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ANESTHETIC CONSIDERATIONS FOR PRETERM LABOR AND DELIVERY

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Title: ANESTHETIC CONSIDERATIONS FOR PRETERM LABOR AND DELIVERY


1
ANESTHETIC CONSIDERATIONS FOR PRETERM LABOR AND
DELIVERY
  • HARRY SINGH, MD
  • DEPT. OF ANESTHESIOLOGY
  • UTMB

2
INCIDENCE AND SIGNIFICANCE
  • Preterm Labor 9.5-1982
  • Preterm Labor 11-1994
  • 69-83 Neonatal deaths
  • Despite improved care the incidence of preterm
    delivery remains greater than 11 in US
  • Current areas of research
  • Determination of causes
  • Early identification of women at risk
  • Optimal recognition and treatment

3
DEFINITIONS
  • Preterm infant 20-37 weeks gestation
  • or 3 weeks before expected date of delivery
  • SGA Small for gestational age
  • Infant weight lt 2500 gms at birth-LBW
  • Infant weight lt 1500 gms at birth-VLBW

4
NEONATAL MORTALITY
  • ?Survival rate with ?gestational age and birth
    weight
  • 70-80 survival in infants weighing 750 to 1000
    gms
  • High mortality rate with weight lt 750 gms
  • 24 weeks-Survival 43
  • 25 weeks-Survival 74
  • 26 weeks-Survival 83
  • Greatest gain achieved by prolonging pregnancy
    beyond 24 weeks gestation

5
NEONATAL MORBIDITY
  • Survival exceeds 90 by 30 weeks gestation
  • 90 Preterm births 30-36 weeks gestation
  • Morbidity primary concern at this gestational age
  • ? Morbidity from RDS gt 36 weeks gestation
  • ? Morbidity from IVH (grade III and IV) gt 27
    weeks gestation
  • ? Morbidity from necrotizing enterocolitis and
    patent ductus arteriosus gt 32 weeks gestation

6
MATERNAL FACTORS
  • History of preterm delivery
  • History of diethylstilbestrol exposure
  • History of second trimester abortion
  • Young agelt18 years
  • Low socioeconomic status
  • Acute or chronic systemic disease
  • Trauma
  • Abdominal surgery during pregnancy
  • Infections Untreated syphilis, Neisseria
    gonorrhoeae, asymptomatic group B streptococcus,
    acute pyelonephritis, cervicovaginal infections
  • Smoking
  • Drug abuse

7
UTERINE CERVICAL CAUSES
  • Overdistention of cavity multiple gestation,
    polyhydramnios
  • Abnormal cavity uterine anomaly, fibroids
  • Foreign body intrauterine device
  • Cervical incompetence
  • Trauma to cervix

8
OTHER CAUSES
  • Faulty placentation placenta previa, placental
    abruption
  • Genetic abnormality
  • Fetal death
  • Premature rupture of membranes
  • Iatrogenic-50

9
OTHER CONSIDERATION
  • 20-25 Preterm deliveries dont follow preterm
    labor
  • Elective delivery
  • Severe preeclampsia
  • Non reassuring fetal heart rate

10
DIAGNOSIS OF PRETERM LABOR
  • Preterm labor vs. false labor
  • Criteria for Diagnosis
  • Gestational age between 20-37 weeks
  • At least 4 documented uterine contractions in 20
    minutes or 8 in 60 minutes
  • Cervical dilation of at least 2 cm
  • Cervical effacement of 80

11
ASSESSMENT AND THERAPY
  • Physical examination
  • Intravenous hydration
  • Bed rest
  • Fetal heart rate monitoring
  • Ultrasonography for gestational age and weight
  • Amniocentesis for fetal lung maturity and to rule
    out infection
  • Speculum examination to rule out PPROM

12
CRITERIA FOR USE OF TOCOLYTIC THERAPY
  • Gestational age between 20 and 34 weeks
  • Fetal weight lt 2500 gms
  • Absence of fetal distress
  • Benefits?Neonatal morbidity and mortality
  • Risks Maternal and/or fetal sepsis
  • Maternal side effects of tocolytics
  • Further compromise of a distressed fetus

13
SHORT COURSE OF TOCOLYTIC THERAPY
  • Indicated for the following scenarios
  • To facilitate transport from a small community
    hospital to a tertiary center
  • To delay delivery for 24-48 hours allowing
    administration of glucocorticoids to accelerate
    fetal lung maturity
  • Fetal resuscitation in utero in fetal distress

14
BENEFITS OF STEROID BEFORE PRETERM DELIVERY
  • Reduced incidence of respiratory distress
    syndrome
  • Reduced incidence of intraventricular hemorrhage
  • Reduction of neonatal morbidity and mortality

15
CONTRAINDICATIONS TO TOCOLYTIC THERAPY
  • ABSOLUTE
  • Fetal death
  • Fetal anomalies incompatible with life
  • Fetal distress warranting immediate delivery
  • Chorioamnionitis/fever of unknown origin
  • Severe hemorrhage
  • Severe chronic HTN and/or PIH
  • RELATIVE
  • Cervical dilation gt 4 cm
  • Ruptured membranes

16
TOCOLYTIC AGENTS
  • ß-adrenergic agents
  • Ritodrine
  • Terbutaline
  • Magnesium sulfate
  • Prostaglandin synthetase inhibitor
  • Indomethacin
  • Calcium channel blockers
  • Nifedipine
  • Ritodrine is only FDA approved tocolytic,
    however, terbutaline, magnesium sulfate,
    nifedipine and indomethacin are widely used in US.

17
ANESTHETIC CONSIDERATIONS
  • During labor and delivery, preterm infant at high
    risk of acidosis and has high incidence of
    intracranial hemorrhage
  • High incidence of CD due to fetal distress
  • Preterm infant more sensitive to depressant
    effects of analgesic and anesthetic drugs.
  • Regional anesthesia technique of choice to avoid
    depressant effects of anesthetic drugs.
  • Epidural prevents precipitous vaginal delivery
    and rapid decompression of vulnerable fetal head

18
BETA-ADRENERGIC AGONISTS
  • Ritodrine and terbutaline commonly used agents
  • May delay delivery for 24-48 hrs however, not in
    substantial prolongation of pregnancy
  • Contraindicated in severe cardiac or pulmonary
    disease
  • Reported incidence of side effects vary from
    0.54 to 9 as per different studies
  • Side effects include hypotension, tachycardia,
    cardiac arrhythmias, myocardial ischemia,
    pulmonary edema, hyperglycemia, hypokalemia and
    fetal tachycardia
  • Side effects dose related
  • Consider delaying administration of anesthesia
    where feasible until maternal side effects have
    subsided

19
MAGNESIUM SULFATE
  • Extensive experience for use of seizure
    prophylaxis in preeclamptic women
  • Little scientific evidence of efficacy of MgSO4
    for tocolysis
  • Many clinicians consider MgSO4 to be tocolytic of
    choice in patients at high risk of bleeding (P.
    Previa)
  • Less frequent and less severe side effects than
    ß-adrenergic agents
  • Side effects include chest pain, palpitations,
    nausea, transient hypotension, blurred vision,
    sedation and pulmonary edema
  • Can attenuate compensatory response to hemorrhage
  • Some concern about possible increase in perinatal
    mortality
  • May increase risk of hypotension during regional

20
MAGNESIUM SULFATE
  • Loading dose 4 gm over 15-20 min
  • Followed by infusion at 1-4 gm/hr
  • Serum levels of 5-7 mg/dl required for tocolysis
  • 8-10 mg/dl loss of tendon reflexes
  • 10-15 mg/dl respiratory depression
  • gt10-15 mg/dl cardiac conduction defects
  • Potentiates both depolarizers and
    non-depolarizers
  • Causes sedation, ?MAC and ?analgesic requirements
  • Modest prolongation of bleeding time due to
    effect on platelet aggregation by antagonizing
    the effects of Ca

21
INDOMETHACIN
  • Acts by inhibiting cyclo-oxygenase
  • Dose 50 mg PO followed by 25 mg PO 4-6 hr
  • Limit course of therapy to less than 72 hr and
    administer only before 32 week gestation to
    minimize neonatal side effects
  • No cardiovascular side effects like other agents
  • ? thromboxane A2 ??platelet aggregation
  • Does not necessitate assessment of coagulation
    status prior to regional due to transient
    reversible effect on platelet function
  • Can cause premature closure of ductus arteriosus
    in utero resulting in persistent fetal
    circulation if administered after 32 weeks
    gestation
  • Other side effects include oligohydramnios and
    neonatal necrotizing enterocolitis

22
NIFEDIPINE
  • Reduced side effect profile compared to
    ß-adrenergic agonists
  • Some investigators suggest as first line
    tocolytic compared to others
  • Can arrest labor for 48 hrs or longer
  • Can be administered orally or sublingually
  • Dose 10-20 mg PO every 4-6 hours
  • More effective with fewer side effects than
  • ß-adrenergic agents and better neonatal
    outcome
  • However, adverse fetal effects as per some animal
    studies
  • Usually mild maternal side effects like flushing
  • Potential to cause vasodilatation, hypotension,
    myocardial depression and conduction defects when
    used in combination with volatile agents

23
INVESTIGATIONAL DRUGS
  • Studies in progress for agents with fewer
    maternal and fetal side effects
  • Oxytocin antagonist
    Atosiban
  • Anticytokine agents
    Urinary trypsin inhibitor
  • Cytokines Promote production of oxytocin and
    corticotropin, corticotropin stimulates
  • prostaglandin release
  • Nitric oxide donors

24
SUGGESTED READING
  • Muir HA, Chestnut DH. Preterm Labor and Delivery
    in Principles and Practice of Obstetric
    Anesthesia, Editor David H Chestnut, Elsevier
    Mosby, PA.

25
PUTNEY BRIDGE, BATH, ENGLAND
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