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Nitrous oxide or laughing gas as it is commonly known was first synthesised by Joseph Priestley in 1772. It was initially used as a dental analgesic forty years after this and has been used extensively in a wide range of surgical procedures for both anaesthesia and analgesia.
The exact mechanism of action of nitrous oxide is unknown, but its effects take place within the pain centres of the brain and spinal cord. It is thought to have an effect on the Gamma Aminobutyric Acid (GABA) cells increasing inhibition of nerve cells causing drowsiness and sleep. It also is related to the release of endogenous neurotransmitters such as opioid peptides and serotonin. The release of these neurotransmitters is thought to activate descending pain pathways that inhibit pain transmission.
There are certain situations where the use of nitrous oxide is contra-indicated. For example, in patients who have undergone recent eye surgery, involving gas bubble insertion (vitrectomy), as there is a risk that the nitrous oxide will diffuse into the bubble, causing it to expand and eventually burst. BOC Healthcare can provide a gas warning wrist band for any patient having undergone this type of eye surgery. This warns the anaesthetist or healthcare professional not to administer nitrous oxide amongst other things.
Nitrous oxide can cause a rise in intra-cranial pressure, so it should not be used in cases of head injury and it must never be used if the patient has any conditions where air is trapped in the body and expansion would be dangerous, for example:
suspected intestinal obstruction
middle ear procedures
following a recent dive
When nitrous oxide is used for more than a total of 24 hours, or more frequently than every 4 days, it must be used with close clinical supervision and haematological monitoring, as it could cause vitamin B12 deficiency in susceptible patients.
In Ireland, the maximum exposure limit for nitrous oxide is set at 100ppm based on an 8 hour Time Weighted Average (TWA).
This level is significantly below the levels where any detrimental health effect could be caused.
Concerns have been expressed about the effects of nitrous oxide on fertility and foetal development after exposure to high concentrations for prolonged periods. In order to prevent personnel being exposed to high levels of nitrous oxide, it should be used in approved locations. The approved design for operating theatres where the gas could be administered includes air exchange requirements and the use of scavenging equipment to maintain a safe working environment.
The environmental impact of medical nitrous oxide is very small. and only plays a very limited part in adding to the greenhouse effect.
Nitrous oxide only accounts for 5% of the greenhouse effect with only 1% of all nitrous oxide released into the atmosphere coming from medicinal use Therefore medical nitrous oxide represents only 0.05% of the total global effect of gas emissions (1).
(1) McGregor DG, Baden JM, Bannister C et al. Task force on anesthetic gases – Information for management in anesthetizing areas in a post-anesthetic care unit (PACU). American Society of Anesthesiologists – 1999 – Park Ridge, IL – USA.