UC San Diego

Background: Pain during osmotic dilator insertion is rated as moderate to severe, even with use of a 1% lidocaine paracervical block (PCB). Buprenorphine, a partial mu-opioid receptor agonist, can improve the analgesic properties of a local anesthetic and also prolong the duration of local anesthetic effect when administered in a perineural block.

Methods: This is a multi-site, randomized, double-blind controlled trial conducted from May 2020–May 2021. Participants presenting for dilation and evacuation who required osmotic dilators for cervical preparation were randomized 1:1 to receive a 1% buffered lidocaine PCB or a 1% buffered lidocaine + 0.15mg buprenorphine PCB. The primary outcome was pain scores during osmotic dilator insertion as rated on an 11-point numeric rating scale. Secondary outcomes included pain at additional time points and side effects. We used a Mann-Whitney U test to compare median pain scores between groups.

Results: We randomized 57 participants. There was no difference in median pain scores between the lidocaine + buprenorphine and the lidocaine alone PCB groups during osmotic dilator insertion (3.5 vs. 4, p=0.88). There were no differences in median pain scores at any time point after dilator insertion. Participants receiving buprenorphine had a higher incidence of vomiting post-dilator insertion (70% vs. 21%, p=0.0007).

Discussion: Addition of buprenorphine to a 1% lidocaine paracervical block did not reduce pain at the time of osmotic dilator insertion or at any time point post-insertion. The addition of buprenorphine to a PCB may increase rate of side effects, particularly vomiting, without any pain control benefit.