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ENTONOX nitrous oxide/oxygen mixture provides the pain relieving properties of nitrous oxide with the benefits of additional oxygen without producing unconsciousness. It is a widely used analgesic for acute, short-term pain relief in a diverse range of clinical situations, from painful procedures to childbirth.


ENTONOX is a potent analgesic with a very rapid onset of action and is quickly eliminated from the body. It is widely used by midwives, hospitals and the ambulance service. It is used exclusively for short-term procedures inevitably involving pain, including (but not limited to): 

  • Acute trauma
  • Tooth extraction and other brief procedures in dental work
  • Wound and burn dressing, wound debribement and suturing
  • Fracture and joint manipulation
  • Colonoscopy
  • Venopuncture
  • Labour


ENTONOX is a ready-to-use medical gas mixture of 50% nitrous oxide and 50% oxygen that provides rapid, safe and effective short-term pain relief. Key features include:

  • Predictable and reliable analgesia,

  • Effective pain relief and sedative effect without loss of consciousness,

  • Rapid onset and offset, which can lead to savings through reduced treatment time and increased patient turnaround,

  • Properties that help to reduce patient anxiety,

  • Easy, self-regulated administration,

  • Minimal side-effects


There are a number of situations where ENTONOX is contraindicated.

For example, ENTONOX should not be used where patients have undergone recent eye surgery involving gas bubble insertion. This is because there is a risk that the nitrous oxide will diffuse into the bubble, causing it to expand and eventually burst.

ENTONOX can also 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 condition where air is trapped in the body and expansion would be dangerous. 

Examples where air may be trapped in the body include:


  • 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 with haematological monitoring. This is because it may 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.