Methods Of Induction - 3

I.V. OXYTOCIN

Synthetic oxytocin by continuous intravenous infusion is commonly used after amniotomy to stimulate uterine contraction. It is also used occasionally with intact membranes e.g. to help stabilise the fetus with a variable lie prior to amniotomy. In this circumstance care should be taken to prevent excessive uterine action which can cause amniotic fluid embolism. Like amniotomy, intravenous oxytocin is also used to augment or accelerate labour. Synthetic oxytocin is a powerful drug and sometimes unpredictable, as uterine sensitivity can show a wide variation. It must be administered with great care by the doctor or midwife who should be present throughout.

Effect on uterine activity: This varies with time and the progress of labour. Since too little oxytocin is useless and too much may cause fetal hypoxia or uterine rupture, it is necessary to adjust the dosage to the individual patient’s response.

The best method of administration is by a suitable semi-automated infusion system
incorporating an accurate drop counter. A solution of 2 units of syntocinon in 500 ml of
Hartmann’s solution is used beginning at a dose of 2.66 mU/minute). This is increased every
15 minutes until satisfactory contractions are established.

Complications of oxytocin

• Poor uterine action

This may occur where amniotomy has been carried out in spite of an unfavourable cervix.
Ripening of the cervix with prostaglandin should be used first in these circumstances.
Sometimes, in spite of apparently satisfactory uterine action, little dilatation of the cervix
occurs and labour has to be terminated by caesarean section. This is due to incoordinate
uterine action resulting in dysfunctional labour.

• Abnormal fetal heart rate patterns

Prolonged or excessive oxytocin administration can cause fetal hypoxia by over-stimulation of
the uterus. Continuous fetal heart rate monitoring is required for all patients undergoing
oxytocin stimulation.

• Hyperstimulation

Overdosage can cause excessive, painful contractions and even a prolonged spasm (tetanic
contraction). If hyperstimulation becomes evident the infusion should be stopped to allow
the uterus to relax.
An intra-uterine pressure transducer may be used in women who are difficult to assess e.g.
the obese.

• Rupture of the uterus

The possibility of rupture must be borne in mind when using oxytocin. It is unlikely in a
primigravida but has been reported. It is more to be expected in the parous woman or in the
patient who has had a previous caesarean section or hysterotomy.The use of an intra-uterine
pressure transducer may be advisable in such patients. Epidural anaesthesia does not mask
the pain of uterine rupture but it should be used with caution.

• Water intoxication

This may result from the prolonged administration of high doses of oxytocin in large volumes
of electrolyte-free fluid.This should not be an issue in labour using normal dosage of
oxytocin in an agent such as Hartmann’s solution.

ACCELERATION OF LABOUR

The progress of spontaneous labour can be speeded up by amniotomy and oxytocin infusion.
By using these techniques most women can be delivered within 12 hours. Prolonged labour
is thus avoided together with its possible accompaniment of maternal exhaustion, fetal
distress and intra-uterine infection. Such interventions should not, however, be automatic
and their indiscriminate application has aroused hostility in some mothers. If acceleration is
considered desirable the reason for this should be explained and discussed with the mother.

Category: Obstetrics Notes