Supplementary Material for: High incidence of signs of neuropathy and self-reported substance use disorder (SUD) for nitrous oxide (N2O) in patients intoxicated with N2O

Introduction: The number of patients with excessive nitrous oxide (N2O) use and neurological disorders has been rising, indicating an addictive potential of N2O. We studied the incidence of self-reported substance use disorder (SUD)-related symptoms, signs of neuropathy and the patterns of use in N2O intoxicated patients. Methods: The Dutch Poisons Information Center (DPIC) provides information by telephone on the management of intoxications to healthcare professionals. Retrospective data on signs of neuropathy and patterns of use were collected for all N2O intoxications reported to the DPIC in 2021 and 2022. Frequent and heavy use were self-reported as “often/frequent/weekly use” and as “use of tanks or >50 balloons/session”, respectively. From this cohort, we included patients with excessive N2O use or signs of neuropathy in a prospective observational cohort study. Online surveys were sent 1 week, 1 month and 3 months after DPIC consultation. The survey included the DUD questionnaire (validated to measure self-reported substance abuse (SA) and dependence (SD) based on DSM-IV-TR criteria), and questions on patterns of use and signs of neuropathy. DSM-IV-TR criteria were translated to DSM-V criteria to score for mild, moderate or severe substance use disorder (SUD), with 2-3, 4-5 or ≥6 symptoms respectively. Results: We included 101 N2O intoxicated patients in the retrospective study. Of these, 41% showed signs of neuropathy (N=41), 53% used N2O tanks to fill balloons (N=53), 71% used frequently (N=72) and 76% used heavily (N=77). We included 75 patients in the prospective study and 10 (13%) completed the first survey. All 10 patients fulfilled the criteria for SA and SD (DSM-IV-TR, median number of questions answered “yes”= 10/12), all used N2O tanks to fill balloons, and 90% (N=9) experienced signs of neuropathy. After 1 and 3 months, 6/7 and 1/1 patients respectively, continued to fulfill SA and SD criteria. Translating to DSM-V criteria, 1/10 patients fulfilled the critera for (self-reported) mild SUD, 1/10 patients for moderate SUD and 8/10 patients for severe SUD, 1 week after consultation. Discussion/Conclusion: The high proportion of N2O intoxicated patients reporting frequent and heavy use of N2O indicates an addictive potential of N2O. Although follow-up rate was low, all patients fulfilled self-reported SA, SD (DSM-IV-TR), and SUD (DSM-V) criteria for N2O. Somatic healthcare professionals treating patients with N2O intoxications, should be aware of possible addictive behaviour in patients. The screening, brief intervention, and referral to treatment (SBIRT) approach should be considered to treat patients with self-reported SUD symptoms.