Oxytocin

Last updated 26.09.12

 

Index

 

 

Definition

- Hormone secreted from pituitary gland

 

Features

- Synthetic analogues used in obstetrics

 

Mechanism

- Let down reflex in lactation

- Uterine smooth muscle contraction

- Cervical dilation

 

Drugs

- Syntocinon

- Syntometrine (Syntocinon + Ergometrine)

 

 

 

Syntocinon

<Oxytocin>

 

Features

- Synthetic peptide analogue of oxytocin

- Metabolised in GIT

- Half life 5-12min

- Does not cross BBB

 

Indications

- IOL

-  When given at time of ARM more likely to deliver in 12hrs & less likely to need operative delivery

- Labour assistance in poor progression

- Active Mx of 3rd stage of labour

- PPH (uterine contraction)

 

Contraindications

- Any contraindications to vaginal delivery

- Fetal distress

- Hyperstimulation

- Placenta or vasa previa

- Placental abruption

- Predisposition to amniotic fluid embolism

 

Side Effects

- Hypotension, flushing, tachycardia

- Nausea, vomiting

- Headache

- May increase risk of DIC

- Prolonged QT interval

- Uterine rupture

- Hyperstimulation

 

Dose

- IM, IV or nasal spray

- 1 ampule = 5 IU in 1ml

- IOL or augmentation

-  IV infusion in 1L NS

-  10 IU in 1L (10mu/ml) for primiparous women

-  Commence at 40ml/hr (6.7mu/min)

-   1 IU = 1000 milliunit (mu)

-   x4 dose of multiparous

-  80ml/hr = 13.3mu/min

-  100ml/hr = 16.7mu/min

-  120ml/hr = 20mu/min

-   Once this is reached reasonable to reassess situation

-  140ml/hr = 23.3mu/min

-  160ml/hr = 26.7mu/min

-  180ml/hr = 30mu/min

-  200ml/hr = 33.3mu/min

-  5 IU in 1L (5mu/ml) for multiparous women

-  Commence at 20ml/hr (1.7mu/min)

-   1/4 dose of primiparous

-  40ml/hr = 3.3mu/min

-  80ml/hr = 6.7mu/min

-  100ml/hr = 8.3mu/min

-  120ml/hr = 10mu/min

-  140ml/hr = 11.7mu/min

-  160ml/hr = 13.3mu/min

-  180ml/hr = 15mu/min

-  200ml/hr = 16.7mu/min

-  Most women achieve adequate activity at 12 mu/min

-  Continuous CTG, regular BP & frequent assessment of uterine response

-  Titrate dose each 30min+

-  Steady plasma concentration by 40min

-  If regular contractions not established after 5 IU then cease

- Active Mx of 3rd stage

-  5-10 IU IM or 5 IU slow IV

- PPH

-  10 IU IM or 5 IU slow IV

-  +/- infusion 40 IU in 1L NS at 4/24 rate

- LUSCS

-  5 IU IV infusion after fetal delivery

 

 

 

Syntometrine

(Syntocninon + Ergometrine)

<Oxytocin>

 

Features

- Syntocinon + Ergometrine

- Uterotonic effect many hrs compared to Syntocinon alone (minutes)

- Used in normotensive pts

 

Indications

- Active Mx of 3rd stage of labour

- PPH (uterine contraction)

 

Contraindications

- HTN, pre-eclampsia, eclampsia

- Occular vascular disease

- Sepsis

- In labour prior to delivery of anterior shoulder

 

Dose

- IM injection

- 1 ampule = 1ml = Syntocinon 5IU + Ergometrine 0.5mg (500mcg)

- 1ml given after anterior shoulder delivered or after expulsion of placenta to prevent PPH

 

 

 

References

 

Induction of Labour at Term, SOGC CPG, August 2001