Oxytocin

Oxytocin is an invaluable drug for making the uterus contract: (1) To induce labour. (2) To accelerate labour. (3) To stop bleeding after abortion or delivery.

The main dangers are that: (1) If you give too much too fast to a patient of high parity late in labour, her uterus may rupture. The sensitivity of the uterus to oxytocin varies greatly. Early in pregnancy it is comparatively insensitive; it becomes much more sensitive later, especially in multips. So in a pregnant patient always give it by intravenous infusion, starting with a small dose. If you do not get the effect you want, give more in an escalating (increasing) oxytocin drip. After delivery, or during an abortion, this rule does not apply, and you can safely give it by bolus intravenous injection, or intramuscularly. (2) In giving oxytocin by infusion, it is possible to give her too much fluid at the same time, especially when you use oxytocin to induce labour early in pregnancy, when you may need high doses. So when you give an escalating oxytocin drip, avoid the danger of water intoxication by giving it in 0.9% saline or Ringer's lactate, not in 5% dextrose, see Section 16.4.

The primigravid uterus is sufficiently insensitive for oxytocin to be safe enough for midwives to give routinely to accelerate labour. Using oxytocin to accelerate labour in multips can be dangerous, so it should only be given when: (1) The midwifery team is experienced, and able to adjust the ''drops per minute' carefully. And, (2) after the doctor on duty has seen and examined the patient, and has excluded a brow presentation, and CPD (which may not be easy). At least one contributor considers that oxytocin should never be used to accelerate labour in multips. In Africa, the head is often high through much of the first stage. Speeding its descent with oxytocin is dangerous for the inexperienced. If a multip's labour is slow, and her previous deliveries were normal, she will probably deliver her present baby eventually, provided he is a cephalic presentation. So it is likely to be safer to leave her, after examining her carefully to exclude a brow, than to risk rupturing her uterus by giving oxytocin unnecessarily.

Fig. 18-5a AN OXYTOCIN TABLE. The dose of oxytocin received by the patient in milliunits per minute depends on the concentration of oxytocin in the bottle and the speed of the drip in drops per minute. The table assumes a standard drip set delivering 15[nd]20 drops per ml. The concentration of oxytocin in the bottle is given in units per litre and [f10]not [f11]in units per 500 ml, as in the text.

OXYTOCIN Here are the main methods and indications for the use of oxytocin. See also: breech presentation 19.8, and multiple pregnancies 19.11, etc.

ADJUST THE DOSE to the patient[md] ''titrate it' against the response. Start with a low dose and increase it until you get the response you need. The dose rate (''drops per minute') is critical. Always start with a slow rate, and increase it if necessary every half hour, until she has the contractions she needs (usually 2 or 3 contractions every 10 minutes). Don't give more than 60 drops per minute, or you will give too much fluid. If you need more than 30 drops a minute, double the concentration and halve the drip rate for the next bottle. Note that we give the units of oxytocin to be added to 500 ml of fluid (''one bottle'), and not to one litre.

TO INDUCE LABOUR:

To induce labour between 10 and 28 weeks when the baby is dead (16.4). The uterus is much less sensitive than it is at term, and there is less danger of rupture, so start with 5 units in 500 ml, at 25 drops a minute, and if this does not work, increase the dose the next day, as in Section 16.4. 100 units in 500 ml is the absolute maximum. Read what Section 16.4 has to say about the dangers of water intoxication.

To induce labour at term in primips or in multips [lt]para-4 (19.3). Use 5 units in 500 ml at 10 drops a minute, and increase the speed of the drip to 60 drops/minute as necessary, as in Section 19.3.

If a multip at term is [mt]para-4, use 2.5 units in 500 ml.

If the baby is dead at term, you can use up to 20 units/500 ml, except in multips [mt]para-4.

CAUTION ! (1) Whenever you give oxytocin to induce labour, give it by day rather than by night, when monitoring her reliably will be more difficult. (2) You can increase the drip rate, but don't exceed the concentrations above for particular categories of patients.

TO ACCELERATE LABOUR:

To accelerate labour in primips. Give 2.5 units/500 ml, and don't increase the concentration. Start at 10 drops a minute and increase the drip rate by 5 drops each half hour as necessary, to a maximum of 60, until you obtain contractions lasting 45[nd]60 seconds at 2[nd]3 minute intervals.

To accelerate labour in multips. This is controversial, so see above. Give the same dose as in primips, but with extra special care! A midwife must monitor the patient all the time. One contributor advises 1 unit in 500 ml. This is also the dose Primary Mother Care advises for the acceleration of labour, and then only in primips.

TO MAKE THE UTERUS CONTRACT AND CONTROL BLEEDING after abortion (16.2) or delivery (19.11a). For this purpose you can give oxytocin as an intravenous infusion, or by bolus intravenous injection. You can also give it by intramuscular injection. For this it is best combined with ergometrine as ''Syntometrine' (ergometrine 0.5 mg, oxytocin 5 units in 1 ml).

If you are giving oxytocin in an intravenous drip to control bleeding after abortion or delivery, add 20 or (with a PPH) even 40 units (the maximum) to 500 ml of fluid. Usually quite a modest drip rate is sufficient to control bleeding, but in emergency, you can run the drip in ''fast'.

CAUTION ! (1) Never give a bolus intravenous injection of oxytocin before the baby has been delivered. (2) Intramuscular injections of ergometrine or oxytocin can only be used safely to empty the uterus and expel the placenta and membranes before 16 weeks. After 16 weeks use an oxytocin drip.

BEWARE OF OXYTOCIN IN MULTIPS! Fig. 18-6 WHERE TO PUT THE CUP OF THE VACUUM EXTRACTOR. You will find a vacuum extractor invaluable. Attach the cup as nearly as you can over his posterior fontanelle.