The origin of vacuum extraction (VE) is in a therapeutic technique in use long before Hippocrates. In this technique, called cupping, a metal or glass cup was heated over an open flame and then applied to a lesion or a skin puncture. As the cup cooled, a vacuum developed, extracting blood or other fluids. Cupping was also used for surgical procedures, such as raising depressed skull fractures. Applications of cupping to assist parturients began early in the 18th century. However, vacuum-assisted deliveries proved difficult for a number of reasons and VE was soon abandoned. A successful extraction required the vaginal application of a cup, a means to apply traction, and the periodic reinforcement of the vacuum because of imperfections of the seal. Before a vacuum delivery device could become practical, new cup design, reliable methods for traction, and technology to generate vacuum on demand were required. James Young Simpson, a professor of obstetrics in Edinburgh famous for his forceps design, was the first to successfully address the limitations of cup design and vacuum replenishment when he introduced his air tractor in 1849. However, Simpson's interest soon moved to other obstetric issues and his vacuum extractor promptly fell from popular attention. In the century that followed, a number of vacuum delivery devices were invented and some were successfully tested by various clinicians. None achieved popularity. The immediate antecedent to modern extractors was a stainless steel cup vacuum device introduced by Malmström in Sweden in the late 1950s. Because of technical problems with the original design and case reports of severe fetal complications, American interest promptly waned. While VE remained common in Europe, the instrument did not regain popularity in the United States until the 1980s, following the introduction of disposable soft-cup extractors and new rigid cup designs that improved both safety and success. Presently, both forceps and the vacuum extractor are used extensively. Controversy continues concerning if, and when, operative vaginal deliveries should be conducted and which instrument is the best to use in specific clinical settings. Despite the growing popularity of VE, forceps remain the instrument of choice for many older clinicians for reasons of medical conservatism, inclination, and original training. VE remains popular because of its reputation for ease of use, lower maternal morbidity, and safety. However, reports exist of severe neonatal complications associated with vacuum operations. While uncommon, these problems remind practitioners of the need for rigorous adherence to proven techniques and the need to restrict vacuum operations to limited indications to ensure success and avoid injury. The retirement of classically trained obstetricians, the inability to conduct training operations, the medical-legal climate, and other changes in practice, including the high frequency of cesarean delivery, now collectively contribute to an unclear future for all types of instrumental delivery.
The indications for vacuum extraction (VE) operations are similar to those of assisted delivery operations performed with forceps. The general prerequisites for instrumental deliveries are discussed below. Mandatory prerequisitesInformed consent An informed consent is required for any surgical procedure, including an instrumental delivery. Informed consent is a process and not simply a signed form. Consent for a surgical procedure includes an explanation of the need for the operation, a discussion of risks and benefits, and a presentation of alternative modes of treatment. The patient must also be given the opportunity to ask questions. This consent process may strike the clinician as being time consuming and unrealistic for an instrumental delivery, especially in the face of urgency. However, the potential medical and legal risks from an assisted delivery are substantially greater than those associated with other surgical procedures wherein consent is routinely obtained. Further, a bedside consent process can be abbreviated, especially in cases of presumed fetal jeopardy. In all cases, excluding extreme emergencies, sufficient time is available to briefly describe the proposed operation, review the indications, and state the limits of effortintended. Routinely discussing possible obstetric interventions with families at an earlier time during the pregnancy is important because of the controversy concerning bedside consents from parturients. Thus, when an instrumental delivery procedure is presented during labor, both the patient and family will already have a general idea about the procedure and its potential risks and benefits. Prepared physician The clinician must have knowledge of the instrument chosen and of VE indications and proven techniques. Most importantly, the accoucheur must be prepared to reconsider or abandon any operation that proves difficult. Prepared patient Prior to an extraction, the patient should have ruptured membranes; empty bladder by Credé, catheterization, or spontaneous voiding; full cervix dilation; an engaged fetal head; and no suspicion of feto-pelvic disproportion. Acceptable analgesia/anesthesia With a willing gravida, some outlet operative VE deliveries can be conducted without anesthesia or analgesia. However, most parturients find operative vaginal procedures uncomfortable. Usually, either a regional anesthetic (eg, pudendal block) or a conduction anesthetic (eg, epidural, spinal, saddle block) is required. IndicationsProlonged second stage of labor An extended second stage of labor is a relative, but not absolute, indication for an obstetric procedure. Clinical reports prior to the 1970s suggested that fetal morbidity and mortality were higher with a prolonged second stage of labor. Recent studies have found a poor relationship between the length of the second stage of labor and infant mortality or morbidity. Clinicians must not ignore tardy progress. Poor progress requires caution and close evaluation because fetal malpositioning, including cranial deflection, a posterior or other uncommon presentation, or feto-pelvic disproportion could be the cause. The second stage can only be extended if the mother can tolerate a longer labor, serial examinations document continued progress, and the fetal condition is reassuring. Shortening of the second stage of labor On occasion, planned shortening of the second stage of labor is the best management. In some maternal disorders (eg, cardiac, cerebrovascular, neuromuscular), voluntary expulsive efforts are contraindicated or impossible. Additional situations that might lead to intervention include maternal exhaustion or overly dense epidural analgesia. Presumed fetal jeopardy/fetal distress The suspicion of a seriously stressed or potentially jeopardized infant is a classic indication for operative delivery; yet, this is exactly the setting in which extra caution is indicated. Remember that the standard techniques of fetal surveillance by electronic fetal monitoring are imprecise and the accurate diagnosis of fetal jeopardy still eludes us, except in extreme instances. When prompt delivery is believed to be indicated, station and position of the fetal head, the feto-pelvic relationship, operator skill, and judgment of the degree of jeopardy dictate the mode of delivery. For most practitioners, cord prolapse, abruptio placentae, or persistent bradycardia at a high station, even at full dilation with an engaged head, are best managed by cesarean delivery. Nonetheless, expedited vaginal delivery using vacuum extraction or forceps is appropriate in selected cases. Such instances usually involve a rapidly progressing labor when the maternal pelvis is adequate, the infant is normally presenting, the parturient is willing and able to assist, and an experienced obstetrician is present. Many of these applications are best conducted as trials, as described below. Trials of instrumental deliveryA trial of instrumental delivery is an operation in which delivery is indicated and the vaginal route is a possibility, but the outcome is uncertain. The following steps are suggested management:
Trials are often best conducted in an operating room but clinical realities may dictate the use of other sites. These operations demand the highest degree of attention and judgment from the surgeon. All trials involve an element of uncertainty. Thus, moving to a cesarean delivery if an extraction is not performed easily does not indicate a clinical failure. Obstetrics is far from an exact science and the accoucheur is neither expected nor required to invariably achieve a vaginal delivery. However, heroic vaginal operations have no place in modern obstetric management. The cardinal admonition whenever a delivery instrument is inserted and traction is applied is not to doggedly persist in the face of failure. Contraindications to vacuum extraction
Relative contraindications
DefinitionsThe American College of Obstetricians and Gynecologists (ACOG) has standard definitions for instrumental delivery operations. These determinations include outlet, low, and midpelvic operations. Coding depends upon the clinical assessment of fetal position and fetal station immediately prior to initiating an operation. While the guidelines were originally written for forceps procedures, the same descriptions are easily applied to vacuum extraction operations with minor modifications. Table 1. Proposed Classification for Vacuum Extraction Procedures According to Fetal Station and Cranial Position
* Dictation of all vacuum operations is recommended, regardless of apparent ease. ** The type of operation coded in the medical record is determined by pelvic examination noting the position and station of the fetal head at the time the extraction is initiated. † Station (+5 to –5) is defined as the distance in centimeters between the leading bony portion of the fetal skull and the plane of maternal ischial spines. Station is recorded by first enumerating this distance in centimeters followed by a notation of the technique employed for reporting. The authors recommend the ACOG ±5 cm system. Thus, if the clinician's estimate is that the bony presenting part is 2 cm below the plane of the ischial spines, the station of +2/5 cm is recorded.
Vacuum extraction instruments All vacuum extractors incorporate several features that include the following:
Rigid-cup designs include the classic Malmström stainless steel vacuum cup and various modifications of this instrument. Various rigid plastic cups designed for use with deflexed or posterior positioned heads are also available. Soft-cup extractors include the infrequently used cone-shaped silastic cup (Kobayashi device) and a number of other disposable polyethylene or combined polyethylene-silastic cup designs. No data exist permitting comparison of the currently popular vacuum extraction (VE) soft cup design in terms of either relative risk or clinical use. The differences observed in cup design largely reflect marketing decisions rather than scientifically proven extraction efficacy or safety. Comparison of instruments Soft or flexible vacuum cups have a higher incidence of failure than either rigid vacuum cups (plastic or metal) or forceps primarily due to their higher frequency of spontaneous detachment. However, soft vacuum cups result in less fetal cosmetic injury (principally scalp injury) than rigid cups. This reflects the inability of soft cups to generate the same degree of scalp traction as is possible when rigid cups are used. Design issues are important to cup choice. In most plastic extractor designs, the relatively rigid tube connecting the handle to the cup precludes accurate placement of the instrument on deflexed or occiput posterior heads. This contributes to failure when such malpositions are present. High success rates have recently been reported with rigid plastic cups similar to the original Malmström design for deflexed and posterior presentations. |
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Technique is vitally important to the safety and success of vacuum extraction (VE) operations. A proper vacuum-conducted extraction operation depends on the following:
After the prerequisites for VE operation are met, the position, station, and attitude of the fetal head are verified by pelvic examination and an instrument is chosen. Thereafter, a specific protocol is followed.
Current data permit the settling of at least one old issue. Two common VE techniques, continuous vacuum throughout the procedure and intermittent vacuum with the vacuum released between contractions, have been studied in a randomized trial. No differences exist between groups with regard to the speed of delivery, rates of instrument failure, or maternal or fetal outcomes. The use of either technique is at the discretion of the surgeon. The limits to effort An important issue in the conduct of any instrumental delivery is the force used in the extraction procedure. Studies performed with forceps, rigid-cup extractors, and soft-cup extractors reveal similar findings. In approximately 85% of births, delivery occurs with 4 or fewer pulls. Table 2. Number of Tractions Required in Vacuum Extraction and Forceps Deliveries *
* Breech, cesarean delivery, tv lies, <600 g, excluded ** Type unspecified If the extraction process is prolonged, carefully consider whether or not true progress has occurred. If not, the procedure must be reconsidered and often abandoned. In considering the extent of effort, the prudent surgeon must apply the rules of reasonable behavior. If cranial delivery is imminent, it is inappropriate to abandon a procedure in favor of a cesarean delivery simply because the fourth or fifth pull has occurred. In contrast, procedures leading to cup pop-offs or procedures requiring multiple traction efforts with limited progress are best abandoned. Prolonged or difficult extractions risk injury. The accoucheur strains to overcome what is usually disproportion or is tempted to abandon the vacuum and apply a forceps. Recognize that optimistic beliefs in continued, but very slow, progress often represent no progress at all, only progressive failure. Special applications At cesarean delivery, a thin lower-uterine segment, combined with a narrow or deep pelvis, predisposes to lacerations or to an extension of the original incision when manual extraction of the fetal head is performed. If a VE may be used during cesarean deliveries is a question of practicality. Deeply engaged fetal heads are best elevated from below by an assistant, obviating a need for the application of any instrument. The most appropriate use for VE at cesarean delivery is for fetal heads that remain high in the uterus after membrane rupture and are not easily delivered into the uterine incision despite fundal pressure. This can occur with either transverse lies or the second of twins. Using the VE can avoid the need for a breech extraction and can also avert a major extension of the original myometrial incision. Note that for instrumental extractions during a cesarean no data exist indicating any advantage to VE over forceps. Sequential instrument use Sequential instrument use (forceps operations followed by VE, or vice versa) is controversial. Recent studies involving large numbers of cases agree that sequential operations are associated with an increased risk for fetal intracranial hemorrhage (ICH), exceeding the risk when either forceps or VE are used alone. Some form of ICH is 3.4 times (95% confidence interval [CI], 1.7, 6.6) more likely to result from sequential procedures than from a VE operation alone. Similar data concerning an enhanced risk from combined procedures comes from review of the 1998 Food and Drug Administration (FDA) advisory paper on VE, as well as other sources. Additional discussion of intracranial injuries and instrumental delivery occurs in Choice of Instrument. The authors believe that the risk is one of degree. When one type of instrument is applied and fails, no absolute prohibition exists to trying a different device. Case choice is critical. The most appropriate cases in which to change instruments are those in which technical problems, such as a malfunctioning hand pump or a misapplied vacuum cup, are suspected. The least desirable cases are those in which multiple tractions or pop-offs occur following a correct application and appropriate traction but without descent of the presenting part. Injuries from multiple instrument use are most likely when a degree of unrecognized feto-pelvic disproportion is present and, despite difficulty, the clinician cannot refrain from pursuing vaginal operative delivery. Operative vaginal deliveries in which an instrument is used after the failure of another must be restricted to highly experienced physicians who have a clear understanding that the risk of birth injury is potentially increased in such operations.
Neonatal injuryThe reported incidence of severe fetal injury or death from vacuum extraction (VE) is low, ranging from 0.1-3 cases per 1,000 extraction procedures. Fetal injuries derive primarily from the physics of how the vacuum cup grasps the scalp. The VE draws the fetal scalp into the body of the cup producing the characteristic mound of scalp tissue and edema, the chignon. Traction also tensions the scalp against its attachments to the fetal skull, drawing it in the direction of the cup. These effects predispose to the common, but clinically unimportant, cephalohematomas and to the relatively rare, but potentially life threatening, subgaleal hemorrhages (see Image 6). Scalp bruising or lacerations and retinal hemorrhages are additional, usually insignificant risks of extraction procedures. Subgaleal/subaponeurotic hemorrhage The most feared complication of VE is hemorrhage in the subgaleal (SG) or subaponeurotic space from rupture of the emissary veins. This condition is potentially life threatening, with a mortality rate reported as high as 22.8%. Approximately half of all SG hemorrhages are related to VE. The rest are most often associated with forceps operations. Less commonly, SG bleeds follow spontaneous deliveries. The reported incidence of SG hemorrhages ranges from 6-50 per 1,000 VE operations. These rates almost certainly are overestimates and do not reflect the rates of injury in modern practice when soft-cup extractors are used and strict protocols for application are followed. In the experience of the authors, SG bleeding is mostly likely when excessive force multiple pop-offs or serial instrumentation with VE and forceps has occurred. However, recall that serious cases have followed outwardly uneventful extractions. SG bleeding was not observed in the large number of cases included in recent vacuum extraction meta-analyses. This documents not only the rarity of these severe scalp injuries but also emphasizes the importance of following strict technical guidelines when performing vacuum extraction operations. Because of this small but significant risk, the authors suggest notifying pediatric personnel whenever an extraction is performed, regardless of the immediate condition of the neonate. SG hemorrhages may not be clinically apparent until some hours postpartum. Scalp bruising/lacerations Ecchymoses and, uncommonly, scalp slough or lacerations can follow VE. Most of these injuries occur when the recommended 30-minute limit to total cup application is exceeded. The ventouse is not a rotating instrument. Attempts at cup rotation simply foster cup displacement or scalp injury. Under traction, the fetal head should rotate automatically as descent occurs. If the clinician feels an obligation to assist or hasten this process, then manual rotation of the head (not the cup) can accompany the extraction. Normally, this is not required. Long-term neonatal outcomesThe few available studies evaluating long-term neurologic sequelae of instrumental delivery reported no differences between children delivered spontaneously versus those delivered by either VE or forceps. Cohorts of 295 and 302 children delivered by VE-assisted procedures versus spontaneous deliveries, respectively, were studied when the participants were aged 10 years. These children scored similarly in scholastic performance, speech, ability for self-care, and neuralgic status. Follow-up studies of infants delivered by VE at aged 9 months and 5 years found no differences in cognitive development between children delivered with either VE or forceps. These studies, though limited in total patient number, provide reassurance of VE safety. Maternal injuryVacuum extraction has a low rate of maternal injury in comparison with forceps operations or cesarean delivery. However, maternal injuries do occur. Such trauma cannot be disregarded in evaluating the risk of the procedure. Lacerations Maternal perineal lacerations are common complications of all operative vaginal deliveries. Many tares are associated with episiotomy. The incidence of severe perineal lacerations (ie, third- and fourth-degree lacerations) during VE procedures ranges from 5-30%. Women who sustain vaginal lacerations in a previous delivery are at a significantly greater risk for a repeat laceration in subsequent deliveries. Women at greatest risk are those who experienced a laceration in the first delivery followed by another delivery combining both an instrumental delivery and an episiotomy. One area in which vacuum extractor has a clear advantage over forceps is perineal trauma. Forceps operations are more likely to result in anal sphincter injury trauma than vacuum extractions. In pooled data from 8 randomized trials studying maternal delivery trauma, a 6% decrease in anal sphincter trauma occurred if VE, and not forceps, were used. Episiotomy is an important risk factor. Electively incising the perineum predisposes to perineal lacerations and rectal injuries by direct extension. The authors favor the selective performance of episiotomy and only if maternal soft tissues impede the delivery process. In Europe, when an episiotomy is required, mediolateral (ML) incisions are preferred. While ML episiotomies are less likely than median episiotomies (ME) to extend into the rectal sphincter or mucosa, the ML is harder to repair, is more likely to result in distortion of the perineum, and results in more pain in the puerperium. Best practice in regard to whether to perform an episiotomy during aninstrumental delivery, the type to empty, and the timing is yet to be established. Stress urinary and anal incontinence Dystocia in labor, vaginal delivery, obstetric lacerations, multiparity, and probably the mode of delivery combine to result in both reversible and permanent injuries to connective tissues of the maternal pelvis. Injury to these support structures and to the rectum constitutes important and perhaps unavoidable risks of instrumental delivery. The female pelvic viscera are suspended from above and supported from below. The intactness of the various support structures depends upon the integrity of their muscular, fascial, and neuralgic constituents. The upper suspensory structures are a complex of pseudoligamentous structures loosely termed pelvic ligaments. This connective tissue accompanies vascular structures into the pelvis to surround the cervix. The lower supports for the uterus are a musculo-fascial complex including the urogenital and pelvic diaphragms. The pelvic diaphragm principally consists of the levator ani muscle. The urogenital diaphragm is a complex of small muscles and accompanying connective tissue that extends from the central perineal body radially to attach to various bony and ligamentous sites in the pelvis. Both labor and the process of passing the fetal body through the birth canal distort and injure these and other pelvic tissues. During parturition, pelvic ligaments and muscles are simply torn or otherwise disrupted and accompanying nerves are traumatized. Various spontaneous lacerations or episiotomy extensions account for additional injuries, especially to the rectal sphincter. The issue is not whether vaginal delivery results in injuries to pelvic soft tissues. The question is the degree of the injury and the extent to which spontaneous postpartum healing or specific muscle strengthening exercises performed in the puerperium may ameliorate this damage. In terms of instrumental delivery, techniques that either reduce or avoid injury to pelvic supports and to the rectum are under study. Long-term, follow-up studies controlling for prepartum pelvic support status (eg, preexisting rectal dysfunction, urinary incontinence) as well as length of labor, type of anesthesia, clinically observed perineal trauma, and delivery method are required before changes in current practice can be confidently recommended. Long-term follow-up studies controlling for prepartum pelvic support status, eg, preexisting rectal dysfunction and/or urinary incontinence, length of labor, anesthesia, clinically observed perineal trauma, and delivery method, are required before changes in current practice can be recommended.
There has been a long-term debate amongst clinicians concerning which instrument, either the vacuum extractor or the forceps, is best. In deciding to use one instrument over the other, a number of factors are involved, including the following:
Table 3. Incidence of Fetal Intracranial Hemorrhage
Clinical practice
Prematurity (<36 wk)
The use of any instrument to assist delivery of a premature infant is controversial. Older data suggest that gentle assisted delivery of the fetal head on the perineum using a classic forceps might reduce cranial trauma. However, this traditional application has unimpressive support in literature. As the inherent risks of fetal intracranial or scalp hemorrhage are greater in premature infants than in full-term infants, the vacuum extractor is relatively contraindicated for application to infants younger than 36 weeks. Yet, as data on this issue are both limited and often anecdotal, this contraindication cannot be absolute. If an extractor is chosen for a preterm pregnancy, a soft-cup design is preferred.
Breech presentations
Multiple gestations
The vaginal delivery of a second cephalic-presenting twin is often a good case for a vacuum extractor. Such extractions are usually easy because of dilation of the birth canal following the delivery of the first infant. A VE operation at cesarean delivery may obviate the need for extraction of the second twin and avoid an extension of the cesarean wound. Here, any VE is acceptable.
The following conclusions are derived from an analysis of the literature, as interpreted by the authors. The level of recommendation that is made follows that used by the ACOG. This derives from the method outlined by the US Preventive Services Task Force and reflects the highest level of available evidence. Table 4. Recommendations
As applied to instrumental delivery and, specifically, to vacuum extraction (VE) operations, the following conclusions are suggested:
Opinions for standard VE procedures These recommendations are based on the authors' experience and on large clinical series that reported a low incidence of injury when similar rules were followed.
The vacuum extractor is an effective and safe device for assisted vaginal delivery and an important addition to the obstetrical armamentarium. Treat this instrument with respect to maximize the possibilities of its success while limiting the risks of maternal or fetal injury.
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