Transcutaneous Electrical Nerve Stimulation (TENS) for Pain Control During Cervical Dilator Placement Prior to Dilation and Evacuation

Dilation and Evacuation is the most common method of second trimester abortion. Studies have shown that adequate cervical preparation is necessary for the procedure to be performed safely and reduce the risk of complications. However, in the majority of cases the placement of these dilators is done with minimal pain management options.

Transcutaneous electrical nerve stimulation (TENS) has been used in pain relief since 1965, when Melzack and Walls proposed using electrical stimulation as analgesia based on the gate control theory of pain relief. TENS units are small, inexpensive, portable, battery-powered devices which deliver mild, alternating electrical currents via electrodes positioned on the skin near the anticipated dermatomal distribution of pain. The parameters of pulse frequency and pulse intensity are adjustable and linked to TENS efficacy. They overall have a favorable safety profile. Contraindications include electronic implants, such as cardiac pacemakers and implantable cardioverter defibrillators.

Two main theories have been proposed regarding how TENS provides analgesia. According to the "gate control" theory, neuromodulation may activate large myelinated afferent nerve fibers in the dorsal horn to inhibit transmission in primary afferent nociceptive fibers. The inhibitory input from the large myelinated afferent fibers is thought to be able to "close the gate" to prevent transmission of pain sensation. The endorphin-mediated theory of pain relief states that a stimulus outside the central nervous system can raise the level of endogenous endorphins and therefore provide analgesia.

The proposed study is a single-blinded randomized controlled trial studying use of TENS for pain control during initial dilator insertion prior to dilation and evacuation. The participants will be randomized in a 1:1 randomization scheme using opaque, sequentially numbered envelopes following consent. The experimental group will have an active TENS unit - Chattanooga Primera - and the control group will have a sham TENS unit. The sham TENS will be the same unit without the true TENS electrical connections. The true TENS unit consists of the active unit and electrode pads connected to the unit via direct wires. The sham group will be given the active unit and have electrode pads placed but without wire connections. These participants will be told the device is a wireless device. They will also be told they may or may not feel sensation from the TENS. This will allow the device to be powered on and run in the same manner as the active group, but will not allow for electrical transmission between the unit and electrodes.

Based on power calculations, 56 participants are needed to detect a 20mm difference in VAS score with a standard deviation of 30mm. This is based on both minimum clinically significant difference in pain scores as well as previous studies regarding pain during dilator insertion. We will attempt to recruit 70 patients to account for possible TENS unit misuse or study dropout.

Eligible patients will have two electrodes will be placed in the suprapubic area in the bilateral lower quadrants. The program that will be used is a high frequency (80Hz) program that runs for an hour in duration. It will be initiated 5 minutes prior to speculum placement. Participants will be instructed to increase the amplitude of the current as needed to provide analgesia but avoiding discomfort from the TENS stimulation. All participants will receive a paracervical block of 20mL 1% lidocaine with sodium bicarbonate followed by rigid dilation and dilator placement per standard cervical preparation protocol. Participants will complete 100mm VAS immediately following dilator placement. VAS is a 100mm line on sheet of paper with 0 being no pain and 100mm being worst pain of their life. The number of dilators, type of dilators, and use of adjunctive mifepristone/misoprostol will be according to providers' clinical judgement. Dilator placement will be performed by either Family Planning Fellow, PGY-3 OB/GYN resident, or Nurse Practitioner. All participants will receive prescriptions for twenty tablets of ibuprofen (600mg) and twelve tablets of hydrocodone/acetaminophen 5/325, which is the standard post-dilator insertion pain protocol for this clinic site. Participants will be allowed to leave prior to the end of the initial one-hour program. They will be sent home with instructions of how to run the TENS unit as needed for pain control.

Following the initial hour of use patients can re-activate the TENS unit as often as desired, using the same program. Participants will be given a log to record when TENS unit was used and whether additional pain medications were taken. They will return their completed log and bring pill bottles on the day of surgery to confirm medications used.

Of note, in our practice a second set of cervical dilators is often placed 6 hours after first set in patients over 20 weeks gestation. During this placement the first set is removed, further rigid dilation is performed, and new dilators are placed per standard cervical preparation protocol. Pain score on 100mm VAS will be recorded following this dilator placement as well as a secondary outcome. Participants will run the TENS unit in the same manner as the initial dilator placement for dilator exchange.

On the day of surgery participants will record their highest interval pain score on 100mm VAS. They will also be asked their satisfaction with the TENS device. The TENS unit will be returned on the day of surgery.