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Nurse administration of Entonox to manage pain in ward settings

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VOL: 98, ISSUE: 46, PAGE NO: 28

Lynn Sealey, BA, RGN, is acute pain sister, Warrington Hospital, North Cheshire Hospitals NHS Trust

The effective management of patients’ pain during their stay in hospital continues to provide multidimensional challenges to health care professionals. When trying to manage pain, nurses are often faced with obstacles such as the fear of litigation relating to written and verbal prescriptions and a lack of knowledge about safe limitations of certain drugs and combinations of analgesics.

These factors can lead to them feeling that they may not be providing the best possible pain relief or the best practice for their patients. Postoperative pain relief is usually given high priority in patient care. However, Brown and Fanurik (1996) suggest that although the pain associated with the disease process is often addressed, the pain associated with a number of necessary medical and nursing procedures is sometimes overlooked. These procedures include the changing of wound packs or the removal of a surgical drain that has become slightly congealed around the insertion site.

Even if the patient’s current analgesic status is satisfactory, procedures such as these may cause great discomfort. This could lead to emotional distress, which Craig (1993) suggests is the most undesirable feature of painful experiences. When carrying out any potentially painful intervention, it is desirable that the patient should experience the minimum amount of distress and anxiety.

Entonox is an analgesic that is widely used and understood in maternity and A&E departments. Also known as ‘laughing gas’, the active ingredient of Entonox - nitrous oxide (N2O) - was discovered in the 18th century and later found use as an anaesthetic in clinical dentistry and medicine. Nitrous oxide is still in common use in modern dentistry. However, it is underused within many primary care trust ward settings, where it could be used to provide short-term analgesia for patients during painful procedures.

There are a number of possible reasons for this underusage, mainly relating to a lack of awareness of:

- The pharmacological effects of Entonox;

- The local hospital policy regarding its prescription by a doctor;

- Physiological effects;

- Side-effects;

- The safe use of Entonox alongside other analgesics;

- Contraindications;

- The requirements for safe storage and handling of cylinders;

- Ordering and resupply of Entonox cylinders.

While in many trusts, Entonox is only provided with a doctor’s prescription, others have local guidelines or patient group directions which give nurses greater independence to administer it.

What is Entonox?

Entonox is a colourless, almost odourless, gaseous mixture of 50 per cent oxygen (O2) and 50 per cent nitrous oxide (N20). It acts as a powerful analgesic when it is inhaled, and with a rapid onset of action and short duration of effect it is a safe method of pain relief with minimal side-effects (BOC, 2001; Pickup, 2000). Entonox provides analgesia within two minutes of inhalation, but its effects are apparent within the first few breaths (BOC, 2001). This rapid action and short duration are due to the physical properties of N20. First, it is not metabolised by the body, but is eliminated completely by the lungs. Second, its low fat solubility does not allow it to accumulate to a great extent within the body and cause toxicity. This also means it can be self-administered by patients.

Mechanism of action

A recent hypothesis by Maze and Fujinaga (2000) suggests that Entonox activates the release of noradrenergic substances within the pain pathway. These substances are thought to activate receptors in the dorsal horn of the spinal cord, which prevent the signal from reaching the brain where it would be perceived as pain. The pharmacological profile of Entonox, with its speedy reversal, allows it to be used in combination with other drugs (BOC, 2001). A potential advantage of this is that it may reduce the requirement for strong analgesics (such as morphine-type substances) which are sometimes used for breakthrough pain. This strategy might reduce the often unpleasant and longer-lasting side-effects such as nausea and sedation that are associated with stronger analgesics.


Entonox can cause dizziness that is usually resolved once the patient stops inhaling the gas. At this point, continued inhalation could cause the patient to lose consciousness. Therefore it is extremely important for patients to hold the facemask or mouthpiece themselves during administration. If excessive sedation occurs, the patient will drop the apparatus and immediately inhale normal air (Lawler, 1995). Entonox can also occasionally cause nausea, but this usually ceases on discontinuation of the gas. Prolonged or frequent administration - more than six to eight hours of continuous use (BOC, 2001) or using it more frequently than once every two days - may lead to interference in bone marrow function. If Entonox is required for frequent use, a full blood count should be checked on a regular basis. It is worth considering, that although the N20 constituent of Entonox is eliminated rapidly, BOC (1995) recommends that patients do not drive or operate machinery for 12 hours after use.

Occupational and environmental considerations

There has been some debate on whether the use of Entonox can cause an increased risk of miscarriage in the first 16 weeks of pregnancy. However, the BOC data sheet (1995) suggests that there is no substantial evidence that Entonox is harmful to the human foetus. There are also no significant environmental implications when using Entonox, although nurses should bear in mind the usual hazards associated with the use of medical gases in confined spaces. Some of these issues are discussed in the following section.

Storage and handling precautions

Entonox is presented in cylinders that are painted blue with a white band around the top. To reach its full potential as an analgesic agent, it is recommended that Entonox is stored horizontally, at a temperature above 10° for 24 hours before it is used (BOC, 1995). If it is stored below 6°C, the nitrous oxide will separate from the mixture, jeopardising its usefulness. Entonox is delivered via a demand valve, which is activated by the inspiratory effort of the user. Therefore, self-administration, via a mask or mouthpiece, depends upon adequate inspiration and, if using a mask, an airtight seal. If disposable equipment is used, cross infection is not usually an issue.

With re-usable equipment, masks must be cleaned either with an alcohol-based cleaner or a similar solution. However, it is good practice to clean the entire administration set on a regular basis. There are also certain precautions that must be observed in accordance with the Health and Safety at Work Act 1974 (Peate and Lancaster, 2000). For example, materials that do not normally burn in air will burn more easily in the presence of most medical, gaseous mixtures. For this reason smoking or naked flames must not be permitted in the vicinity of the gas cylinder or the patient who is using Entonox. Also, because of the high risk of spontaneous combustion that is associated with highly pressurised gases such as nitrous oxide, the cylinder should not be lubricated with oil or grease (BOC, 1995).

Indications and contraindications for use

Entonox can be used within the ward environment for short, painful procedures such as:

- Removal of nasal packs;

- Removal or insertion of wound packs;

- Physiotherapy;

- Suturing;

- Removal of drains;

- Removal of adherent dressings;

- Labour pains;

- Manipulation and examination of fractures.

Entonox should not be used for any condition in which air may be trapped in a confined space within the body (BOC, 2001). In such conditions, the N20 content of Entonox passes into tall gas-containing spaces in the body faster than nitrogen passes out of these spaces (BOC, 1995). This causes expansion and/or an increase in pressure within the space.

Entonox should not be used in cases of:

- Tension pneumothorax;

- Air embolism;

- Decompression sickness;

- Chronic lung disease;

- Myringoplasty;

- Suspected intestinal obstruction;

- When the patient has had a recent underwater dive (Pickup, 2000; BOC, 2001).

Entonox is also contraindicated where there is an actual or potential impaired level of consciousness such as with head injury, intoxication and maxillofacial injury. Furthermore, as with most analgesics, addiction is a possibility and should be considered in the use of Entonox.


Its rapid action and safety profile make Entonox a useful analgesic for many patients undergoing painful procedures. In order for nurses to use it confidently and competently in their practice, they need clear, local procedural guidelines, including information regarding the availability of cylinders and equipment. Guidelines should also indicate whether Entonox needs to be prescribed by a doctor or can be used under patient group directions, as policy at local hospitals can vary on this issue. Training and education on the pharmacology, indications, contraindications and safe use of Entonox (perhaps provided by the acute pain service) may help nurses to feel competent in the administration of Entonox. It may also give them the confidence to use it in a wider range of situations, or to request that it be prescribed for administration during painful procedures.


Hollinworth, H. (1995)Nurses’ assessment and management of pain at wound dressing changes. Journal of Wound Care; 4: 2, 77-83.

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