Since nitrous oxide/oxygen mixture is effective to reduce pain and anxiety induced by various painful procedures in children, the investigators hypothesized that its inhalation would reduce pain during nasogastric tube placement in young children.

The purpose of this study is to evaluate the analgesic efficacy of 50%/50% nitrous/oxide mixture in reducing pain induced by nasogastric tube insertion in children aged 3 months to 3 years in the pediatric emergency department.

In the context of mild to moderate dehydration in young children, enteral rehydration is the treatment of choice because it is more physiological than parenteral rehydration which has more serious side effects. Thus, nasogastric tube placement has become a more common procedure in the pediatric emergency care setting. Although, it is widely accepted that this procedure is invasive and painful, to date, no analgesic approach has been shown to be effective for children aged 3 months to 3 years. Currently, standard care is the placement of nasogastric tube without any analgesic intervention.

Inhalation of nitrous oxide mixed with oxygen (50/50) has been shown to be effective to reduce pain and anxiety induced by invasive procedures in children, adolescents and adults. Its use is very safe and it is associated with only minor and transient side effects such as nausea, vomiting or dizziness in les than 10% of patients. Its use is very common in many countries such as France, United Kingdom, The Netherlands or Australia. The investigators hypothesized that its inhalation would reduce pain during nasogastric tube placement in young children.

The purpose of this study is to evaluate the analgesic efficacy of 50%/50% nitrous/oxide mixture in reducing pain induced by nasogastric tube insertion in children aged 3 months to 3 years in the pediatric emergency department.

A randomized controlled trial will be performed in two pediatric emergency departments to assess the efficacy of 50/50 nitrous oxide/oxygen during nasogastric tube insertion. The control group will receive standard care.

Primary outcome: Pain assessed with the FLACC scale during tube insertion

The investigators believe that this randomized study comparing nitrous oxide inhalation against current practice (no analgesic means) will highlight the intensity of pain caused by nasogastric tube placement and will assess the effectiveness of nitrous oxide inhalation to reduce pain and anxiety induced by the procedure

Inclusion Criteria:

• Child from 3 months to 3 years old.
• Admission to the Pediatric Emergency Department
• Medical prescription for the insertion of a nasogastric tube.
• Child with gastroenteritis and / or bronchiolitis and / or food intolerance with mild to moderate dehydration
• Parental presence and parental consent

Exclusion Criteria:

• Vital emergency.
• Refusal of parents to be filmed or to have their child filmed.
• Child already included in the study or in course of participation in another study.
• Tube placement performed by a medical student or nursing student.
• Patient requiring 100% oxygen ventilation.
• No social security.
• Child with a mental handicap or known retardation.
• History of child intolerance to Nitrous oxide ( excessive sedation or respiratory depression during previous use).
• Child with head trauma in the previous 3 days.
• Child with new-onset neurological abnormalities or other altered states of consciousness.
• Child with intracranial hypertension.
• Child with pneumothorax
• Child having received in the last 3 months prior to inclusion an ophthalmic gas ( SF6, C3F8, C2F6)
• Child with known vitamin B12 deficiency or unsubstituted folic acid.
• Child who has had a diving accident.
• Child with abdominal gas distension abdominal
• Child with gas embolism
• Child with pulmonary emphysema

Premature discontinuation of study participation :

• Parents' request to stop participating in the study.
• Insertion of the nasogastric tube is not possible

The primary outcome will be assessed on video recordings of the procedures which will be prepared so that assessors will not know to which group the children assigned. This correspond to a blind assessment of the primary outcome.