ENTONOX MEDICINAL GAS

Entonox is administered through a facemask or mouthpiece. The facemask or mouthpiece is connected to an Entonox supply through a demand valve system which allows the Entonox to be self-regulated by the patient. The demand valve is operated by the act of inhalation of the patient and closes down when the patient ceases to inhale.

In nearly all cases, Entonox is self-administered, but it may be administered by attendant medical personnel. Since pain is usually relieved by a concentration of 25% nitrous oxide, continued inhalation does not occur. However, should inhalation continue, light anaesthesia occurs and the mask or mouthpiece drops away as the patient relaxes, or is removed if administration has been by attendant personnel.

There are no contra-indications to the use of Entonox in any age group. 8).

Events such as euphoria, disorientation, sedation, nausea, vomiting, dizziness and generalised tingling are commonly described. These events are generally minor and rapidly reversible. Prolonged or frequent use of Nitrous Oxide, including heavy occupational exposure and addiction, may result in megaloblastic anaemia.

4). Myeloneuropathy and sub-acute combined degeneration have also been reported following prolonged or frequent use. 4). Addiction may occur. Nitrous oxide passes into all gas containing spaces in the body faster than nitrogen passes out.

Prolonged exposure may result in bowel distension, middle ear damage and rupture of ear drums. Tabulated summary of adverse reactions System organ class Very common (≥1/10) Common (≥1/100 to <1/10) Uncommon (≥1/1 000 to 1/100) Rare (≥1/10 000 to 1/1 000) Very rare (<1/10 00 0) Not known (cannot be estimated from the available data) Blood and lymphatic system disorders - - - - - Megaloblastic anaemia Psychiatric disorders - Euphoria - - - Confusion, Addiction Nervous system disorders - Dizziness, light- headedness, Somnolence - Myelopathy, neuropathy, subacute degeneration of the spinal cord Generalised seizures Ear and labyrinth disorders - - Feeling of pressure in the middle ear - - Gastrointestinal disorders - Nausea, vomiting Bloating, increased gas volume in the intestines - - General disorders and administration site conditions - Sense of intoxication - - - Respiratory, thoracic and mediastinal disorders Respiratory depression Reporting of suspected adverse reactions Reporting suspected adverse reactions after authorisation of the medicinal product is important.

It allows continued monitoring of the benefit/risk balance of the medicinal product. uk/yellowcard or by searching for MHRA Yellow Card in the Google Play or Apple App stores.

Repeated administration or exposure to nitrous oxide may lead to addiction. Caution should be exercised in patients with a known history of substance abuse or in healthcare professionals with occupational exposure to nitrous oxide. The nitrous oxide constituent of Entonox causes inactivation of vitamin B12, which is a co-factor of methionine synthase.

Folate metabolism is consequently interfered with and DNA synthesis is impaired following prolonged administration of Entonox. Prolonged or frequent use of Entonox may result in megaloblastic marrow changes, myeloneuropathy and sub acute combined degeneration of the spinal cord.

Entonox should not be used for more than a total of 24 hours, or more frequently than every 4 days, without close clinical supervision and haematological monitoring. Specialist advice should be sought from a haematologist in such cases.

Haematological assessment should include an assessment for megaloblastic change in red cells and hypersegmentation of neutrophils. Neurological toxicity can occur without anaemia or macrocytosis and with B12 levels in the normal range.

In patients with undiagnosed subclinical deficiency of vitamin B12, neurological toxicity has occurred after single exposures to Nitrous Oxide during general anaesthesia. Caution should be exercised before using Entonox with patients who have known Chronic Obstructive Pulmonary Disease (COPD) or other conditions where compromised chemoreceptor sensitivity/function may be present.

This is due to the relatively high concentration of oxygen contained in Entonox and as such may cause respiratory depression and increases in PaCO2. Reduced fertility in healthcare personnel has been reported where they have been repeatedly exposed to levels of nitrous oxide above the specified occupational exposure limits in inadequately ventilated rooms.

There is no documented evidence to confirm or exclude the existence of any causal connection between these cases and exposure to nitrous oxide. In patients taking other centrally acting depressant medicinal products, such as morphine derivatives and/or benzodiazepines, concomitant administration of Entonox may result in increased sedation, and consequently have effects on respiration, circulation and protective reflexes.

5) Where the patient has been exposed to agents which are toxic to the lungs, such as Paraquat, the use of gases containing more than 21% oxygen should be avoided. Thorough ventilation or scavenging of waste gases should reduce operating theatre and equivalent treatment room levels of ambient nitrous oxide to a level below 100 ppm.

Entonox is non flammable but strongly supports combustion and should not be used near sources of ignition. Smoking should be prohibited when using Entonox. Under no circumstances should oils or grease be used to lubricate any part of the Entonox cylinder or the associated equipment used to deliver the gas to the patient.

Where moisturising preparations are required for use with a facemask or in nasal passages, oil based creams should not be used. Check that hands are clean and free from any oils or grease. Where alcohol gels are used to control microbiological cross-contamination ensure that all alcohol has evaporated before handling Entonox cylinders or equipment.

Entonox should not be used in any condition where gas is entrapped within a body and where its expansion might be dangerous, such as with: • artificial, traumatic or spontaneous pneumothorax • air embolism • decompression sickness • following a recent dive • following air encephelography • severe bullous emphysema • use during myringoplasty • gross abdominal distension • in patients having received recent intraocular injection of gas (such as SF6)