Normal Uterine Resting Tone on Pitocin with IUPC
Normal uterine resting tone during oxytocin (Pitocin) administration measured by intrauterine pressure catheter (IUPC) should be less than 15-20 mmHg between contractions. 1
Defining Normal Resting Tone
Baseline intrauterine pressure should remain below 15-20 mmHg between contractions during oxytocin infusion, as elevated resting tone above this threshold indicates uterine hyperstimulation and potential complications. 1
The FDA oxytocin label specifically warns that resting tone of 15 to 20 mmHg or more between contractions constitutes hyperstimulation and can lead to serious complications including tumultuous labor, uterine rupture, uteroplacental hypoperfusion, and fetal compromise. 1
Clinical Monitoring Parameters
Continuous monitoring of resting uterine tone is essential when using IUPC during oxytocin administration, along with assessment of contraction frequency, duration, and intensity. 2
The IUPC provides accurate measurement of both contraction amplitude and baseline resting tone, which cannot always be reliably assessed with external tocodynamometry. 2
Research demonstrates that mean baseline uterine tone measurements with IUPC systems typically range around normal physiologic levels, though correlation for resting tone measurements between different IUPC systems can be variable (r = 0.34). 3
Critical Action Thresholds
Immediate discontinuation of oxytocin is mandatory when baseline intrauterine pressure reaches or exceeds 15-20 mmHg, as this indicates overdosage and uterine hyperstimulation. 1
If baseline pressure reaches 40 mmHg during oxytocin administration, this represents severe hyperstimulation requiring immediate cessation of oxytocin, maternal repositioning to left lateral position, supplemental oxygen administration, and consideration of tocolysis if fetal heart rate abnormalities develop. 4
Management of Elevated Resting Tone
Stop oxytocin infusion immediately as the first intervention when elevated resting tone is detected, as oxytocic stimulation of uterine musculature will rapidly wane after discontinuation. 1
Implement intrauterine resuscitation measures including left lateral positioning, oxygen at 6-10 L/min via face mask, IV fluid bolus, and continuous fetal heart rate monitoring. 5, 4
Perform vaginal examination to assess for rapid descent, cord prolapse, or signs of uterine rupture when elevated baseline tone is detected. 4
Consider tocolysis with terbutaline to reduce uterine tone if fetal heart rate abnormalities (Category II or III patterns) develop in conjunction with elevated resting tone. 4
Common Pitfalls
Do not rely on external tocodynamometry alone to assess uterine resting tone during oxytocin administration, as external monitoring cannot accurately measure baseline intrauterine pressure or contraction intensity. 2
Do not continue oxytocin infusion if resting tone remains elevated after initial dose reduction—complete discontinuation is required when hyperstimulation is present. 1
Do not delay intervention waiting for fetal heart rate changes, as elevated resting tone itself (≥15-20 mmHg) is an indication to stop oxytocin regardless of fetal status. 1