Krieglsteiner et al., Bamberg obstetrical forceps 87

Original articles

J. Perinat. Med.14 (1986) 87

Experience with the Bamberg obstetrical forceps

Peter Krieglsteiner1, Heinrich Adolf Krone2, and Dieter von Zeppelin1

1 Department of Obstetrics and Gynecology and Out-Patient Department,University Hospital, Technical University of Munich, and

2Department of Obstetrics and Gynecology, Bamberg Main Hospital, Fed.Rep. Germany

1 Introduction

Since its introduction by MALMSTRÖM [14] in1954, use of the vacuum extractor has surpassedthat of forceps delivery in Europe [14, 15].The ease and presumed safety with which thevacuum extractor can be applied, coupled withthe ability to apply this instrument to the fetalvertex, prior to the cervix having obtained fulldilatation, has been responsible for this trend.However, vacuum extraction has been shownto be associated with a significant risk of trau-ma and fetal cephalhematomas [17]. This hasled to a renewed interest in the development ofalternative varieties of obstetrical forceps andsafer techniques of forceps delivery.Clinical experience has shown that the perfor-mance of outlet forceps deliveries expeditesbirth in cases of fetal distress and that the useof parallel forceps such as the SHUTE varietyoffers significant advantages in protecting thefetal cranium during the extraction process [20,21].Earlier varieties of obstetrical forceps still inuse, especially those with crossed shanks, oftenproduce a significant amount of trauma bothto the fetus and the mother [1]. Their applica-tion to the fetal head produces a significantdegree of compression during the extractionprocess, thereby increasing the risk of localtissue injury, intracranial damage and local

nerve palsies [5]. Moreover, the blades of theseforceps characteristically have a wide pelviccure which tends to distend and traumatize softtissues of the pelvic outlet during the processof extraction.In Germany, the NAEGELE and KIELLAND for-ceps are the most widely used crossed shankvarieties. The SHUTE type is the most commonlyemployed parallel forceps, while the LAUFE for-ceps [12, 18] is the most commonly used instru-ment with divergent blades. Unfortunately, useof the above varieties of obstetrical forceps areassociated with an unacceptably high incidenceof complications [8].This paper presents our experience with a newinstrument, the divergent Bamberg forceps,which we believe offers distinct advantages overother varieties currently in use in Germany.

2 Materials and methods

In 1975, a new obstetrical forceps was devel-oped at the Bamberg Obstetrical Clinic in WestGermany [22]. This forceps is presented infigure 1. Since its introduction, the Bambergforceps has been widely used, both at the Bam-berg Obstetrical Clinic and in the ObstetricalDepartment of the Technical University of Mu-nich.

1986 by Walter de Gruyter Co. Berlin · New York

Krieglsteiner et al., Bamberg obstetrical forceps !

Figure 1. Bamberg divergent forceps (conventional de-sign, ZEPPELIN Medizintechnik GmbH, D-8023 Pul-lach/M nchen F.R.G.). The slide mechanism ensuresautomatic limitation of the applied force and constantfixation of the blades on the fetal head.

Applied force — A1; Extraction force — EContact force — A 2; Compressive force — C :Once introduced into the vagina and appliedto the fetal head, the blades of the Bambergforceps can be made to mold by simply adjust- 'ing the slide mechanism on the handle. Thedegree of head compression as well as the ,applied force involved during the extraction canbe evaluated by the following equation:

μ αAI = -S-sin α-cos —cos β 2

(figures 3 and 4)

Based on this formula, a sliding force of s = j2 kp will produce an applied force of only |

0.1 kp. The fact that the eccentrically arranged f\slide lock will lock automatically whenever the :forceps handles are forced together, makes it

Figure 2. Bamberg divergent forceps (advanced designwith closed blades). The slide mechanism is unchanged.To prevent pelvic injuries, the closed blade surface arecoated on the outside with teflon [10].

We contend that a major advantage that theBamberg forceps has over other varieties lies inthe fact that it makes efficient use of the diver-gent arrangement of its blades and handlesabout a common pivot — the tapered pin lock.The forces that are applied directly or indirectly Fi8«re 3. The forces occurring during extraction: theto the fetal head during the application of for- comPref ?ve force C acting on the fetal head can be

j j · *u Γ 4.· r> resolved into components A 1 (applied force) and A 2ceps and during the extraction process are four (contact force). Τ1£ forceps des4PgP

uarantees an applie5in number (figure 2) [10]. force of maximum 300 g.

VE

J. Perinat. Med. 14 (1986)

Krieglsteiner et al., Bamberg obstetrical forceps 89

Ai[kp] :Aimax. = 0,25kp

S[kp]Figure 4. Applied force A 1: The sliding force 's' exertedby the excentric on the sliding curve (right blade) withnormal manual pressure gives rise to an applied forceA 1 of maximum 300 g. This force remains constantduring extraction.

impossible to increase the applied force inad-vertantly during extraction of the fetus. Thisrenders the Bamberg obstetrical forceps es-pecially useful in cases of mild to moderatecephalopelvic disproportion and represents aunique feature not found with any other obstet-rical forceps. The use of the Bamberg forcepsenables applied force to remain constant duringthe extraction with a theoretical maximum of300 g.An additional force which is superimposed onthe applied force during the extraction processis the contact force (A 2). This force is directlyproportional to but less than the extractionforce (E). The sum of the applied force (A 1)and the contact force (A 2) equals the compres-sive force (C), which is exerted to the fetal head.This can be expressed as follows:C = AI + 2 = 1 + E(sin β) (figure 5)

3 ResultsWe have performed 483 forceps deliveries usingthe Bamberg divergent forceps. In addition tothis number, there were 36 cases where theBamberg forceps was used in conjunction witha vacuum extraction.These forceps deliveries represent approximate-ly 3% of all births at the two institutions (figure6). In approximately 50% of cases, the indica-tion for forceps delivery was acute fetal distress,while in about 40% of the cases, the indicationfor forceps delivery was delay in the secondstage of labor.Additional indications for forceps delivery in-clude factors such as malposition of the fetalhead and assistance in the case of maternaldisease. 84% of the forceps deliveries were out-let procedures, while 14% were low-mid-for-ceps. In the last years of this study outlet proce-dures were performed almost exclusively.

3,0

20

M U N I C H

^-BAMBERG

1977 1978 1979 1980 1981

Figure 6. Proportion of forceps deliveries in total collec-tive.

C[kp],*2-

A1-const. =0,1 k p

Elkp]Figures. Compression force C: With a normal andconstant applied force A 1 of 0.1 kp the compressiveforce acting on the fetal head is only a function of theextraction force. This in turn, is dependend on the sta-tion of the head in the pelvis and can thus be influencedby the operator's range of indications.

APGAR SCORES {Ntotal = 483)100-

80-

60-

40-

20-

ΠDUD

^ CSD7/8910

E*:ji] Γτττ

:̂

·:·:·

'*·*·'·***.

n= 59167123134 112256394 1 3194211min 5min 10min

Figure 7. Apgar scores.

J. Perinat. Med. 14 (1986)

90 Krieglsteiner et al., Bamberg obstetrical forceps

? rTable I. Fetal injuries.

divergent forceps (n = 483)

external hematomas 50peripheral paralysis 9clavicular fractures 7abrasions, pressure scores 6neonatal seizures 4neonatal death 1(multiple malformations)

10.41.91.41.20.80.2

A retrospective analysis of Apgar scores at 1,.5 and 10 minutes is presented in figure 7. Only10% of cases were associated with mild to mo-:derate degrees of fetal trauma, such as abra-sions, bruises and hematomas. No serious se-quelae were noted on follow up (table I).

4 Discussion

In Europe, the incidence of forceps delivery issignificantly lower that in the United States [4]and Australia [7], where one-fourth to one-third of all deliveries are assisted with obstetricforceps. However, there has in recent times beenan increase in the relative number of forcepsdeliveries as compared to vacuum extractionsperformed in Europe. This appears to havestemmed from the fact that currently, almostall labors are being electronically monitored,which in turn has resulted in a tendencytowards early intervention as soon as "suspi-cious" fetal heart rate tracings are detectedduring the second stage of labor. The result isthat more forceps deliveries are being per-formed for fetal distress than has been the casein the past [3, 4, 9, 16, 19, 23]. The fact thatmost German obstetricians still regard vacuumextraction as a safer procedure than forcepsdelivery [2, 6] has recently been contested [20].We similarly contend that not a single studyhas conclusively shown that vacuum extractionis safer than forceps delivery, and our data isin support of this view.

Figure 8. Bamberg divergent forceps: Lock with pivotin the left and cavity in the right 'handle.

Numerous studies support the contention thatdivergent forceps provide the safest option withregard to assisted outlet deliveries [1, 7, 11, 12,13]. Our own experience with the divergentBamberg obstetrical forceps reveals that not asingle severe fetal injury could be. attributedto the use of this instrument. Moreover, theexcellent five and ten minute Apgar scores fol-lowing delivery using the Bamberg forceps fur-ther support our view that it is a safe instru-^ent. The helmet effect provided by the blades"of these forceps limits the constant contactpressure and protects the fetal cranium frominjury during birth.

J. Perinat. Med. 14 (1986)

Krieglsteiner et al., Bamberg obstetrical forceps 91

Figure 9. Bamberg divergent forceps: Excentric in theright handle and friction groove in the left handle. Withthe blades applied, the excentric is pushed forward withnormal manual pressure (2 kp) until it blocks. Slippageof the blades is then effectively prevented.

The Bamberg forceps is also ideally suited formid- or low-mid forceps rotations and deliver-ies. The excentric slide on the instrument auto-matically locks in place. This reduces the likeli-hood of slippage and allows for a considerable

degree of traction to be safely applied. More-over, the moderate pelvic curve of the bladelimits fetal and maternal trauma during theprocess of forceps rotation.The Bamberg forceps, as with most other ob-stetrical instruments, can readily be appliedunder pudendal or saddle block. Applicationof the forceps is relatively simple. The bladesare locked, as illustrated in figures 8 and 9.Note that each handle is separately guided intoa position which allows the pivot and the cavityof the lock to cross each other. Simple thumbpressure enables the application mechanism tobe moved towards the blades. Following deliv-ery of the head, the application mechanism isshifted backwards by simply using the thumband the first finger of the (right) hand. Disen-gagement of the forceps is achieved by simplycompressing the handles.The distinct advantage of being able to applythe cup to the fetal head prior to full cervicaldilatation has earned for the vacuum extractora permanent place in the obstetric armamenta-rium. In most situations where instrument de-livery is required, however, the time requiredto obtain good application of the vacuum cupto the fetal head, limits its use. In such cases,provided the cervix has attained full dilatationand the fetal head has engaged the pelvis, theforceps offers a far better option. Moreover, itis possible to exert a much greater degree ofcontrol on the fetal fead using the forceps thanthe vacuum extractor.We submit, based upon the data presented,above, that when opting for forceps delivery,the Bamberg forceps is an ideal choice.

Summary

The design and use of a divergent obstetrical forceps,which was developed at the Staatliche Frauenklinik undHebammenschule in Bamberg by SIPLY and KRONE arepresented. The major advantage associated with the useof this instrument is that it permits the exertion of alimited constant application force (max 300 g) on thefetal head. Thus, compression injuries are effectivelyprevented and slippage of the forceps with resultanttrauma is precluded.

The Bamberg forceps was evaluated at the Frauenklinikund Poliklinik der Technischen Universität Münchenand at the Staatliche Frauenklinik und Hebammenschu-le Bamberg, Federal Republic of Germany. An evalu-ation of 483 cases where this forceps was used is pre-sented. No serious complications directly attributable tothe use of this instrument could be documented.

Keywords: Fetal outcome, forceps delivery.

J. Perinat. Med. 14 (1986)

92 Krieglsteiner et al., Bamberg obstetrical forceps

Zusammenfassung

Erfahrungen mit der „Bamberger Divergenzzange"Der Hauptvorteil der Konstruktion der „Bamberger Di-vergenzzange", die erstmals 1975 von SIPLI und KRONEvorgestellt wurde, liegt in einer begrenzten und konstan-ten Anlegekraft von maximal 300 g. Durch diese geringe,auf den kindlichen Kopf wirkende Kraft werden Kom-pressionsschäden sicher vermieden. Die konstante Anle-gekraft verhindert auf der anderen Seite ein Abrutschender Zangenlöffel und hieraus resultierende Abschürfun-gen.

Diese an der Bamberger Frauenklinik entwickelte Zangewurde kurz danach an der Frauenklinik und Poliklinikder Technischen Universität München ebenfalls einge-setzt. Es wird hier ein Erfahrungsbericht über insgesamt483 mit diesem Instrument durchgeführte vaginale Ent-bindungen vorgelegt.Es konnten keinerlei ernsthafte mit der Benutzung derZange in Zusammenhang stehende Komplikationen re-gistriert werden.

Schlüsselwörter: Forceps-Entbindung, kindliche Verletzungen.

Resume

Experiences avec la pince obstetrique de BambergLa pince divergente de Bamberg a ete presentee en 1975par SIPLI et KRONE. Son principal avantage resulte dela force d'une pression constante et reduite ä 300 gr. Dufait de la faible pression exercee sur la tete de l'enfant,il n'y a plus de risque de lesion de compression nid'eraflure causee par la branche de la pince qui s'echap-pe, cegi grace ä la construction speciale.

Cette pince con?ue et mise au point ä la maternite deBamberg a ete employee un peu plus tard ä la materniteet dans la policlinique de l'universite de Munich.II ressort du rapport paru a la suite de 483 accouche-ments pratiques ä l'aide de cette pince dans les deuxhöpitaux qu'aucune complication serieuse n'a pu etreattribuee a Pemploi de cet instrument.

Mots-cles: Accouchements par forceps, blessure de l'enfant.

References

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Received November 7, 1984, Revised June 19, 1985.Accepted July 9, 1985.

Prof. Dr. Peter KrieglstcinerFrauenklinikim Malteser Krankenhausvon Hompescb-Stra c lD-5300 Bonn l, Fed. Rep. Germany

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