Addition of Buprenorphine to Paracervical Block for Pain Control During Osmotic Dilator Insertion

Dilation and evacuation (D\&E) is the most common method of second trimester abortion in the United States. Cervical preparation prior to the procedure is essential in order to allow passage of operative instruments and pregnancy tissue safely through the cervix and to decrease the risk of complications. In the second trimester, cervical preparation is typically achieved with placement of osmotic dilators prior to the procedure. Women have described the pain of osmotic dilator insertion as moderate to severe yet there have been few studies aimed at addressing pain during osmotic dilator insertion. A lidocaine paracervical block is commonly used for pain control during other gynecologic procedures including procedures involving cervical dilation like dilation and curettage. One randomized controlled trial found that use of a paracervical block with 1% lidocaine decreased pain with osmotic dilator insertion compared to a sham block. Because the dilators slowly expand after insertion, there is continued discomfort for several hours after placement. Research has shown that pain after osmotic dilator insertion peaks at 2 hours post-insertion with use of a lidocaine paracervical block and a local anesthetic is not sufficient to provide lasting pain relief. Systemic medications, such as gabapentin and narcotic analgesics have been studied to treat post-insertional dilator pain, however these treatments have not been shown to be effective.

There are many adjunct treatments to optimize the duration of local analgesia from a peripheral nerve block. Buprenorphine, a partial mu-opioid receptor agonist, is a high potency, lipophilic opioid and has a high binding capacity for the mu-opioid receptor. Because of the high binding capacity, buprenorphine has the longest duration of action of all opioids. When administered perineurally in combination with a local anesthetic, buprenorphine has been found to drastically increase the duration of analgesia at several anatomic sites, including axillary and subclavian brachial plexus blocks and infragluteal sciatic nerve blocks. With the addition of buprenorphine at doses of 0.15 - 0.3mg, there is significant prolongation of the anesthetic sensory blockade up to three times the duration of the local anesthetic alone. The use of perineural buprenorphine is well established for postoperative analgesia. Buprenorphine itself also has local anesthetic properties. Buprenorphine blocks voltage gated sodium channels and inhibits C-fiber action potentials, thereby contributing to an analgesic effect. Buprenorphine not only prolongs the duration of local anesthetic effect but also improves the analgesic properties when administered in a perineural block.

The addition of buprenorphine to a perineural local anesthetic has not been studied in a paracervical block. This study will be the first trial to assess the efficacy of buprenorphine to provide analgesia for a gynecologic procedure. This medication has the additional benefit of providing long lasting pain relief for procedures that cause continued discomfort after the end of the procedure. The investigators hypothesize that the addition of 0.15mg of buprenorphine to a lidocaine paracervical block will improve pain during osmotic dilator insertion and provide continued pain relief several hours after osmotic dilator insertion. If this intervention proves to provide better pain control than a lidocaine paracervical block alone, it would be an intervention for women during a painful clinic procedure.

A total of 114 women undergoing D\&E who require cervical preparation with osmotic dilators will be randomized to one of two study groups: (1) paracervical block with 20mL of 1% buffered lidocaine or (2) paracervical block with 20mL of 1% buffered lidocaine plus 0.15mg of buprenorphine. Participants, clinicians performing the procedure, and study personnel administering questionnaires will be blinded to study assignment. Participants will rate their level of pain on an 11-point numeric rating scale (NRS) during the insertion of osmotic dilators and at several time points after insertion. The primary outcome is to compare the median pain score at the time of osmotic dilator insertion in women randomized to a 1% lidocaine and buprenorphine paracervical block compared to a 1% lidocaine paracervical block alone. Secondary outcomes are to compare the median pain score 2 hours after osmotic dilator insertion; to assess overall narcotic and ibuprofen use after osmotic dilator placement and before dilation and evacuation procedure; to assess opioid related side effects; and to determine patient satisfaction with pain control during and after osmotic dilator insertion.

Primary Hypothesis: The addition of buprenorphine 0.15mg to a paracervical block using 1% lidocaine will be associated with a lower median pain score on the NRS at time of osmotic dilator insertion compared to women who receive a lidocaine paracervical block alone.

Secondary Hypothesis: The addition of buprenorphine 0.15mg to a paracervical block using 1% lidocaine will be associated with a lower median pain score on the NRS 2 hours after osmotic dilator insertion compared to women who receive a lidocaine paracervical block alone.