Nitrous Oxide Use for Intrauterine System Placement in Adolescents

Fowler KG, Byraiah G, Burt C, et al. 

JPAG 2022; VOLUME 35, ISSUE 2, P159-164, APRIL 2022

1. What were the primary and secondary outcomes of the study? 

A: The primary outcome was to evaluate adolescent patient-reported pain after IUS insertion with N2O compared to IUS insertion with current pain relief measures. The secondary outcome was to assess comparative patient satisfaction between the two groups, using willingness to recommend IUS to a friend to measure patient satisfaction. 

2. Were the two groups randomly selected? What were the differences procedurally? How might this bias the study results? 

A: No, this was not a randomized controlled trial and the N2O group was patient/family selected. In the N2O group the procedure had to be scheduled in the future on a different day. The baseline group in the study received a intracervical block (prior to placement of a cervical stabilizer), 500 mg naproxen and distraction with iPad games. The N2O group received N2O starting 2 minutes prior to speculum placement and stopped with speculum removal as well as intracervical block. To assess for bias, the authors compared the two groups and the only significant difference was baseline sexual activity status (same day placement group were more likely to report prior sexual activity). One demographic variable that was not reported was socioeconomic status, and it’s possible this could have influenced a family's decision to avoid scheduling at a future date. Although not statistically significant in this study, it would be interesting to see if gender identity may be significantly different in a larger sample size. 

3. What statistical model did the authors use to analyze differences in patient reported pain in the study? Why did they choose this model?

A: The authors used a multilevel model to account for the nested data structure. This means that because they were comparing two pain scores reported by the same individual, it was unrealistic to assume the two pain scores were independent. The authors postulate that this type of "nested data" would create bias if a traditional linear regression model was used. 

4. How many patients selected an IUS during the recruitment period and how many ended up being enrolled in each arm (nitrous oxide versus in-clinic placement without nitrous oxide)? What were the exclusion criteria involved? 

A: 129 patients selected an IUS during the treatment period. 53 patients were excluded. 74 patients remained, of which 29 selected N20 and 45 selected immediate in-clinic placements. Exclusion criteria included those with cognitive delay, those who desired a higher level of sedation, those with a previous pregnancy and those with any contraindication to IUS placement. 

5. For the outcome of patient satisfaction, how many patients were completely likely or very likely to recommend an IUS to a friend from each group? Please see Figure 3. 

A: Among the patients receiving nitrous oxide, 29% were completely likely to recommend an IUS to a friend and 46.4% were very likely to recommend this. Among the patients with an in-clinic placement, 20% stated they were completely likely and 37.8% were very likely to recommend an IUS to a friend. In both groups, zero patients stated that they were not at all likely to recommend an IUS to a friend. 

6. What are some of the limitations and strengths of this study? 

A: The lack of randomization is a limitation. Nitrous oxide could not be withheld to patients who wanted this, due to the proven benefit of this when used for other minor pediatric procedures. Additionally, same-day IUS placement was unable to ethically be withheld from those who wanted an IUS placed immediately. This led to a self-selection bias where higher levels of anxiety and anticipated pain concerns were more likely in those selecting IUS placement with nitrous oxide.  Another limitation was the relatively homogenous patient population of non-Hispanic, white patients, and gynecologists as placing the IUS (opposed to other types of clinicians).

Strengths included being the first to analyze nitrous oxide use for adolescents desiring an IUS. Different genders and ages were also broadly represented. While statistical significance was assessed by analyzing visual analog scale scores, clinical significance may be represented by patients more likely to recommend the use of nitrous oxide.