https://www.obsgynaecritcare.org/wp-content/uploads/2017/08/Oxytocin-in-labour-increases-PPH.m4a

 

The use of oxytocin to induce or augment labour is an established, commonly used practice that underpins a lot of modern obstetric practice. This technique is a undoubtedly a useful tool which has allowed us to improve maternal and fetal outcomes. For example to induce a timely delivery when maternal illness such as PET occurs or to avoid an operative delivery for a mother when their spontaneous progress in labour is slow.

However, like most things in medicine (and life in general) there is no such thing as a "free lunch" and it is perhaps a less well recognised fact that the use of oxytocin in labour - especially at higher doses and for prolonged periods - is associated with an increased risk of postpartum haemorrhage due to uterine atony.

Uterine atony is becoming more common in developed countries:

The incidence of uterine atony causing postpartum haemorrhage in developed countries has increased markedly in the last 2 decades - one of the important factors contributing to this is thought to be the increased prevalence and use of oxytocin during labour.

Lutomski JE1, Byrne BM, Devane D, Greene RA. Increasing trends in atonic postpartum haemorrhage in Ireland: an 11-year population-based cohort study. BJOG. 2012 Feb;119(3):306-14. 

Epidemiological investigation of a temporal increase in atonic postpartum haemorrhage: a population-based retrospective cohort study.

What is the mechanism underlying this phenomenon?

Exposure to oxytocin used during labour over time leads to downregulation and desensitisation of the oxytocin receptors on the myometrium. This leads to a decreased response to oxytocin when used after delivery as a uterotonic to prevent PPH.¹

"Fatigued / tired myometrium". Women who are not progressing well and have been in prolonged labour may have a "tired" myometrium (it is a muscle and it tires after prolonged use). These women may often then receive augmentation with oxytocin in an effort to achieve vaginal delivery. The presence of the oxytocin infusion could also be considered a marker of the presence of a "fatigued / tired" uterus in these individuals.²

1. Oxytocin exposure during labor among women with postpartum hemorrhage secondary to uterine atony. Am J Obstet Gynecol 2011; 204: 56.e1-6.

2. Predictors of severity in primary postpartum hemorrhage. Arch Gynecol Obstet. 2015 Dec;292(6):1247-54.

Recognise these patients BEFORE delivery. Anticipate and prepare for uterine atony!

In Theatre: When patients come from labour ward to theatre for a non elective caesarean during the patient assessment and the team time out specifically enquire about the length of labour & oxytocin use, duration and dose.

In Labour Ward: The midwifery and obstetric team should specifically have a discussion regarding their planned management of the third stage in patients on oxytocin infusions.

Oxytocin is still the best first line uterotonic but anticipate that it may not be effective.

In vitro rat and human studies indicate that oxytocin is less effective in myometrium exposed to oxytocin in labour, but still appears to be more effective than the other uterotonics - at least in vitro anyway.¹

Use oxytocin first but start with your highest recommended dose of oxytocin don't wait until haemorrhage is already well established! At our institution at caesarean delivery I would give a 2-3 unit bolus (and I personally repeat this a few times every few minutes if there is haemodynamic stability) and start the 40u/500ml infusion at 250ml/hr.

1 - Comparative efficacy of uterotonic agents: in vitro contractions in isolated myometrial strips of labouring and non-labouring women. Can J Anaesth. 2014 Sep;61(9):808-18.

In the presence of oxytocin receptor downregulation will the other uterotonics still work?

The ergot and prostaglandin F2α uterotonic drugs work via different receptors and the...