Entonox (50% Oxygen – 50% Nitrous Oxide)
Medicinal gas, compressed.
The characteristics of oxygen are:
- Odourless, colourless gas
- Molecular weight 32.00
- Boiling point -183.1°C (at 1bar(g))
- Density 1.335kg/m3 (at 15°C).
Oxygen is present in the atmosphere at 21% and is an absolute necessity for life.
At the concentrations in ENTONOX, oxygen has no discernible pharmaceutical effect other than the beneficial effects of an oxygen enriched mixture in certain cases.
The characteristics of nitrous oxide are:
- Sweet smelling, colourless gas
- Molecular weight 44.00
- Boiling point -88.6°C (at 1bar(g))
- Density 1.875kg/m3 (at 15°C).
Nitrous oxide is eliminated unchanged from the body mostly by the lungs.
Nitrous oxide is a potent analgesic and a weak anaesthetic.
Endorphins are probably involved in the analgesic effect; a concentration of 25% nitrous oxide is usually adequate to provide a marked reduction in pain.
- Onset - rapid
- Peak - immediate
- There are no essential observations about the pharmacokinetics of oxygen at this concentration.
- Nitrous oxide is a low potency inhalation anaesthetic and high potency analgesic.
- At a constant inspired concentration the rise time of alveolar concentrations is faster than that of any other anaesthetic agent.
- The elimination of nitrous oxide equally is faster than that of any other anaesthetic. This characteristic is especially valuable in analgesia for short-term pain relief.
The blood/gas partition co-efficient of nitrous oxide at 37°C is 0.46 compared with that of nitrogen of 0.015 causing nitrous oxide to expand into the internal gas spaces.
- Relief of moderate to severe pain.
- Cardiac related chest pain where nitroglycerin will be of no value or is contraindicated. Must be followed by high flow oxygen when discontinued.
- Isolated extremity injuries, pain associated with burns excluding mechanisms associated with potential inhalation injury, etc.
- Artificial, traumatic or spontaneous pneumothorax
- Air embolism
- Decompression sickness
- Following a recent scuba dive
- Severe bullous emphysema
- Gross abdominal distension
- Altered mental status
- Inability to comply with instructions
- Inhalation injury
- Nitroglycerin use within 5 minutes of administration
- Safety Alert: Entonox should not be used in a confined space that cannot be adequately ventilated; when used inside an ambulance or other vehicle always operate the exhaust fan and/or open windows to allow for the ventilation of expired gases
- Safety Alert: Entonox should not be used in aircraft due to the potential that expired gases may impact the pilot(s)
C - Ability to comply
D - Decompression sickness
C - Altered level of consciousness
P – Pneumothorax
A - Air Emboli
I - Inhalation in jury
N - Nitroglycerin use within 5 mins
- Ensure adequate ventilation of confined spaces, including operating the exhaust fan and/or opening windows in the ambulance
S - Shock
A - Abdominal distention
D - Depressant drugs
C - COPD
F – Facial injuries
- Lightheadedness, dizziness, sedation, drowsiness, disorientation.
- Nausea and/or vomiting.
Drug to Drug
- Depressant effects are potentiated by the presence of other CNS depressants such as alcohol, sedatives, antihistaminics, or psychotropic drugs.
- Self administered to effect.
- Self administered to effect.
- Ensure ENTONOX cylinders are maintained at a temperature above 10°C to ensure the gases are mixed correctly. If this is not possible D, CD and ED size cylinders may be used immediately if inverted three times before use to ensure mixing.
- Always use a bacterial/viral filter between the patient and the Entonox demand valve regulator.