We conducted a multisite, double blind, randomized clinical trial to assess the utility of nitrous oxide for pain relief in early second trimester abortion. This study randomized participants to receive either inhaled nitrous oxide or intravenous (IV) sedation with fentanyl and midazolam. We included women desiring abortion at gestational ages between 12 weeks 0 days and 16 weeks 0 days. We planned to enroll 150 women, 75 in each treatment arm, in two clinical sites, the University of New Mexico (fellow: Lauren Thaxton) and the University of Colorado (fellow: Jennifer Pitotti). We hypothesized that nitrous oxide will prove to be an effective and acceptable method among patients and clinicians.
Between August 2016 and March 2017, 170 women were assessed for eligibility and 39 were enrolled, 19 in the nitrous group and 20 in the IV sedation group. Seven women within the nitrous group (36.8%) and none in the IV sedation group were converted to IV sedation due to need for additional pain medications. This exceeded our predefined stopping rule and enrollment was halted. Our stopping rule was, on quarterly review, if greater than 35% of women in either group are requiring additional pain medications, the study will be halted and a full review triggered. Immediate pain scores were lower among women randomized to IV sedation by 20.1mm (95% CI -38.6 to -1.6).
We found that nitrous oxide is an inferior method of anesthesia for 12-16 week abortion procedures compared to IV sedation. There is still a need to identify an effective, rapidly reversible method of anesthesia to preserve quality and privacy of the abortion care experience for women.