Labour analgesia effects on foetal heart rate. A mini-review

doi:10.4236/ojog.2011.13020

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Open Jo urnal of Obst etrics and Gynecology, 2011, 1, 113-120 OJOG

doi:10.4236/ojog.2011.1302 0 Published Online September 2011 (http://www.SciRP.org/journal/ojog/).

Published Online September 2011 in SciRes. http://www.scirp.org/journal/OJOG

Labour analgesia effects on foetal heart rate. A mini-review

Nicole Mari a Anna Adela Engel1*, Marc Van de Velde2, Jan Gerrit Nijhuis3,

Marca Abraham Emmanu e l M arc us1

1Department of Anaesthesiology an d Pain Management, Maastricht University Medical Centre, Maastricht, Netherlands ;

2Department of Anaesthesiology, Katholieke Universiteit Leuven, University Hospitals Gasthuisberg, Leuven, Belgium;

3Department of Obstetr ics and Gynaecology, Maastricht University Medical C entre, Maastricht, Netherlands.

E-mai l : *

Hnico l e.engel@mumc.nlH

Received 24 June 2011; revised 1 September 2011; accepted 8 September 2011.

ABSTRACT

Foetal well-being during labour is of utmost impor-

tance. One of the ways to attempt to assess foetal well-

being is by recording foetal heart rate (F HR). Loss of

variability and deceleration patterns are known to be

associated with foetal distress. Decelerations and foe-

tal bradycardia have been described after any type of

effective labour analgesia. This review addresses the

questions if certain analgesic techniques and/or anal-

gesics lead to clinically relevant FHR changes, what is

their aetiology, and how we should manage these

FHR cha nges.

Keywords: Labour Analgesia, Foetal Heart Rate

Changes, Epidural Analgesia, Combined Spinal Epidural,

Intravenous Ana l ges i a

1. INTRODUCTION

Foetal well-being during labour is of utmost importance.

One of the ways to attempt to determine foetal well-

being is by recording foetal heart rate (FHR). Loss of beat

to beat varia bility and deceleration patter ns are known to

be associated with foetal distress. Gynaecological factors,

maternal and foetal factors, but also anaesthesiological

factors can influence these FHR tracings. Decelerations

and foetal bradycardia have been described after all types

of effective labour analgesia (epidural, spinal and Com-

bined Spinal Epidural (CSE), and intravenous opioids).

Early descriptive reports were conflicting. Lieberman

et al. [1] compared intramuscular meperidine to epidural

bupivacaine and only detected significant FHR changes

in parturients with hypotension or uterine hyper stimu-

lation. In contrast, Boehm et al. who studied epidural li-

docaine with or without epinephrine, found that 53%

(eight patients) revealed a reduction in FHR variability

without indication of the exact mechanism [2]. Later

studies failed to demonstrate these effects of epidural li-

docaine with or without epinephrine [3,4]. Unfortunately

these studies are difficult to interpret because of a lack o f

randomization, small sample sizes and inconsistent dose

schemes.

This mini-review provides a comprehensive intrapar-

tum data on FHR effects of a multitude of analgesic

regimens which makes it different from previously pub-

lished repor ts. It attempts to address the questions if cer-

tain techniques and/or analgesics lead to clinically rele-

vant FHR changes, such as loss of baseline variability,

late decelerations or severe variable deceleration patterns,

what is their aetiolog y, and how we should manage these

FHR changes.

2. METHODS

A MEDLINE-based search of all the literature on FHR

changes due to labour analgesia was performed. The

following keywords were used: labour analgesia; foetal

heart rate changes; epidural analgesia; combined spinal

epidural; intravenous analgesia; and acupuncture. No

date or language restriction was used. The reference lists

of retrieved articles were searched by hand. Articles that

did not report on the FHR outcomes were excluded. In

this mi ni -re vi ew, no meta-analysis was performed.

3. EPIDURAL ANALGESIA

Continuous epidural analgesia is commonly used for

analgesic treatment during labour and delivery as it ef-

fectively relieves labour pain. In reviewing the literature

many r epo rts a bo ut change s in F HR in la bour ing p ati ents

with epidural analgesia were found. Historically abnor-

mal FHR patterns have been found to be most common

when epidural analgesia was accompanied by maternal

hypotension [5], or supine position of the parturient [6].

Stavrou et al. [7] conducted a retrospective study trying

to find a relationship betwee n prolonged foetal bradycar-

dia and epidural analgesia during labour. They concluded

that administration of epidural analgesia is associated

with episodes of prolonged foetal bradycardia, as they

found that prolonged bradycardia (defined as a fall in

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114

FHR at least 50/ min belo w baseline and lasting at least 3

minutes) developed in 40 of 366 (11%) of parturients

with epidural analgesia. These FHR changes were not

accompanied by maternal hypotension (hypotension oc-

curred only in one patient) and FHR returned to normal

in all patients. Most episodes of foetal bradycardia oc-

curred within 20 minutes of local anaesthetic administra-

tion. Neonatal outcome was not influenced.

Another retrospective comparative study between pa-

tients with and without epidural analgesia showed sig-

nificant differences in variable decelerations and late

decelerations in FHR tracing before and after institution

of epidural analgesia. An increase in variable and late

decelerations was observed after injection of the main

dose of epidural analgesic. Twenty four percent of car-

diotocograph tracings (CTGs) showed variable decelera-

tions before, and 35% showed decelerations after epidu-

ral analgesia [8]. Neonatal outcome was similar in both

groups. As mentioned by the authors, groups were per-

haps not comparable as the epidural group contained

more primipara, more frequent induction of labour, first

and second stages of labour were longer (possibly an

effect of the epidural) and the duration of ruptured mem-

branes was longer. The authors suggest that these FHR

changes might be attributed to direct effects of the local

anaesthetic on the foetus. However, Phillips et al. [9]

studied PR interval, RR interval, T/QRS ratio and the

PR-RR correlation coefficient using foetal electrocardio-

gram waveform analysis during epidural analgesia with

bupivacaine and found a significant increase in FHR and

a fall in T /QRS ratio. Their c onclusion was that epidural

bupivacaine does not alter foetal myocardial conduction

as measured by PR interval nor does it induce ischemic

cardiac changes as assessed by the T/QRS ratio. Thus the

FHR c han ges o ccur rin g dur in g epi dura l ana lge sia a re no t

caused by a direct depression of the foetus by bupiva-

caine.

Durin g the last fifteen years, the ad dition of opioid s to

local anaesthetics for epidural analgesia has become in-

creasingly popular because it offers the advantage of re-

duction of the local anaesthetic dose with faster onset of

analgesia and resulting in the same amount of analgesia

than with local anaesthetics alone [10]. Dose reduction of

local anaesthetic results in less motor blockade which

can allow for ambulation during labour, and may reduce

the risk of dystocia and caesarean section. Purported ad-

vantages of ambulation consist of increased intensity of

contractions, less pain, shorter first stage of labour, and

patient’s appreciation of mobility [10]. Studies on the

effect of ambulation on labour have not shown any det-

rimental effects [11,12]. Hoffman et al. studied the ef-

fects of continuous opioid epidural on FHR but without

letting the parturient ambulate. They discovered that

there are no significant differences between opioid and

non-opioid epidurals with respect to maternal blood pre-

ssure, FHR tracings, and neonatal outcome [10]. These

results were confirmed by a double blind, randomized,

controlled study, by Amant and co-workers [13], 109

parturients who received bupivacaine 0.25% with addi-

tion of either b uto r phanol, fentanyl, sufentanil or saline.

Prophylactic administration of ephedrine to prevent

maternal hypotension and FHR changes has also been

studied. In a prospective randomised trial by Kreiser et al.

[14], 145 parturients were scheduled to either receive

ephedrine 10 mg i.v. bolus followed by a continuous in-

fusion of 20 mg i.v. during one hour at time of initiation

of the epidural analgesia, or no prophylactic ephedrine.

FHR monitoring was used during the first 40 minutes

after anaesthetic administration. The analgesic dose in

this study was relatively high (3 ml of 2% lidocaine for

initiation, follo wed by 8 ml of b upivacaine 0.25%). FHR

changes occurred in 2 out of 72 treated patients and in 11

of 73 controls. In another randomised trial Cleary-

Goldman et al. [15] studied the effects of intramuscular

ephedrine 25 mg versus placebo in 100 parturients

treated with CSE analgesia. Significantly fewer women

in the ephedrine group developed hypotension. There

were no differences in FHR decelerations in the hour

following initiation of analgesia. There was however an

increased risk for development of foetal tachycardia in

the group treated with ephedrine.

Prophylactic use of ephedrine does not seem indicated

for low dose labour analgesia (“walking epidural”). Con-

tinuous infusion of ephedrine is not recommended be-

cause it has been associated with foetal acidosis in cases

of elective caesarean section [16].

Studies conducted on epidural opioids alone gave dif-

ferent results. Capogna and co-wor kers [17] conducted a

prospective, sequential allocation study to determine the

minimum effective concentration of epidural sufentanil

in spontaneous and induced labours. A transient reduc-

tion (mean 30 minutes) of FHR long-term variabilit y was

found in 53% of spontaneous and in 63% of induced

labours within 10 minutes of administration of epidural

sufentanil 18 µg - 32 µg. All FHR changes resolved

sponta- neously. According to the authors one explana-

tion for these FHR changes could be a direct depressant

effect of opioids as was determined for morphine and

pethidine by Petrie et al. [18]. Although epidural sufen-

tanil i n therapeutic doses (10 µg - 30 µg of sufentanil in

the epidural mixture) is detectable in the maternal circu-

lation [19], it seems unlikely that these low doses used

for epidural analgesia have any important systemic im-

pact [19,20].

4. INTRATHECAL OPIOIDS, COMBINED

SPINAL-EPIDURAL ANALGESIA (CSE)

Combined spinal epidural (CSE) analgesia has become

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115

increasingly popular as a met hod for labour pain relief as

it has a very rapid onset of analgesia. FH R cha nges have

been observed with intrathecal analgesia using small

doses of local anaesthetic or opioids, alone or in combi-

nation.

At first, the increase in variable decelerations noted in

a prospective, double blind, comparative study among

intrathecal fe ntanyl, meperidine, a nd sufentanil b y Honet

et al. [21], was deemed to be of little clinical signifi-

cance.

Two years later however Clarke and co-workers re-

ported several episodes of uterine hyperactivity in some

cases associated with foetal bradycardia following in-

trathecal administration of 50 µg of fentanyl [22]. A de-

crease in foetal heart rate to 80 - 100 beats/min was

noted in 7 of 30 consecutive patients. In two other pa-

tients the foetal heart rate decreased below 70 beats/min.

These FHR alterations occurred without maternal hy-

potension and all appeared within 30 minutes after in-

trathecal injection of fentanyl. Five out of the nine pa-

tients with foetal bradycardia also exhibited uterine hy-

peractivity detected by external or internal pressure

transducer. This uterine hyperactivity following intrathe-

cal fentanyl has since been confirmed on several occa-

sions [23-25].

Yet there is no agreement about the association be-

tween uterine hyperactivity and non-reassuring FHR

patterns caused by spinal opioids.

Gambling et al. [26] conducted a large randomized

trial comparing i.v. meperidine with CSE (with intra-

thecal sufentanil 10 µg) and reported FHR decelerations

in 18% in the CSE group compared to 21% in the me-

peridine group. However bradycardia necessitated cae-

sarean section in 8 out of 400 women with CSE com-

pared to 0 out of 352 mothers in the meperidine group.

Cautious interpretation of these results is necessary. The

mothers who received i.v. meperidine had intermit ten t

FHR monitoring, while the mothers with CSE had con-

tinuous monitoring of FHR for at least 30 minutes after

intrathecal injection. Furthermore these results are not

corroborated by later studies. Eberle and co-workers con-

cluded that the risk of prolonged foetal deceleration after

epidural bupivacaine or intrathecal sufentanil labour an-

algesia is unrelated to analgesic technique [27]. Fogel et

al. also failed to demonstrate significant differences in

the incidence of new prolonged decelerations or late de-

celerations between epidural and CSE analgesia [28].

In a prospective study by Nielsen et al. [29] a compa-

rison was made between the incidence of intrapartum

FHR abnormalities and obstetric outcome after epidural

bupivacaine and intrathecal sufentanil. The authors con-

clude that in b oth gro ups the re was a signi ficant ly highe r

risk of caesarean section in patients who’s previously

normal FHR tracing became abnormal after analgesia

when compared to patients without a new onset FHR

abnormality. These new onset FHR abnormalities might

be due to a pre-existing problem. However intrathecal

sufentanil was not associated with a higher incidence of

new onset FH R abnormalities.

In a review article by Norris [30], the author concludes

that there is insufficient evidence to accept that spinal

opioids are responsible for a more frequent occurrence of

new FHR abnormalities when compared to conventional

epidural analgesia.

On the other hand there are reports by Van de Velde et

al. [31] who performed a retrospective analysis on the

FHR effects by sufentanil 7.5 µg intrathecally, compared

to conventional epidural and compared to sufentanil 1.5

µg intrathecally during CSE. They conclude that sufen-

tanil in a dose of 7.5 µg has the potential to result in

more non-reassuring foetal heart rate tracings compared

to both other groups.

A systematic review of intrathecal opioids compared

with other neurax ial tech niques co ncluded that despite a n

increased risk for foetal bradycardia: odds ratio 1.8 (95%

confidence interval 1.0 to 3.1) the risk for subsequent

caesarean section is not increased [32].

More recently Abrao and co-workers [33] performed a

randomized controlled trial on 77 parturients to estimate

the effects of combined spinal-epidural and traditional

epidural analgesia on uterine basal tone and its associa-

tion with the occurrence of FHR abnormalities. This is

the only study in wh ic h i ntr a u te r ine p r es s ure was d ir ec tl y

prospectively measured. Patients in the CSE group re-

ceived bupivacaine 2.5 mg plus sufe ntanil 2.5 µg. In the

epidural group patients received bupivacaine 12.5 mg of

a 0.125% solution plus of sufentanil 10 µg. The type of

analgesia was shown to be the only independent predi-

ctor of uterine hyper tonus. The authors concluded that

CSE is associated with a significantly greater incidence

of FHR abnormalities related to uterine hyper tonus

compared with epidural a nalge sia, but thi s did not le ad to

a higher incidence in caesarean section.

In comment of this study by Abrao and co-workers

[33], Landau et al. [34] state that the two analgesic regi-

mens used in this study may not be equipotent as shown

by the higher pain scores in the epidural group compared

to the CSE group. Also the slower onset of pain relief

with epidural analgesia makes it likely that FHR and

intrauterine tone changes only become apparent after the

study period of fifteen minutes. This may have exagge-

rated the differences reported between study groups.

Landau et al. also comment on the late initiation of la-

bour analges ia in this study (6 cm cervical dilation) as it

is known that neuraxial analgesia in this stage of labour

is more commonly associated with FHR abnormalities

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116

than when it is initiated earlier [35]. FHR changes and

abnormalities may also be influenced by parity and use

of oxytocin which are not adequately detailed in the

study by Ab rao and co-workers [33].

The 2.5 µg of sufent anil fo r int rathecal ana lgesia in the

study by Abrao et al. [33] is also substantially higher

than the dose in group 2 used earlier by Van de Velde and

co-workers [36] in a double-blind, double placebo-con-

trolled trial comparing two forms of CSE with epidural

analgesia. In this study a comparison was made between

epidural bupivacaine 12.5 mg plus 7.5 µg sufentanil 7.5

µg wit h epinep hrine 1 2.5 µg, intrathecal bupivacaine 2.5

mg pl us sufe ntani l 1.5 µg with ep inephri ne 2.5 µg, and a

third group with sufentanil 7.5 µg intrathecally. Twenty

four % of the patients in the high dose intrathecal sufen-

tanil group developed FHR abnormalities compared to

11% in the lower dose intrathecal sufentanil and 12% in

the epidural group. Uterine hyperactivity occurred in

12% of the high dose intrathecal sufentanil group com-

pared to 2% in the other two groups, but tocolytic the-

rapy was rarely needed.

The data from these recent studies warrant caution in

the use of higher doses of opioids intrathecally because

of the risk of uterine hyperactivity and FHR abnormali-

ties, without however increasing the risk for caesarean

delivery or detrimental effects o n neonatal outcome.

One study has been done with addition of intrathecal

tramadol to CSE analgesia. Since there is no human

toxicolog y a vailable for intrathecal ad ministratio n of tra-

madol, such studies ethically need to be conducted under

specific approval from the appropriate government

source. Frikha et al. [37] conducted a randomized pro-

spective study comparing bupivacaine 2.5 mg with su-

fentanil 2.5 µg to bupivacaine 2.5 mg with tramadol 25

mg intrathecally. The purpose of this study was to com-

pare tramadol and sufentanil in terms of duration of an-

algesia and frequency of adverse maternal or foetal ef-

fects. FHR tracings of all patients were done from one

hour before analgesia to one hour after initiation of an-

algesia. All FHR tracings were normal before initiation

of CSE. FHR tracings after initiation of analgesia were

comparable between the sufentanil and tramadol groups.

No patient in this study had a non-reassuring FHR trac-

ing. The group of patients receiving tramadol had sig-

nific antl y longer-la s ting a nalgesia. Five of the 2 0 patients

receiving tramadol also presented with vomiting, which

is the only major side effect noted with tramadol in this

study.

5. INTRAVENOUS ANALGESIA

Neuraxial analgesia has become the ‘gold standard’ for

obstetric analgesia. Unfortunate ly it ca nnot b e us ed in a ll

parturients, e.g. tendency towards bleeding, spinal de-

formities, spinal instrumentation, and patient refusal. In

these cases alternatives need to be explored for pain re-

lief.

Pethidine is most widely used for labour pain analge-

sia because of familiarity and low cost, although the ef-

ficacy of pethidine has been questioned. Pethidine has

been shown to significantly affect FHR variability, ac-

celerations and decelerations, during labour [38]. No

significant differences in FHR changes were shown be-

tween pethidine and epidural analgesia [39].

Long et al. [40] studied tramadol patient controlled

analgesia (PCA) compared to CSE with patient con-

trolled epidural analgesia and a control group without

analgesia for comparison of risks and benefits. CSE an-

algesia resulted in faster onset and better pain relief than

PCA with tramadol. There were no differences in FHR

and uterine contractions among the three groups. The

authors concluded that PCA with tramadol is a useful

alternative to CSE but may be accompanied by newborn

depression as Apgar scores were lower in the tramadol

group.

The reported analgesic properties of systemic opioids

in labour are poor, but PCIA has proven to have phy-

chological benefits, and when used with remifentanil

allows for very rapid d rug titration. [41 ] .

The reported use of remifentanil for labour pain anal-

gesia in the literature have described various methods of

administration with inconsistent results. Mostly remifen-

tanil is used i n PCA setting, with or without a basal in fu-

sion. In one study by D’Onofrio et al. 205 parturients

received a continuous infusion of remifentanil without

PCA to examine analgesic effect, patient satisfactio n and

maternal and neonatal safety of this method of admini-

stration [42]. Infusion rates varied between 0.025 µg/kg/min

– 0.15 µg/kg/min. Oxygen saturation remained above

95% at all times without oxygen supplementation. No

changes in FHR variability score were detected, and dur-

ing the 30 minute study period moderate analgesia was

observed with good patient satisfaction.

PCA wit h remifenta nil compar ed to ep idural levobupi-

vacaine with fentanyl was studied in a randomized con-

trolled, double-blinded trial [43]. This study concluded

that analgesia with epidural is superior, sedation was

more common in the remifentanil group and the number

of parturients with nausea was larger in the remifentanil

group. The groups were not different in terms of abnor-

malities in FHR tracings.

However, d iscussion remains about safety and efficacy

of PCA with remifentanil. Labour pain analgesia by re-

mifentanil is modest and the risk for maternal sedation

and oxygen desaturation even in the presence of oxygen

supplementation remains [43]. On the other hand, PCA

with pethidine has an even higher risk for oxygen de-

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117

saturation [44]. Less FHR changes have been reported

using PCA remifentanil as compared to PCA pethidine

[44]. Hill [45] performed a retrospective analysis of 5410

consecutive deliveries. 28% PCA remifentanil, 22% epi-

dural analgesia and 33% intramuscular pethidine analge-

sia with similar neonatal outcomes in all three groups.

Van de Velde [46] on the other hand argues that remifen-

tanil crosses the placenta readily and causes foetal im-

mobil it y (duri ng i n utero surg ery) and los s of foetal heart

rate variability. He concludes that routine use of PCA

with remifentanil cannot be promoted before extensive

studies have been done to evaluate the effects of remi-

fentanil on foetus and neonate [46].

6. ACUPUNCTURE AND ACUPRESSURE

As many women like to avoid invasive and/or pharma-

cological methods of pain relief during labour sometimes

acupuncture is recommended. The evidence on acupunc-

ture remains unclear. Acupuncture seems to have no de-

trimental effects on FHR. In one study there seemded to

be a reduction of foetal baseline heart rate and more ac-

celerations were observed during acupuncture [47]. In

another study by the same group the foetal heart rate was

reduced only by acupuncture and moxibustion combined

[48].

In a study of moxibustion alone cardiotocograms were

made 10 minutes before, 20 minutes during and 10 mi-

nutes after each session and there was no alteration or

abnormality detected [49]. Cochrane review concludes

that acupuncture and acupressure may have a role in re-

ducti on o f pain d uring l abour, but t here i s a nee d for fur-

ther research [50].

7. AETIOLOGY OF FHR CHANGES

Several hypotheses have been proposed in the literature

as to the origin of the FHR changes and foetal bradycar-

dia observed with effective labour analgesia. In 1971 a

comparison was made between FHR changes and pH of

foetal blood. Decelerations and a loss of beat-to-beat va-

riability appeared to be associated with foetal acidosis

and therefore foetal asphyxia [51]. Huovinen et al. [6]

found a higher incidence of FHR changes in the supine

position when co mpared to latera l position. P reston et al.

[52] reported a 15% incidence of severe FHR changes in

parturients in supine wedged position compared to the

left lateral position. These changes were attributed to

occult aortocaval compression. This was contradicted by

Eberle and co-workers [27] who found that prolonged

decelera tions were not related to maternal p osition, but 8

of the 11 episodes they noted were associated with uter-

ine hyper tonus or tetany.

Segal and co-workers [53] used gravid rat uteri to

show that epinephrine and norepinephrine have effects

on uterine tone. Epinephrine caused dose dependent re-

ductions in uterine activity. Norepinephrine alone in-

creased uterine activity. Maternal epinephrine levels de-

cline after effective labour analgesia but norepinephrine

level s remain relativel y unchanged.

Four years earlier Clarke et al. [22] proposed the fol-

lowing mechanism for foetal bradycardia following an-

algesia: Pain relief leads to a decrease in output of the

sympathetic nervous system (effective labour analgesia

leads to a decrease in circulating epinephrine levels).

Epinephrine is a tocolytic. Decreasing epinephrine will

cause an increase in uterine tone which will decrease

placental blood flow. If placental blood flow is decreased

enough there will be a subsequent foetal bradycardia.

Cascio et al. [54] also noted a reduction in maternal

plasma epinephrine concentrations following both epi-

dural and spinal analgesia, while plasma norepinephrine

stayed the same or even increased slightly. They also ob-

served faster decrease in plasma epinephrine in partu-

rients who received spinal opioids when compared to

epidural bupivacaine, which offers a possible explanation

for the fast er onse t of FHR c hanges i n CSE co mpared to

epidural analgesia. The mechanism by which higher

doses (fentanyl 25 µg - 50 µg [23,25], sufentanil 7.5 µg

[31]) of intrathecal opioids more often lead to FHR

changes remains unclear.

8. CLINICAL MANAGEMENT OF

FOETAL HEART RATE

ABNORMALITIES ASSOCIA TED

WITH LABOUR ANALGESIA

There are few data to determine the impact of epidural

analgesia on pre-existing FHR abnormalities. Most stu-

dies exclude these patients. Fogel et al. [28] included 30

patients with FHR abnormalities pre-analgesia. In most

cases these FHR abnormalities persisted.

Regardless of the aetiology of the FHR abnormalities,

the key is managing these changes correctly when they

occur. In all of the studies reviewed the incidence of FHR

changes is relatively high, 3 % - 20% [25,27,28], but this

does not lead to higher incidence of caesarean section.

Caesarean section is probably avoided by adequate tr-

eatment of these FHR changes. The use of uterine dis-

placement and changing maternal position to relieve any

aortocaval compression. Correcting any hypotension

using phenylephrine in 50 µg - 100 µg increments (or

ephedrine in 5 mg - 10 mg increments) and intravenous

fluids. Giving extra oxygen. Stopping administration of

oxytocin because of the association of FHR change s with

uterine hyper stimulation. Administration of a tocolytic

agent should be considered [20,55]. Uterine hyper tonus

may be reversed by intravenous nitro-glycerine 60 µg -

90 µg, to be repeated when hyper tonus remains [56].

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118

Nitro- glycerine reduces uterine contractility by raising

intracellular cyclic Guanosine Monophosphate (cGMP)

whic h in turn inactivates myosin light-chain kinase. One

can also relax the uterus by terbutaline 0.25 mg i.v. but

this causes a much longer relaxation of the uterus com-

bined with maternal tachycardia because of action on

beta-2-receptors. Activation of beta-2-receptors leads to

inhibition of myosin light-chain kinase resulting in re-

laxation of the uterine muscle. Effective treatment of

uterine hyper stimulation allows for normalisation of

uterine and placental perfusion, and thus for normalisa-

tion of FHR tracings.

9. CONCLUSIO NS

From the available literature we conclude that induction

of labour analgesia can result in FHR cha n ges and se ve r e

foetal bradycardia. Most likely this is due to uterine hy-

per tonus secondary to an acute drop in plasma levels of

epinephrine. As higher doses of intrathecal opioids seem

to be related to more frequent non-reassuring FHR trac-

ings, administration of high doses of intrathecal opioids

(≥7.5 mcg sufentanil) is best avoided.

Mechanisms of action for this high dose opioid effect

are unknown. Many other factors may be related to FHR

changes after labour analgesia. Further research on the

different factors influencing FHR changes during labour

analgesia is needed, as well as research directed at clari-

fying the specific mechanism of action of “high” doses

of intrathecal opioids on FHR. Only then can prevention

of FHR changes after labour analgesia be achieved.

When F HR c hange s o ccur it is of vital importance that

the parturient is treated immediately. FHR changes are

not an uncommon effect of effective labour analgesia but

should not affect the outcome of the delivery or neonatal

health.

10. COMPETING INTERESTS/FUNDING

The authors declare that they have no competing interests, and that

there was no funding for this review art ic le.

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