Other Names

Entonox, Nitronox


General Anesthetic


Entonox is a homogeneous gas containing a mix of 50% oxygen and 50% nitrous oxide compressed into a cylinder. Entonox is a potent analgesic with properties comparable to that of strong opioids. It can provide short term pain relief, sedation and reduced anxiety during a wide range of painful situations.


Moderate to severe pain


  1. Hypersensitivity to the medication

  2. Entonox must never be used in any condition where air is trapped in the body and expansion (up to 3x original size) would be dangerous. For example, it will exacerbate pneumothorax and increase pressure from any intracranial air. Air in any other cavities such as the sinuses, middle ear and gut may also expand. 

  3. Entonox is contraindicated in the following:

  4. Head injuries with impaired consciousness.

  5. Maxillofacial injuries.

  6. Artificial, traumatic or spontaneous pneumothorax.

  7. Air embolism.

  8. Middle ear occlusion, ear infection

  9. Decompression sickness.

  10.   Abdominal distension / intestinal obstruction


  1. Since nitrous oxide is self-administered, it should also not be used on intoxicated or incompetent patients.

  2. Nitrous oxide is thought to cause an increase in intra-cranial pressure

  3. Should not be used on COPD patients because it may swell and rupture blebs, leading to pneumothorax

  4. If the patient complains of earache inhalation should be stopped and alternative analgesia prescribed in order to prevent potential perforation of the ear drum.

Adverse Reactions

  1. Earache

  2. Dry mouth

  3. Dizziness or disorientation

  4. Over sedation

  5. Nausea & vomiting

  6. A dry mouth is a common side-effect but is not usually distressing. The patient should be encouraged to continue inhaling the Entonox.


  1. Can potentiate the effects of other CNS depressants such as narcotics, hypnotics, sedatives and alcohol.

  2. If nitrous oxide and oxygen are in the same tank, make sure the tank stays above 4 degrees Celsius (40 F) or the nitrous will assume the liquid state and only oxygen will be administered.

Special Considerations

  1. Be careful that paramedics (especially driver) are not affected by off-gasses.  Use vent system on high.  Driver should partially open window and have fresh air blowing in on vents.

  2. Documented cases of abuse are rare, but addiction may result with long term use and this can lead to myeloneuropathy and subacute combined degeneration.

  3. It is essential that only the patient holds the  mask/mouthpiece in order to prevent the onset of deeper  stages of analgesia and sedation  and loss of protection of the  laryngeal reflex.


Allow patient to titrate dosage to effect by controlling their own inhalation.


Onset          2-5 minutes after initiation

Peak            2-5 minutes after initiation

Duration      2-5 minutes after cessation

Want to help out?  Feel free to fill in a template for a medication that you use in your system and send it to me.  These templates are (and always will be) free for anyone to use.  Send it to Marc.