• Parent's anxiety 10 scale. [ Time Frame: During procedure ]
  The parent evaluates himself his anxiety. It's a simple scale graduate one by one, from 0 (better outcome) to 10 (worse outcome). Based on their subjective interpretation of their own anxiety
• Child's constraint needed during the procedure [ Time Frame: During procedure ]
  Scale for grading the level of constraint during the procedure It is composed to three subscales from 0 to 3 (head, arms, legs). 0 is no contention, 1 is soft hold, 2 is firm support, 3 is very firm hold And one subscale from 0 to 1 (trunk). 0 is no contention, 1 is necessary maintenance. The outcome measure is the sum of these four subscales: from 0 (better outcome, that is to say no contention) to 10 (strongest contention).
• The potential side effects of the mixture 50%/50% nitrous oxide/oxygen for a brief inhalation are : Euphoria, dreaming, hallucinations, sedation, headaches, nausea, and vomiting. [ Time Frame: from the start of inhalation to nearly 5 to 10 minutes after the end of inhalation ]
  The rate of side effects will be described

• Parent's anxiety assessed on a 0 to 10 scale. [ Time Frame: During procedure ]
• Child's constraint needed during the procedure [ Time Frame: During procedure ]
  Scale for grading the level of constraint during the procedure
• The potential side effects of the mixture 50%/50% nitrous oxide/oxygen for a brief inhalation are : Euphoria, dreaming, hallucinations, sedation, headaches, nausea, and vomiting. [ Time Frame: from the start of inhalation to nearly 5 to 10 minutes after the end of inhalation ]
  The rate of side effects will be described

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

• Active Comparator: Nitrous oxide
  Inhalation of a 50%/50% mixture of nitrous oxide and oxygen. Reassurance of the child during procedure
  Intervention: Drug: Nitrous Oxide
• No Intervention: Standard care
  Infants will be reassured as currently performed in routine clinical practice

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.
• Refusal of parents to be 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

Premature discontinuation of study participation :

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