MEOPA (Equimolar Oxygen-Nitrogen Protoxide Mix) is a gas used in emergencies for short-term painful acts. It is often very effective with an analgesic, anxiolytic and muscle relaxant action. It is often combined with other analgesic medicines. It has already been proven in emergency medicine for short-term pain and trauma. It seems that it could be used more particularly for pains of medical origin. A study has already proved its effectiveness in the treatment of migraines in emergencies. The first phase of the NEPHROPAIN study began in 2016 after a favorable opinion from the Regional Ethics Committee. NEPHROPAIN phase AVANT was a prospective non-interventional study on the use of analgesic drugs in nephritic colic in emergencies by Dr. Alexandre Tanneau. This study was conducted at the University Hospital of Rennes and included 60 patients admitted to the emergency department for suspected renal colic. It made it possible to recruit the control group of the NEPHROPAIN study. Its main objective was to describe the suspected population of renal colic in Rennes emergencies, to determine NEPHROPAIN's primary endpoint and the number of NEPHROPAIN needed subjects.

Inclusion Criteria :

• Age greater than or equal to 18,
• Presenting a suspicion of renal colic, that is to say a pain at the level of a lumbar fossa radiating towards the external genital organs, of rapidly progressive, non-febrile appearance,
• Having given free, informed and written consent,
• Affiliated to the social security system.

Exclusion Criteria :

• Patient in shock of all types, defined here as an acute cardio-circulatory failure with mean arterial pressure less than 65 mm Hg.
• Oxygen saturation below 93% in ambient air,
• With suspicion of pneumothorax,
• Having a history of emphysema and / or COPD (chronic obstructive pulmonary disease),
• Contraindications to the administration of MEOPA: Patients requiring ventilation in pure oxygen; Intracranial hypertension (headache associated with jet vomiting); Any alteration of the state of consciousness, preventing the cooperation of the patient (Glasgow score less than 15); Head trauma; Pneumothorax; Emphysema bubbles; Gas embolism; Diving accident; Abdominal gas distension; Patient who has recently received an ophthalmic gas (SF6, C3F8, C2F6) used in ocular surgery as long as a gas bubble persists inside the eye and at least for a period of 3 months; Known and unsubstituted deficiency of vitamin B12 or folic acid; Neurological abnormalities of recent appearance and unexplained)
• Contraindication to NSAIDs,
• Patient treated in the long course by analgesic stage 3,
• Pregnant or lactating woman,
• Concomitant participation in another research involving the interventional or minimal risk and minimal human person,
• Major persons subject to legal protection (legal safeguards, guardianship, tutorship) and persons deprived of their liberty.