Intrauterine Pressure Catheter Placement

An intrauterine pressure catheter (IUPC) is a device placed into the amniotic space during labor in order to measure the strength of uterine contractions.

External tocodynamometers are used to measure tension across the abdominal wall and detect only contraction frequency and duration. The appearance of contractions by external monitoring may be affected not only by contraction strength but also by maternal habitus, position, gestational age, and monitor location on the abdomen.

Intrauterine pressure catheters work by directly measuring pressure within the amniotic space using a pressure transducer at the tip of the catheter which allows for quantification of contraction strength. After connection to the appropriate cable, contractions are measured in mm Hg and displayed on the monitor in a graphic fashion (see image below).

With an intrauterine pressure catheter in place, Montevideo units (MVUs) can be calculated to assess for adequacy of labor in cases of suspected labor dystocia or during labor induction. MVUs are calculated by subtracting the baseline uterine pressure from the peak uterine pressure of each contraction in a 10-minute window of time and then taking the sum of these pressures. Two hundred Montevideo units or more is considered adequate for normal labor progression.[1]

Routine use of intrauterine pressure catheters is not recommended. A large randomized trial of internal versus external tocodynamometry for monitoring labor showed no difference in rates of operative delivery or fetal outcomes between the two groups. Internal tocodynamometry is more costly and more invasive and thus should be reserved for specific circumstances (see Indications).[2, 3]

An intrauterine pressure catheter is placed when quantification of contraction strength is desired, typically to assess the adequacy of spontaneous contractions in cases of arrested cervical dilation.

It may also be used to facilitate titration of the oxytocin dosage during induction or augmentation of labor. Placement of an intrauterine pressure catheter can reduce the use of oxytocin during high-risk labor with signs of fetal distress.[4]

An intrauterine pressure catheter can provide a more accurate assessment of contraction duration, length, and strength in patients in whom external tocodynamometry does not pick up contractions well, such as in obese patients.

In cases of fetal heart rate decelerations, an intrauterine pressure catheter can be used to clarify the relationship between the timing of the deceleration and the contraction.

Finally, intrauterine pressure catheter placement also allows an amnioinfusion to be performed in cases of severe variable fetal heart rate decelerations.

An intact fetal membrane is a contraindication to intrauterine pressure catheter placement, as the desired location is within the amniotic space. Amniotomy just prior to intrauterine pressure catheter placement is acceptable in the absence of contraindications to amniotomy.

Equipment used in intrauterine pressure catheter placement is as follows:

• Sterile gloves

• Intrauterine pressure catheter (see image below)

• Intrauterine pressure catheter cable (see image below)

  An intrauterine pressure catheter and cable.

• Labor monitoring equipment (see image below)

  An example of a fetal heart rate and contraction monitor.

Anesthesia

No anesthesia is required for intrauterine pressure catheter placement. Patients usually experience only slightly more discomfort than that associated with cervical examination alone.

Positioning

Intrauterine pressure catheter placement is most easily accomplished in the supine, frog-leg position. However, any position in which the provider and patient are comfortable with the procedure is acceptable, including lateral and knee-chest.

Overall, complications of intrauterine pressure catheter placement are uncommon.

The most serious risks are associated with extraovular catheter placement. Several case reports have described placental abruption,[5] placental laceration, and laceration of a fetal placental vessel[6] requiring emergent cesarean delivery following intrauterine pressure catheter insertion. Each of these cases described fetal heart rate changes, including decelerations and bradycardia, within several minutes of intrauterine pressure catheter insertion. These complications highlight the importance of verifying intraamniotic placement of the catheter and carefully monitoring the fetal heart rate tracing following insertion. Introduction of a foreign body also increases the risk of intraamniotic infection.[7]

In an observational study of 16,887 women who had a cesarean delivery, intrapartum placement of an intrauterine pressure catheter was associated with a greater risk of post-cesarean surgical site infections.[8]

The first step of intrauterine pressure catheter placement is examination of the cervix and presenting part. The cervix must be adequately dilated to place the catheter, at least 1-2 cm.

The tip of the firmer plastic introducer, which contains the intrauterine pressure catheter, is inserted just through the cervix into the amniotic space.

Once the end of the introducer is appropriately positioned, the practitioner’s examining hand holds the introducer in place while the other hand is used to advance the pressure catheter through the introducer into the amniotic space about 10-12 cm. The catheter should thread easily. With correct placement, clear or blood-tinged fluid will be seen within the lumen of the catheter. If blood or no fluid returns, the catheter is likely located between the membranes and endometrium (extraovular), and it should be withdrawn and repositioned.

Once correct position is confirmed, the catheter is farther advanced until the “stop” marking on the catheter is located at the introitus. The introducer is then removed while the catheter is held in place to prevent its inadvertent removal. The catheter is then secured to the inner thigh and attached to the cable.[9]

Intrauterine pressure catheters are removed by simply pulling gently on the catheter.

Occasionally, the catheter does not advance easily through the introducer or may be felt coiling just past the cervix, likely because the catheter is being blocked by a fetal part. The introducer should be held in place while the catheter is withdrawn. The introducer should then be rotated around to a different position on the presenting part and advanced again. If frank blood returns through the catheter, it has likely been incorrectly placed in the extraovular space. The catheter and introducer should be withdrawn and repositioned while the patient is closely monitored for continued bleeding.