1021 Use of electromyography to determine quantitative effects of oxytocin during the 1st stage of labor

Abstract

Electrical activity (EA) is the underlying basis of uterine contractility. The objective of this study is to assess the utility of electromyography (EMG) in measuring uterine EA after oxytocin treatments during the 1st stage of labor. EA was obtained from electrodes (n=4) placed on the abdominal surface near the navel of 61 parturients at a university-based hospital using PowerLab hardware and LabChart software (ADInstruments, New South Wales, Australia). Uterine muscle EA was evaluated by filtering signals from 0.3 to 1.0 Hz. Detailed EA characteristics of uterine activity were further quantified before oxytocin administration (an increase of 2 milliunits per minute) and immediately after treatment using RMS (a quantitative measure of signal magnitude) of EA and rectified EA (a measure of total positive and negative EA signals). Patient records (n=6) with oxytocin infusions (n=7) were analyzed. Data was analyzed using Wilcoxon paired ranks test with SPSS software. EMG records indicate that the onset, magnitude and duration of stimulatory effects of oxytocin are reflected as changes in RMS and rectified EA. There was a significant increase in median values (p=0.027, about 250% increase) in uterine RMS activity and an increase in median values (p=0.090, approaching significance, about 400% increase) in rectified EA following oxytocin administration. 1) This study demonstrates that EMG is an effective and valuable technique to evaluate the quantitative effects of oxytocin, including onset, duration and efficacy on uterine contractility during labor and delivery. 2) Understanding how oxytocin changes the EA of the uterus may improve clinicians’ ability to objectively titrate oxytocin and develop more accurate standardized protocols for its use in labor induction or augmentation. 3) EMG may be used to evaluate the effects of other medications and procedures which stimulate or inhibit labor.