Nitrous Oxide as an Effective Analgesic in Office Operative Hysteroscopy: Insights from a Randomized Controlled Trial

Highlight

Inhaled nitrous oxide (N2O) significantly reduced intraprocedural pain during office operative hysteroscopy compared to placebo (ambient air). The analgesic effect was notably stronger in postmenopausal women. Use of N2O improved procedure completion rates and patient satisfaction with a low rate of adverse events.

Study Background and Clinical Context

Office hysteroscopy is increasingly employed for diagnostic and operative uterine procedures due to its minimally invasive nature and cost-effectiveness compared to traditional operating room settings. However, pain management remains a critical challenge since the procedure can be distressing, limiting patient comfort, procedure success, and clinical uptake. Currently, analgesic strategies vary widely, ranging from local anesthetics to systemic analgesics, but many have limitations related to efficacy, onset time, side effects, or practicality in outpatient settings.

Nitrous oxide (N2O) is a well-known inhaled analgesic agent with rapid onset and minimal respiratory depression, widely used in dentistry and some emergency settings. Its applicability for office gynecologic procedures, such as operative hysteroscopy, remains underexplored. This study addresses an important unmet need by systematically evaluating N2O’s analgesic efficacy and safety during office operative hysteroscopy.

Study Design

A prospective, randomized, double-blind, placebo-controlled trial was conducted at a university-affiliated tertiary care hospital from July to November 2025. Women scheduled for office operative hysteroscopy were randomized 1:1 to receive either inhaled nitrous oxide via a self-administered face mask or ambient air (placebo) during the procedure. Blinding was maintained for both patients and proceduralists. Pain intensity was assessed using a 10-point visual analog scale (VAS) at three critical timepoints: uterine entry, during the operative procedure, and postprocedure. Secondary endpoints included procedure completion rate, patient satisfaction, and adverse events.

Demographic and procedural variables were comparable between groups, ensuring balanced baseline characteristics.

Key Findings

A total of 214 women were included: 110 in the N2O group and 104 in the ambient air group. The primary outcome—intraprocedural pain—was significantly reduced with inhaled N2O (mean VAS 2.23±3.29) compared to placebo (3.96±3.31), with a highly significant P value (<.001), indicating clinically meaningful pain relief.

Notably, subgroup analysis revealed that postmenopausal women derived even greater benefit. Pain scores at uterine entry were markedly lower in the N2O group (5.47±3.38 vs 8.00±2.72; P =.013), and during the procedure (2.42±3.86 vs 6.56±2.79; P =.002), highlighting a potentially increased sensitivity or analgesic responsiveness in this population.

Procedural outcomes favored the N2O arm, with higher rates of completed procedures (93.6% vs 83.7%, P =.021), which could reflect improved tolerance and reduced procedural interruption due to pain. Additionally, patient satisfaction was substantially higher in the N2O group (80.9% vs 47.1%, P <.001), demonstrating enhanced procedural experience and acceptability.

Adverse event incidence was low and comparable between groups, supporting the safety and tolerability of inhaled nitrous oxide in this outpatient setting.

Expert Commentary

This trial provides robust evidence endorsing inhaled nitrous oxide as an effective analgesic adjunct for office operative hysteroscopy, a procedure traditionally hampered by procedural pain. The double-blind, placebo-controlled design strengthens the validity of the findings.

The pronounced analgesic effect among postmenopausal women aligns with known factors such as decreased endogenous estrogen potentially increasing uterine sensitivity and pain perception, making effective analgesia crucial.

While the study confirms procedural benefits and patient satisfaction, further multicenter studies could explore generalizability across diverse populations and procedural complexity. Additionally, mechanistic studies may elucidate the neurophysiological basis for differential analgesic responses in menopausal status.

Limitations include the single-center design and the absence of long-term follow-up regarding patient outcomes or rare adverse effects. Nonetheless, the low incidence of adverse events reported affirms N2O’s favorable safety profile.

Conclusion

Inhaled nitrous oxide offers a safe, effective, and well-tolerated analgesic option during office operative hysteroscopy, significantly decreasing procedural pain and enhancing patient satisfaction, especially in postmenopausal women. Its use also improves procedure completion rates, suggesting practical benefits in clinical workflow and patient care quality.

Incorporating nitrous oxide analgesia into outpatient hysteroscopic practice could optimize patient comfort and procedural success, addressing a key limitation in office gynecologic care. Future research should further evaluate implementation strategies, cost-effectiveness, and broader patient populations.

Funding and Clinical Trial Registration

This study was conducted at a university-affiliated tertiary care hospital. It was prospectively registered on ClinicalTrials.gov with identifier NCT07074795.

References

Razdolsky S, Yaniv-Tamir R, Raz M, Kolp-Asis S, Katz T, Elbaz L, Tzur T. Nitrous Oxide for Pain Management in Office Hysteroscopy: A Randomized Placebo-Controlled Trial. Obstetrics and Gynecology. 2026 Apr 9;148(1):71-79. PMID: 41955620.

Additional literature supporting N2O analgesia and office hysteroscopy practice guidelines may be referenced from current American Congress of Obstetricians and Gynecologists (ACOG) and pain management consensus statements.