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Nitrous Oxide Compared With Intravenous Sedation for Second-Trimester Abortion

A Randomized Controlled Trial

Thaxton, Lauren, MD, MBA; Pitotti, Jennifer, MD, MSc; Espey, Eve, MD, MPH; Teal, Stephanie, MD, MPH; Sheeder, Jeanelle, MSPH, PhD; Singh, Rameet H., MD, MPH

doi: 10.1097/AOG.0000000000002915
Contents: Abortion: Original Research

OBJECTIVE: To assess whether inhaled nitrous oxide is noninferior to intravenous (IV) sedation for pain control during outpatient surgical abortion between 12 and 16 weeks of gestation.

METHODS: We enrolled women undergoing surgical abortion at 12–16 weeks of gestation into a multisite, double-blind clinical trial. Participants were randomized to sedation with nitrous oxide (70% nitrous/30% oxygen) or IV fentanyl (100 micrograms) and midazolam (2 mg). Paracervical block was administered to both groups. The primary outcome measure was immediate postabortion recall of maximum pain on a 100-mm visual analog scale.

RESULTS: Between August 2016 and March 2017, we assessed 170 women for eligibility and enrolled 39, 19 in the nitrous group and 20 in the IV sedation group. Seven participants in the nitrous group (36.8%) required conversion to IV sedation for inadequate pain control. No participants in the IV sedation group required additional medication. The proportion of women requiring additional pain control in the nitrous group exceeded our predefined stopping rule. Intention-to-treat analysis demonstrated that immediate postabortion visual analog scale pain scores were lower by 20.1 mm (95% CI 1.6–38.6) in women randomized to IV sedation than in women randomized to nitrous.

CONCLUSION: Intravenous sedation is a better choice than inhaled nitrous oxide for pain control in second-trimester abortion.


Inhaled nitrous oxide provides inferior pain control compared with intravenous sedation for surgical abortion at 12–16 weeks of gestation.

Department of Obstetrics and Gynecology, University of New Mexico School of Medicine, Albuquerque, New Mexico; and the Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Denver, Colorado.

Corresponding author: Lauren Thaxton, MD, MBA, Department of Obstetrics and Gynecology, University of New Mexico Hospitals, Mail Stop Code 10 5580, Albuquerque, NM 87131; email:

Supported by a grant from the Society of Family Planning Research Fund and by National Institutes of Health/National Center for Research Resources Colorado Clinical and Translational Science Institute Grant Number UL1 RR025780. The contents are the authors' sole responsibility and do not necessarily represent official National Institutes of Health views.

Financial Disclosure The authors did not report any potential conflicts of interest.

Presented at the Fellowship in Family Planning Annual Meeting, May 5–7, 2017, San Diego, California.

Peer review history is available at

Received June 03, 2018

Received in revised form July 25, 2018

Accepted August 02, 2018

© 2018 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.