Oxytocin (Pitocin)

Anesthesia Implications

Classification: Uterotonic
Therapeutic Effects: Induce/augment labor, uterine contraction, reduce uterine hemorrhage
Time to Onset: IV – Immediate
IM – 3-5 minutes
Time to Peak: IV: < 20 minutes
IM: 40 minutes
Duration: IV: 20 – 60 minutes
IM: 2 – 3 hours

Contraindications

Significant cephalopelvic disproportion
Fetal distress (where delivery is not imminent)

Use with caution in patients with preeclampsia, essential hypertension, cardiac disease

Primary Considerations

Pressors – Oxytocin potentiates sympathomimetic effects of pressors (eg. ephedrine, phenylephrine)

Water Intoxication – Structurally, oxytocin is similar to antidiuretic hormone, which is where the concern for water intoxication comes from. Watch fluid intake carefully.

Transient vasodilation – high doses of oxytocin can produce transient vasodilation and subsequent hypotension, which is usually accompanied by a baroreceptor reflex (temporary increase in heart rate).

Uterine Rupture – When used for labor induction, oxytocin MAY increase the risk of uterine rupture

Side effects – water retention, hyponatremia, hypotension, hypertension, reflex tachycardia, coronary vasoconstriction, nausea, vomiting, subarachnoid hemorrhage.

Math conversion – Each unit of Oxytocin is roughly 1.7 mcg.

IV infusion dose

10-40 units added to 1 liter of crystalloid. Typically infused ‘wide open’ after delivery of the baby. The exact dose for adequate uterine tone (in 95% of parturients) in a non-laboring elective cesarean delivery is a 1 unit bolus of oxytocin followed by an infusion rate of oxytocin at 7.72 units/hr.

IM dose

3-10 units

Method of Action

Endogenous oxytocin is naturally released from the posterior pituitary in response to cervical, vaginal, or breast stimulation. With oxytocin, uterine contractions become more forceful and in higher frequency. Uterine tone is increased.

Metabolism

Hepatic