anesthetic effects on newborn and parturient

7/27/2019 Anesthetic Effects on Newborn and Parturient

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Effects on the fetus and newborn of maternalanalgesia and anesthesia: a review[Les effets de l'analgbsie e t de l'anesthesie de la mere sur le fwtus e t le nouveau-nb:

- . .the fetuslnewbom, if any, of maternally administered medimticduring labour and delivery, o r d uring surgery for non-obstetric in(cations. Supposition n this regard is limited in part by methodolo;previously used t o study the transplacental passage of various drugThis wo rk needs t o be repeated using a human model. Routkmaternal supplemental oxygen adm inistration is being questionedlight of research showing th at free radical generation and oxidate2 ~~ ~~- .. . , ~ ~> .... . ...~

j'nncmal finflmes: NO one test clearly separates the effects oni nii -BYF.i ein/e

mess are impticarea as me unuciiying meuidnisms in severalneonatal conditions. Maternal hypotension is associated withneonatal acidemia and base excess correlates with neonatal out-come. Comm on postp artum analgesics transfer minimally intobreast milk. Maternal o r fetal surgery con dunecessitates modifica tion of b oth anesthetic

The key t o resuscitation of th e fetus is resintra-uterine maneuvers, including p

tion, aim to reverse treatable causes ofoxygenation, and cor rec t fetal acidosis.

Conclusions: The well-being o f the infant 1s a major crirenon lorevaluating the anesthetic management of pregnant wom en. Many

t-ionstwtar~onspftnctpales~ u c u n est nesepore ciarement iesefits surle fetudnouveau-n6, si effet ily a, des medicaments admi-nist& 6 a mere pendant Ie travail et /'accouchement ou pendant uneintervention chimrgicale non obst&icate. Les hypotheses possiblesdans ce contexte sont fimitbes en partie par la mSthodofgeant6rieurement utilish pour btudier le passage transplacentoire de@rents medicaments. On doit +ter ces essais sur un modelehumain. Ladministration courante d'un SLmere est remise en question par la rechgMration de radicaux fibres et te stressm4canismes sous-jacents de certaines p o u i u i ~ > ~ W V C U U - ~ KLhycotension matemelle est m a & ed I'acid4mie &onatale e t I'ex-lotion avec revolution n6onotale. Les anal-

fement en postpartum pase nt tr^s peu danstervention chirurgicale matemelle w fcetalelbc&te une modification des approdies'ale. La cl6 de to danimo tion du fetus est la: es manceums intro-ut6rines. y compris to , , lliu,.~~,,nt pour bu t de renverser 1 s causes deJa-

phyxie fcewle, de restaurer I'oxyg&nation fcetote e t de comger I'aci-

cted during pregnancy c^s ba3que est en cornand surgical approach- gkiques utilisk habitue/,.usctationofthe moth- !e hi t matemel. Une iner imor tem Cesarean pendant la grossesse Ifetal asphyxia, restore anesthesique et chimrgic

&animation de la m6re. . . ~~ ,


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Littleford: EFFECTS OF MATERNAL ANESTHESIAETWEEN the mid 1800's and the 1950's,descriptive reports of the presumed effectof maternally administered medication onthe fetus and newborn appeared sporadical-

ly in the literature. Two developments eventuallyencouraged physicians to acknowledge the potentialproblems associated with placental transmission ofanesthetic drugs:'

1.Recognition that morphine, a popular ingredi-.~ . . . . . . .

In 1952, the pioneering work of anesthesiologistVirginia Apgar converted an intangible phenomenon,the clinical condition of a newly born baby, into a for-mally defined measurement? Thereafter, the well-being of the infant became a major criterion forevaluation of the obstetric and anesthetic manage-ment of pregnant women.

The purpose of this article is to review the effects ofmaternal anesthesia and analgesia on the fetus and. . . "


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CANADIAN JOURNAL OF ANESTHESIA

PART I: f : ample is kept a t room temperature for5 min.'

Evaluation of fetal and neonatal well-being 1 h e supply of oxygen and th e removal of volatile. . . . ..Se s by theveral meth ods o f evaluation have been used by anes-.esiologists in a n attem pt to separate ou t thetal/neonatal effects of their interventions from con-imitant medical and nursing mana gement, a nd frome influence of pre-existing maternal conditions.

The Apaar scoreT h e Apgar score rates each o f five physical signs tradi-tionally used by anesthesiologists to monitor apatient's co ndition: heart rate, respiratory effort, mus-cle tone, reflex irritability, and colou r, at on e, five, andten m inutes after birth. T he results depict the status ofthe newborn and, when scores are compared, theeffectiveness of resuscitation. Th e nume rical compos-ite is partly dependent on the physiologic maturity ofthe infant. Likewise, neonatal conditions such as brad-yarrhythmias affect heart rate, while infection, neuro-muscular conditions, and certain medications affectrespiratory effort and tone.4 g a r demonstrated that her score was sufficientlysensitive to detect differences amo ng new borns whosemothers had received spinal vs general anesthesia fo rCesarean ~ e c t i o n .~t is used to assess the condition ofthe infant at birth,3 it is no t specific for th e effects ofanesthesia on the newborn.Umbilical writ bloodijas analysisCord blood gas analysis is the gold standard for assess-ing fetal acid-base status and uteroplacental functionat birth. Umbilical artery pH , base excess, and pCO,reflect fetal and imm ediate neonatal con dition where-as umbilical vein values reflect matern al acid -base sta-tus and placental function."Norm al" values vary depending o n the definitionof normality and the influence of factors (for example,altitude, parity, breech vaginal delivery, and durationof labour) on the population studied? Helwig et a13retrospectively examined the records of 1 5,00 0 vigor-ous newborns with a five-minute Apgar sco re of > 7.Median umbilical artery values, with the 2.5th per-centile value in parentheses, were p H 7.26 (7.1 0) andbase excess -4 mmo1.L"' (-1 1 mm ol-L-I). T h e means 2 standard deviations were similar. The generallyaccepted lower limit of normal umbilical artery pHextends to 7.10 and base excess to -12 m rn ~ l- L " ? ~ ~Values for p H , pCO ,, and base excess also vary withdifferences in sam pling technique. Pre-analytical errorcan be introduced if the cord is no t clamped immedi-ately, there is an excess quantity of hepa rin in relationto the am ount of blood collected, air is present in the

(GO,) and fixed (for example, lactate) acidplacenta for excretion by the maternal lungsneys, respectively, allow the fetus t o m aintain ;balance within a narrow range. Interruptionprocesses can lead to acidemia in t he fetus. Inrespiratory acidosis alone is not associated wborn complications; rather, it reflects adecrease in uteroplacental or umbilical perfusas placental abruption or cord prolapse i n n-----A:..- >. n... --.-~~ -~-,~~..

and kid-acid-baseof thesegeneral,i th new-sudden:ion suchnediately

p r c ~ c u i n ~cuvcry. isase excess values nave greaterusefulness than p H values because base excess doesno t change significantly with respiratory acidosis anddemonstrates linear, rather than logarithmic, correla-tion to the degree of metabolic acidosis. Umbilicalartery base excess is the mo st d irect measure of fetalmetabolic acidosis. Human and animal studies haveconfirmed normal values before and during labourand rates of base excess change in relation to eventscausing fetal hypoxemia (maternal hypoxemia, nrnbil-ical cord occlusion, and reduc ed uterine blood flow).6Th e process of normal labour a nd delivery withoutanesthetic intervention stresses the fetus such thatmild acidosis develops in almost all labours? Reynoldset al. recently completed a meta-analysis comparingepidural with systemic opioid analgesia to determinethe effect of these anesthetic interventions on acid-base status at birth? They concluded that epiduralanalgesia was associated with an im proveme nt in baseexcess, suggesting that placental exchange is well pre-served in association with this technique.While umbilical artery pH , base excess, and pCO,are considered sensitive and objective indicators offetal hypoxia during labour, the results represent asna psh ot" of fetal status and depict the mixed efflu-ent of all fetal tissues. Cord gases do not distinguishbetween primary fetal pathologic conditions, fetaleffects of m aternal conditions (for example, acid-basedisorders), or the influence of inadequate placentalblood flow. They also d o no t indicate in which direc-tion the condition of the fetus is moving, or at whatrate, nor do they reflect events that occurred remotefrom delivery.Evaluation of newborn neurobehaviourBrazelton, Scanlon, and Amiel-Tison assessed theeffect of anesthetic medications on the neurobehav-iour of term, healthy newborn^.^"-^^ Their belief wasthat central nervous system depression from drugsadministered to the mother during labour and deliv-ery c ould b e distinguished from effects associated with


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Littleford: EFFECTS OF MATERNAL ANESTHESIA

H G U R E 1 OxiFirstm Fetal Pulse O x i m c w . Rcpnntcd with per-mission from TvcuHcakhcarc. Coowirht 2000 Mallinckrodt, Inc.. .All rights reserved.

perinatal asphyxia and trauma at birth. Several reviewarticles have described these tests in detail and com-pared the Brazelton Neonatal Behavioral AssessmentScale (NBAS)1 nd EarlyXeonatal NeurobehavioralScale (ENNS)" to the Neurologic and AdaptiveCapacity Score (NACS).12Researchers in obstetric anesthesia have tended tofavour the NACS. A systematic review of the literatureregarding use of the NACS in obstetric anesthesiaresearch concluded that reliability and validity evalua-tions of the tool were lacking and it was unclearwhether the NAGS could detect the existence of sub-tle neurobehavioural effects.13 Subsequently, it hasbeen determined that the NACS has poor reliabilitywhen used to detect the effects of intrapartum drugsand other interventions on the neonate.'*Electronic feta l monitoringElectronic fetal monitoring, one technique in theoverall strategy of intrapartum fetal surveillan~e,1~~'~aims to improve outcomes by identifying fetuses withhypoxic acidemia at a point when the process is stillcompletely reversible by intra-uterine resuscitation orexpedited delivery. The fetal heart rate (FHR), indud-ing variability, accelerations, and decelerations, if anyoccur, is recorded electronically on a paper trace.Baseline FHR normally ranges between 110 to 160beats-min-l. A reactive (normal or reassuring) car-diotocogram (CTG) is defined by the presence ofaccelerations. Reduced variability and the presence ofdecelerations are abnormal findings.A systematic review of studies comparing the effica-cy and safety of routine continuous electronic fetal

monitoring vs intermittent auscultation of the FHRreveals the former to be associated with a significantlyhigher rate of Cesarean and operative vaginal delivery1'In the antecedent Cochrane review of this same topic,the incidence of general anesthesia to facilitate obstetricinterventionwas also increased. This aspect of manage-ment was not examined in the current review.Difficulty in the visual interpretation of CTG pat-terns during labour can result in unnecessary operativeintervention, while some significant changes go unrec-ognized. Computerized CTG systems, which do notrely on observer reading of the FHR tracing, are moreaccurate and reliable. Evaluation of the FHR pattern isgiven on-line continuously and warnings are displayedif there is signal loss, reduction in fetal movements, oran abnormally flat or decelerative trace.18Retrospective analysis of several thousand recordsenabled investigators to conclude that the most reli-able single parameter of fetal condition was variability(short- and long-term). Absence of accelerations,presence of decelerations, decrease in the number ofmovements, and changes in baseline FHR all occurredoccasionally in normal fetuses.19Recently, automatic ST segment and T wave analy-sis of the fetal electrocardiogram (ECG; recorded con-tinuously from a fetal scalp electrode) has beencombined with conventional CTG. Elevation ordepression of the ST segment occurs when the fetus isexposed to a hypoxic stress. When CTG is accompa-nied by computerized analysis of the ST segment, thenumber of operative deliveries for the indication offetal distress" can be reduced without jeopardizingfetal outcome and, cases of significant fetal hypoxianecessitating obstetric intervention are more readilyidentified.19.20Anesthesiologists have used continuous fetal CTGrecordings to evaluate the effect of maternal analgesiaon FHR and variability. Solt et a1. demonstrated thatintrapartum iv administration of meperidine (pethi-dine) 50 mg and promethazine 25 mg resulted indecreased variability and fewer accelerations on com-puterized CTG for the duration of their 40 minreco~ding .~~t is unclear whether the effect can beattributed to one of the two drugs or the combina-tion, although this is a typical fetal response to sys-temic maternal opioid administration.

A randomized study was conducted to examine theeffect of continuous epidural anesthesia with or withoutnarcotic on intrapartum FHR characteristics as mea-sured by computer analysis. The narcotic epidural con-sisted of an initial bolus of 10 to 12 mL 0.125%bupivacaine with 50 pg fentanyl, followed by continu-ous bupivacaine 0.125%with fentanyl 1.7 g-mL-' infu-


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Littleford:EFFECTS OF MATERNAL ANESTHESIAmaternal environment. Under normal circumstances,the reduction in sympathetic tone created by epiduralanalgesia does not affect Doppler flow characteristicsof either the uterine or umbilical artery vessels becausethe spiral arterioles are maximally dilated and the feto-placental circulation is stable and tolerant of environ-mental changes. However, epidural analgesia has beenshown to improve uteroplacental perfusion and effec-tively reduce maternal blood pressure in labouringpatients with pregnancy-induced hyperten~ion.3~Static chawe-sensitive bed (SCSB)A method for long-term monitoring of respiration,heart rate, cardiac function, and body movements innewborn infants was presented in 1984 and possibleclinical applications were discussed.36The technologyhas been used to evaluate neonatal sleep states follow-ing unmedicated vaginal delivery or elective Cesareandelivery under spinal anesthesia37and, in combinationwith pulse oximetry and ECG recording, to examinethe influence on the newborn baby of maternal fen-tanyl analgesia in labour.38

In the first study, mode of delivery did not affect sleepstate distribution during the first day of life.37Vaginallyborn neonates had fewer body movements and moreepisodes ofSpO,


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sion. The non-narcotic epidural was initiated with abolus of 10 to 12 mL bupivacaine 0.25% nd followedby a bupivacaine 0.125%nfusion. Investigators foundno difference in pre- and post-epidural baseline PHR,accelerations, or variability between the gr0ups.2~

In a double-blind randomized study of bolusepidural opioid effect on FHR variability, butorphanol2 mg, fentanyl 50 pg, sufentanil 15 pg, or saline incombination with buuivacaine 0.25%did not change


being is dependent on perfusion ofvital organs with oxy-genated blood, SpO, correlates with saturation as mea-sured by blood gas analysis, and a critical threshold forSpOa exists, above which the fetus will be non-acidemicand below which, acid-base decompensation may 0ccur.2~

Based on animal and human data, fetal SpO, values2 30%can be considered reassuring, whereas SpO,values < 30%may be associated with acidosis. LowSoO, values warrant further assessment if thev oersist

early labour was associated with abolishment of fetalbreathing at ten minutes post dosing, fewer bodymovements, and reduced ~ariab'ility.2~he effect lasted- 30mi& in keeping with the pharmacodynarnic profileof fentanyl. This should be taken into account whenfentanyl is administered close to the time of delivery. Inthis study, none of the neonates required resuscitation,and all had umbilical artery p H values > 7.2.FetalpiFetal o:(SPO,)and is

ulse oximetryxygen saturation monitoring by pulse oximetryrelies on established, non-invasive technology,

based on the following assumptions: fetal well-

ma1 and abnormal labour, in addition to variousmaternal conditions associated with fetal compromise(for example, pregnancy-induced hypertension).Fetal DopplerFlow velocity waveforms from maternal vessels (uter-. .ine arteries), placental circulation (un-' - ' -and fetal systemic vessels (for example,artery), collectively known as Dopplervide prognostic and diagnostic detailtion and fetal ad a~ ta ti on .~ ~

Regulation of the circulation is ;behaviour, influenced by gestations


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FIGURE 2 Potential adverse effects of untreated maternal painon the fc m (adapted and modified from- R r m n n d ~ e , Cohen SE , WardME. Neural blockade tor obstetrics and wnccologic suwery In Cousins MI , Bridcnbaugh PO (Eds). Neural Blockade in ClinicalAnesthesiia and Management of Pain, 3rdcd. ~ h i a d e l ~ h i a :i ~ ~ i n c o t t ,illiams &Wilkins; 1998:557-604)

occurred independently of the maternal reaction.Pretreatment of the fetus with fentanyl for this sameprocedure attenuated the rise in fi-endorphin?'

Hormonal stress responses do not provide a directindex of pain. While it is true that a rise in cortisol andendorphin is seen as a consequence of painful stimuliin children, other non-painful situations (for example,exercise) are also associated with an increase in the lev-els of these hormones. Nonetheless, the editorialreview of Fisk's fentanyl pretreatment study suggeststhat fetal analgesia should be given during invasive i nutero procedures.'

At present, thiuring labour or I

Analgesic techniques for abour:effects on the fetusand newbornNonpharmacolofficmethodsIn a systematic review of comfort measures, S iand O'Hara commented on five methods scientificallyevaluated for their effectiveness in reducing indicatorsof labour pain.50Continuous labour support was asso-dated with a decrease in duration of labour, requestsfor analgesia, rates of instrumental and Cesarean deliv-eries, and occurrence of lower Apgar scores. The useof baths offered temporary pain relief and was consid-

safe provided water temperatures were main-i at or below maternal body temperature andimmersion duraidity and mart:branes were ruphere had been uusions regarding


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C A N A D IA N JOURNAL OF ANESTHESIA

tormeperidine, in ~ m .Luu -Lu LLL-.)f 1 7 o 25 h r for this metabolite are common in[other, whereas the half-life exceeds 60 hr in the'newborn. Norm eperidine is associated with res-iry depression that is not reversible by naloxone,and seizures.Fentanyl offers prompt analgesia coupled with. ashort duration of action and no active metabolites.Both maternal an d fetal dru g levels decline in a para -lel fashion following a single dose of the d rug.57 n th efirst repo rt of its adm inistration t o labouring patients,fentanyl (50-100 pg iv every hour) was comparedwith meperidine (25-50 mg iv q 2-3 hr).@' Moremothers were nauseated and sedated and more babiesrequired naloxone in the m eperidhe group.Sufentanil is the most lipid soluble (octanol:waterpartition coefficient 177 8) of the comm only used opi-oids.52 This feature should enhance placental transferafter a single dose, b ut transfer is imped ed by the ex tentof maternal plasma protein binding (a,-acid glycopro-

-- A ..--I-- h., -ha 1 ---- - 'Z..C--+..-:l ,---.----.

'hen fetal delivery is iRemifentanil has 1ffect, shortest confer+ .

LC U,U UyUL "y ".L yL*LL.&-. u " L L A . - u L"....L..ua-tion in the fetus rises slowly, reaching a plateau between45 and 80 min pos t -admin is t ra t i~n .~~t is a usefulmaternal analgesic for painrelief during second stage,w mminent (< 45 min).the most rapid onset of peaka :t-sensitive half time, and great-est clearance o r me commonly used o p i o i d ~ . ~ ~ts con-centration decreases by 50% within three to fiveminutes of stopping d ru g administration, regardless ofthe duration of the infusion.52Th e dr ug rapidly cross-es the placenta and is quickly metabolized by fetals t er a~ es .6 ~ educed FH R variabil ity has beenbserved.6' Newborns exposed to remifentanil inktero up until the tim e of delivery have been vigorous.'here have been no reports of lower Apgar scores,nacceptable umbilical cord gas analyses, or respirato-y depression necessitating naloxone use.60'62,63Naloxone is used to reverse respiratory depression

in narcotic-exposed newborns. It is contraindicatedfor infants of narcotic-dependent mothers, as adminis-tration may precipitate acute withdrawal and seizures.Naloxone has never been shown to reduce the needfor assisted mechanical ventilation o r reduce ad missionrates to special care nurseries,64N o studies have eval-uated the effect of naloxone o n time t o spontaneouseffective respiratio nApnist-antagonist 'Nalbuphine is comiduring labour. Repcular and respiratorto carry out a study designed to delineate placen-

- ~ ~ ~ s f e rnd disposition of nalbuphine in theneona te. T he estimated half-life was 4.1 hr (v s 0.9 hrin infants and two hours in adults). Given that theliver extensively metabolizes nalbuphine, the authorsspeculated that the slower neonatal plasma disappear-ance rate compared to t he infant or adult could be duein part t o immature hepatic function or bypass of theliver via the ductus venosus. All 28 babies had five-minute Apgar scores of 1 0. Fifty-four percent of theFH R tracings showed reduc ed variability lasting 1 0 to35 m in after maternal injection.One potential use for this class of drugs is in thetreatment of opiate-dependent pregnant women.Babies born to mothers o n a buprenorphine mainte-nance program showeable n eonatal a b s ~ tfindings with methadltenance programs."Nitrous oxide (N,0)N 2 0 readily crosses the placenta. Th e maternal-fetalconcentration ratio reaches 0.8 w ithin 1 5min of con-tinuous inhalation. It has no effect on uterine con-tractions or F H R It is not m etabolized, and iseliminated quickly and entirely by the lungs with theonset of respiration at birth. This is true whether themother inhales N 2 0 for five minutes or five hours.N 2 0 does n ot affect Apgar scores or sucking behav-iour.6' Inhalatio n analgesia with N, 0 during labourand delivery, as the prim ary analgesia me thod, as a co-analgesic, or as a tem porizing measure pending othe rforms of pain relief is less common in the UnitedStates than in other developed countries.Paracervical blockThis peripheral block provides a therapeutic alterna-tive for first stage labour pain when central neuraxialblockade is contraindicated o r unavailable. The tech-nique involves transvaginal injection of LA on eitherside of the cervix in or der t o interru pt pain transmis-sion at the level of the uterine and cervical plexuses(located at the base of the broad ligament).Paracervical block (PCB) is relatively easy to performand, wh en effective, it provides go od to excellent anal-gesia that lasts one t o tw o hours.Since its introduction in the 194 03, reports of seriousng injection of LA directly into:tal head, fetal death, and pro-resulted in nchanges tohere are statdock in situ;cental insutticiency or non-reassuring

modification of thethe concentrationements cautioningitions o f uteropla-FH R tracings.

or long-term outcome. adverse sequelae, includiithe uterine arteries or fcopioids found bradycardia, havenon ly used as a systemic analgesic injection technique andort s of severe perinatal cardiovas- and type of LA used. Ty depression prompted Nicolle e t against employing this I. . . . . . . . - .


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Littleford: EFFECTS OF MATERNAL ANESTHESIAOverall, in current practice, the incidence of fetal

bradycardia post block is about 15%,68with the onsetbeginning two to ten minutes after injection and thebradycardia lasting 15 o 30 min. The exact etiology isunknown; however, a recent investigation comparingepidural with PCB using Doppler flow velocity wave-forms of the maternal femoral and uterine, and umbil-ical and fetal middle cerebral arteries has shed somelight on this phe n~ m e non .~ ~CB was associated witha small but significant increase in uterine arteryimpedance, indicating uterine artery vasoconstriction.In this study, Apgar scores and umbilical arterial, andvenous pH determinations were within the normalrange in both groups.New axia l analgesiaSpinal, epidural and combined spinal-epidural (CSE)techniques are used to administer opioids, LA, andother pain-modulating adjuvants.NEURAXIAL OPIOIDSFetal bradycardia may develop following administra-tion of intrathecal opioid, although its occurrence canfollow any type of effective labour analgesia." Whiletechnique-specific etiologies can occur (for example,maternal hypotension or fetal LA toxicity), uterinehypertonus as the mechanism inciting the transientbut profound drop in heart rate was first reported in1994." This topic has been the subject of study7' andsystematic review?3

Pain relief can affect uterine function. Hunterreported in 1962 that bilateral lumbar sympatheticblock for first stage labour pain caused abnormal uter-ine contraction patterns to normalize and previouslynormal patterns to become hypera~tive.7~lthoughthere is likely more than one mechanism, the etiologyis thought to be related to a change in the balance ofcirculating catecholamines occurring with the adventof analgesia, favouring a- over fi-activation of smoothmuscle receptor^?^^^^ Uterine muscle tone and vascu-lar resistance increase as a result of the contraction-inducing norepinephrine influence predominatingover the contraction-relaxingepinephrine effect. FHRdecreases because of a reduction in uteroplacentalblood flow. The effect may be more pronounced inthe face of oxytocin stimulation.

There is a temporal relationship between the speedof onset of labour pain relief and the appearance,if any,of the bradycardia. It occurs faster with spinal analgesia(less than ten minutes) and more slowly with epiduralanalgesia (15-30 min)?O However, as Van de Velde c tal. point out, speed of onset of labour pain relief cannotbe the only factor at work. NonreassuringFHR tracings

did not occur after CSE using a mixture of bupivacaineand sufentanil(1.5 pg) when compared to a larger doseof intrathecal sufentanil (7.5 pg) alone, despite equallyfast pain relief? A meta-analysis performed during awell-conducted systematic review of this topic revealeda significant increase in the risk of fetal bradycardia dueto intrathecal opioid (odds ratio 1.8, 95% confidenceinterval 1.0 to 3.1)?3

The clinical implications are not obvious becausethe occurrence of FHR changes in response to labouranalgesia has not prompted an increase in the rate ofinterventional deli~ery.7~he hypertonus usually lastsless than ten minutes and can be relieved by adminis-tration of a nitric oxide donor such as nitroglycerin(50-100 pg iv), or a 6, agonist such as terbutaline(125-250 pg iv), in cases of prolonged fetal bradycar-dia. The observed changes in FHR have not correlat-ed with observable clinical differences in neonataloutcome, including Apgar scores, cord pH, prevalenceof cord pH < 7.15, or admission rate to a neonatalintensive care unit,"NEURAXIAL LAIn general, when LA are used alone, concentrated solu-tions are required to afford pain relief. Since block den-sity is dose dependent, the more concentrated thesolution used, the greater the degree of motor blockexpected; this has been implicated in pelvic musclerelaxation-induced fetal malposition, maternal inabilityto push, and need for instrumental delivery?' In arecent meta-analysis comparing randomized clinical tri-als of techniques using epidural LA alone with intrathe-cal opioid alone,77 the authors were unable to findsufficient information to comment on either similaritiesor differences in maternal and fetal outcomes. Thisstudy was accompanied by an insightful editorial thatwill assist readers to critically interpret the results of thisand other systematic reviews and ~neta-analyses.~~COMBINING OPIOIDS, LA, AND PAIN-RELIEVINGADJUVANTSWhen spinal, epidural, and CSE techniques involvecombinations of pain-modulating drugs (sodiumchannel blocking agents, opioid-receptor agonists, a-adrenergic agonists and/or acetylcholinesteraseinhibitors) acting by different mechanisms, there ispotential to afford analgesia with minimal motorblockade and other relevant side e f f e ~ t s .~ ~ ,~ 'Labour epiduralsand outcomeAn erudite and interesting historical review of anes-thesia for childbirth by Caton, Frolich, and Eulianoprovides the foundation for a discussion of the con-


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scores." No consiste~: ncidence of neonat;h epidural. There was- - . ' . - e was not diffe1ent.9~;e Epidural analgesia has been associated with a high-i- er rate of operative vaginal d e l i v e r i e ~ ? ~ ~ecently,. --- . 0- . . . .

mcasuic&&u'ii d-n.pga a i - u r n i iin -i I C SLUL~ ui umuiu , uni-nca u c u v e n - u uy V~LUUU L A L L ~ L U U Ucord blood gas analysis. Some issues remained showed a higher incidence of cephalohematomas,unproven; for instance the suggestion that "epidural although need for resuscitation at birth, admission toanalgesia is associated with less naloxone use and high- a neonatal intensive care unit, and neonatal death rateer one-minute Apgai [it pictmemerged vis-a-vis the il adveneffects associated wit little evdeuce regarding the effectsot epidural on tetal physi- the U U M ~ ~tudy group7-' snowed mat mere was aologic mechanisms. decreased incidence of instrumental vaginal delivery4. pidnral analgesia was associated with (not nec- when lower doses of medication (CSE, low dose LA

essarily a causal relationship): plus opioid infusion) were used in labour compared toi. longer second stage labour (- 14min), conventional doses of LA (0.25%bupivacaine). Theii. more fetal malposition (occiput posterior), presumed mechanism is the preservation of motoriii. a higher rate of instrumental vaginal deliveries, tone and the bearing-down reflex. Mild neonataliv. maternal fever, and depression necessitating neonatal resuscitation wasv increased use of oxytocin augmentation. This more common among babies whose mothers were in

serves as an example of the association vs causation the low dose LA plus opioid epidural infusion group,debate?' most likely due to the cumulative effect of the opioid

Halpern e t al. noteds2 hat the quality of the clinical over time. Neither the Apgar scores at five minutestrials included in their review improved with time; all nor the rates of admission to a neonatal care unit dif-trials after 1995 reported outcomes with patients fered between groups.grouped by intent to treat. Analysis conducted in this Newer methods of epidural analgesia offer the bestway (i.e., by groups to which patients were random- chance of spontaneous delivery with satisfactory painized) is vital because women who choose epidurals dif- ~ o n t r o l ? ~fer demographically from those who choose othermethods of labour analgesia. The former are more like- Delayed pushingly to be nulliparous, be admitted to hospital earlier in The "Pushing Early or Pushine Late with E~idural"labour with higher fetal head positions, have slower (PEOPLE) study, arates of cervical dilation, bear heavier babies, and need trolled trial, compa~commencing at full c'

more than two houdelivery was reduced

oxytocin augmentation more frequently. All of thesefactors and degree of maternal pain independently pre-dict the need for Cesarean delivery for dy~tocia.8~


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Littleford: EFFECTS OF MATERNAL ANESTHESIAumbilical arterial pH < 7.10 occurred more frequent-ly among babies whose mothers were in the delayedpushing group. The two groups had similar rates ofneonatal morbidity, including asphyxia. Protocolsadvocating delayed pushing result in longer secondstages and increased incidences of maternal feve1.9~Maternal feverMothers who receive an epidural are more likely todevelop a fever during labour.95 The link betweenepidural analgesia, maternal fever, and the purportedincrease in neonatal septic work-ups is lessThe concern is that babies are more likely to be treat-ed with antibiotics since it is not currently possible todistinguish between maternal fever from infectiousand noninfectious causes during labour. Many investi-gators believe the association of an epidural with feveris probably attributable to noninfectious causes, forexample altered thermoregulation resulting fromepidural analgesia. Neonates born to mothers whoreceive epidural analgesia do not have an increased riskof s e p s i ~ ? ~ . ~ ~

-Breastfeed*A succinct and thorough review of this topic con-eludes that intraparturn epidural analgesia does notadversely affect a baby's or mother's ability to breast-feed." The most critical factors for breastfeeding suc-cess are support of, and education for, the mother.ForthcomingExamination of the fetal/newborn effects of maternaland fetal anesthesia for surgical procedures duringpregnancy is presented in Part 11,along with a discus-sion of anesthetic medications, techniques, and inter-ventions related to surgical issues that arise for themother and fetus during pregnancy and for the new-born during the early postpartum period.


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-- -- - -.- - ---- . -- --- -- ----- -- -...,techniques, and interventions related to surgical issuesthat arise for the mothe r and fetus during pregnancy andfor the ne wborn d urin g the early postpartum period.Anesthetictechniques for Cesareansection: effects o nth e fetusand newbornGeneral anesthesia (GA)Given enou gh time, all medication administered to themother crosses the placenta and enters the umbilicalvein; therefore, gauging drug administration duringthe indu ction and maintenance phases of GA is neces-sary. An importan t factor affecting neonatal ou tcome isthe elapsed time between the induction of anesthesiaand clamping of the umbilical cord, as this representsthe time o f fetal exposure to maternally adm inisteredmedication. A second factor is the time from uterineincision to delivery of the baby. A long incision todelivery time is associated w ith an increased incidenceof fetal acidosis, presumably caused by uteropla centalvasoconstriction. If possible, induction to damp timeshould be Jess than ten minutes a nd u terine incision todelivery time less than three minutes .loOThe three determinants of placental transfer ofdrugs to the fetus include the physical-chemical prop-erties of th e dr ug, the characteristics of the maternal,placental, and fetal circulation s, and placental anatomyand physiology. Fetal and neonatal pharmacologicaleffects of anesthetic agents given to the mother duringa Cesarean section conducted under GA depend onthe a moun t of dr ug reaching the fetus. Estimating thisis not an easy task.There are difficulties associated with human in vivostudies o f placental transfer du ring pregnancy.101 Thefeto-placental unit is inaccessible in situ and there areethical considerations in conjunction with maternal andfetal safety. In vivo studies are most commonly per-formed at birth by collecting maternal venous andumbilical cord arterial and venous blood samples. It isdifficult to draw conclusions based on one set of mea-surements. Likewise, the applicability of animal placentasas models for t he human placenta is limited because thestruc ture and function of the placenta is species-specific.Many studies of anesthetic pharmacology to date havebeen conducted using animal models. The alternative isto use a human ex vivo placental perfusion model. Ala-Kokko and colleagues make a strong case for the h um anplacental perfusion model as the best method availablefor study ing transplacental passage of drugs. lolIt will take time t o study anesthesia drugs using thismethodology. Th e conclusions reached in most of the

- ~~...sodium thiopental, methohexital, ketamine, propofol,and midazolam. Ketamine is usually reserved for situ-ations involving maternal hernodynamic instabilitybecause it preserves sympathetic outflow. The othershave been studied and Midazolamand propofol have been associated with longer induc-tion times, a lighter plane of maternal anesthesia (asmeasured by electroencephalogram), and lower Apgarscores. Sodium thiopental and methohexital sharepharmacokinetic properties with thiamylal, anotherlipid soluble barbiturate tha t peaks in umbilical arteri-al plasma at three to five minutes and declines rapidlyuntil 11min?00J04 ndu ction to umbilical cord clamptimes of approximately ten minutes coincide withdeclining fetal levels of these agents and therefore lit-tle neonatal depression.Neuromuscular blocking drugs share a structuralsimilarity, a quaternary ammonium ion, which slowsbut does n ot eliminate transfer of these drug s acrossthe placenta.100Succinylcholine is degraded so rapidlyby plasma cholinesterase that virtually none reachesthe fetus, whereas the percentage of nondepolarizingneuromuscular blocking dr ug (for example rocuroni-um, pancuronium, and atracurium) that crosses theplacenta ranges from 7 to 22%, depending on thedrug. T he literature is vague w ith respect to effects onthe neonate. However, in the setting of high-dosenondepolarizing neuromuscular blockade (for exam-ple, EXIT procedures), i t may be necessary to suppo rtneonatal ventilation for a period of time or to admin-ister reversal age nts.The inhalation agents, desflurane and sevofluranewould be expected to cross the placenta and equili-brate in fetal tissues more rapidly than their more sol-uble counterparts (for example, isoflurane),potentially resulting in a more depressed neonate.Equally expected, however, once the newborn estab-lishes ventilation, is that the lungs would excrete("b low off") these relatively insoluble drugs m orequickly. Desflurane is more pungent and irritating tothe airway and may result in laryngospasm. Thisshould be considered when suctioning the neonatewhose mo ther has received desflurane.lWWhen com-pared w ith isofluran e 0.5%, sevoflurane 1%equianes-thetic concentration) was found to produce similarmaternal and neonatal results.'05 Cord blood gasesand 4 g a r scores were equiv alent. Desflurane in a su b-anesthetic do se (3%),mixed with N,0-O ,, was con-sidered safe and effective for Cesarean section inhealthy parturients when compared to enflurane 0.6%.


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Littleford: EFFECTS OF MATERNAL ANESTHESIAHigher doses of desflurane delayed time to sustainedrespiration in the newborn?06Regional anesthesia (RA)Under normal maternal and fetal conditions, skillfullyconducted GA and RA are almost equivalent withrespect to neonatal ~ e l l - b e i n g . ~ ~ ~ . ~ ~ 'evertheless,given the risks to the mother and the association oflower Apgar scores with GA, RA for elective, andsometimes emergent, Cesarean section is pre-ferred.79J09"111 compromised fetus may even benefitfrom anticipatory maternal epidural catheter place-ment in labour when there is a high risk of Cesareansection1I2or, primary epidural or spinal anesthesia forelective Cesarean ~ e c t i o n . ~ ~ O J ~ ~A results in lessneonatal exposure to drugs (especially when the spinaltechnique is used), allows the mother and her partnerto participate in the birth of their baby, and providesbetter maternal postoperative pain relief.ll*For all the advantages of spinal anesthesia such assimplicity of technique, rapid onset, reduced risk of sys-temic toxicity, density of anesthetic block, and postop-erative pain relief afforded by neuraxial morphine, thepotential for hypotension with this technique poses thegreatest threat to the mother and fetus?9 The incidenceof hypotension is similar between epidural and spinalanesthesia, but occurs earlier and more rapidly with thespinal approach. Hypotension results from temporarysympathectomy, an inevitable but undesirable compo-nent of midthoracic blockade. Reduced preload(increased venous capacitance and pooling of blood vol-ume in the splanchnic bed and lower extremities) andreduced afterload (decreased systemic vascular resis-tance) lower maternal mean arterial pressure (MAP),leading to nausea, lightheadedness and dysphoria, andreduced uteroplacental perfusion. When maternal MAPis maintained, maternal symptoms are averted anduteroplacental perfusion improves.

In their epidemiological study of 5,806 Cesareandeliveries, Mueller et al. concluded that fetal acidemiawas significantly increased after spinal anesthesia,115and maternal arterial hypotension was by far the mostcommon problem encountered. The prevalence offetal acidemia with RA for Cesarean section has beenconfirmed in another study.110 However, isolatedacidemia does not correlate with Apgar scores and is apoor indicator of outcome. Low umbilical artery pHreflects both the respiratory and metabolic compo-nents of acidosis, whereas base excess reflects only themetabolic component. It is base excess that correlateswith neonatal outcome, values more negative than -12mmol-L-I having an association with moderate tosevere newborn en~ephalopathy.~ owever, preven-

tion of hypotension is advantageous to minimize anyinfluence on neonatal acid-base status.

The routine measures used to maintain uteropla-cental perfusion include left lateral tilt position, lowerleg compressive stockings, and iv fluid 10ading.~~~J~7Vasopressor therapy is reserved for the treatment ofhypotension. Prophylactic use of ephedrine in onestudy118 and therapeutic use in anotherl10 possiblycontributed to fetal acidemia. Likewise, ephedrine usewas associated with lower umbilical arterial pH valueswhen compared with phenylephrine in a systematicreview.119The literature is replete with debate regard-ing which vasopressor, a mixed a6 agonist (for exam-ple, ephedrine) or a pure a agonist (for example,phenylephrine), would be more appropriate for themanagement of hypotension during spinal anesthesiafor Cesarean d e l i ~ e r y . ~ ~ ~ ~ ~ ~he controversy revolvesaround the etiology of fetal acidemia: is it due to themetabolic effects of 8-stimulation in the fetus or insuf-ficient maintenance of uteroplacental perfusion by fail-ure to reclaim sequestered blood from the splanchnicbed in order to augment preload? Regardless, thechoice of a vasopressor drug is perhaps less importantthan the avoidance of h y p o t e n s i ~ n .~ ~Fetal effects o maternal oxygen administrationProviding supplemental oxygen to the parturient dur-ing Cesarean section is common clinically, whether theprocedure is elective, urgent, or eme1gent.1~~his prac-tice has been justified by the belief that raising the oxy-gen reserve of the mother is universally beneficial forthe fetus. Since the advent of pulse oximetry, patientswho may benefit from oxygen therapy are more easilyidentified, and clinicians can be more selective aboutadministering oxygen therapeutically. For example,pulse oximetry readings obtained during electiveCesarean section conducted under spinal anesthesiashowed that maternal saturation was well-maintainedon room air, and administration of 35%oxygen by face-mask failed to significantly change umbilicalvein pH orpartial pressure of oxygen.Iz6 This finding was furthersubstantiated in a study by Coghano et al.Iz7

Oxygen given to the mother does not increase fetaloxygenation to the same extent because of utilizationduring intermediary placental metabolism. In compar-ison, neonatal oxygen therapy has the potential toraise newborn PaO, substantially. There is a growingbody of clinical and experimental evidence that seemsto indicate the practice of routine supplemental oxy-gen during neonatal resuscitation may be injuri-oils,11&130

Oxidative stress is implicated as a common under-lying mechanism in several neonatal conditions,


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ANESTHESIA

t h e in terest i n tree radicals as narDingers or disease nasprompted investigators to explore potential fetaleffects of giving oxygen t o mothers. Accordingly, theprocess of routine oxygen supplementation for healthyparturients u ndergo ing elective Cesarean delivery withRA has been q ~ e s t i 0 n e d . l ~ ~Free radicals have a brief life span, making theirdetection difficult. Therefore, studies investigatingoxidative stress usually measure surrogate markers,namely products of the attack by free radicals onlipids, proteins and nucleotides. This methodologywas used to examine the effect on the newborn ofadministering air o r oxy gen-enriched air to parturientsundergoing elect ive Ce~ are an sec tio n.1 ~~here was aclear difference betwee n groups , with gre ater free rad-ical activity in the babies born to mothers breathingoxygen-enriched air. Th e main site of free radical gen-eration was the placenta, as evidenced by the higherconcentration of free radicals in the umbilical veincompared to the arter s pointout, "At present, we h ng freeradical formation with neonatal outcome followingelective Cesarean section. ....in a low risk situationsuch as [this], a favourable outcome is unlikely to bein flu en ce d by mate rn al h y p e r ~ x i a " . ~ ~ ~The signifi-cance of [ the K haw e t al. study] relates to the use ofhigh inspired maternal oxygen fractions (2 60%) forthe delivery of comprom ised and premature [babies]".The re are n o published trials addressing maternal oxy-gen therapy for fetal distress.i38Postpartumpain managementThis section is limited t o pharmacological therapy andits implications for the breastfeeding mother.Breastfeeding calls for use of analgesic agents that aretransferred minimally into breast milk and have littleeffect o n t he neonate.13'Th e act of breastfeeding results in milk production,secretion, let-dow n, and increased breast blood flow.Therefore, the timing of breastfeeding relative to dru gadministration influences the amount of drug thatappears in the breast milk. D rug exposure can be min-imized if the mother takes medication immediatelyafter nursing o r just before the baby is due to have alengthy sleep, an d uses short-acting medications. Th eneonatal dose of most medications obtained throughbreastfeeding is 1 o 2%of the maternal dose.140

ent of drug: lipid solu-colostrum,same pH as1 far as nar-es are not

sequesterea in coiosuu m via ion napping a nd thereforedo not accumulate. Colostrum morphine concentra-tions have been measured during the first48 hr of postCesarean iv patient-controlled a na lge ~ia .1~ ~he milk t omaternal plasma ratio for morphine was less than one.Mo rphine was seen in very small conce ntrations in lessthan half of the milk samples. The authors concludedthat the am ount o f dru g likely to be transferred to thebreastfed neonate was negligible. Only small amountsof colostrum are secreted during the first few postpar-tum days (10-120 mL -day1), so newborn exposurefrom volume is limited . Ultimately, the con centration ofdru g in the baby's plasma is mo re importan t than th econcentration of the d rug in colostrum o r breast milk.This d epends o n absorption across the gastrointestinaltract, the volume of distribution, and the extent ofmetabolism and excretion in the newborn. Little isknown about the bioavailabiity of analgesics and theirmetabolites because of ethical issues involved in repeat-ed blood sampling from babies.Milk composition continues to change over the firstten davs after birth. There is a eradual increase in fa tand 1: i pH .By A solu-bility, low molecular weight, minimal protein binding,and the un-ionized state facilitate secretion of medica-tions in to m ature breast milk.142 Women w ho breast-feed and require GA for surgery are usually counseledto feed their baby before the surgery and temporarilyinterrupt feeding postoperatively by wasting the firstmilk sample (express with a breast pump and discard).After that, if the mother feels well enoug h and there areno surgical contraindications, she is encouraged toresume feeding. Most anesthetics are rapidly clearedfrom the mother; some authors argue that n o portionof human milk need be wasted.142The American Academy of Pediatrics (AAP) pub-lished a statement o n d rug transfer into hum an milkand possible effects on the infant or on lactation inorder t o assist prescribing practices.143The AAP con-. . . . . "siders acetaminophen, m ost non-smatory drugs, and morphinebreastfeeding.

iteroidal anti-inuam-: compatible with

Surgeryduring pregnancyUrgent surgery during pregnanction of anesthetic and surgical aty requires modifica-iproaches to address


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the safety of the mother and herAnesthetic considerations include:

1.Management of maternal risk factors resultingfrom physiological adaptation to the demands of agrowing fetus and ongoing support of the placentalunit;2. Maintenance of the pregnant state;

3. Optimization of uteroplacental perfusion andfetal oxygenation, and maintenance of a stable intra-uterine environment;

4. Attention to the direct and indirect actions ofmaternally administered medications on fetal well-being.

The choice of anesthetic technique is guided bymaternal indications, taking into account the site andnature of surgery. Efforts are made to reduce fetaldrug exposure and, with reassurance, allay maternalanxiety. Most abdominal procedures, however, requireGA to provide sufficient muscle relaxation to facilitatesurgical exposure.

Approximately 2% of pregnant women requiresurgery during pregnancy.145 The procedure may bedirectly related (for example, cervical cerclage), indi-rectly related (for exampie, ovarian cystectomy), orunrelated (for example, appendectomy) to pregnancy.Semi-elective procedures should be delayed until thesecond trimester. Surgery at this time avoids the vul-nerable period of organogenesis (-15-60 days gesta-tion) and the technical difficulties of maneuveringaround a large, gravid uterus or managing the mater-nal airway in an advanced stage of pregnancy. Specialtechniques, including laparoscopy, cardiopulmonarybypass, transplantation, and induced hypothermiahave all been performed safely during pregnancy.lM

Premature labour represents the greatest risk to thefetus in the perioperative period. Neonatal mortalityin the developed world is approximately 50% at 25weeks, dropping to about 10% at 30 weeks.147Postponing surgery during this period of rapid fetalmaturation should weigh the advantages to the fetusagainst the hazards that delay poses to the mother.There is no evidence to suggest that any anestheticagent, dose, or technique influences the risk ofpreterm labour.145Rather, it is more likely to be relat-ed to the surgery itself, manipulation of the uterus, orthe underlying condition of the mother (for example,infection). The more advanced the pregnancy, thegreater the probability of uterine irritability. Certainmedications can be used as part of the anesthetic tech-nique to promote uterine quiescence (for example,magnesium sulfate, inhalational anesthetic agents, orfi, agonists) and surgical strategies can be employed toavoid handling the uterus. Intravenous, sublingual or

transcutaneous administration of nitroglycerin is usu-ally reserved for uterine relaxation during brief proce-dures, or to manage refractory uterine activity.14'The decision to monitor the fetus during surgerynecessitates that someone be available for ongoinginterpretation of fetal well-being, and that there be aplan for intervention should fetal distress be diag-nosed or suspected. Indicators of fetal distress areoften indistinct because technical limitations at variousgestational ages eclipse data acquisition, and FHRvariability is reduced or eliminated by certain anes-thetic drugs. Intervention may include delivery,reassessment of anesthetic depth, or a more aggressiveapproach to maximize uterine blood flow, tocolysis,and/or maternal oxygenation.lM If delivery of thefetus is planned to occur at the same time as surgery,a coordinated team approach involving anesthesia,obstetrics, surgery, nursing, respiratory therapy, andneonatology is vital.The well-being of the fetus is dependent on theadequacy of the maternal blood supply to the placen-ta, which is mainly derived from the uterine arteries.l16The uterine vascular bed is a low resistance system, notcapable of further dilatation, and devoid of autoregu-lation. Therefore, placental blood flow varies directlywith net perfusion pressure (uterine artery pressure -uterine venous pressure) across the intervillous spaceand inversely with uterine vascular resistance. Whenfaced with maternal hypotension, in order to preserveuteroplacental perfusion in a "pressure-passive" sys-tem, a more aggressive approach to management(rapid fluid loading, vasopressor therapy,Trendelenburg and left lateral positioning) is requiredcompared to strategies for the non-pregnantpatient.146Hypotension may be due to many differentetiologies but commonly results from aortocaval com-pression in the supine position, general or high spinalanesthesia, or hemorrhage. Maintaining homeostasisin the intra-uterine environment also requires atten-tion to maternal oxygenation, temperature, and acid-base balance (respiratory and metabolic).

Most anesthetic agents are not known to be terato-gens. When evaluating the possibility of teratogenicityfrom maternally administered anesthetic medications,points to be considered in~ lude :~~ ~J *'

1.The incidence of congenital anomalies in thedeveloped world is 3%;2. Human teratogenicity studies are impossible toperform for ethical reasons;3. Extrapolation from animal studies may not bevalid;4. Hypoxemia and hypotension cause physiologicalderangement that may be teratogenic.


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CANADIAN JOURNAL OP ANESTHESIA

Drugs that are usually avoided during anestnesiafor long surgical procedures in early pregnancyinclude N 20 and benzodiazepines. N20 is avoidedbecause it causes oxidation of vitamin B12, renderingit incapable of functioning as a co-factor for methion-ine synthetase, an enzyme necessary for DNA synthe-sis in humans. Benzodiazepines are avoided becauseepidemiological studies have shown a link to the. .development of congenital inguinal hernia.14"

Postoperative pain management may include plexusblocks or epidurals, where appropriate, in order tolimit fetal exposure to drugs, Opioids and aceta-minophen are used widely. Prolonged use of non-steroidal anti-inflammatory drugs is avoided due toconcerns about premature constriction of the ductus'arteriosus and development of oligohydramnios.FetalswyeryFetal surgery is defined as "the performance of proce-dures on the fetus or designed to alter thenatural history of a fetal disease that is diagnosed i n~ t e r o " . ~ ~ ~urgery can vary from minimally invasivencrmtaneous nrocednres. facilitated hv local. sninal.-.--.-...-. r - . ~~ ~~ ., -c - ~ ,or epidural anesthesia, to-direct fetal operations fol-lowing a hysterotomy incision. The latter requiresmaternal GA and attention to the possibility of inilict-ing pain on the fetus.lS0Anesthetic considerations areidentical to those for non-obstetric surgery duringpregnancy although the fetus is the primary patient inthese circumstances.

Fetal sedation by placental transfer of maternallyadministered medication is not reliable and does notensure an anesthetized or immobile fetus. Givenenough time, and subject to their individual solubili-ties, the inhalation anesthetic agents used for maternalGA and uterine relaxation equilibrate in fetal tissues.Deep maternal inhalation anesthesia may result in pro-gressive fetal acidosis by an uncertain mechanism.Fetal blood pressure, heart rate, oxygen saturation,and base excess can decrease due to direct impairmentof fetal myocardial contractility, redistribution of fetalblood flow, or changes in uterine perfusion. Fetal dis-tress and response to maneuvers can be recognizedand managed by measuring heart rate, blood pressure,and umbilical blood flow, and by monitoring pH,

which help elevate the FHRand maintain cardiac out-put. Fentanyl, in relatively large doses (12.5-25pg-kg'l estimated fetal weight), attenuates the auto-nomic and hormonal stress response during potential-ly painful pr~cedures?*J~~n the face of intenseuterine tocolysis, maintenance of maternal blood pres-sure may require concomitant vasopressor therapy.The Ex Utero Intrapartum Treatment (EXIT) pro-cedure was developed for fetuses that hadictably compromised airway, either becausin utero surgery (for example, to treat Idiaphragmatic hernia) or due to an obstrucsuch as cystic hygroma or thyroid goiter.occurs by planned Cesarean section with anic approach that maintains uterine relaxaticterotomy incision is made with a device Iuterine bleeding, and the fetus is partial1through the incision. The surgeon perforgoscopy or tracheotomy and secures the aimtracheal tube or tracheotomy tube) while tlstill attached to the umbilical cord and mairuteroplacental perfusion. Attention is paid t


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TJttleford:EFFECTS OF MATERNAL ANESTHESIAage. I t is diagnosed or suspected when characteristi-cally "abnormal" features emerge in one or more ofthe tests used to evaluate fetal well-being. The term'non-reassuring intrapartum surveillance" hasreplaced the term "fetal distress".Intra-uterine resuscitation consists of a series ofmaneuvers designed to reverse treatable causes of fetalasphyxia, restore fetal oxygenation, and correct fetalacidosis. These maneuvers are fundamental to thepractice of obstetric anesthesia and are summarized,using an evidence-based template, by Thurlow andKin~ella. '~~he circumstances surrounding the onsetof fetal distress direct the order of application anddetermine which aspects of intra-uterine resuscitationare appropriate for a particular patient. The goals andmeasures are:

1.Increase blood flow to the placentai. treat maternal hypotension aggressively by

administering a non-glucose containingcrystalloid/colloid iv fluid bolus, stopping the epidur-al infusion, and giving vasopressor therapy,ii. alleviate aortocaval compression by changingthe mother's position until an improvement in FHRoccurs (left lateral, followed by right lateral, and final-ly, knee chest position),iii. reverse uterine artery vasoconstrictioninduced by hypocapnia from maternal hyperventila-tion by managing pain and providing verbal reassur-ance.2. Relax uterine muscle

i. stop oxytocin infusion,ii. administer a tocolykic such as nitroglycerin50-100 pg iv .3. Increase fetal oxygenationi administer 100% oxygen to the mother by

face mask,ii. relieve umbilical cord compression by chang-

ing the mother's position or, if oligohydramnios ispresent, consider amnioinfusion.4. Rule out umbilical cord prolapse or, if present,provide manual elevation of the presenting part pervagina, maintaining warmth and moisture for the corduntil emergent delivery.

5. Confirm fetal asphyxia by an alternate test.6. Prepare for emergent delivery.Maternal cardiac arrestThe management of cardiac arrest in pregnancy is out-lined in the Guidelines 2000 for CardiopulmonaryResuscitation and Emergency Cardiovascular Care.155Acute Cardiac Life Support protocols are modified inpregnancy, but the standard adult algorithms for med-ication, intuhation, and defibrillation still apply.

The key to resuscitation of the fetus is resuscitationof the mother. Relief of aortocaval compression isparamount. Chest compressions are performed higheron the sternum to adjust for the shift of abdominalcontents toward the head. Consideration of arrest eti-ologies unique to pregnancy (for example, amnioticfluid embolism) and diagnoses exacerbated by thephysiological changes of pregnancy (for example, peri-partum cardiomyopathy) is important if response toresuscitative efforts is lacking.All medication infusionssuch as magnesium sulfate, oxytocin, or epidural arediscontinued and early intubation is encouraged toreduce the risk of aspiration. Fetal surveillance moni-tors (for example, scalp electrode lead) must be dis-continued prior to defibrillation. The decision toperform open-chest cardiac massage or emergentCesarean section should occur earlier rather than laterif circulation is not restored by usual measures.Perimortem Cesarean section has the highest chanceof improving outcome for both mother and babywhen uterine size is > 20 weeks (some would say > 24weeks) and delivery occurs within five minutes of theonset of the arrest.lS6Perimortem Cesarean sectionPerimortem Cesarean section refers to emergent oper-ative delivery of the fetus through a midline, classicaluterine incision in situations where the mother ismoribund or pulseless and is being actively resuscitat-ed. Emptying the uterine cavity increases maternalcardiac output (contraction of the myometriumresults in autotranshion of blood previously directedto the uterus and improved preload secondary to reliefof inferior vena cava compression) and lung volumeand, mates it easier to perform effective chest com-pressions.

Accurate data regarding the incidence and outcomeof this procedure for the mother or the neonate aredifficult to obtain. For example, the BritishConfidential Enquiry does not report deliveries wherethe mother has been successfully resuscitated.157There have been several case reports of expedientCesarean delivery where both mother and baby havesurvived fully intact. Perimortem Cesarean section isan established part of the resuscitation process in near-term pregnant women.155 n the largest series to date,Katz et at. reviewed the literature from 1900 to 1985for papers where time from cardiopulmonary arrest todelivery was listed.158Most fetal survivors were deliv-ered within five minutes. The general consensus is thatthe likelihood of perimortem Cesarean section result-ing in a living and neurologically normal baby is relat-ed to the interval between onset of maternal cardiac


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arrest and delivery. Also, the chances of normal sur- 7 National Committeefor Clinical Laboratoryviva1 are pond following' delivery if t h e fetus lives nast Standards.Blood eas ore-analytical consideratinn :.- - --... ..--.a --,- -.. -..--- ~.r---the first few days.157 For this technique to be anoption, it must be considered in the context of imme-diately available staff and equipment t o perform theCesarean section, and staff and equipment to conductthe neonatal resuscitation.

-- -c 4-1,-


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606 CANADIAN IOURNAL OF ANESTHESIAes to invasive procedures are independent of maternal sia for labour using remifentad: a feasibility study. Brresponses. J d i n Endocrinol Metab 2001; 6: 104-9. JAnaesth2001; 87: 415-20.

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