Transcutaneous Electrical Nerve Stimulation (TENS) for Pain Control During Cervical Dilator Placement Prior to Dilation and Evacuation: A Randomized Controlled Trial

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.