Transcutaneous electrical nerve stimulation (TENS) has been used in pain relief since 1965, when Metzger and Walls proposed using electrical stimulation as analgesia based on the “gate control” theory of pain relief. According to the theory, neuromodulation may activate large myelinated afferent nerve fibers in the dorsal horn to inhibit transmission in primary afferent nociceptive fibers. The inhibitory input “closes the gate” to prevent transmission of pain sensation. TENS units are small, inexpensive, portable devices which deliver mild, alternating electrical currents via electrodes positioned on the skin near the area of pain and in the same dermatomal distribution. Pulse frequency and pulse intensity are adjustable and linked to TENS efficacy. They have a favorable safety profile and few contraindications, one of which is electronic implants, such as cardiac pacemakers.
In gynecology, TENS has been shown to provide significant pain relief for medical and surgical conditions including but not limited to primary dysmenorrhea, office hysteroscopy, post-operative pain from gynecologic laparoscopy, cesarean section and postabortal pain. It has never been studied during cervical dilator placement prior to dilation and evacuation. If successful, this could provide an inexpensive, accessible, non-pharmacologic method of improving pain control.
This is a single-blinded, randomized controlled trial to evaluate TENS as a method of pain relief during cervical dilator placement prior to dilation and evacuation. The primary outcome is a 25mm decrease in pain with dilator placement as measured on VAS. Secondary outcomes include pain during dilator exchange (if applicable), maximum interval pain prior to dilation and evacuation, quantity and type of adjunctive pain medications taken, and patient acceptability. We will attempt to recruit 50 participants with a 1:1 randomization scheme based on sample size calculations of minimum effect detectable and standard deviation. Alpha error will be set at 0.5 and power of 80%. We will recruit english-speaking women over 18 years of age at 14 weeks to 23 weeks 6 days gestation without contraindication to TENS usage.
After informed consent is obtained, participants will complete a questionnaire eliciting demographic information. Patients will be randomized to either TENS unit or sham TENS. Clinicians will not be blinded. Two electrode pads will be placed in the T10 dermatome in the suprapubic area. The TENS unit will be activated 5 mins prior to placement of speculum and started at high frequency and at a moderate intensity of 30mA. Studies have shown this setting profile to be most effective during acute pain episodes. The patient will then be instructed to modify the amplitude as needed for pain relief, while continuing the TENS for a total of 4 hours. The patient will be instructed to restart TENS as needed before her dilation and evacuation procedure.
Patients will rate pain using 100mm VAS scale, with 0 being no pain and 100 being worst pain, with first pain score being recorded immediately after dilator placement. The minimum clinically significant difference on VAS scale is 13-15mm and prior studies have shown that dilator placement pain ranges from 40-70mm with SD of 20-23mm. Patients will complete logs where they will enter the time, pain score, how long TENS unit was run, whether pain relief was felt, and adjunctive medications taken. Patients will rate their satisfaction with the device. During dilator placement all patients will receive a paracervical block of 10mL 1% lidocaine. Number of dilators inserted, whether a second set is needed, and adjunctive cervical ripening medications (mifepristone, misoprostol) will be according to provider’s clinical judgement. All procedures will be performed by either a Family Planning attending physician with Family Planning fellow or third year OB/Gyn resident, or by a nurse practitioner.