Nitrous Oxide - oxygen mix

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  • See also

    Ketamine use for procedural sedation

    Procedural sedation
    Emergency Airway Management
    Acute Pain Management
    Communicating procedures to children

    Key points

    1. Nitrous oxide provides amnesia, anxiolysis and modest analgesia with minimal respiratory and cardiovascular compromise
    2. Nitrous oxide is safe to commence at a concentration of 70%. There is no evidence to support gradual weaning of nitrous oxide concentration
    3. Administration of nitrous for more than 30 minutes is more likely to result in side effects such as vomiting


    • Nitrous is used for short, potentially painful procedures due to its rapid onset and offset. Onset is within minutes and peak effect is 3-5 minutes
    • Nitrous for sedation is delivered using a continuous flow mixer (in concentrations titratable from 30-70% nitrous oxide)
    • A pre-mixed 50:50 combination of nitrous oxide and oxygen (Entonox) can be used for analgesia on a demand triggered system


    Nitrous can be considered for procedures that may cause pain, discomfort or anxiety and that require only short-term sedation

    Procedures for consideration of nitrous oxide



    Lumbar puncture
    Suprapubic aspirate
    Urinary catheter insertion
    Peripheral cannula insertion

    Foreign body removal
    Simple fracture manipulation
    Simple burns dressings
    Incision and drainage of abscess
    Local anaesthetic injection

    Absolute contraindications

    • Airway and/or breathing compromise: acute respiratory depression, current exacerbation of asthma
    • Expansion of gas filled airspaces: pneumothorax, lung cyst, obstructive airways disease, recent craniectomy or trauma with pneuomocephalus, air embolus, decompression illness, bowel obstruction, middle ear disease or surgery with air trapping
    • Pulmonary hypertension associated with decreased exercise tolerance
    • Increased risk of nitrous oxide induced bone marrow suppression, neurotoxicity or increased homocysteine level: methionine synthetase deficiency, homocystinuria and methylmalonic academia
    • GCS <15 from head injury
    • Very painful or prolonged procedures (>30 minutes)

    Relative contraindications

    • Increased risk of airway compromise: acute respiratory infection, history of difficult airway or airway obstruction
    • Expansion of gas filled airspace: chest injury, abdominal distension, head injury with GCS 15 but ongoing symptoms
    • Increased risk of nitrous oxide induced bone marrow suppression: nutritionally compromised patients, current severe illness, severe infection or extensive tissue damage
    • Age <12 months. NB some paediatric centres with appropriate expertise use nitrous oxide in children from 6 months of age
    • If using Entonox (premixed 50:50 nitrous and oxygen) the child must cooperate and generate enough negative pressure on inspiration to open the valve.  This usually restricts its use to school aged children


    • Circuit to deliver gas
    • Suction
    • Oxygen source
    • Nitrous oxide source
    • Mask or mouthpiece (for older children)
    • Scents/essences for distraction and rapport building
    • Variable concentration nitrous oxide machine with:
      • Flow meter
      • Nitrous and/or oxygen concentration control
      • Oxygen flush
    • Entonox cylinder with appropriate mask/circuit


    Potential side effects and complications

    • Mild side-effects include:
      • nausea
      • vomiting
      • dizziness
      • agitation
    • More serious side effects are rare in short term usage, but include:
      • aspiration
      • airway obstruction
      • diffusion hypoxia (avoided with post-sedation with supplemental oxygen)
      • hallucinations
    • Sedation failure (see below)

    Inform families of these effects as part of consent



    • Consider fasting times (see local guidelines)
    • In children outside of the ED, consider local ward guidelines and concomitant use of other agents
    • A minimum of two staff are required: proceduralist with experience in paediatric resuscitation including airway skills and an assistant trained to administer nitrous oxide and monitor child for side effects
    • Provide parent information for sedation procedures (See sedation for procedures)
    • Plan options for sedation failure – consider alternate agent early if adequate sedation not achieved

    During the procedure

    • Attach saturation probe for monitoring
    • Ensure line of sight monitoring of the child at all times
    • Commence with 100% oxygen
    • Apply face mask ensuring adequate seal, aim for smallest fitting mask
    • Adjust the nitrous oxide concentration dial and gas flow to achieve desired nitrous concentration and flow
    • Commencing nitrous oxide at a concentration of 70% is considered safe. The staff member providing the sedation may prefer to titrate the dose of nitrous oxide, doing so does not decrease the risk of side effects and may increase the length of time to the desired sedation
    • The bag should be inflated enough so there is a continuous supply of nitrous for the patient to breathe, but not over expanded as this makes it difficult for the patient to breathe against
    • Ensure that the bag is inflating and deflating with each breath so that nitrous oxide is being inhaled
    • At the end of the procedure commence 100% oxygen. Gradual weaning of nitrous is not required

    Post procedure

    • Administration of 100% oxygen for 3-5 minutes post the procedure is recommended to prevent diffusion hypoxia
    • Saturation monitoring is recommended for 5 minutes post procedure

    Specific considerations and challenges

    • Facial lacerations may be challenging to repair under nitrous oxide due to positioning of the mask. A nasal circuit or mouth piece can assist where available
    • Consider utilising distraction techniques and involving child life therapy to initiate play with the mask prior to administration of nitrous in children who may have anxiety around its use
    • A small amount of flavoured lip balm or cooking essence can be used to make the mask smell better

    It is important to communicate with the child in child friendly language (See Communicating procedures to children)

    Post-procedure care and discharge instructions

    The child should not be discharged home until they have returned to their premorbid neurological baseline

    If nitrous oxide sedation is unsuccessful:

    Consider use of alternative sedation, eg Ketamine, general anaesthetic

    Consider transfer when

    It is not possible or safe to provide alternative sedation option in your location

    For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services

    Parent information

    Sedation for procedures

    Additional notes

    American College of Emergency Physicians: Nitrous Oxide

    Last updated December 2021

  • Reference List

    1. Babl FE, et al. Pre-procedural fasting state and adverse events in children receiving nitrous oxide for procedural sedation and analgesia. Pediatric Emergency Care. 2005;21(11):736-43
    2. Babl FE, et al. High-concentration nitrous oxide for procedural sedation in children: adverse events and depth of sedation. Pediatrics. 2008; 121(3):e528-e532.
    3. Jacques KG,  et al. Procedural sedation and analgesia in the emergency department. Trauma. 2015;17(3):166-74
    4. Pasarón R, et al. Nitrous oxide procedural sedation in non-fasting pediatric patients undergoing minor surgery: a 12-year experience with 1,058 patients. Pediatric Surgery International. 2015;31(2):173-80
    5. Zier J, et al. Safety of High-Concentration Nitrous Oxide by Nasal Mask for Pediatric Procedural Sedation: Experience With 7802 Cases. Pediatr Emerg Care. 2011;27(12):1107-12
    6. American College of Emergency Physicians. Managing Acute Pain in the ED – Nitrous Oxide. ACEP // Nitrous Oxide (viewed July 2021)