Oxytocin administration in patients with a BP >160mmHg

Thank you for your MedicASK question regarding Oxytocin and the condition that the patients with sustained blood pressure above 160 mmHg have a risk of potential adverse events. This condition stems from the product monograph (see links below) that state it is contraindicated in patients with “uterine inertia or severe toxemia”. Toxemia is an outdated term for pre-eclampsia. “Preeclampsia refers to the new onset of hypertension and proteinuria or the new onset of hypertension plus significant end-organ dysfunction with or without proteinuria in a previously normotensive patient, typically after 20 weeks of gestation or postpartum” (UpToDate, 2023). Preeclampsia prevalence is 2-10% of pregnancy worldwide. The Ontario Base Hospital Group (OBHG) chose the limit of 160 mmHg based on this product monograph provided by the manufacturer as an extra level of safety for our patients.

It is understood that obstetrician guidelines and midwives recommend and use Oxytocin "off-label" as they engage in risk benefit evaluation in each case and concerns about causing hypertension. If you think that your patient would benefit from Oxytocin, and they have a sustained systolic blood pressure above 160 mmHg, recognizing that giving birth will drive BP up at time of labor, then a base hospital patch and discussion with the physician would be needed.

The companion document also mentions that there is some "evidence indicating that oxytocin can induce vasoconstriction, therefore exacerbating hypertension" and while most of these studies were done with IV Oxytocin, there is always the potential for these effects with this medication no matter the route of administration.

You mention that Oxytocin has a natriuretic effect and therefore could cause a decrease in blood pressure. However, as mentioned above, a risk benefit approach should be taken. One study done by Langesæter et. al mention that, “findings suggest that patients with preeclampsia may have a more unpredictable response to oxytocin” and is another reason it is currently not recommended for these patients.

We are currently conducting a review of these types of calls that have occurred in the RPPEO region over a period of 5 years. This review is to determine if Oxytocin could have potentially been given to patients with registered blood pressures above 160mmHg and what safety factors we need to further consider. We hope to obtain supplementary understanding of these calls, our patients, and of course the potential to help our communities. This review could lead to support for changes to the ALS PCS Emergency Childbirth Medical Directive.