ANESTHETIC CONSIDERATIONS FOR PRETERM LABOR AND DELIVERY

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ANESTHETIC CONSIDERATIONS FOR PRETERM LABOR AND
DELIVERY

• HARRY SINGH, MD
• DEPT. OF ANESTHESIOLOGY
• UTMB

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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

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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

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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

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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

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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

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UTERINE CERVICAL CAUSES

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

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OTHER CAUSES

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

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OTHER CONSIDERATION

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

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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

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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

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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

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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

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BENEFITS OF STEROID BEFORE PRETERM DELIVERY

• Reduced incidence of respiratory distress
  syndrome
• Reduced incidence of intraventricular hemorrhage
• Reduction of neonatal morbidity and mortality

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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

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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.

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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

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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

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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

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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

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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

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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

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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

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SUGGESTED READING

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

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PUTNEY BRIDGE, BATH, ENGLAND