Nitrous Oxide (Entonox® or Nitronox™)
presentation - what the drug is sealed in, its concentration and how it might look
It is stored in medical cylinders that have a blue body with white shoulders.
It is an invisible odourless gas.
It has a concentration 1ml per 1ml medical gas is a combination of nitrous oxide 50% and oxygen 50%.
INDICATIONS - reasons you should administer this drug
Mild to moderate pain
Labour pains
CONTRAINDICATIONS - reasons you should not administer this drug
Nitrous oxide may have a deleterious effect if administered to patients with closed body cavities containing air since nitrous oxide diffuses into such a space with a resulting increase in pressure. Therefore do not give nitrous oxide to patients with:
Clinically suspected pneumothorax (whatever cause).
Severe head injuries with impaired consciousness due to possible presence of intracranial air.
Decompression sickness (the Bends) where nitrous oxide can cause nitrogen bubbles within the blood stream to expand, aggravating the problem further.
Consider anyone that has been diving within the previous 24 hours to be at risk.
Violently disturbed psychiatric patients.
An intraocular injection of gas within the last eight weeks. Check to see if these patients have an information leaflet, card or wristband.
The information leaflet may advise that nitrous oxide can be administered less than eight weeks after intraocular injection of gas.
Abdominal pain where intestinal obstruction is suspected.
cautions - reasons that if you administer this drug you must monitor for side effects more than usual
Due to the list of contraindications and the reason for these, we must be very cautious when administering nitrous oxide to any patient presenting with significant polytrauma and/or penetrating torso injuries.
pharmacological action - what does it to the body and what does the body do to it?
FREC 3 and FREC 4:
Nitrous oxide is a is a self-administered analgesic gas.
FREUC 5 and L4 AAP
Pharmacokinetics:
Absorption: Rapid via lungs; onset in 30–60 seconds.
Distribution: Quickly reaches the brain; low solubility; minimal accumulation.
Metabolism: Not metabolised at all.
Elimination: Exhaled unchanged; effects wear off within minutes.
Pharmacodynamics
Potentially provides analgesia through blocking neural synapses, but this is poorly understood.
Causes mild sedation (sedative) and reduces anxiety (anxiolytic).
Minimal respiratory or cardiovascular depression.
Expands in air-filled spaces hence why we avoid in injuries such as pneumothorax, bowel obstruction, ear problems, or trapped gas injuries.
side effects - unwanted secondary effects of this drug
Very few side effects are associated with nitrous oxide administration.
If any do arise that the patient cannot tolerate advise the patient to stop self-administering this drug and the side effects will resolve rapidly.
Other options may include for example: Ondansetron (anti-emetic) for nausea.
dosage and administration - how much do we give and how do we give it?
Adults:
Nitrous oxide should be self-administered via a facemask or mouthpiece, after suitable instruction. It takes about 3–5 minutes to be effective, but it may be 5–10 minutes before maximum effect is achieved.
Children:
Nitrous oxide is effective in children provided they are capable of following the administration instructions and can activate the demand valve.
legislation and regulations - what legal class of drug is it, who can possess it and who can give it?
As of 8 November 2023, Nitrous Oxide is classified as a Class C drug under the Misuse of Drugs Act 1971 and placed in Schedule 5 of the Misuse of Drugs Regulations 2001. This means that Nitrous Oxide is:
A Controlled Drug (CD) and therefore:
Should be stored securely in line with organisational medicines management policy.
(Note: Schedule 5 CDs do not legally require a CD cabinet under the Safe Custody Regulations, but secure locked storage is strongly recommended.)Stock levels must be monitored and recorded appropriately.
Access must be restricted to authorised staff only, with keys held securely (e.g., coded key safe or controlled access system).
And a Prescription-Only Medicine (POM) and therefore:
POMs almost always require a prescription from an authorised prescriber such as a medical Doctor or Advanced Paramedic, However:.
Ambulance personnel are legally exempt from requiring a prescription when administering Nitrous Oxide under the provisions of the Medicines Act 1968 meaning they may possess and administer it in the course of their duties.
additional information
Prolonged use for more than 24 hours, or more frequently than every four days, can lead to vitamin B12 deficiency.
B12 is an essential vitamin for the formation of myelin, the fatty-protein sheath that protects nerve fibres.
Administration of nitrous oxide should be in conjunction with pain score monitoring.
Advantages of nitrous oxide include:
Rapid analgesic effect with minimal side effects.
No cardiorespiratory depression. Self-administered.
Analgesic effect rapidly wears off.
The 50% oxygen concentration is valuable in many medical and trauma conditions.
Nitrous oxide can be administered whilst preparing to deliver other analgesics.
The usual precautions must be followed with regard to caring for the Entonox® equipment and the cylinder MUST be inverted several times before use to mix the gases when temperatures are low.