Oxytocin for Induction of Labour

Section 2.1

Midwives may administer this drug after consulting with and on the order of a medical practitioner.

Oxytocin is a hormone that simulates uterine smooth muscle to contract by activating protein receptors which act on myofibrils. Oxytocin increases production of prostaglandin which further stimulates uterine contractions.

Contraindications:

Hypersensitivity to oxytocin or any component of the formulation. For induction and augmentation, any contraindication to labour including: placenta previa, vasa previa, cord presentation, fetal malpresentation such as transverse or footling breech, prior classical or inverted T cesarean section, previous uterine surgery such as myometrial incision, active genital herpes, pelvic structural deformities, cervical carcinoma, previous uterine rupture.

Warnings and Precautions:

Oxytocin is structurally and functionally related to vasopressin and its antidiuretic action can lead to water retention. For this reason electrolyte-containing solutions should be used when administering oxytocin. Water intoxication can lead to hyponatremia, confusion, convulsions, coma, congestive heart failure, and death. Fluid overload and hyponatremia with concurrent oxytocin administration may be prevented by strict intake and output recordings anduse of balanced salt solutions such as normal saline or lactated Ringer’s.

Pregnancy:

Compatible for induction or augmentation of labour

Lactation:

Category L2 – Limited Data – Probably Compatible

Adverse Reactions:

Arrhythmias, hypertensive episodes, nausea, vomiting, uterine hypertonicity, tetanic contraction of the uterus, uterine spasm, anaphylactic reaction, subarachnoid hemorrhage, severe water intoxication with convulsions, coma, and death is associated with a slow oxytocin infusion over 24 hours.

Dosage and Administration:

30 international units (IU) of oxytocin in 500 mL of normal saline or 500 mL of Dextrose 5% normal saline in a secondary IV line via infusion pump to give 60 milliunits/mL.
Conversion Note: 1 mL/hr = 1 milliunit/minute (mU/min)

Low-dose oxytocin

– Increase by 1-2 mU/min

Indication:

All augmentations in 2nd stage
Parous augmentation
Grand multiparous induction
VBAC augmention/induction (increase by 1 mU/min)

High-dose oxytocin

– Increase by 2-4 mU/min

Indication:

Parous induction
Nulliparous augmentation/induction in 1st stage

Initiate oxytocin infusion at 1-2 mU/min
Increase oxytocin at 30-minute intervals until regular uterine activity is established
Usual dose for labour = 8-12 mU/min

Maximum dosage:

30-36 mU/min or 20 mU/min for VBAC

If tachysystole (more than 5 contractions in 10 minutes over 30 minutes or one contraction lasting more than 2 minutes):

  • Decrease oxytocin dose to achieve the desired uterine activity.
  • If fetal heart pattern is normal and uterine activity is normal, resume titration of oxytocin infusion.
  • Discontinue oxytocin if tachysystole persists greater than 30 minutes and is unresponsive to decreasing dose. Notify physician immediately.

If fetal heart assessment is atypical:

  • Follow FH Surveillance/Intrapartum Electronic Fetal Monitoring guidelines.
  • Notify physician to seek guidance regarding dose and management plan.

If fetal heart assessment is abnormal:

  • Discontinue oxytocin.
  • Request physician attendance to seek guidance regarding dose and management plan.

Onset of Action:

IM: 2-5 minutes
IV: 1-5 minutes

Half-life:

IM and IV: 6-15 minutes.

Elimination: Excreted by the kidneys.