While IUP catheters accurately read what they “see” readings may not accurately represent the general amniotic space pressure due to improper placement outside the membranes or placement in an isolated pocket.  Your clinical expertise is needed to assess intrauterine pressure readings as one factor in patient care.

IUP in Different Locations

In a later study with multiple intramuscular sensors and an intrauterine pressure catheter, Caldeyro-Barcia and Alvarez^[ii] showed that good synchronization of uterine activity is characteristic of normal uterine contractility.  This same study confirmed that asynchronical uterine activity occurs which hampers contraction intensity, baseline tonus, and the birth process.  This may provide evidence that explains why IUP monitoring can go smoothly and provide information consistent with clinical assessment and at other times not.

Neuman^[iii] inserted two IUP catheters into the same gravid uterus and found that “…no single uterine pressure observation is an accurate reflection of uterine pressure during labor.”  Neuman postulates that localized intrauterine pressures occur “once the membranes are ruptured and amniotic fluid is lost, local regions of amniotic fluid can be formed between the fetus and the uterine wall.  When there is hydrostatic communication between these regions and the fetal head is tightly seated against the cervix…and a ‘good’ contraction results with the pressure being equal at all points.  If the regions are isolated each will have a pressure which is determined only by local conditions.”

IUP in the Same Location

Clinical Assessment

There are several steps you can take to ensure the accuracy of intrauterine pressure monitoring and assess pressure readings.  First of all it is important to properly place the catheter.  Do this by inserting the catheter 4-6cm and watching for a flashback of amniotic fluid before advancing the catheter.  If you don’t see fluid, withdraw the catheter and insert in a different quadrant until fluid is seen.

The catheter must be properly zeroed.  If using a transducer tipped catheter, be sure zero the catheter before insertion because once the transducer is inserted it can no longer be exposed to atmosphere and properly zeroed.  To zero catheters with the transducer outside the patient simply expose the transducer to atmosphere by disconnecting the catheter or opening the stopcock and zero the monitor.

To clinically assess a catheter that has already been placed, start by ascertaining placement location.  Look at the contents in the clear amniolumen or open the amniocommunication port.

• If there is amniotic fluid, bloody show tinged fluid, meconium, or vernix in the lumen the catheter should be in the amniotic space.
• If there is frank blood, it is most likely placed outside the membranes and possibly near the placenta.  Take into account that readings outside the membranes may not represent the general amniotic space pressure and remember not to amnioinfuse.
• If the lumen is empty, you don’t know where the catheter is placed.

Check zero and for proper function of the electronics.

• With external transducers disconnect the catheter or open the stopcock.  This way you not only can check zero but you eliminate any concern the electronics are causing problems.
• Transducer tipped-catheters must be zeroed before insertion since the transducer is inserted into the uterus and can no longer be exposed to atmosphere. Most systems have a switch that you can use to short out the transducer from the monitor and adjust the monitor independent of the transducer. Using these switches does not zero the system and may introduce error since the transducer is not communicating with the monitor.

Reposition patient and/or catheter and flush

• You can have the patient change positions and document how this affects the readings.
• Withdrawing and/or advancing the catheter slightly or flushing a small amount of fluid through the amnioport may move the tip out of an isolated pocket or open a pocket to communication with the general amniotic space pressure.

You’re the Expert

Remember that an IUPC is a valuable tool that provides accurate measurement of what is affecting it at the sensor, but an IUPC does not replace your expertise of clinically assessing the patient based on multiple factors.

Assessment tools of Koala

The Koala Intrauterine Pressure System makes assessment easy. You can easily verify placement by viewing the contents of the clear amniolumen and truly zero by simply disconnecting the catheter from the cable. Disconnecting the catheter from the cable also verifies the function of the electronics and eliminates them from your clinical assessment.

CI offers onsite IUPC training, CME and CEU courses, and nurse insertion training programs. Please contact us at koala@clinicalinnovations.com or call 888.268.6222.

References:

[i] Caldeyro, R., Alvarez, H, Reynolds, S.R.M., “A Better Understanding of Uterine Contractility through Simultaneous Recording with an Internal and a Seven Channel External Method,” Surgery Gynecology and Obstetrics, December 1950, Vol. 91, No. 6
[ii] Caldeyro-Barcia, R. Alvarez, H., “Abnormal Uterine Action in Labour.” Journal of Obstetrics and Gynaecology, pg 646-656
[iii] Neuman, M.R., Jordan, J., Roux, J.F., Knoke, J.D., “Validity of Intrauterine Pressure Measurement with Transcervical Intra-Amniotic Catheters and an Intra Amniotic Miniature Pressure Transducer during Labor.” Gynec. Invest. 1972, Vol. 3, Pg 165-175
[iv] Dowdle, M., “Comparison of Two Intrauterine Pressure Catheters During Labor,” The J Reprod Med, 2003; 4807-0501 - Dowdle Article