Appropriate Use of Oxytocin for Labor: Why the Fastest Uterus May not Win

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Appropriate Use of Oxytocin for Labor Why the
Fastest Uterus May not Win

• Catherine H. Ivory, RNC, MSN
• January 10, 2007

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Objectives

• Review the physiology of endogenous and exogenous
  oxytocin in labor
• Discuss current research related to the use of IV
  oxytocin and labor progress
• List current accrediting body and liability
  concerns related to oxytocin use

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Current Trends in Labor Induction

• In 2001, 20.5 of labor was induced, a 125
  increase since 1989
• 17.5 of labor was augmented, a 64 increase
• Two thirds of inductions are now for non-medical
  indications

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Trends in Labor Induction

• psychosocial now one of the most common
  induction indications in the U.S.
• Professional OB/GYN organizations in other
  countries (the UK and Canada) discourage elective
  induction

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Explanation for Increased Induction Rates

• Plan timing of delivery (provider, family
  concerns, employment)
• Availability of cervical ripening agents
• Presumed medical liability for expectant
  management
• Relaxed attitude toward non-medical or elective
  induction

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Induction Demographics

• More common in the South
• More common in community rather than university
  medical centers
• Women who choose induction are usually
• White
• Well-educated
• Insured
• Have had good prenatal care

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Endogenous Oxytocin

• Unconjugated estrogen reaches peak levels at term
• Estrogen increases the sensitivity of myometrial
  receptor sites to oxytocin
• Myometrial sensitivity to oxytocin is greater at
  night

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Endogenous Oxytocin

• Uterine tissue (myometrium, placenta, amnion)
  produces oxytocin
• Fetal adrenal DHEA converts estrogen in the
  placenta, leading to increased oxytocin
  production and storage in decidua.
• Labor process stimulates prostaglandin (PGE2 and
  PGF2) in the amnion and decidua

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Endogenous Oxytocin

• Stretching of cervix and vagina stimulates
  oxytocin release from the posterior pituitary
• Oxytocin is maintained by both tonic baseline
  action and pulsatile release action that
  increases as labor progresses

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Endogenous Oxytocin

• During the 1st stage of spontaneous labor,
  average concentration of endogenous oxytocin is
  2-4 mU/min
• The fetus secretes oxytocin at 3mU/min during
  labor
• In active labor, the average plasma concentration
  of oxytocin is 4-6 mU/min

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Exogenous Oxytocin

• Half-life of oxytocin is 7-15 minutes
• 3-4 half-lives are needed to reach steady state
  of plasma concentration
• Once steady state of plasma concentration has
  been reached, uterus responds within 3-5 minutes

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Exogenous Oxytocin

• Uterine activity increases in phases of increased
  contraction strength and intensity, followed by a
  stable period
• A 40 minute or gt interval between oxytocin
  increases allows for full uterine effect and
  minimizes the need for excessive oxytocin
• Once the stable contraction period has been
  reached, additional dose increases will not lead
  to further normal changes in contractions

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Factors Effecting Maternal Response to Oxytocin

• Maternal body surface area
• Gestational age
• Parity
• Cervical status
• Individual bioassay-individual response
• At full-term, most women can have successful
  labor induction with oxytocin rates at 6mU or less

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Fetal Response to Uterine Activity

• Fetal O2 sats decrease with uterine activity with
  the greatest decrease 90 seconds after the
  contraction
• An additional 90 seconds are required for
  complete recovery
• Recovery incomplete with contractions more
  frequent than 2 minutes

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Whats Our Goal with Oxytocin?

• Uterine activity effective enough to result in
  cervical change and fetal descent while avoiding
  uterine hyperstimulation and fetal compromise

ACOG, 2003
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Labor Progression Review
Cervical Dilation (cm)
From To Time Interval (hr) Rate (cm/hr)
2 3 3.2(0.6, 15.0) 0.3 (0.1, 1.8)
3 4 2.7(0.6, 10.1) 0.4 (0.1, 1.8)
4 5 1.7(0.4, 6.6) 0.6 (0.2, 2.8)
5 6 0.8 (0.2, 3.1) 1.2 (0.3, 5.0)
6 7 0.6 (0.2, 2.2) 1.7 (0.5, 6.3)
7 8 0.5 (0.1, 1.5) 2.2 (0.7, 7.1)
8 9 0.4 (0.1, 1.3) 2.4 (0.8, 7.7)
9 10 0.4 (0.1, 1.4) 2.4 (0.7, 8.3)
Zhang, et al, 2002, taken from Creasy and
Resnick, 2004, p672
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What About the Bishop Score?

• Higher the score, the greater the chance of
  successful induction
• Higher scores
• Less length of stay
• Decreased cost
• Decreased risk of cesarean section

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The Bishop Score
Score Dilation(cm) Effacement() Station Cervical Consistency Cervical Position
0 Closed 0 30 -3 Firm Posterior
1 1 2 40 50 -2 Medium Midposition
2 3 4 60 70 -1, 0 Soft Anterior
3 5 6 80 1, 2 - -
Station reflects a -3 to 3 Modified from Bishop, EH. Pelvic scoring for elective induction. Obstet Gynecol 1964 24267 (ACOG, 1999) Station reflects a -3 to 3 Modified from Bishop, EH. Pelvic scoring for elective induction. Obstet Gynecol 1964 24267 (ACOG, 1999) Station reflects a -3 to 3 Modified from Bishop, EH. Pelvic scoring for elective induction. Obstet Gynecol 1964 24267 (ACOG, 1999) Station reflects a -3 to 3 Modified from Bishop, EH. Pelvic scoring for elective induction. Obstet Gynecol 1964 24267 (ACOG, 1999) Station reflects a -3 to 3 Modified from Bishop, EH. Pelvic scoring for elective induction. Obstet Gynecol 1964 24267 (ACOG, 1999) Station reflects a -3 to 3 Modified from Bishop, EH. Pelvic scoring for elective induction. Obstet Gynecol 1964 24267 (ACOG, 1999)
Factor
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Common Areas of Litigation Related to Oxytocin Use

• Excessive doses of oxytocin resulting in uterine
  hyperstimulation, with or without the presence of
  non-reassuring fetal heart rate pattern
• Failure to accurately assess maternal-fetal
  status during induction or augmentation

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Common Areas of Litigation Related to Oxytocin Use

• Failure to fully inform the woman about the risks
  and benefits of elective induction
• Iatrogenic prematurity related to elective
  induction prior to 39 completed weeks of
  gestation
• Failure to accurately determine gestational age
  prior to elective induction

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Elective Induction Bundle

• Components of the bundle to be Documented prior
  to start of Pitocin
• Gestational Age gt 39 weeks
• Reassuring Fetal status
• Pelvic Exam
• Absence of Hyperstimulation with Increases of
  Pitocin

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Augmentation Bundle

• Components of the bundle to be Documented prior
  to start of Pitocin
• Estimated Fetal weight (AGA, LGA, SGA)
• Reassuring Fetal Status
• Pelvic Exam
• Absence of Hyperstimulation with Increases of
  Pitocin

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Common Allegations Related to Misoprostol
(Cytotec)

• Excessive doses resulting in uterine
  hyperstimulation (with or without non-reassuring
  fetal heart rate pattern)
• Uterine rupture
• Use of misoprostol for women with previous
  cesarean birth or uterine scar
• Failure to accurately assess maternal-fetal status

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Assessment of Uterine Activity

• With external toco, palpation should be used to
  assess relative contraction frequency and/or
  strength
• Reconsider dose increases if unable to accurately
  assess uterine activity
• Consider IUPC if unable to assess uterine
  activity externally

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All We Need is an IUPC, Right?

• IUPC pressure measurement varies, depending on
  position of the catheter, the patient, and the
  fetus
• Accurate labor progress has been shown with MVUs
  ranging from 95-395
• No evidence to support improvement of outcomes or
  reduction in neonatal morbidity by calculating
  MVUs (internally measuring uterine activity)

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Summary Recommendations

• Provide complete informed consent for elective
  inductions
• Use only enough oxytocin to achieve a contraction
  pattern which results in labor progressno more
• Start at 1mU/min
• Increase no sooner than 40 minutes
• Make sure uterine activity and fetal status are
  accurately assessed
• Starting dose of Cytotec should be no more than
  25 mcg. Subsequent doses every 3-6 hours.
• Pay closer attention to contraction frequency and
  duration and less attention to MVUs