Less than 10% of patients with a traumatic pain have been managed by a physician before to be admitted in an emergency service. 50 % of those patients have been carried by paramedics. Premixed nitrous oxide and oxygen is often used by paramedics, but no scientific studies have demonstrated its efficacy. The aim of the study is to demonstrate the efficacy of premixed nitrous oxide and oxygen in patients with out-of-hospital moderate acute pain.

The study will evaluate the efficacy of premixed nitrous oxide and oxygen (MEOPA) in patients with out-of-hospital moderate acute pain.

The primary endpoint is the percentage of patients with pain relief (with a numerical rating scale of 3/10 or lower) 15 minutes after randomisation. Secondary endpoints are treatment safety and adverse events, time to analgesia and duration of analgesia. This study will expect 60 patients assigned in two parallel groups, defined by a randomization scheme. Group assignments were sealed in opaque envelopes and will be open sequentially by the dispatcher when the paramedic is ready to include the patient. The letter contained in the envelope corresponds to the cylinder to use. Eligible patients with a numeric rating scale (NRS) score between 3 and 6/10 are randomly allocated to receive either MEOPA, or medical air. Fifteen minutes after the randomisation, all patients will receive MEOPA from a distinct cylinder. Pain score will be measured at baseline and every 5 minutes until pain relief will be obtained. The paramedic blinded to the analgesic treatment groups will do all assessments of patients. The safety evaluation will include non invasive monitoring of blood pressure, heart rate, oxygen saturation by pulse oximetry (SpO2) and adverse events collection.

Inclusion Criteria:

• Patients aged 18 years old
• Patients with a moderate acute pain (NRS score between 3 and 6)

Exclusion Criteria:

• Contraindication of premixed 50% nitrous oxide and oxygen
• Recent treatment of analgesic (less than 6 hours)