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Oxytocin binds to a G-protein–coupled receptor. Activation triggers elevation of intracellular calcium that stimulates uterine smooth muscle contraction. Its function is regulated by:
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Changes in receptor expression
Receptor internalization leading to oxytocin desensitization
Local changes in oxytocin concentration
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The effects of oxytocin on vascular smooth muscles depend on types of vasculatures and vascular basal tones. While oxytocin induces uterine contractions, higher concentration of oxytocin relaxes the high-resistance vasculatures of skeleton muscles, liver, kidney, and spleen.1 Rapid injection of a large dose of oxytocin in severe hypovolemic patients with postpartum hemorrhage may result in worsening hypotension, myocardial ischemia, circulatory collapse, and even maternal death.2
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Large total oxytocin doses should be avoided to minimize the antidiuretic effect. The patient on high dose of oxytocin for induction of labor for a prolong period could be at increased risk to develop severe hyponatremia or seizure.
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DOSAGE AND ADMINISTRATION
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Dosage and Administration3
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Standardized oxytocin protocols have been shown to reduce the incidence of postpartum hemorrhage.4 Oxytocin should be given as a small initial dose after delivery, followed by a controlled infusion. Oxytocin dose requirements are higher for intrapartum cesarean deliveries.5 FDA mandates to use infusion pump for oxytocin administration (Fig. 4-1).
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A second-line medication (ergot or prostaglandins) should be considered EARLY if oxytocin fails to produce good uterine tone.
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REFERENCES
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Altura
BM, Altura
BT. Actions of vasopressin, oxytocin, and synthetic analogs on vascular smooth muscle.
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Bolton
TJ, Randall
K, Yentis
SM. Effect of the confidential enquiries into maternal deaths on the use of Syntocinon at caesarean section in the UK.
Anaesthesia. 2003;58(3):277–279.
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Heesen
M, Carvalho
B, Carvalho
JCA,
et al. International consensus statement on the use of uterotonic agents during caesarean section.
Anaesthesia. 2019;74:1305–1319.
[PubMed: 31347151]
4. +
Doyle
JL, Kenny
TH, Gothard
MD,
et al. A standardized oxytocin administration protocol after delivery to reduce the treatment of postpartum hemorrhage. Jt Comm J Qual Patient Safety. 2019;45:131–143.
5. +
Lavoie
A, McCarthy
RJ, Wong
CA. The ED90 of prophylactic oxytocin after delivery of the placenta during Cesarean delivery in laboring compared with nonlaboring women: an up-down sequential allocation dose-response study.
Anesth Analg. 2015;121:159–164.
[PubMed: 25902327]