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Evidence‐based approaches

Rationale

There are several advantages to using Entonox:
  • As the gas is inhaled, it is painless, in contrast to systemic methods of administering analgesia (such as injections).
  • It has a rapid onset of effect.
  • The side‐effects are few and are self‐limiting as the gas is self‐administered.
  • It does not depress respiratory or cardiovascular function when used as directed.
  • Effects wear off rapidly, usually within 5 minutes.
  • The patient is in full control, which provides reassurance that they have instant, self‐regulated access to analgesia. This also provides a focus or distraction from the procedure taking place. These factors can both help to reduce anxiety. Entonox also has sedative properties, which means it can act as an anxiolytic (BOC Healthcare [16]).
Because of these properties, Entonox is an ideal agent for short‐term pain relief following injury or trauma and during therapeutic and investigative procedures. It is used in a variety of settings, including accident and emergency (Huang and Johnson [81]), obstetrics (Collins [41]), paediatrics (BOC Healthcare [18]) and endoscopy, and for biopsy procedures (Wang et al. [191]) and dental procedures (Bonafé‐Monzó et al. [24]).

Indications

Entonox is indicated for the following:
  • wound and burn dressing, wound debridement and suturing
  • normal labour
  • changing or removing of packs and drains
  • removal of sutures from sensitive areas, for example the vulva
  • invasive procedures such as catheterization and sigmoidoscopy
  • removal of radioactive intracavity gynaecological applicators
  • altering the position of a patient who experiences incident pain
  • manual evacuation of the bowel in severe constipation
  • acute trauma, for example applying orthopaedic traction following pathological fracture or in reduction of joint dislocation
  • physiotherapy procedures, particularly post‐operatively.

Contraindications

Entonox should not be used in any of the following conditions:
  • maxillofacial injuries (BOC Healthcare [20]), as the patient may not be able to hold the mask tightly to the face or use the mouthpiece adequately, there is a risk of causing further damage to facial wounds, and there may also be a significant risk of blood inhalation
  • head injuries with impairment of consciousness
  • heavily sedated patients, as they would be unable to breathe in the Entonox on demand, and to potentiate sedation further may be hazardous
  • intoxicated patients, as drowsiness and aspiration would be a hazard in the event of vomiting
  • laryngectomy patients, as they would be unable to use the apparatus.
Additionally, Entonox should not be used in any condition in which gas is entrapped within the body and where its expansion may be dangerous. This is because the nitrous oxide constituent of Entonox passes into any air‐filled cavity within the body faster than nitrogen passes out. As the gas expands, this is likely to result in a build‐up of tension, which will increase the patient's symptoms. These conditions include:
  • pneumothorax (artificial, traumatic or spontaneous)
  • air embolism
  • severe bullous emphysema
  • abdominal distension or bowel obstruction
  • decompression sickness
  • following a recent dive
  • following air encephalography
  • during myringoplasty
  • bowel obstruction
  • in patients who have received recent intraocular injection of gas (BOC Healthcare [18]).

Use during pregnancy and lactation

Entonox is not absolutely contraindicated for use during pregnancy and lactation. However, it has been suggested that prolonged exposure to high levels of nitrous oxide may affect a woman's ability to become pregnant (Boiano et al. [22]). Mild skeletal teratogenic changes have been observed in pregnant rat embryos when the dam (pregnant mother) is exposed to high levels of nitrous oxide during the period of organogenesis. However, no increased incidence of foetal malformation has been discovered in eight epidemiological studies and case reports in humans (BOC Healthcare [16]). No published material shows that nitrous oxide is toxic to the human foetus. Therefore, there is no absolute contraindication to its use in the first 16 weeks of pregnancy. There are no known adverse effects to using Entonox during the breast‐feeding period (BOC Healthcare [19]).

Principles of care

Cautions

Prior to Entonox use, consideration should be given to the following:
  • The high level of oxygen (50%) in Entonox may depress respiration in patients who have chronic obstructive pulmonary disease and are carbon dioxide (CO2) retainers.
  • Entonox should not be used as a replacement for intravenous analgesia or general anaesthesia in procedures requiring increased levels of medical intervention.
  • Concomitant administration of Entonox in patients who are already on opioids and/or benzodiazepines may result in increased sedation and affect respiration; in this situation, the use of Entonox should take place under close supervision (BOC Healthcare [18]).
  • BOC Healthcare ([19]) states that when Entonox is used as a sole analgesic or sedative agent, driving or operating complex machinery is not recommended until all of the following are true:
    • the healthcare professional has judged that the patient has returned to normal mental status (Entonox can cause psychotropic effects)
    • the patient feels they are competent to drive or operate the machinery after the relevant procedure is completed
    • at least 30 minutes have elapsed after the administration of Entonox has ceased.
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