Previous section | Next section

Pre‐procedural considerations

Equipment

Cylinders

Entonox cylinders are available from BOC Healthcare in a variety of sizes. All cylinders have blue and white markings on their shoulder (Figure 10.12). The lightweight, smaller cylinders have the following advantages:

They are easier to carry.
They have a live contents gauge.
Changing an empty cylinder is simple because it is not necessary to fit a regulator or use a cylinder key.

Expand Download

Figure 10.12 Entonox cylinder and hose.

The smaller cylinders tend to be used in ambulances and by midwives due to their portability in home births. Some clinical areas may have piped Entonox, such as accident and emergency departments, high‐dependency units and critical care units. The larger cylinders, which require a trolley to move them around, are more suitable for ward areas.

Demand apparatus

There are a number of different companies that supply the demand apparatus for self‐administered Entonox use. The face‐mask or mouthpiece is connected to an Entonox supply through a demand valve system. The demand valve allows the Entonox gas to flow when the patient inhales, and then the valve closes when the patient stops inhaling the gas (BOC Healthcare [18]) (Figure 10.13). This method of administration makes use of a demand unit, which safeguards the patient from excessive inhalation of Entonox. Thus, patients are able to self‐regulate the dose of Entonox (a method of patient‐controlled analgesia). The patient must hold the mask firmly over the face or hold the mouthpiece to the lips to produce an airtight fit and breathe in before the gas will flow. Expired gases escape via the expiratory valve on the hand piece (BOC Healthcare [19]). It is essential to adhere to this method of self‐administration as it is then impossible for patients to overdose themselves because, if they become drowsy, they will relax their grip on the handset and the gas flow will cease when no negative pressure is applied. However, should inhalation continue, light anaesthesia supervenes and the mask drops away as the patient relaxes.

Expand Download

Figure 10.13 Patient using an Entonox demand valve.

Entonox has an oxygen content 2.5 times that of air and is therefore a good way of giving extra oxygen as well as providing analgesia.

Bacterial filters and mouthpieces or face‐masks

Because Entonox equipment is a potential source of cross‐infection, bacterial filters (single use only) should be fitted between the face‐mask or mouthpiece and the demand valve if the demand valve is not for single use (BOC Healthcare [19]). Face‐masks and mouthpieces must also be single use only and disposed of once therapy ceases. Local policies must be followed for the cleaning and sterilization of non‐disposable equipment between patient use.

Assessment

The patient's ability to administer Entonox safely and effectively (particularly in the very young or very old) must be assessed prior to use. Patients should be able to:

understand the instructions for Entonox use
hold the demand valve to self‐administer the gas
inhale the gas through the mask or mouthpiece while breathing normally (patients who have impaired lung function may not be able to inhale the gas sufficiently to provide adequate analgesia).

Duration and frequency of administration

The duration and frequency of Entonox administration should always be tailored to individual patient needs. Because prolonged exposure to Entonox causes inactivation of vitamin B₁₂, impaired folate metabolism and pernicious anaemia (BOC Healthcare [18]), it is recommended that:

Entonox is used on a short‐term rather than a long‐term basis.
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 and haematological monitoring for vitamin B₁₂ deficiency (BOC Healthcare [18]).
If daily use is required for more than 4 days, this should be accompanied by close supervision and haematological monitoring (blood tests) (BOC Healthcare [18]). Consideration should also be given to the administration of B₁₂ and folate supplements.

Procedure guideline 10.6

Entonox administration

Table 10.11 Prevention and resolution (Procedure guideline 10.6)

Problem	Cause	Prevention	Action
Patient not experiencing adequate analgesic effect	Entonox cylinder empty. Apparatus not properly connected.	Check equipment before use.	Change to a full cylinder.
	Patient not inhaling deeply enough ( BOC Healthcare [19]).	Educate patient prior to use.	Encourage the patient to breathe in until a hissing noise can be heard from the cylinder. Reassess the suitability of the patient for Entonox use. The patient may not be strong enough to inhale deeply or may have reduced lung capacity.
	Patient inhaling pure oxygen – that is, cylinder has been stored below −6°C and nitrous oxide has liquified and settled at the bottom of the cylinder.	To ensure that the gas is suitable for immediate use, all cylinders should be stored horizontally at a temperature of 10°C or above for 24 hours before use ( BOC Healthcare [19]).	Initially this is safe, but later the patient may inhale pure nitrous oxide and be asphyxiated. Discontinue the procedure. Ensure adequate warming and inversion of the cylinder to remix the gases adequately.
	Not enough time has been allowed for nitrous oxide to exert its analgesic effect.	Allow at least 2 minutes of Entonox use before evaluating any analgesic effect or before commencing the procedure.	Stop the procedure. Allow 2 minutes of Entonox use. Restart the procedure.
Patient experiencing generalized muscle rigidity	Hyperventilation during inhalation ( BOC Healthcare [16]).	Educate patient prior to starting procedure.	Discontinue Entonox and allow the patient to recover. Explain the procedure again, stressing deep and regular inspiration. Use a mouthpiece in place of a mask.
Patient unable to tolerate a mask	Smell of rubber. Feeling of claustrophobia.	Assess patient preference to use either mask or mouthpiece before Entonox use.	Use a mouthpiece in place of a mask.
Patient feels nauseated, drowsy or dizzy	Effect of nitrous oxide accumulation ( BOC Healthcare [18]).		Discontinue Entonox administration; the effect will rapidly subside after removal of the gas. Restart Entonox use; if the same effect occurs, stop using Entonox and use an alternative form of analgesia.
Patient afraid to use Entonox	Patient associates gases with previous hospital procedures, for example anaesthesia before surgery ( BOC Healthcare [16]).	Assess suitability of patient for Entonox use. Address fear and anxiety issues before starting Entonox use.	Reassure the patient and reiterate instructions for use and short‐term effects.