Entonox: Ward administration of

The purpose of this guideline is to provide guidance about the administration of Entonox at Great Ormond Street Hospital (GOSH). 


Entonox is a homogeneous gas containing a mix of 50 per cent oxygen and 50 per cent nitrous oxide compressed into a cylinder. It was introduced commercially in 1965 and is most commonly used as a method of pain control during labour and to control trauma-related pain, both by paramedics and in accident and emergency departments. As well as providing analgesia, Entonox can produce feelings of relaxation or euphoria, and is therefore also useful to relieve anxiety.

Entonox use should be considered for painful procedures in children who are able to co-operate (Howard et al. 2012). It is a potent analgesic with properties comparable to that of strong opioids. It can provide short-term pain relief, sedation and reduced anxiety during a wide range of painful procedures such as chest drain removal, pin site dressings, physiotherapy and lumbar punctures. 

Nitrous oxide is an anaesthetic gas; the misuse of Entonox could result in loss of consciousness. Due to this risk, Entonox must be self-administered: if the patient receives more gas than necessary, they will become drowsy; causing them to drop the mouthpiece or mask and the gas will stop flowing. As the patient breathes ambient air, the Entonox effects rapidly wear off. The child or young person must therefore be able to co-operate by holding the demand valve and inhaling the gas him/herself. If the patient is unable to do this alternative analgesia should be given. 

Use of Entonox is designated as ‘minimal sedation’ however if used in combination with other sedatives or potent analgesia there is an increased risk of sedation (NICE 2010). 

Health care professionals administering Entonox should be trained in its use and familiar with the side effects and contra-indications. Staff should also be aware that Entonox is a habit-forming drug and has been subject to abuse. Documented cases of abuse in the UK are rare, but addiction may result in long-term use and this can lead to myelo-neuropathy and serious neurological problems. Due to the potential for problems related to repeated/long-term use, Entonox should only be used for painful procedures. Procedures that are primarily frightening in nature should be managed using psychological input and sedation/anxiolytics as appropriate. 

The Pain Control Service at GOSH advises that Entonox should not normally be considered for procedures, such as cannulation or venepuncture, as other more appropriate analgesic techniques, such as topical local anaesthetics and distraction, are proven to be effective. Please contact the Pain Control Service for guidance on other options for procedural pain management if required.

Staff training

Entonox should only be administered by staff that are:

  • Competent in the administration of Entonox and basic life support (Rationale 1).
  • Familiar with the side effects of Entonox and its contra-indications (Rationale 2).
  • Aware of the criteria for patient selection and exclusion (Rationale 2).

Staff should also have attended:

  • An Entonox training session and been assessed as competent (Rationale 3).
  • Resuscitation training as detailed in the Resuscitation Policy (Rationale 3).

The Pain Control team can administer Entonox in clinical areas where staff have not been trained in its use. They should be contacted on bleep 0577 well in advance of the procedure.

Initial assessment

Assess the degree of pain likely for the procedure being performed (Rationale 4).
An initial assessment of the patient's suitability for Entonox must be undertaken by a trained clinician and this should be documented in the child or young person’s notes (Rationale 5). This should include:

  • Confirmation that Entonox is not contra-indicated for the patient (Rationale 6).
  • Basic assessment of the child or young person's respiratory function including respiratory rate and comfort of breathing pattern.
  • A baseline assessment of oxygen saturation should be made (>93% or appropriate to a child or young person's known cardiac condition). If there is concern about a potential airway or breathing problem seek advice from the Pain Control Service/duty anaesthetist before administering Entonox (Rationale 6).
  • Entonox should not be used if the patient has any conditions where air may be trapped in body cavities (Rationale 7). Examples of this include: 
    •  artificial, traumatic or spontaneous pneumothorax
    •  intestinal obstruction
    •  severe bullous emphysema
    •  maxillofacial injuries
    •  following air encephalography
    •  decompression sickness
    •  air embolism
    •  middle ear occlusion
    •  head injuries with impaired consciousness (Rationale 8

Entonox should also be used with caution in patients with poor nutritional status (Rationale 9). Examples of this include: 

  • Patients with poor intake or on a diet low in animal products e.g. vegans. 
  • Patients with malabsorption syndromes, particularly those with ileal resections.
  • Patients requiring synthetic diets (e.g. phenylketonuria, maple syrup urine disease)
  • Patients on a diet for which special vitamin and mineral supplements are prescribed for deficiency states (more than standard vitamins such as abidec).

Patients who have repeated or prolonged exposure to Entonox may be at risk of inhibition of Vitamin B12 synthesis. Prolonged or frequent exposure can also cause alterations to folate metabolism and impairment in DNA synthesis, impairing bone marrow function. This can lead to megaloblastic anaemia, peripheral neuropathy and depression of white cell formation (BOC 2015, APA 2012). 

Any person receiving Entonox for more than 24 hours consecutively or more frequently than every four days must have routine blood cell count and folate level analysis undertaken (Rationale 13). Folate supplements may be required if there is evidence of deficiency or if taking a blood sample is inappropriate.

Assess individual child or young person or young person for their ability to use Entonox. They should be able to:

  • Understand simple instructions (via an interpreter if necessary*) (Rationale 10).
  • Hold the demand valve and inhale the gas through a mask or mouthpiece while breathing normally.

*NB: if an interpreter is used they must be present throughout the procedure.

The age at which a child or young person or young person is able to use Entonox will vary depending on the individual child or young person and the procedure to be performed.

If Entonox is considered inappropriate for the patient or the procedure alternative analgesia/sedation should be prescribed.


The child or young person and family have the right to make an informed decision about their care and so must be provided with adequate information about the potential risks and benefits of Entonox, alternative analgesia, and have the opportunity to discuss these. All families should be offered a copy of our information sheet Pain relief using Entonox. Copies are also available with each Entonox cylinder.

Verbal consent/assent should be obtained prior to the procedure and documented in the child or young person’s clinical record (Rational 5).

Ensure the Entonox has been prescribed (Rationale 11).

Prescription charts can be obtained from the Anaesthetic Department on ext. 8645, or downloaded from the Pain Control Service clinical specialty web pages.

Prescriptions should be printed on yellow paper (available to GOSH staff from VCB Theatre reception). Please ensure the ‘Entonox back page’ containing the pre-procedure checklist is also printed.

Complete the checklist on the reverse side of the prescription to record that safety checks have been made.

Liaise with the person carrying out the procedure. The person supervising the child or young person’s use of Entonox should not be involved with the procedure (Rationale 12).

The area should be well ventilated to prevent the accumulation of nitrous oxide. The occupational exposure standard (OES) for long-term exposure is 100 parts per million (ppm), averaged over an eight-hour period (BOC 2013) (Rationale 14).

Staff in the first trimester of pregnancy or planning to conceive may wish to avoid the area if Entonox is being administered for long periods. Staff who administer Entonox have a duty of care to ensure that those in the immediate vicinity, including the child or young person, and family members where appropriate, are aware of this risk and have the opportunity to remove themselves from the immediate area discreetly if they choose (Rationale 15). 

Gather and prepare the following equipment (all available to GOSH staff if required from VCB theatre reception or stores) (Rationale 16):

  1. Entonox cylinders are stored in the gas store room in VCB theatres. Record the removal of the cylinder from the store in the log book at VCB Main theatres desk.
  2. Entonox cylinder and administration set: cylinders should be checked carefully before use to ensure they contain the correct mix of 50% nitrous oxide and 50% oxygen. Entonox cylinders have a blue and white collar (Rationale 18).
  3. Check the cylinder to ensure it is at least a quarter full. If it is not, request the theatre porter change the cylinder. 
  4. Switch cylinder on and prime the administration set by pressing the test button on the back of the demand valve. 
  5. Hygroboy™ filter (these are available from main theatres).  
  6. Anaesthetic-style mask/mouth piece: if selected, the facemask must have a soft-seal ring to ensure adequate seal is achieved, and be appropriately sized for the child or young person.

Ensure that the equipment is clean (Rationale 17):

  • Wipe the equipment with a sanitising wipe (e.g. Clinell® universal wipe) (before and after use)
  • Remove the fabric bag prior to going to the child’s bed space 
  • Clean the cylinder with a  sanitising wipe (e.g. Clinell® universal wipe) prior to going to the ward

Attach the Hygroboy™ filter to mask or mouthpiece before attaching this to the demand valve (Rationale 16). Ensure the mask if selected will provide an adequate seal.

If the patient has respiratory or cardiac problems ensure that a saturation monitor is used to monitor oxygen saturations (Rationale 19).

To prepare the patient: (Rationale 20)

  • Explain the procedure to be carried out and how Entonox will be used, including information about the side effects. 
  • Reassure them that if side effects occur they wear off quickly once they stop inhaling the gas.
  • Give supplementary analgesia as prescribed: oral or rectal drugs should be given approximately an hour before starting the procedure (Rationale 22).

The patient should not eat or drink for an hour before the procedure (Rationale 21).

A bolus of intravenous opioid may be given if a high degree of pain is anticipated, however please note this may increase the level of sedation experienced. 

The patient should be allowed to practice using the Entonox before the procedure is started (Rationale 23). If the patient is unable to maintain an effective seal or inhale the gas effectively the use of Entonox should be abandoned and alternative analgesia and/or sedation should be prescribed.


To administer the Entonox:

  • Explain the procedure to the patient. Reassure them and explain that they should concentrate on breathing normally (Rationale 24). 

Offer the demand valve to the patient and advise that: 

  • If they have chosen to use a mask they should hold it over their mouth and nose, maintaining an airtight seal, and breathe normally. 
  • If they have chosen the mouthpiece they should hold it between their teeth and breathe through their mouth only, sealing the mouthpiece with their lips. 
  • Inhalation should commence for at least four breaths before the procedure starts (Rationale 25). 

The patient may need considerable encouragement to start inhaling the gas. It is worth persevering as any initial reluctance usually disappears once the patient realises that the Entonox is working.

Once administration has commenced:

  • The patient should continue to use the Entonox as required throughout the procedure and should be encouraged to breathe slowly and deeply (Rationale 26).
  • If the patient hyperventilates they should be encouraged to exhale slowly, and then breathe normally.

An Entonox-trained member of staff must observe the patient throughout the procedure to determine the following (Rationale 27):

  • increasing level of sedation
  • the level of pain
  • the presence of any side effects
  • whether the patient is using the Entonox effectively
  • available to intervene appropriately if any difficulties occur

Oxygen saturations should be monitored throughout the procedure if patients have an underlying cardiac or respiratory condition (Rationale 19).

Patients should be encouraged to take deeper breaths of Entonox if the pain intensity increases.

The patient may continue to use their Patient Controlled Analgesic pump if they have one. 

If use of Entonox is unsatisfactory at any stage it may be necessary to stop the procedure and give alternative analgesia.

Other strategies to minimise the pain experienced, such as use of adhesive removers and distraction techniques, should be considered and deployed alongside the administration of Entonox.

Administration: Monitoring for adverse effects


Ensure the child or young person remains responsive and alert throughout the procedure. In most circumstances, if the patient becomes drowsy, the seal around the mask or mouthpiece is lost and they will no longer inhale the gas (Rationale 30). This is why it is essential that only the child holds the mask/mouthpiece.

If the supervising clinician has any concerns that the child or young person is becoming over sedated they should remove the handset from the patient and allow the effects of the Entonox to wear off before continuing.

If respiratory compromise is observed, place the child in the recovery position or commence basic life support (BLS) if required.

Other side effects

If the patient experiences any Entonox-related side effects they should be reassured, and cease inhalation until the side effects wear off (Rationale 27 and 31).

For particularly painful procedures it may be advisable to wait for the patient to recommence inhalation before continuing.

Entonox-related side effects include:

  • earache
  • dry mouth
  • dizziness or disorientation
  • nausea and vomiting

If the patient complains of earache, inhalation should be stopped and alternative analgesia prescribed (Rationale 28).

A dry mouth is a common side effect but is not usually distressing. The patient should be encouraged to continue inhaling Entonox (Rationale 29).

If the patient starts to feel dizzy or disorientated they may cease inhalation until the sensation starts to wear off and the sensation of pain starts to return (Rationale 27).

The patient may choose to accept these sensations and continue inhalation to maintain effective analgesia.
If the patient complains of nausea they should be encouraged to cease inhalation if they wish (Rationale 31).

Less commonly the patient may vomit. If so:

  1. Remove the demand valve immediately.
  2. Reassure the patient and clear any obstruction to breathing.
  3. Clean or replace face mask/mouthpiece and Hygroboy filter.
  4. Clear vomit from the demand valve by vigorously shaking it using a ‘flicking’ downward action (Rationale 32).
  5. The patient may then recommence inhalation if clinically appropriate (Rationale 31).
  6. If the demand valve is contaminated, send the delivery set for cleaning after the procedure.

Administration: Technical problems

If any of the following technical problems occur they should be reported to the biomedical engineering department immediately (Rationale 33):

  • Equipment not delivering gas.
  • Leak at joint between regulator and cylinder valve.
  • Demand valve leaks or does not shut cleanly.

Completing procedure

After use:

  • Ensure the patient is comfortable.
  • Check the cylinder gauge to assess volume of Entonox used by patient (Rationale 34):
    • If less than ¼ full, request the theatre porters replace the cylinder.
    • If ½ full check that a new cylinder has been ordered.

Turn off the cylinder and depressurise the system fully by operating the test button (Rationale 35).

Monitoring of the child should continue for 30 minutes after the procedure to ensure that the effects of the Entonox have completely worn off (Rationale 36).

Patients should not walk around unaided, or commence oral intake, until any dizziness or disorientation has gone.

If the patient has respiratory or cardiac problems they may benefit from oxygen therapy for 10-15 minutes after using the Entonox. Liaise with medical staff and ensure oxygen prescribed if required (Rationale 37).

To clean the equipment (Rationales 14 and 17):

  • Ensure the system has been depressurised.
  • The external surfaces of the demand valve and the administration set must be cleaned with a sanitising wipe (e.g. Clinell® universal wipe)
  • If any contamination is suspected between the hose connection and the demand valve it must be sent to HSDU to be autoclaved.

Single-use facemasks, mouthpieces and Hygroboy™ filters are for single patient use and must be discarded. They may be kept by the patient’s bed if they are going to use Entonox again within the next 48 hours. The mask should be labeled with the time and date of first use.

Document that Entonox has been given, how effective it was and any side effects experienced by the child or young person (Rationale 5):

  • On the audit form attached to the Entonox trolley.
  • In the child or young person’s health care records.

Entonox cylinders should be kept in a designated storage cupboard when not in use (Rationale 14), at GOSH this is in the VCB theatres, situated near the reception desk. The cylinder should be 'signed out' of the store and ‘signed back in’ by the person collecting and returning the cylinder.

The Pain Control Service and the Biomedical Engineering Department are jointly responsible for ensuring that an annual check of the equipment has been carried out by the Biomedical Engineering Department. (Rationales 14 and 38). This is in accordance with the manufacturer's instructions.

Entonox cylinders should be stored above minus six degrees Celsius wherever possible. 

BOC advise that after storage at low temperature the cylinder should be warmed on its side at room temperature for two hours and inverted three times prior to use to mix the gases. If the cylinder has been stored at minus six degrees, the two gases will have separated, which could result in the child or young person receiving either oxygen only or high concentration nitrous oxide. (BOC Medical Gases 1995a, BOC Medical Gases 1995b)

Re-ordering equipment

Entonox cylinders (cylinder size Hx) are checked daily by theatre staff and replaced if the cylinder is less than ¼ full. (Rationale 39) Spare cylinders are stored in the goods yard.

Do not wait until the cylinder needs to be replaced.

Mouthpieces are disposable (Rationale 40)

ORDER CODE:  071.598.99

Hygroboy™ filters are available from main theatres. 

ORDER CODE:  355/5430


Rationale 1: To ensure that Entonox is administered safely and effectively.
Rationale 2: To reduce the likelihood of side effects and complications.
Rationale 3: To establish and maintain the required level of knowledge.
Rationale 4: To provide an accurate record.
Rationale 5: To determine whether Entonox is required.
Rationale 6: To reduce the likelihood of complications.
Rationale 7: Nitrous oxide diffuses into air filled cavities, and may cause them to expand to three times their original size (Anderson et al 1983).
Rationale 8: Nitrous oxide is also thought to cause an increase in intra-cranial pressure (Anderson et al 1983).
Rationale 9: Exposure to nitrous oxide depletes the body's stores of vitamin B12 and very rarely this can precipitate neurological complications.
Rationale 10: To ensure the patient is able to use Entonox effectively.
Rationale 11: To adhere to hospital drug policy.
Rationale 12: To determine a suitable time for both parties and ensure patient safety.
Rationale 13: To observe for evidence of megaloblastic change in red cells, reduced production of leucocytes and hypersegmentation of neutrophils (Bruce and Franck 2000; Evans 1995).
Rationale 14: To maintain a safe environment (Henderson 1990)
Rationale 15: Exposure to high levels of nitrous oxide can reduce fertility (Hennrikus 1995), and may be harmful to a foetus.
Rationale 16: To ensure immediate availability of Entonox once inhalation commences.
Rationale 17: To reduce the risk of infection.
Rationale 18: To prevent drug errors as stronger concentrations of nitrous oxide are available in the hospital in similar cylinders.
Rationale 19: To observe for post-inhalation hypoxia.
Rationale 20: To relieve anxiety and determine level of co-operation likely.
Rationale 21: To reduce the likelihood of nausea and vomiting.
Rationale 22: To provide additional pain relief.
Rationale 23: To ensure an effective technique is established.
Rationale 24: To establish an effective inhalation technique (British Medical Association (BMA) and Royal Pharmaceutical Society (RPS) 1999).
Rationale 25: To ensure Entonox has taken effect before introduction of painful stimuli (BMA and RPS 1995).
Rationale 26: To provide effective analgesia with minimal side-effects.
Rationale 27: To ensure that adequate pain relief is provided with minimal side effects.
Rationale 28: To prevent perforation of the eardrum.
Rationale 29: To provide effective analgesia.
Rationale 30: To prevent the onset of deeper stages of analgesia and sedation and loss of protection of the laryngeal reflex (British Medical Association (BMA) and Royal Pharmaceutical Society (RPS) 1999).
Rationale 31: The side effects of Entonox wear off quickly once inhalation ceases.
Rationale 32: To prevent inhalation of vomit.
Rationale 33: To ensure equipment is safe and in good working order.
Rationale 34: To ensure that there is an adequate supply of Entonox for the next patient.
Rationale 35: To prevent misuse and to maintain a safe ward environment.
Rationale 36: To maintain patient safety.
Rationale 37: To prevent post administration hypoxia.
Rationale 38: To minimise the risk of cross infection.
Rationale 39: To ensure equipment is in good working order.
Rationale 40: To ensure that there is an adequate supply within the hospital.
Rationale 41: To ensure there is an adequate supply on the ward.


Anderson CT, Zeltzer LK and Franurik D (1983). Pain in Infants and Adolescents. Williams & Wilkins: Baltimore.

BOC Medical Gases (1995a). Entonox: the non-invasive patient controlled analgesia - suggested protocol. BOC: Surrey.

BOC Medical Gases (1995b). Entonox Datasheet. BOC Medical: Manchester.

BOC Medical Gases (2015). Entonox: the essential guide. [Accessed 12.04.16]. 

Bruce E, Franck L (2000). Self-administered nitrous oxide (Entonox) for the management of procedural pain. Paediatric Nursing 12(7): 15-19. [Accessed on 12.04.16]

Evans JK (1995). Analgesia for the reduction of fractures in chilren: a comparison of nitrous oxide with intramuscular sedation. Journal of Pediatric Orthopaedics 15: 73-77. [Accessed on 12.04.16]

Henderson J M (1990). Administration of nitrous oxide to patients provides analgesia for venous cannulation. Anesthesiology 72(2): 269-71. [Accessed on 12.04.16]

Hennrikus WL, Shin AY, Klingelberger CE (1995). Self-administered nitrous oxide and a hematoma block for analgesia in the outpatient reduction of fractures in children. J Bone Joint Surg Am 77 (3): 335-9. [Accessed on 12.04.16]

Howard R., Carter B., Curry J., Jain A., Liossi C., Morton N., Rivett K., Rose M., Tyrrell J. & Walker S. (2012). Good practice in post operative and procedural pain management. Paediatr Anaesth 22:s1, 1-79. 

National Institute for Health and Care Excellence (NICE) (2010). Sedation in under 19s: using sedation for diagnostic and therapeutic procedures. [Accessed on 12.04.16].

Paediatric Formulary Committee (2016). BNF for Children (online). London: BMJ Group, Pharmaceutical Press, and RCPCH Publications [Accessed on 12.04.16]

Document control information

Lead Author(s)

Judy Peters, Clinical Nurse Specialist, Pain Control Service
Liz Robinson, Clinical Nurse Specialist, Pain Control Service

Additional Author(s)

Dr Richard Howard, Lead Consultant, Pain Control Service

Document owner(s)

Dr Richard Howard, Lead Consultant, Pain Control Service

Approved by

Guideline Approval Group

Reviewing and Versioning

First introduced: 
01 February 2003
Date approved: 
11 April 2016
Review schedule: 
Three years
Next review: 
11 April 2019
Document version: 
Previous version: