MEDICAL NITROUS OXIDE

Use in adults, including the elderly and children For respiratory use at concentrations of 79% or less. 8) Instructions for Use and Handling of Medical Nitrous Oxide cylinders Care is needed in the handling and use of medical nitrous oxide gas cylinders as nitrous oxide is stored in high pressure gas cylinders as a liquid under pressure.

Rapid opening of the valve can cause the discharged gas to re- liquefy. This liquid can cause cold burns if in contact with the skin. Cylinders should only be used in the vertical position with the valve uppermost. If not liquid may be discharged when the valve is opened.

Scavenging of waste nitrous oxide gas should be used to reduce operating theatre and equivalent treatment room levels to a level below 100ppm of ambient nitrous oxide. Preparation for use 1. Cylinder valves should be opened momentarily prior to use to blow any foreign matter out of the outlet.

2. Ensure that the connecting face on the yoke, manifold or regulator is clean and the sealing washer or ‘O’ ring where fitted is in good condition. 3. Cylinder valves must be opened slowly. 4. Only the appropriate regulator should be used for the particular gas concerned.

5. Pipelines for medical gases should be installed in accordance with the conditions set out in HTM 02. 6. Cylinder valves and any associated equipment must never be lubricated and must be kept free from oil and grease. Leaks 1. Should leaks occur this will usually be evident by a hissing noise.

2. Leaks can be found by brushing the suspected area with an approved leak test solution. 3. There are no user serviceable parts associated with these valves, do not attempt to correct any problems with leakage from any part of the valve itself.

Label any faulty containers, and return them to Air Liquide for repair. 4. Sealing or jointing compounds must never be used to cure a leak. 5. Never use excessive force when connecting equipment to cylinders. Use of Cylinders 1. Cylinders should be handled with care and not knocked violently or allowed to fall.

2. Cylinders should only be moved with the appropriate size and type of trolley. 3. When in use cylinders should be firmly secured to a suitable cylinder support. 4. Cylinders containing liquefiable gas must always be used vertically with the valve uppermost.

Events such as euphoria, disorientation, sedation, nausea, vomiting, dizziness and generalised tingling are commonly described. These events are generally minor and rapidly reversible. Nausea and vomiting has been reported to occur post-operatively in approximately 15% of patients.

Prolonged or frequent use of nitrous oxide, including heavy occupational exposure and addiction, may result in megalobastic anaemia. 4). Myeloneuropathy and sub acute combined degeneration, have also been reported following prolonged or frequent use.

4) . Nitrous oxide passes into all gas containing spaces in the body faster than nitrogen passes out. Prolonged anaesthesia may therefore result in bowel distension, middle ear damage and rupture of ear drums. Addiction to nitrous oxide has been reported.

5)

Nitrous oxide should never be given with less than 21% oxygen. Nitrous oxide causes inactivation of vitamin B12 (a co-factor of methionine synthase) which interferes with folate metabolism. Thus DNA synthesis is impaired following prolonged nitrous oxide administration.

8). Nitrous oxide should not be used as an analgesic or anaesthetic agent 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 blood 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. Assessment of vitamin B12 levels should be considered in people with risk factors for vitamin B12 deficiency prior to using nitrous oxide anaesthesia.

Risk factors include the elderly, those with poor or vegetarian diet, and previous history of anaemia. At altitude, in the presence of disorders affecting oxygenation and in obstetrical anaesthesia the proportion of nitrous oxide should be less than 70% with oxygen greater than 30% for anaesthesia.

At the end of a nitrous oxide/oxygen anaesthesia, withdrawal of the mask leads to an outpouring of nitrous oxide from the lung and consequent dilution of oxygen in incoming air. This results in “diffusion hypoxia” and should be counteracted by giving 100% oxygen for a few minutes when the flow of nitrous oxide is stopped.

Care should be exercised in the administration of nitrous oxide to patients who have had epidural anaesthesia. If air has been injected into the epidural space to determine the placement of the needle for epidural anaesthesia nitrous oxide should not be given unless the volume of air injection was limited.

g. intestinal obstruction) o if air has been injected into the epidural space to determine the placement of the needle for epidural anaesthesia Nitrous oxide should not be used in heavily sedated patients. Nitrous Oxide should not be used in patients having received recent intraocular injection of gas (such as SF6, C3F8, C2F6) as long as an intraocular gas bubble persists and at least for 3 months.