The primary objective is to obtain data to inform the design of a population pharmacokinetic study of oxytocin after administration at CD as per standard institutional practice.
In this pilot study the investigators will compare plasma oxytocin concentrations measured in arterial and venous blood, after oxytocin administration at cesarean delivery, in order to assess the validity of venous samples. They will also measure oxytocinase to explore how levels vary around the time of delivery of the placenta and to assess the effect that this may have on the metabolism of oxytocin.
Study Type
OBSERVATIONAL
Enrollment
30
PK measurements of oxytocin
The investigators will take serial readings from a digital durometer at the uterine fundus at 3, 6, 9 and 12 minutes following OXT administration to provide data that will inform an estimate of the timing of peak effect. Shore durometers measure the hardness of materials on a scale of 0-100 Shore Units (SU). Preliminary (unpublished) data provided a range of 10-56 SU after oxytocin administration at cesarean delivery. Durometer readings were also shown to correlate positively with the obstetrician's manual assessment of uterine contractility, which is traditionally used to determine the success or failure of uterotonic therapy.
Washington University in St. Louis
St Louis, Missouri, United States
Arterial [OXT]
Concentration of oxytocin in arterial samples
Time frame: Scheduled samples during the first 30 minutes after oxytocin administration
Venous [OXT]
Concentration of oxytocin in venous samples
Time frame: Scheduled samples during the first 30 minutes after oxytocin administration
Arterial [OXTase]
Concentration of oxytocinase in arterial samples
Time frame: Scheduled samples during the first 30 minutes after oxytocin administration
Uterine tone
Uterine tone measured using a Shore Durometer or assessed by obstetrician using numerical rating score (NRS, 0-10)
Time frame: Scheduled measurements during the first 30 minutes after oxytocin administration
Hypotension
Incidence of systolic BP reduced by 20% from baseline
Time frame: Measured intraoperatively
Nausea & Vomiting
Incidence of nausea and vomiting
Time frame: Recorded intraoperatively
EBL
Estimated blood loss in milliliters
Time frame: Estimated at the end of surgery
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