 1992;99:360-3.[4.] Duchon MA, DeMund MA, Brown RH. Laboratory comparison of modern vacuum extractors. Obstet Gynecol 1988;71:155-8.[5.] Cunningham FG, MacDonald PC, Gant NF, Leveno KJ, Gilstrap LC. In: Cunningham FG, Williams JW, eds. Williams obstetrics. 19th ed. Norwalk, Conn.: Appleton & Lange, 1993:555-76.[6.] Epperly TD, Breitinger ER. Vacuum extraction. Am Fam Physician 1988;38:205-10.[7.] Williams MC, Knuppel RA, O’Brien WF, Weiss A, Kanarek KS. A randomized comparison of assisted vaginal delivery by obstetric forceps and polyethylene vacuum cup. Obstet Gynecol 1991;78(5 Pt 1):789-94.[8.] Johanson RB, Rice C, Doyle M, Arthur J, Anyanwu L, Ibrahim J, et al. A randomised prospective study comparing the new vacuum extractor policy with forceps delivery. Br J Obstet Gynaecol 1993;100:524-30.[9.] Kuit JA, Eppinga HC, Wallenburg HC, Huikeshoven FJ. A ramdomized comparison of vacuum extraction delivery with a rigid and a pliable cup. Obstet Gynecol 1993;82:280-4.[10.] Ross MG. Vacuum delivery by soft cup extraction. Contemp Ob/Gyn 1994;39:48-53.[11.] Muise KL, Duchon MA, Brown RH. The effect of artificial caput on performance of vacuum extractors. Obstet Gynecol 1993;81:170-3.[12.] American College of Obstetricians and Gynecologists. ACOG Technical Bulletin No. 196. Operative vaginal delivery 1994;196:1-6.[13.] Lucas MJ. The role of vacuum extraction in modern obstetrics. Clin Obstet Gynecol 1994;37:794-805.[14.] Scott JR, DiSaia PJ, Hammond CR, Spellacy WN. Practical diagnosis and management of abnormal labor. In: Scott Jr, et al., eds. Danforth’s obstetrics and gynecology. 7th ed. Philadelphia: Lippincott, 1994:544-57.[15.] Yeomans ER, Hankins GD. Operative vaginal delivery in the 1990s. Clin Obstet Gynecol 1992;35:487-93.[16.] Muise KL, Duchon MA, Brown RH. Effect of angular traction on the performance of modern vacuum extractors. Am J Obstet Gynecol 1992;167:1125-9.[17.] Sultan AH, Kamm MA, Bartram CI, Hudson CN. Anal sphincter trauma during instrumental delivery. Int J Gynaecol Obstet 1993;43:263-70.[18.] Robertson PA, Laros RK Jr, Zhao RL. Neonatal and maternal outcome in low-pelvic and midpelvic operative deliveries. Am J Obstet Gynecol 1990;162:1436-44.[19.] Williams MC, Knuppel RA, O’Brien WF, Weiss A, Spellacy WN, Pietrantoni M. Obstetric correlates of neonatal retinal hemorrhage. Obstet Gynecol 1993; 81(5 Pt 1):688-94.[20.] Florentino-Pineda I, Ezhuthachan SG, Sineni LG, Kumar SP. Subgaleal hemorrhage in the newborn infant associated with silicone elastomer vacuum extractor. J Perinatol 1994;14:95-100.[21.] Benaron DA. Subgaleal hematoma causing hypovolemic shock during delivery after failed vacuum extraction: a case report. J Perinatol 1993;13:228-31.[22.] Hall SL. Simultaneous occurrence of intracranial and subgaleal hemorrhages complicating vacuum extraction delivery. J Perinatol 1992;12:185-7.[23.] Plauche WC. Subgaleal hematoma. A complication of instrumental delivery. JAMA 1980;244:1597-8.[24.] Smith SA, Jett PL, Jacobson SL, Binder ND, Kuforiji TA, Gilhooly JT, et al. Subgaleal hematoma: the need for increased awareness of risk. J Fam Pract 1995;41(6):569-74.
SCOTT A. PALUSKA, M.D. is a resident in the Department of Family Medicine at the University of Michigan Medical School in Ann Arbor, where he also attended medical school.
Address correspondence to Scott A. Paluska, M.D., Chelsea Family Practice Center, 14700 E. Old US Highway 12, Chelsea, MI 48118-1140.
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