A Comparison of Paracervical Block Volumes Before Osmotic Dilator Placement: A Randomized Controlled Trial.

Objective: To evaluate whether a 12-mL paracervical block is noninferior to a 20-mL block in reducing pain with osmotic dilator insertion.

Methods: In this single-blinded noninferiority trial, we randomized individuals undergoing insertion of osmotic dilators before second-trimester abortion to receive either a 12-mL or 20-mL 1% lidocaine paracervical block. The primary outcome was pain immediately after insertion of osmotic dilators. Prespecified secondary outcomes included pain with paracervical block administration, overall pain, and side effects, with 88 participants being required for a noninferiority margin of 15 mm on a 100-mm visual analog scale assuming an SD of 28. We analyzed data using Wilcoxon rank sum, χ2, and t tests and performed analysis of variance to account for repeated measures. Secondary analysis included multivariable regression to explore potential confounders.

Results: From January 2018 to October 2020, of 232 eligible individuals, 174 were approached and 96 randomized (48 participants to each group); 91 were available for analysis (45: 12 mL, 46: 20 mL). Group demographics were similar, with a mean gestation of 21 weeks and four osmotic dilators placed. The 12-mL paracervical block was noninferior to the 20-mL paracervical block for pain with osmotic dilator insertion with a difference in means of -1.36 (95% CI -12.56 to 9.85) favoring 12 mL. Median pain scores after dilator placement were 47 mm (interquartile range 22-68) and 50 mm (interquartile range 27-67) in 12-mL compared with 20-mL paracervical block, respectively (P=.81). No difference was seen in median pain at baseline, with paracervical block administration, postprocedure or with overall pain or experience. At least one lidocaine-related side effect occurred in 4% of participants in the 12-mL group compared with 13% for those receiving 20 mL (P=.15), with metallic taste, ringing in ears, and lightheadedness being most common.

Conclusion: A 12-mL paracervical block is noninferior to a 20-mL block for pain reduction with osmotic dilator insertion.

Clinical Trial Registration: ClinicalTrials.gov, NCT03356145.