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Obstetrics Simplified - Diaa M. EI-Mowafi

Ecbolics (Uterine Stimulants)

Definition

These are agents that induce and/ or maintain uterine contractions.
The commonest of them in current use are:

  • Oxytocics.
  • Prostaglandins.
  • Ergot alkaloids.

OXYTOCICS

Types

  • Posterior pituitary extract: which is composed of;
    • oxytocin or pitocin and
    • vasopressin which has vasopressor and antidiuretic action. It is not used in obstetrics as it may cause coronary spasm.
  • Synthetic oxytocics:
    • Oxytocin (Pitocin): a purified posterior pituitary extract.
    • Syntocinon: synthetic oxytocin.

Mode of Action

Oxytocics act on the pregnant uterus within 1 minute if injected IV, within 2 minutes if injected IM and its action lasts for 30 minutes. These cause initiation and increase in frequency, strength and duration of uterine contractions. These are more effective with the advancement of pregnancy.

Routes of Administration

  • IV drip is the most common use.
  • IV pump using an electronic pump: is the most accurate for calculation of the infused dosage.
  • IM and IV bolus may be given postpartum.
  • Direct intramyometrial: during caesarean section.
  • Nasal spray: to help evacuation of the engorged breasts.

Indications

  • Inevitable, incomplete and missed abortions.
  • Induction of labour.
  • Augmentation of labour.
  • Evacuation of vesicular mole.
  • Prophylaxis and treatment of postpartum haemorrhage.
  • Oxytocin challenge test.

Contraindications

  • Previous uterine scar as C.S, hysterotomy or open uterus metroplasty.
  • Some malpresentations as shoulder and brow presentations.
  • Foetal distress and placental insufficiency.
  • Contracted pelvis.
  • Grand multipara. 6-Incoordinate uterine actions.

Complications

  • Rupture uterus. 
  • Foetal distress and asphyxia.
  • Constriction ring and hypertonic inertia.
  • Amniotic fluid embolism.
  • Water intoxication due to its antidiuretic effect and the large amount of IV fluids when given as a drip.
  • Coronary spasm if the crude posterior pituitary extract was used.

PROSTAGLANDINS (PG)

Nature

PGs are naturally occurring unsaturated fatty acids present in different body fluids and tissues as the seminal fluid, endometrium, amniotic fluid, lungs and brain.
PGs are resulted from the action of PG synthetase enzyme on arachidonic acid.

Obstetric Actions

  • Ripening of the cervix: Natural and synthetic PGs can ripen the cervix at any stage in pregnancy by inducing collagen breakdown and tissue hydration.
  • Initiation and/or stimulation of uterine contractions: at any stage of pregnancy.

Obstetric Indications

  • Induction of abortion.
  • Induction of labour.
  • Treatment of postpartum haemorrhage.

Routes of Administration

  • Intramuscular: PGF2α 15-methyl (Prostin 15 M) 250m g/2 hours.
  • Intravenous: PGF2α 0.25m g / minute.
  • Oral: PGF2α (Prostin tablets 0.5 mg) 0.5-1 mg/ hour.
  • Vaginal tablets: PGE2 3 mg.
  • Vaginal gel: PGE2 1-2 mg.
  • Endocervical gel: PGE2 0.5 mg.
  • Extra-amniotic gel: PGE2 400-500m g.
  • Intramyometrial: PGF2α 1 mg.
  • Intra-amniotic and extra-amniotic PGF2a: see induction of abortion.

Complications

  • Nausea.
  • Vomiting.
  • Diarrhoea.
  • Flushing.
  • Tachycardia.
  • Pyrexia.

ERGOT ALKALOID

Ergometrine = Methergin

Action

It induces sustained uterine contraction lasts for 3-4 hours.

Routes of Administration

Route Dose Onset of action
Oral 1mg 7 minutes
IM 0.5 mg 4 minutes
IV 0.25 mg 1 minute

Indications

  • Inevitable and incomplete abortions.
  • Prophylaxis and treatment of postpartum haemorrhage.
  • Subinvolution of the uterus.

Contraindications

  • Before delivery of the foetus as it will cause foetal asphyxia and rupture uterus.
  • Cardiac disease.
  • Hypertension.

Complications: In misuse only;

  • Rupture uterus.
  • Constriction ring.
  • Foetal asphyxia.
  • Hypertension.
  • Retained placenta.

Syntometrine

Is a combination of 5U syntocinone and 0.25 mg methergin given only IM.

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