Dental Update - Overview of paediatric dental sedation: 2. nitrous oxide/oxygen inhalation sedation

Abstract

The use of conscious sedation for the management of anxious paediatric dental patients is extremely beneficial. Inhalation sedation with nitrous oxide and oxygen remains the mainstay for paediatric sedation in the UK.

Clinical Relevance: Dentists carrying out inhalation sedation for dental treatment must be fully conversant with the technique and the principles of patient management.

Article

Inhalation sedation with nitrous oxide and oxygen is the mainstay of conscious sedation for paediatric dental patients in the UK. It has a high success rate and is well tolerated.1^,2^,3^,4^,5^,6^,7^,8^,9^,10

This paper will review the principles of inhalation sedation with nitrous oxide and oxygen, including indications and contra-indications, equipment requirements, patient assessment, the technique itself and management of complications.

Inhalation sedation can be defined as: ‘A semi-hypnotic technique of conscious sedation in which nitrous oxide and oxygen are employed to produce physiological changes which enhance the patient's suggestibility. The patient should remain conscious and co-operative throughout with all vital reflexes intact.’

The main aim of inhalation sedation is to produce anxiolysis, thus alleviating fear and improving the patient's co-operation to enable dental treatment to be carried out effectively.

The technique involves the administration of low to moderate concentrations of nitrous oxide in oxygen using a specifically designed machine. The use of semi-hypnotic suggestion throughout the procedure to reassure and encourage the patient is an integral part of the process.

It is important to be familiar with the physical properties of nitrous oxide and how these relate to its therapeutic application.

Physical properties of nitrous oxide

Presentation

Nitrous oxide is a colourless, slightly sweet smelling gas at room temperature. It is stored as a liquid in light blue cylinders at a pressure of 750 pounds per square inch (Figure 1).

Blood/gas solubility

It is relatively insoluble in blood and therefore produces a rapid induction of its sedative effect. Likewise, when the nitrous oxide is discontinued it leaves the circulation rapidly and is exhaled through the lungs.

Potency

Nitrous oxide is a weak anaesthetic and therefore, when administered in combination with oxygen, it has a very wide margin of safety; titrated carefully loss of consciousness is extremely unlikely. Nitrous oxide is fairly potent, but the analgesic effect is generally not sufficient to anaesthetize the dental or oral tissues for operative procedures. Effective local anaesthesia is therefore essential.

Sedation

Nitrous oxide produces a good level of sedation in patients and has both a depressant and euphoric effect on the central nervous system (CNS). This property makes it a useful agent for use in anxious patients.

Side-effects

Nitrous oxide used therapeutically has few side-effects for the patient. However, at higher levels it can lead to nausea and headache.

Occupational hazards

Nitrous oxide use is subject to health and safety regulations as it can produce adverse effects for healthcare personnel exposed to high levels over long periods of time. The UK Health and Safety Executive have therefore set an exposure limit of 100 parts per million over an eight hour time-weighted period. To comply with this regulation, it is important for those regularly using nitrous oxide/oxygen inhalation sedation for their patients to test exposure levels periodically. This can be carried out using a computerized system or gas analyser cells (Figure 2).

Nitrous oxide pollution in the surgery can be minimized by using:

Active scavenging systems;

Good ventilation;

Floor level extractor fans;

A good technique with the patient;

Equipment that has been checked and serviced on a regular basis.

Inhalation sedation with nitrous oxide and oxygen

The three main elements of inhalation sedation are illustrated in Figure 3.

Figure 3. Three main elements of inhalation sedation.

The success of inhalation sedation relies on the combination of the pharmacological effects of nitrous oxide and good behavioural management. This can be described as psycho-pharmacological sedation.

Indications and contra-indications for inhalation sedation

Inhalation sedation can be useful for both adults and children. The main indications and contra-indications are illustrated in Table 1.

Table 1. Indications and contra-indications for inhalation sedation.

Indications	Contra-indications
Management of dental anxiety Management of traumatic procedures Management of gag reflex Management of medically Mouth breathers compromised patients	Upper respiratory tract infection Blocked nose Chronic respiratory disease Pre-cooperative children If the patient has had a medical procedure involving the use of intracranial gases (eg some ocular procedures)

Children must be able to understand the reason for, and administration of, inhalation sedation to enable co-operation. Although generally used to alleviate fear and anxiety, inhalation sedation is also helpful in children who may not be particularly worried but who require orthodontic extractions, multiple extractions or a surgical procedure.

Advantages and disadvantages of inhalation sedation

Nitrous oxide/oxygen inhalation sedation has many advantages and a few disadvantages (Table 2) and these should be considered during the patient assessment.

Table 2. Advantages and disadvantages of inhalation sedation.

Advantages	Disadvantages
Simple, non-invasive technique Rapid onset and recovery Depth of sedation can be easily regulated Moderate analgesia produced Minimal effect on cardio-respiratory system Minimal interaction with other drugs Easily reversed with 100% oxygen	Nose mask not accepted by all patients The technique requires a reasonable degree of patient compliance Limited degree of sedation for more invasive techniques Cost of equipment

Clinical effects of nitrous oxide/oxygen sedation

The clinical effects produced by nitrous oxide and oxygen sedation are dependent on the percentage of nitrous oxide administered. The clinical effects appear in the first stage of anaesthesia, which is divided into three planes of analgesia. The planes of analgesia and the common associated clinical effects are illustrated in Table 3.

Table 3. Planes of analgesia and clinical effect of nitrous oxide.

Plane of analgesia	Average % nitrous oxide	Level of sedation/analgesia	Clinical effects
Plane I	10–25%	Moderated sedation/analgesia	General relaxation Slight paraesthesia in fingers/toes Slight feeling of warmth Alert/responds to questioning
A gradual transition may be noted between planes I and II with an increase in intensity of the clinical effects
Plane II	20–55%	Dissociation sedation/analgesia	Marked relaxation and tiredness Moderate/widespread paraesthesia A feeling of detachment Dreamy, faraway look Reduced gag reflex
The transition from Plane II to Plane III can occur quickly, emphasizing the need for slow titration of nitrous oxide
Plane III	50–70%	Total analgesia	Marked sleepiness/closed eyes Total analgesia Nausea/headache are common Unresponsive to questioning May lose consciousness

Equipment used for inhalation sedation

Purpose-designed machines dedicated for the administration of inhalation sedation with nitrous oxide and oxygen should be used. These may be either free-standing (Figure 4) or piped systems (Figure 5). Scavenging of waste gases must be active (45 litres/min) and breathing systems should have separate inspiratory and expiratory limbs to allow for appropriate scavenging (Figure 6). As the equipment delivers medical gases to the patient, safety is paramount. Both types of inhalation sedation machines have important safety features (Figure 7) and appropriate safety checks should be carried out at the beginning of each sedation session (Figure 8) when used to provide inhalation sedation.

Figure 4. Stand alone inhalation sedation machine.

Figure 5. Piped inhalation sedation machine.

Figure 6. Active scavenging breathing system.

Figure 7. Safety features of the inhalation sedation machine.

Figure 8. Pre-inhalation sedation checklist.

Patient assessment for inhalation sedation

Prior to carrying out treatment under inhalation sedation for child dental patients, a full pre-operative assessment must be carried out. The aim of the assessment is to ascertain whether the child would benefit from sedation to support him/her through the treatment. It is important to include both the child and the parent in the decision-making process.

At this visit the following should be recorded:

Dental history

Frequency of attendance;

Previous dental treatment;

Previous sedation/GA;

Any anxieties/worries.

Medical history

Medical conditions;

Current medication;

Known allergies;

Patency of airway;

Allocate ASA grade.

Social history

Age and co-operation;

Siblings;

Who they live with;

Who can legally sign consent;

Availability of appropriate escort;

Availability of transport.

Current oral health

Full dental charting;

Soft tissue examination;

Radiographs if appropriate.

The type of dental treatment to be carried out should be taken into account when considering the use of inhalation sedation. For example, one or two deciduous extractions in a 5-year-old would be reasonable, but extraction of multiple grossly carious teeth in the same child may be best carried out under general anaesthesia.

Pre-operative instructions

It is important to give a full explanation of the inhalation sedation procedure to both the child and parent/guardian. This should include how the sedation or ‘Happy Air’ is administered. Showing the child the nosepiece and allowing him/her to try it on is helpful and allows for the opportunity to become familiar with the technique.

It is important to explain how the child may possibly feel during the sedation; floaty, heavy, tingling in hands and feet, a bit sleepy.

Many people believe that because they are having ‘Happy Air’ they will not require local anaesthetic (‘the injection’). It is important to explain that local anaesthetic will be used to numb the teeth to assist with treatment. When explaining this to a child it is important to use appropriate words that will not worry him/her. For example, saying that the tooth will be ‘washed’ to make it feel ‘tingly’ before it is ‘wiggled out’ or ‘made better’.

The level of explanation should be pitched according to the age and level of understanding of the patient.

Full pre- and post-operative instructions should then be given to the patient and parent/guardian and should include:

Have only a light meal 2 hours before the appointment;

Children must be accompanied by an adult who has no other dependents with them;

Transport home should ideally be in a car or taxi.

Children should take it easy for the rest of the day. They should not:

Ride bikes;

Use outdoor playground equipment;

Use any electrical appliances for the rest of the day;

Children must be supervised by an adult for the rest of the day.

A written consent for treatment and sedation must be obtained prior to commencing any treatment.

Administration of inhalation sedation.

On the day of treatment, pre-operative patient checks should be carried out before any treatment is administered:

The patient/parent knows what treatment is planned;

The patient is able to breathe through his/her nose;

An up-to-date consent has been obtained;

The medical history is up-to-date;

Any medication has been taken as normal;

What time did the patient last eat/drink?;

Escort present and transport home?

An example of a checklist can be seen in Figure 8.

The patient is then escorted into the surgery; when sitting comfortably in the dental chair he/she can be shown the nosepiece. It is important to ensure that the correct size is chosen to ensure a tight seal against the face (Figure 9).

With 100% oxygen flowing, at a rate of 4 to 6 litres per minute, the nosepiece can then be placed on the nose with the patient's assistance. The patient should be encouraged to breath for one to two minutes and, by observing the reservoir bag, the flow rate can be adjusted accordingly.

The nitrous oxide is then titrated at a rate of 10% every minute, according to the patient's needs (Figure 10). During administration, it is essential to use hypnotic suggestions and distraction to enhance the sedative and anxiolytic effect of the nitrous oxide. If titrating past 30%, ideally the nitrous oxide should be administered in 5% increments.

Figure 10. Administration of inhalation sedation.

The endpoint, when treatment can be commenced, is when the patient is happy to proceed. It is important therefore to communicate with the patient and ask when he/she is ready for treatment. The signs and clinical effects of inhalation sedation are illustrated in Table 3.

During the treatment stage, the patient should be encouraged to continue breathing through his/her nose; the reservoir bag should be observed to ensure that this is happening.

At the end of the dental treatment, the nitrous oxide should be stopped and 100% oxygen administered. This will prevent the occurrence of diffusion hypoxia, a transient hypoxic episode which occurs due to the rapid diffusion of nitrous oxide back into the lungs, diluting the oxygen levels. The patient should breathe 100% oxygen for at least three minutes, after which he/she should be asked if normal feeling has returned; only then should the nosepiece be removed. Next:

Sit the patient up;

Check that he/she does not feel dizzy or nauseous; then

Ask him/her to stand up and walk a short distance unassisted.

Post-operative instructions should then be given to the child and his/her parent/guardian prior to being discharged home.

Management of over sedation

It is important to be aware of the signs of over sedation and how these can be managed (Table 4). The provision of inhalation sedation should be subject to regular audit to consider the occurrence of treatment outcomes and complications.

Table 4. Signs and symptoms of over sedation.

Signs of over sedation	Symptoms	Management
Early signs Anxiety Distressed look	Early symptoms Slight dizziness Mild headache	Reduce the nitrous oxide by 5–10% and reassure the patient. Generally treatment can then continue.
Late signs Extreme anxiety Crying Vomiting	Late symptoms Severe headache Nauseous Feeling totally numb	Press oxygen flush button and switch off the nitrous oxide. Allow the patient to breath 100% oxygen and monitor. Treatment should be postponed and the patient assessed for future treatment needs.

Failure of the technique

Should the technique not prove effective, there may be several reasons for this (Table 5).

Table 5. Reasons for failure of inhalation sedation.

Reason for failure	Management
The patient may not be breathing adequately through his/her nose	Encourage nose breathing Ensure the nose is not blocked
There may not be an effective seal around the nosepiece	Ensure the nosepiece is securely fitted
The patient may be too anxious and not able to co-operate	Stop treatment and reconsider management options
There may be a fault in the machine	Stop treatment and have the equipment checked by a service engineer
The patient may be resisting the effects of the sedation	Consider other management options

Conclusion

Sedation for the paediatric dental patient can be extremely beneficial in some cases, mainly where the child is anxious or requires a traumatic procedure.

The main type of sedation used for children in the UK is inhalation sedation with nitrous oxide and oxygen. It has a high success rate, is simple and safe to use and is an acceptable technique for patients.

However, there may be some cases where this form of sedation is not appropriate or is not effective and, in these instances, other sedation techniques or general anaesthesia may be considered more appropriate.

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References

Overview of paediatric dental sedation: 2. nitrous oxide/oxygen inhalation sedation

Authors

Katherine E Wilson