1. Background to the clinical research project Nitrous oxide is a valuable tool in medicine for its rapid and effective analgesic and sedative properties. It is used in 50% gaseous form for painful procedures. One frequent application is obstetric analgesia. However, in addition to its analgesic effects, many articles mention the psychotropic, even psychedelic, effects of nitrous oxide use. In one of the most recent studies, entitled More than just joy: A qualitative analysis of participant experiences during nitrous oxide sedation, involving healthy volunteers, it is reported that the sensations and feelings of the subjects are not necessarily pleasant, and many volunteers report psychedelic-like sensations, dreams or disturbed perceptions. The authors then question whether these effects are due to an absence of painful stimuli and therefore an absence of a beneficial effect. The same effects have been reported by Atkinson et al, also on volunteer subjects. Parturients feelings are highly variable, with a stronger focus on analgesic efficacy.

2. Objectives of the clinical research project 2.1 Primary objective: The main objective will be to evaluate the effects of nitrous oxide, other than analgesia, in the specific context of childbirth. The study will focus mainly on subjective feelings, as well as the effects of disconnection from reality.

   2.2 Secondary objectives: As secondary objectives, we will study the efficacy on pain.

3. Methodology of the clinical research project All patients who have received nitrous oxide for delivery as part of the standard course of treatment in the delivery room will be contacted within 24 hours by one of the investigators. The protocol, i.e. the questionnaire, will be explained to the patients and, if they accept the protocol, written consent will be obtained. Patients will then complete the questionnaire in the presence of one of the investigators, who will be able to explain the questions if necessary. The questionnaire will take around 20 minutes to complete.

4. Design of the clinical research project Prospective study based on a questionnaire.

5. Participants Any person who received nitrous oxide for childbirth at Hôpital Érasme between October 1, 2024 and April 30, 2025 and who signed the informed consent form for this study.

Inclusion Criteria:

• Any person who received nitrous oxide for childbirth at Hôpital Érasme between October 1, 2024 and April 30, 2025 and who signed the informed consent form for this study.

Exclusion Criteria:

• No informed consent

Women in labour

Any woman who received nitrous oxide for childbirth at Hôpital Érasme between October 1, 2024 and April 30, 2025 and who signed the consent form for this study.