Vacuum Extraction |
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INTRODUCTION AND HISTORY | ¡@ |
In the Elements of Physics in 1831, Neil Arnott, MD, wrote, "The simple contrivance now described, and which may be called a pneumatic tractor, seems well suited to various purposes of surgery."
Vacuum extraction (VE) has deep historical roots. The origin of vacuum extraction is in ”cupping,?a therapeutic technique used long before Hippocrates. In cupping, a metal or glass cup was heated over an open flame, then applied to a lesion or skin puncture. As the cup cooled, a vacuum developed, extracting blood or other fluids. Cupping also occasionally was used for a number of surgical procedures, such as raising depressed skull fractures.
The use of cupping to assist delivery began in the early 18th century. Obstetric use proved problematic. Delivery assistance required a vaginal application of the cup and periodic reinforcement of the vacuum. In order to make the cranial vacuum cup practical, a technology to generate a vacuum on demand was needed. This technology was not to come for another 100 years.
James Young Simpson invented the first practical vacuum extractor in 1849 (see Picture 1). Simpson, a professor of obstetrics in Edinburgh, was a clinician and obstetric innovator who was famous for his forceps design and the introduction of chloroform into obstetrical practice. Simpson experimented with vacuum devices, producing a working delivery instrument in the late 1840s that he successfully employed. However, his interest soon moved to other obstetric issues and his “air tractor?fell from popular attention. In the decades that followed the creation of Simpson’s instrument, a number of vacuum delivery devices were invented and tested by various clinicians, but none achieved popularity.
The immediate antecedent to modern extractors was the stainless steel cup device, introduced by Malmström in the late 1950s. This device entered US practice late in the 1960s; however, because of technical problems with the original design and case reports of severe fetal complications, interest promptly waned. Within the last several years following the introduction of disposable soft-cup extractors and improved rigid cup designs, VE has experienced a revival. This renewed interest also has led to a more scientific study of vacuum technique, improving both the success and safety of VE.
At present, both forceps and the vacuum extractor are in widespread use. Controversy continues concerning if and when to conduct operative vaginal deliveries and which instrument is best. This and related issues are of importance because VE currently is employed in about 6% of all births in the US (nearly 50,000 operations per year).
Despite the growing popularity of VE, forceps remains the instrument of choice for many older clinicians for reasons of medical conservatism, inclination, and original training. The future for all instrumental delivery remains unclear, as adequate training in all aspects of these operations is increasingly difficult to obtain because of the retirement of classically trained obstetricians; the inability to conduct training operations; a malevolent medico-legal climate; and changes in practice, including the high frequency of cesarean delivery.
VE is popular because of its reputation for ease of use, lower maternal morbidity, and safety. However, the sporadic but continuous reports of severe neonatal complications associated with VE should serve to remind practitioners of the need for rigorous adherence to proven techniques and limited indications to best assure success while avoiding injury.
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PREREQUISITES, INDICATIONS, AND CONTRAINDICATIONS | ¡@ |
In general, VE operations have similar indications as operations with forceps.
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Informed consent
An informed consent is a process, not simply a signed form. For instrumental delivery, a proper informed consent includes an explanation of the need for the operation, a discussion of risks and benefits, and a presentation of alternative modes of treatment. Furthermore, the parturient must have the opportunity to ask questions. In its entirety, the consent process may strike the clinician as being excessively time consuming and unrealistic, especially in the face of urgency.
Obviously, in most instances, a bedside consent process is abbreviated. In all situations but extreme emergencies, there should at least be sufficient time to briefly describe the proposed operation and to indicate the limits of effort intended to the patient.
Because of the difficulties of obtaining bedside consents from laboring patients, discussing possible obstetric interventions with families at an earlier time during the pregnancy is prudent; thus, when these data are presented during labor at the time of intervention, they are not entirely new or unanticipated.
Prepared physician
The clinician must have knowledge of the instrument chosen and of VE indications and proven techniques. Specifically, this preparation includes the willingness to abandon an operation if it proves difficult.
Prepared patient
Prior to considering an extraction, the patient should have ruptured membranes; an empty bladder by Cred? catheterization, or spontaneous voiding; full cervical dilation; an engaged fetal head; and no suspicion of feto-pelvic disproportion.
Acceptable analgesia/anesthesia
While some operative VE deliveries can be conducted under a “local and vocal?with a willing gravida, most parturients find operative vaginal procedures uncomfortable. Either a regional (eg, pudendal block) or a major conduction anesthetic (eg, epidural, spinal) may be required.
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Prolonged second stage of labor
Clinical studies before the 1970s suggested that the risk of fetal morbidity and mortality was higher with a prolonged second stage of labor; however, studies involving almost 36,000 parturients found no direct relationship between the length of the second stage and infant mortality or morbidity. These data indicate that a prolonged second stage, according to American College of Obstetricians and Gynecologists (ACOG) criteria, is not an indication for immediate operative intervention unless the maternal or fetal status becomes bothersome or progress ceases.
Do not ignore tardy progress. Poor progress requires caution because cranial malpositioning, deflection, asymmetries, or true feto-pelvic disproportion could be present. The safety of an extended second stage depends upon close maternal or fetal monitoring, with judicious intervention as required. Therefore, an extended second stage is a relative, but not absolute, indication for obstetric intervention.
Shortening of the second stage of labor
On occasion, shortening the second stage of labor is appropriate. Maternal disorders (eg, cardiac, cerebrovascular, or neuromuscular conditions) in which voluntary expulsive efforts are contraindicated or impossible exist. Additional situations that may lead to intervention include the vastly overdiagnosed condition of maternal exhaustion or the uncommon instances of overly dense epidural analgesia.
Presumed fetal jeopardy/fetal distress
While a potentially distressed infant is a classic indication for operative intervention, this is the setting in which extra caution is indicated. Operative heroics have no place in obstetric management. The means for diagnosis of presumed fetal jeopardy are imperfect, except in extreme instances such as fixed bradycardia or cord prolapse. When prompt delivery is 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 carefully selected cases of rapidly progressing labor when pelvic adequacy is good, the parturient is willing and able to assist, and an experienced surgeon is present. Many of these applications are best conducted as trials, as described below.
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A trial of instrumental delivery is an operation in which delivery is indicated and the vaginal route remains a possibility, but the outcome is uncertain. In this type of procedure, the most experienced clinician remains at the perineum, encouraging maternal efforts of bearing down and assisting with an instrument, while other personnel simultaneously prepare for an urgent cesarean delivery. If the extraction does not proceed easily with descent of the presenting part beginning subsequent to the initial traction effort, the attempt at instrumentation is abandoned and a cesarean delivery is performed.
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Operator inexperience
Inability to achieve a proper application
Inadequate trial of labor
Uncertainty concerning fetal position/station
Suspicion of feto-pelvic disproportion
High fetal head
Malpositioning (eg, breech, face, brow)
Known or suspected fetal coagulation defect
Prior failed forceps
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Prematurity (fetuses <36 wk gestation)
Prior scalp sampling
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The ACOG has established standard definitions for instrumental delivery operations (see Picture 2). These definitions include outlet, low, and mid pelvic operations and depend upon assessment of fetal position and station. While the ACOG guidelines originally were written for forceps procedures, the same descriptions may be applied to vacuum extraction operations with minor modifications.
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DESIGN OF THE VACUUM EXTRACTOR | ¡@ |
Available vacuum extraction instrumentation
In the US, vacuum extractors are of 2 basic designs, employing either a rigid or a flexible vacuum cup of varying composition (eg, polyethylene, silastic plastic, stainless steel). All of the cups have several standard features (see Picture 3), including the following:
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Rigid-cup designs include the classic Malmström stainless steel vacuum cup and various modifications of this instrument, such as the Bird cup (see Picture 4). Rigid plastic cups designed for use with deflexed or posterior positioned heads also are available (see Picture 5). Many other modified rigid-cup types exist, varying in details of cup design and in arrangement of the traction attachment site or the vacuum port.
Soft-cup extractors include the infrequently used cone-shaped silastic cup, the Kobayashi device, and various other disposable polyethylene or combined polyethylene-silastic cup designs. Limited data exist comparing the clinical utility or the relative risk of use of the currently popular soft cup VE designs.
Comparison of instruments
In general, the soft or flexible vacuum cups have a higher incidence of failure than either rigid vacuum cups (plastic or metal) or forceps due to their higher frequency of detachments. However, soft vacuum cups also produce less fetal cosmetic injury (principally scalp injury) than rigid cups. This lack of injury most likely reflects the inability of soft cups to generate the same degree of scalp traction as rigid cups.
There are design issues to consider. The relatively rigid rod connecting the handle and cup in most plastic extractor designs precludes accurate placement of the instrument on deflexed or posterior heads; this contributes to failure. However, high success rates with a rigid but plastic "M" cup (similar to the original Malmström stainless steel cup) recently have been reported in operations involving these common cranial malpresentations. The newly introduced KIWI extractor, consisting of a rigid plastic Malmström-type cup attached by a wire to a unique combined handle/pump, is especially useful for cases involving cranial deflexion/malpositioning.
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VACUUM EXTRACTION TECHNIQUE | ¡@ |
Technique is vitally important to the safety and success of VE operations. A proper vacuum extraction depends upon (1) the accuracy of cup application, (2) the traction technique, (3) the fetal cranial position and station at the time of application, (4) the cup design, and (5) the feto-pelvic relationship.
After the prerequisites for VE operation are met, the position, station, and attitude of the fetal head is verified by pelvic examination and an instrument is chosen. Thereafter, several specific steps are taken, including the following:
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When correctly positioned, the edge of a standard 60-mm cup lies approximately 3 cm or 2 fingerbreadths behind the center of the anterior fontanelle in the midline over the sagittal suture. Thus, in VE operations, the anterior fontanelle becomes the reference point for checking the instrument application because access to the posterior fontanelle is partially blocked once the extractor cup is in place, rendering this familiar landmark unusable.
The farther the cup is placed from the midsagittal position on the fetal head over the cranial pivot or flexion point, the greater the failure rate. Oblique applications result in cranial deflexion or asymmetry as traction is applied. This increases the work of extraction by presenting a larger cranial diameter to the birth canal than would occur had the application been correct (see Picture 7).
Once an approximate cup application is established, partial vacuum sufficient to fix the cup to the fetal head is applied. A careful check of cup placement follows (eg, midsagittal, over pivot point, no maternal tissue included). Once the surgeon is convinced of an appropriate placement, full vacuum is applied (ie, 550-600 mm Hg) and traction follows, paralleling contractions.
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During traction, the best technique for the surgeon is to place the nondominant hand within the vagina, placing the thumb on the extractor cup and 1 or more fingers on the fetal scalp (see Picture 8). When positioned like this, the surgeon follows the descent of the presenting part and can better judge the appropriate angle for traction while gauging the relative position of the cup edge to the scalp, helping to detect cup separation while limiting unnecessary rocking motions or torque. Descent must begin with the initial traction effort; failure to achieve station mandates prompt reassessment of the procedure.
Current data permit the settling of at least one old issue. Two common VE techniques, continuous vacuum throughout the procedure versus intermittent vacuum with the vacuum released between contractions, have been studied in a randomized trial. No differences between groups with regard to the speed of delivery, rates of instrument failure, or maternal or fetal outcomes exist. The use of either technique becomes the discretion of the surgeon.
For standard VE procedures, the authors' general recommendations include (1) limit the number of tractions to 4 or 5, (2) limit unintended cup detachments or ”pop-offs?to 2 or 3, (3) require advancement of the presenting part with the initial traction, (4) restrict the overall duration of the procedure to less than 30 minutes (some propose 20 min). These recommendations are based on large clinical series that reported a low incidence of injury when these limitations were followed. Lastly, detailed documentation of the operative delivery in the medical record, including the aforementioned points is paramount.
The limits to effort
Studies performed with forceps, rigid-cup extractors, and soft cup extractors essentially have the same findings. Approximately 85% of births requiring VE are delivered with 4 or fewer than 4 pulls (see Picture 9). Thus, if a prolonged extraction with any instrument occurs, carefully consider if progress truly is taking place. Procedures leading to multiple cup pop-offs or procedures requiring a large number of traction efforts are best abandoned because it is believed that this practice risks injury as the accoucheur strains to overcome disproportion. Recognize that optimistic beliefs in continued but very slow progress may represent no progress at all, only a growing caput. However, the rule of reason also must apply. If cranial delivery is imminent, do not abandon a procedure in favor of a cesarean delivery simply because the fourth or fifth pull has occurred.
Special applications
A number of clinicians have used the vacuum extractor to assist in cesarean delivery. At surgery, a thin lower-uterine segment, combined with a narrow deep pelvis, predisposes the infant to laceration or extension when manual extraction of the fetal head is performed. The question here is one of practicality. Deep fetal heads usually are best elevated from below by an assistant, obviating a need for the application of any instrument. Yet, on occasion, the engaged fetal head can be grasped with the ventouse and the infant can be extracted, limiting trauma to the mother or infant. The flexible or semirigid cups are best for this application; however, no data suggesting any advantage to VE exist, as opposed to forceps for this indication. A better use for VE is for fetal heads that remain high in the uterus when fundal pressure fails to promptly dislodge them. In this setting, VE (or forceps) can easily be applied, leading to prompt delivery and avoiding the need for a breech extraction.
Sequential instrument use
Sequential instrument use (forceps operations followed by VE or vice versa) is problematic. Occasional papers involving small patient numbers and uncontrolled technique repeated in previous years suggested that sequential instrument use is safe; however, recent studies have reported 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. 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 come from review of the 1998 Food and Drug Administration (FDA) advisory paper on VE and other birth injury reviews.
Some believe that the risk is one of degree. When one type of instrument fails, no absolute prohibition to trying a different device exists; however, such applications must be restricted to highly experienced physicians who have a clear understanding that the risk of birth injury can be increased in such operations. Injuries from multiple instrument use most likely occur when a degree of unrecognized feto-pelvic disproportion is present and when, despite difficulty, the clinician cannot refrain from pursuing vaginal operative delivery.
Thus, case choice is critical. Obviously, the best cases in which to change instruments are those in which a technical problem, such as a malfunctioning hand pump, is suspected. The least desirable cases are those in which multiple tractions/pop-offs occur following appropriate technique without descent of the presenting part, causing an inadequate or inconsistent vacuum.
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BIRTH INJURIES | ¡@ |
The reported incidence of severe fetal injury or death from VE is low, ranging from 0.1-3 cases per 1,000 extraction procedures. Vacuum use results in shearing forces to the scalp, leading to the common, but clinically unimportant, cephalohematomas and the relatively rare, but potentially life-threatening, subgaleal hemorrhages (see Picture 10). Scalp bruising or lacerations and retinal hemorrhages are additional, but minor and clinically insignificant, risks of extraction procedures.
Subgaleal/subaponeurotic hemorrhage
The most feared complication of VE is hemorrhage in the SG subgaleal (SG)/subaponeurotic space from rupture of the emissary veins. This condition can be life threatening, with a mortality rate reported as high as 22.8%. Approximately half of all SG hemorrhages are related to VE. The remainder of SG hemorrhages is associated with forceps operations; less commonly, they occur following 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 rare unless excessive force and/or multiple instrumentation has been performed. This complication was not observed in the cases included in recent vacuum extraction meta-analyses. This documents the rarity of severe scalp injuries while emphasizing the importance of following strict technical guidelines when performing vacuum extractions/operations. Nonetheless, notifying pediatric personnel whenever an extraction is performed is suggested, regardless of the immediate condition of the child because SG hemorrhage 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 limits to total cup applications are exceeded (30 min is the maximum). Also, recall that 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.
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The few available studies evaluating long-term neurological sequelae of instrumental delivery have found no differences among children delivered spontaneously and children 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 neurologic status. Follow-up studies of infants who were vacuum extracted were performed when the children were aged 9 months and 5 years; no differences in cognitive development were found between children delivered with VE and forceps. These studies, though relatively small in numbers, provide reassurance of VE safety.
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Vacuum extraction has a low rate of maternal injury in comparison to forceps operations or cesarean delivery. However, maternal injuries do occur, and this trauma cannot be disregarded in the evaluation of the risk of the procedure.
Lacerations
Maternal perineal lacerations are common complications of all operative vaginal deliveries. Many tears accompany episiotomy. The reported incidence of severe laceration (ie, third-degree and fourth-degree laceration) during VE procedures ranges from 10-30%. Women who sustain vaginal lacerations in a previous delivery are at a significantly greater risk for repeat laceration in subsequent deliveries. Women at greatest risk are those who experienced a laceration in the first delivery followed by a subsequent delivery combining both instrumentation and episiotomy.
This is one area in which the vacuum extractor has a clear advantage. Forceps operations are more likely to result in anal sphincter trauma than vacuum extractions. In pooled data from 8 randomized trials studying maternal delivery trauma, a 6% decrease (95% CI -.10, -.02) in anal sphincter trauma occurred if VE, and not forceps, was employed.
Stress urinary and anal incontinence
Delivery trauma is suspected to predispose the patient to subsequent pelvic floor dysfunction; however, recent data indicate that the long-term effects of operative vaginal delivery on rectal and/or urinary incontinence are more complex than originally believed. Although severe perineal lacerations are more frequent with forceps operations compared to operations with VE, recent studies evaluating remote outcomes (9 mo to 5 y) show no long-term differences between stress urinary and anal incontinence of mothers delivering with the aid of VE and those delivering with the aid of forceps. As an example, in a 5-year follow-up of 228 women who randomly delivered an infant by forceps or VE, no differences were found in urinary or bowel dysfunction between the groups.
A prospective observational study involving 278 women found an initial association between instrumental delivery (both forceps and VE procedures) and anal incontinence at 5 months after delivery but no association at 9 months after delivery. Clinically detected sphincter tears were more likely to result in involuntary loss at 9 months after delivery.
In another prospective survey of 1008 women at 34 weeks gestation, which was repeated 8 weeks postpartum, no difference in noted stress urinary incontinence was found between women who had normal vaginal delivery and women who had instrumental delivery. These studies also noted a high incidence of incontinence occurring spontaneously during pregnancy.
Interpretation of all these data is problematic. The suggestion is that vaginal childbirth is a major culprit, but not the sole culprit, of long-term perinatal dysfunction. Not surprisingly, the greater the degree of perineal trauma, the more likely are residual sphincteric abnormalities.
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.
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CHOICE OF INSTRUMENT | ¡@ |
Debate among clinicians persists concerning which instrument is best, either the vacuum extractor or the forceps. A number of factors are involved, including the following:
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Not surprisingly, facial nerve (VII) palsies were more common following forceps operations (4.5 per 1,000) than VE procedures (0.46 per 1,000). These data implicate labor and vaginal delivery, as opposed to the specific delivery instrument, in the etiology of many sustainable birth injuries, at least in large population statistical studies.
Clinical practice
The accoucheur must carefully consider the fetal condition, available resources, extent of analgesia, likelihood of maternal cooperation, and personal skill level when choosing the instrument for operative vaginal delivery. When an urgent delivery is required and a vaginal operative delivery trial is elected, greater success and less danger result when instruments are chosen based on operator experience and skill in the setting equipped for urgent cesarean if necessary.
In presumed fetal jeopardy at a low station (+2/5 +/- cm), many prefer to apply forceps rather than the vacuum. However, prospective trials demonstrate no differences in either the safety or speed between these instruments. Thus, either the ventouse or forceps is appropriate in these urgent cases, depending upon the comfort level of the clinician.
When the situation is without exigency, other issues deserve consideration. The forces of labor normally result in cranial molding and the formation of caput. The combination of molding and caput succedaneum formation can obscure landmarks to such a degree that even an experienced clinician can have difficulty in assessing fetal position and station. Careful attention to palpation of the cranial fontanelles, suture lines, orbital ridges, or the fetal ear helps establish the correct cranial orientation and station.
In difficult cases, real-time ultrasound scanning is useful in evaluating fetal cranial positioning and, to some extent, station, particularly in occiput posterior positions. Visualization of the fetal orbits, cranial anatomy, position of the fetal spine, and other anatomic landmarks are helpful.
The instrument chosen should best fit the clinical situation. Certain vacuum cup designs have special advantages in particular circumstances.
Choice of instrument for cephalic presentations
Outlet operations/low-pelvic operations (rotation <45?: With adequate analgesia, the vacuum extractor and forceps are equivalent instruments. If a VE is chosen, any instrument can successfully be applied.
Low-pelvic operations (rotation >45? and midpelvic operations: Procedures that do not involve significant cranial asynclitism are equally well managed by any vacuum instrument. For asynclitic heads in transverse position, the appropriate cup choices include an occiput posterior (OP) metal cup (eg, Bird design, O’Neil design) and a plastic OP design (eg, KIWI, Mityvac ‘M?. Forceps also may be used for these positions, but operations involving VE and forceps are restricted to the experienced physician only.
If extraction is performed with a direct OP cup, appropriate choices include an OP metal cup (eg, Bird design, O'Neil design) or a plastic OP design (eg, KIWI, Mityvac ‘M?. Forceps also may be applied to OP either for a direct "face to pubes" pull or a rotation. Both the pull and a rotation can prove difficult and risk maternal soft-tissue injury. Again, these procedures are restricted to the experienced surgeon only.
Breech presentation
A vaginal breech delivery is a clear indication for the application of forceps. In a breech presentation, VE is contraindicated. Either Piper or Kjelland forceps are appropriate for the after-coming head.
Multiple gestations
The delivery of a second cephalic-presenting twin is a potential indication for the use of a vacuum extractor. Such applications are usually easy because of dilation of the birth canal following the delivery of the first infant. Normally, any standard extractor design is appropriate.
Prematurity (<36 wk)
The use of any instrument to assist delivery of a premature infant is controversial. Older data suggests that gentle assisted delivery of the fetal head on the perineum using a classic forceps may reduce cranial trauma. However, this traditional application generally has unimpressive literature support. As the inherent risks of fetal intracranial or scalp hemorrhage are believed to be greater in premature infants than in full-term infants, the vacuum extractor is relatively contraindicated for application to infants younger than 36 weeks. However, as data on this issue are limited or anecdotal, this contraindication is relative. In summary, remain cautious about applying delivery instruments to premature infants because the risks/benefits are not well established. If an extractor is chosen, a soft-cup design is preferred.
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CONCLUSIONS | ¡@ |
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 in order to maximize the possibilities of its success while limiting the risks of maternal and fetal injury.
The following conclusions are derived from an analysis of the literature, as interpreted by the authors. The level of recommendations follows that prompted by the ACOG and is based on the highest level of evidence found in the data. The level of recommendation that follows each statement parallels that promoted by the ACOG and is based on the highest level of evidence found in the data. Recommendations are graded according to the following categories:
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These data, while incomplete, prompt care in all deliveries and special caution in instrumental deliveries to limit the performance of episiotomy and to avoid perineal injury when possible. The likelihood of serious infant injury probably is increased when either the forceps or a vacuum extractor is attempted following a failed operation with the alternative instrument. Sequential instrument use is restricted to selected cases conducted by highly experienced surgeons only.
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PICTURES | ¡@ |
| Caption: Picture 1. J.Y. Simpson, 1849 "Air Tractor" |
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| Caption: Picture 2. Classification for vacuum extraction procedures according to fetal station and cranial position |
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| Caption: Picture 3. Standard soft-cup vacuum extractor |
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| Caption: Picture 4. Bird design. Standard steel vacuum extractor cup. |
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| Caption: Picture 5. Mityvac "M" cup vacuum extractor |
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| Caption: Picture 6. Flexion or pivot point |
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| Caption: Picture 8. Two-handed traction technique |
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| Caption: Picture 10. Cross-section of fetal scalp, indicating the site of possible injury |
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BIBLIOGRAPHY | ¡@ |
