18.6 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.