26 Operative Interventions for Fetal Compromise. Handbook CTG

 26

Operative Interventions for Fetal

Compromise

◈

Mary Catherine Tolcher and Kyle D. Traynor

Handbook of CTG Interpretation: From Patterns to Physiology, ed. Edwin Chandraharan.

Published by Cambridge University Press. © Cambridge University Press 2017.

Key Facts

Operative Vaginal Delivery

The use of vacuum or forceps can result in apparent deterioration in fetal status

(usually prolonged fetal deceleration) when traction is applied.

Failed operative vaginal delivery is associated with increased neonatal

morbidity and necessitates emergent caesarean delivery.

Operative vaginal delivery with either vacuum or forceps can serve as a useful

alternative to caesarean delivery when a delivery is required during the second

stage of labour.

Common indications for operative intervention include suspected fetal

compromise, prolonged second stage of labour, fetal malposition, maternal

paraplegia, known contraindication to valsalva (pushing) including

cardiovascular or neurological disease, or maternal exhaustion.1Anticipated CTG Changes Following

Instrument Application

Prerequisites must be met prior to attempts at operative vaginal delivery.

Clinical criteria outlined in National Institute for Health and Care Excellence

(NICE) guidelines include vertex presentation, full dilation, ruptured

membranes, clinically adequate pelvis and knowledge of fetal position. Other

important elements include informed consent, adequate skills on the part of the

operator and availability of staff and facilities for caesarean delivery if

required.2

Additionally, the preparation for complications including shoulder dystocia and

postpartum haemorrhage should be undertaken. Personnel trained in neonatal

resuscitation should be present for delivery.

Following the application of a vacuum with suction to pressures up to 600 mm

Hg,3 fetal heart rate (FHR) decelerations can be expected. This phenomenon is

explained by known mechanisms of FHR regulation including the interaction of

the sympathetic and parasympathetic nervous systems. When suction is applied

to the fetal head, the increased intracranial pressure results in increased systemic

vascular resistance which stimulates baroreceptors in the fetal heart to activate

the vagus nerve and slow the FHR.4,5 In addition, there may be direct stimulation

of parasympathetic nerve endings on the fetal scalp resulting in a prolonged

deceleration.

Anticipated effects following forceps application are similar to those seen with

vacuum-assisted delivery as the mechanism of increased intracranial pressure is

similar (Figure 26.1). Kelly evaluated 62 operative vaginal deliveries including

44 forceps and 18 vacuum deliveries by measuring the intensity of traction in

pounds and the effects on FHR during application, traction and posttraction.6

Fetal decelerations were commonly elicited when traction was applied to either

instrument (84 per cent).Figure 26.1 Acute drop in FHR following the removal of fetal scalp electrode and

application of the vacuum cup (arrow). This precipitous fall in FHR is not secondary to

hypoxia but due to an intense parasympathetic stimulation.

Failed Operative Vaginal Delivery

Scientific evidence suggests that the reflex cardiac deceleration is triggered

when intracranial pressure exceeds 40 mm Hg.

While the goal of vacuum or forceps is to achieve a vaginal delivery, not all

attempts are successful. Attempted vacuum-assisted vaginal delivery is more

likely to result in a failed trial of operative vaginal delivery as compared to

forceps (7.5 per cent versus 1.4 per cent in one study and 15.7 per cent versus

0.4 per cent in another).7,8

Risk factors for failed trial include maternal body mass index over 30 kg/m2,

estimated fetal weight >4,000 g, occipito-posterior position and midcavity

delivery or when more than one-fifth of the fetal head is palpable per abdomen.2

Other potential contributors to a failed attempt include fetal caput succedaneum,

hair, asynclitism/malposition and improper instrument placement.3

According to current guidelines, operative vaginal delivery should be

abandoned when there is no evidence of progressive descent with the

application of moderate traction during each uterine contraction. Alternatively,

further attempts at operative vaginal delivery should be abandoned if delivery is

not imminent following three contractions in which traction was applied using aDecision to Delivery Interval

Risks of intracranial haemorrhage, facial nerve injury, convulsions, central nervous

system depression and mechanical ventilation are significantly higher in infants

delivered by caesarean delivery following a failed attempt at operative vaginal delivery

than in those delivered spontaneously.10

correctly placed instrument by an experienced operator.2 No more than three

vacuum pop-offs has also been suggested.3

When attempts at operative vaginal delivery have failed, the subsequent

caesarean delivery can be complicated by a deeply impacted fetal head. Forces

exerted to deliver the fetus may compound effects on increased intracranial

pressures. Further, uterine contractions or fetal malposition can make delivery

difficult.

Uterine relaxants and disengagement techniques including the push (vaginal hand

from below) and pull (reverse breech extraction) methods have been described.9

Care must be taken to prevent hysterotomy extensions resulting in excessive

blood loss and fetal injury. Reported fetal injuries associated with difficult fetal

extraction at the time of caesarean include long bone and skull fractures.9

Delivery by caesarean may be essential if the likelihood of a failed operative

vaginal delivery is deemed high based on clinical circumstances and experience

of the operator.

Because of known increased neonatal morbidity associated with failed trial of

operative vaginal delivery, expeditious delivery by caesarean is essential,

especially if there are features suggestive of fetal decompensation on the CTG.

According to NICE guidelines, caesarean delivery following a failed trial of

operative vaginal delivery is considered category 1 (emergent) and should occur

as soon as possible, generally within 30 minutes as an audit standard.2

According to one study of operative vaginal deliveries in Scotland, of 998

operative vaginal deliveries attempted, 965 were successful (96.7 per cent).8 OfPitfalls

Consequences of Mismanagement

the 965 successful operative vaginal deliveries, 798 were performed in the

labour room (82.7 per cent) with a decision to delivery interval of 14.5 minutes

(SD 9.5), while 167 were performed in the operating room (17.3 per cent) with

a decision to delivery interval of 30.3 minutes (SD 14.1).

Misapplication of instrument due to incorrect diagnosis of fetal position.

Choice of wrong instrument (use of a nonrotational forceps for a malrotated fetal

head).

Prolonged attempts at failed trial of operative vaginal delivery (e.g. greater than

three pop-offs with vacuum or use of multiple instruments).

Abandonment of trial of operative vaginal delivery due to fetal decelerations

with traction.

Failure to effect delivery by caesarean expeditiously in cases of failed trial of

operative vaginal delivery if there are features suggestive of fetal

decompensation on the CTG trace.

Inadequate management of an impacted fetal head at the time of caesarean

delivery following a failed trial of operative vaginal delivery leading to fetal

trauma and increased intracranial pressure resulting in a reduction in carotid

circulation.

Failed instrumental delivery due to the use of excessive/inappropriate force after

observing a deceleration secondary to expected parasympathetic stimulation

after the application of forceps or vacuum cup.

Fetal complications may occur secondary to an unnecessary operative vaginal

delivery due to overreaction to patterns observed on the CTG trace withoutReferences

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2009;2(1):5–17.

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vaginal delivery. London: RCOG; 2011.

3. Kiwi Complete Vacuum Delivery System with Palm Pump. Clinical Innovations.

Instructions for use. www.clinicalinnovations.com/site_files/files/Kiwi%20IFU.pdf. Accessed

26 March 2015.

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myocardium (unstable baseline FHR or a prolonged deceleration with loss of

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9. Berhan Y, Berhan A. A meta-analysis of reverse breech extraction to deliver a deeply

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acted head during cesarean delivery. Int J Gynaecol Obstet 2014;124(2):99–105.

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nulliparous women on neonatal intracranial injury. N Engl J Med 1999;341(23):1709–14.