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Evidence‐based approaches

Rationale

There are several advantages to using Entonox.
  • As the gas is inhaled, it is painless when compared 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, which also provides a focus or distraction from the procedure taking place. Both of these can help reduce anxiety. Entonox also has sedative properties which can act as an anxiolytic (BOC [19]).
Because of these properties, Entonox is an ideal agent for short‐term pain relief following injury or trauma and during therapeutic and investigative procedures. Although its use is mainly in emergency care (O'Sullivan and Benger [162]), obstetrics (Rosen [193]), paediatrics (Bruce and Franck [27], Pickup and Pagdin [173]) and endoscopy/biopsy procedures (Forbes and Collins [76], Manikandan et al. [133]), there is a place for Entonox in the oncology setting. Parlow et al. ([168]) performed a case review of the use of Entonox in the management of breakthrough cancer pain. Although the review was small they noted that five of the seven patients achieved pain control when compared with placebo.

Indications

  • Wound dressing, wound debridement.
  • Changing or removal 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.
  • Physiotherapy procedures, particularly post‐operatively.

Contraindications

Entonox should not be used with any of the following conditions.
  • Maxillofacial injuries (BOC [17]). This could be as a result of surgery or local disease‐altering anatomy. 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 injury and there may also be a significant risk of blood inhalation if there are any open wounds or aggravation at the surgical site.
  • 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 or those with impaired level of consciousness related either to disease state or concurrent medications. Aspiration would be a hazard in the event of vomiting.
  • Any condition in which gas is entrapped within the body and where its expansion may be dangerous, such as:
    • pneumothorax (artificial, traumatic or spontaneous)
    • air embolism
    • severe bullous emphysema
    • abdominal distension or bowel obstruction
    • decompression sickness or following a recent dive
    • following air encephalography
    • during myringoplasty
    • in patients who have received a recent intraocular injection of gas (BOC [19]).
      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.
  • Laryngectomy patients, as they will be unable to use the apparatus.
  • Temperatures of below −6°C, as the gases separate (BOC [16]). If this occurs the cylinders will initially deliver a high concentration of oxygen but will eventually deliver nearly pure nitrous oxide.

Use during pregnancy and lactation

Although this may be rare in the cancer setting, it is important to consider if your patient is trying to become pregnant that prolonged exposure to high levels of nitrous oxide may affect a woman's ability to become pregnant (Axelsson et al. [4]). However, there is no published material to show that nitrous oxide is toxic to the human fetus, 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 [19]).
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