Clinical Practice Guidelines

Nitrous Oxide - oxygen mix

  • See also:

    Ketamine Guideline
    Analgesia & Sedation Guideline 

    Note - at RCH these guidelines are for use in the Emergency Dept. For use in other areas see also  Procedural Sedation Guideline


    Nitrous oxide has been used for many years in obstetric care during labour. It has both analgesia and amnestic properties. It has a quick onset of action and fast offset which makes it ideal for use in an emergency department. It has no sedative properties and thus must be used on patients who are co-operative (i.e. >4yrs of age).

    It comes as a pre-mixed 50:50 combination of nitrous oxide and oxygen on a demand triggered system, or as a continuous flow via a mixer (maximum concentration is 70% NO:30% O2).


    • fracture manipulation
    • abscess incision and drainage
    • injection of local anaesthetic
    • removal of foreign bodies from ear / soft tissues
    • other painful procedures


    • Head injury with LOC or altered conscious state
    • Chest injury or suspicion of pneumothorax
    • Current acute asthma episode



    • Patient should be kept nil orally prior to the procedure
    • Either two doctors or a senior nurse & doctor are required - one giving the Nitrous Oxide and the other performing the procedure.

    Entonox (i.e. demand valve)

    • Check cylinder has a tight seal to the regulator pipe.
    • Can use either an appropriate sized mask or mouth piece.
    • Connect the mask / mouth piece to the filter and then attach filter to the demand valve.
    • Turn the cylinder to the open position and the regulator will record the amount of Nitrous Oxide left in the tank (if less than 500 KPa then cylinder needs changing).

    Continuous Flow Meter

    • Make sure the oxygen and nitrous oxide tubing are connected to their respective outlets
    • Attach filter and appropriate mask to the circuit
    • Add a few drops of flavouring as needed
    • Make sure the suction is connected to the "bassoon" on the machine and is on low suction only


    Entonox (i.e. demand valve)

    • Patient should self-administer Nitrous Oxide for a few minutes immediately prior to commencement of painful procedure, with a doctor supervising. A harsh sound is heard on inspiration if the gases are flowing properly.
    • Procedure is performed with patient continuing to breathe Nitrous Oxide for the duration of the painful part of the procedure and 1 minute after painful part of procedure is finished.

    Continuous Flow Meter

    • Turn black knob to allow black bag to inflate.
    • Start with 100% oxygen and have patient breathe regularly through mask; adjust amount of flow to maintain the bag as being full but not over distended. Bag should empty with patients breath.
    • Decrease concentration of oxygen with central knob without adjusting the black flow knob. The flow of nitrous and oxygen will be automatically adjusted
    • Continue decreasing the oxygen (which increases the nitrous) until desired effect felt (ie between 30-50% oxygen (ie 50-70% nitrous))
    • If using more than 50% nitrous then allow patient to breathe 100% oxygen for 2-3 minutes after procedure has finished

    Post- procedure:

    • Turn the cylinder valve to closed position. The regulator valve will not go back to zero until the line from the regulator to the face mask is emptied.
    • Patient may be discharged after the procedure is complete if the patient is back to their pre-procedure mental status.