Nitrous oxide
Nitrous oxide or laughing gas as it is commonly known was first synthesised by Joseph Priestley in 1772. It was used as a dental analgesic forty years after this and has been used extensively in a wide range of surgical procedures for both analgesia and anaesthesia since.
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 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.
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NextNitrous oxide in anaesthesia
Nitrous oxide is predominately used as a background anaesthetic which is usually supplemented with either a potent, volatile or intravenous anaesthetic. When used in this way; it can reduce the dosage of the other agents required due to the additive effects of the compounds. Further benefits to administering general anaesthesia in this manner include:
- reduced respiratory depression (1)
- fast onset and rapid recovery from anaesthesia (2)
- excellent safety profile in paediatric sedation (3)
- proven safety with the cardio-vascular and respiratory systems (4)
- extremely safe and cost-effective
- cost-effective in reducing the volume (cost) of other anaesthetic agents
- 40% propofol reduction (5)
- 60% less sevoflurance consumption (6)
Nitrous oxide in analgesia
Nitrous oxide is the analgesic component of ENTONOX®, which is a mixture of 50% nitrous oxide and 50% oxygen, combining the benefits of oxygen with the pain relieving properties of nitrous oxide.
ENTONOX is widely used in obstetrics during childbirth and in the ambulance service. The benefits of ENTONOX for relieving acute pain and discomfort during short procedures in accident and emergency departments – and hospital wards – are now being increasingly recognised by healthcare professionals.
ENTONOX is an analgesic and sedative agent for use in all situations where analgesia and sedation with rapid onset and offset is sought: It is fast, safe and easy to handle.
For more information on ENTONOX click here.
Contra-indications
There are certain situations where the use of nitrous oxide or ENTONOX is contra-indicated. For example, in patients who have undergone recent eye surgery, involving gas bubble insertion, 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 receiving gas bubble eye surgery. This warns the anaesthetist or healthcare professional not to administer nitrous oxide or ENTONOX. For further information click here.
Nitrous oxide or ENTONOX 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:
- pneumothorax
- abdominal distension
- suspected intestinal obstruction
- bullous emphysema
- middle ear procedures
- following a recent dive
It should also be avoided where the patient is unable to effectively make use of the gas delivery equipment such as maxillo-facial injuries, impaired consciousness, sedation or intoxication
When ENTONOX 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 (usually related to prolonged use of the gas or where an existing deficiency is present). Prolonged inhalation can also result in dryness of the mouth and discomfort.
Environmental responsibility
Occupational safety
In the UK, the maximum exposure limits for nitrous oxide is set at 100ppm based on a time weighted average of 8hours. This level is significantly below the concentrations where any detrimental effect will 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. It is advised that to prevent personnel exposed to these high levels, nitrous oxide or ENTONOX should either be administered in a well ventilated area or scavenging equipment should be used to maintain safe working environment.
Greenhouse effect
Medical nitrous oxide plays only 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 (7).
The environmental impacts of nitrous oxide are too small to justify the replacement of nitrous oxide with alternative drugs that have not yet proven to be better or safer.
References:
(1) Einarsson S, Bengtsson A, Stenqvist O, Bengtson JP. Decreased respiratory depression during emergence from anesthesia with sevoflurane/N2O than with sevoflurane alone. Can J Anesth 1999; 46 (4): 335-341
(2) Einarsson SG et al. Emergence from isoflurane/N2O or isoflurane anaesthesia. Acta Anaestehsiol Scand 1997; 41:1292–9.
(3) Gall O, Annequin D, Benoit G, et al. Adverse events of premixed nitrous oxide and oxygen for procedural sedation in children. Lancet 2001; 358: 1514-1515.
(4) Eisele and Smith. Cardiovascular effects of 40% nitrous oxide
in man. Anesth Analg 1977; 51:956-61.
(5) Kodaka M, Handa F, Kawasaki J, Miyao H. Cp50 of propofol for laryngeal mask airway insertion using predicted concentrations with and without nitrous oxide. Anaesthesia 2002; 57: 956-959
(6) Jakobsson J, Heidvall M, Davidson S. The sevoflurane-sparing effect of nitrous oxide: a clinical study Acta Anaesthesiol Scand 1999; 43: 411-414.
(7) 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.
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