Conscious sedation in dentistry
Chapter Contents
Overview
The use of drugs to help in the management of patients’ anxieties regarding dental care is not new. The use of alcohol predates the invention of local analgesia, and a perusal of many art galleries will show travelling tooth pullers where patients sedate themselves prior to treatment.
The use of sedative techniques in dentistry tends to fluctuate in popularity. The administration of centrally-acting drugs by dentists is also an area that has attracted some concern over safety.
The techniques described in this chapter are safe and amenable to use by suitably trained dentists working in general dental practice, community dental clinics or hospitals.
6.1 Sedation
There have been many definitions of sedation put forward over the years. The current definition that must be accepted in the UK is found in the Standing Dental Advisory Committee’s report Conscious Sedation in the Provision of Dental Care and the Scottish Dental Clinical Effectiveness Programme’s document Conscious Sedation in Dentistry. The definition is:
a technique in which a drug, or drugs, produces a state of depression of the central nervous system enabling treatment to be carried out, but in which verbal contact is maintained throughout the period of sedation.
The drugs and techniques used should carry a margin of safety wide enough to render loss of consciousness unlikely.
Techniques for producing conscious sedation can be divided into two groups – basic and advanced.
The basic techniques are:
provided adequate competence in intravenous techniques has been demonstrated.
The advanced techniques are:
• benzodiazepine plus any other agent, for example opioid, propofol, ketamine
• propofol either alone or with any other agent, for example benzodiazepine, opioid, ketamine
• inhalation sedation using any agent other than nitrous oxide/oxygen alone
This definition was published in 2007 by the Standing Committee on Sedation for Dentistry of the Faculty of Dental Surgery, The Royal College of Surgeons of England.
This text concentrates on the basic techniques. Further information on the advanced techniques can be found in specialist sedation textbooks.
Indications for sedation
The indications for sedation can be considered under three main headings: psychosocial, medical and dental.
Psychosocial indications
Indications relating to anxieties regarding dental treatment include:
Medical indications
Some conditions may be aggravated by the stress of undergoing dental treatment:
Many patients with these conditions can be treated quite ‘normally’ with local analgesic injections and tender loving care on the part of a sympathetic dentist. There are, however, a group of patients who, in addition to having a medical condition, also become quite anxious about dental treatment. A history of aggravation of the pre-existing condition in the dental environment may be the only clue as to the patient’s concerns.
Some conditions affect the patient’s ability to co-operate with dental treatment:
The use of sedation aids the management of these patients. The most important requirement is that the patient is able to understand what is being done. Lack of understanding will lead to failure of the technique. The assessment of a patient’s understanding is extremely difficult.
Dental indications
Sedation may be required for difficult or unpleasant procedures (e.g. extraction of wisdom teeth) or for orthodontic extractions, particularly in patients with limited previous dental care experience. The proper prescribing of sedation for these indications can help to prevent many patients having to suffer unpleasant experiences. It is well recognised that patients who have had a wisdom tooth surgically removed are more likely to fail than attend the appointment for the second surgical removal.
Contraindications to sedation
Contraindications can be grouped in a similar manner as indications.
Psychosocial contraindications
Patients must be willing and co-operative. A failure to consent for treatment is an absolute contraindication to the provision of care under sedation. Similarly, patients must co-operate to allow the administration of the sedative agents by a given route. Failure to do so will prevent the dentist being able to treat the patient.
Unaccompanied patients
A responsible adult, who will remain with them until their recovery is complete, must accompany patients who are receiving sedation. The only exception to this rule is for adult patients who are receiving inhalation sedation with nitrous oxide and oxygen. Such patients may be allowed to attend without an escort provided that the dentist feels it is appropriate. A responsible adult must accompany children receiving inhalation sedation.
Medical contraindications
Severe or uncontrolled systemic disease
Patients who are to receive sedation should have any general medical problems controlled prior to the commencement of their dental treatment. The administration of sedative drugs masks the patient’s ability to detect if they are becoming unwell. It is recommended that patients who would be considered as grade III or worse in the American Society of Anesthesiologists’ (ASA) classification of anaesthetic risk (Table 6.1) should not receive sedation outside an environment where the staff are trained to deal with the potential problems. This generally will mean these patients should not be treated outside a hospital setting.
Table 6.1
American Society of Anesthesiologists’ classification of anaesthetic risk
| Grade | Description |
| I | Fit and well patient, no intercurrent disease |
| II | Patient with mild intercurrent disease that is well controlled and does not affect lifestyle |
| III | Patient with moderate intercurrent disease that does affect lifestyle |
| IV | Patient with severe intercurrent disease that is a constant threat to life |
| V | Patient who is unlikely to survive 24 hours with or without medical intervention |
| VI | A clinically brain dead patient awaiting organ harvest |
Severe learning or movement difficulties
The key to success in sedation is that the patient understands the procedure. If this understanding is lacking, then sedation is prone to failure.
Chronic obstructive pulmonary disease
Chronic bronchitis causes a severe upset in respiratory physiology. It results in the respiratory drive being dictated by hypoxia rather than by changes in carbon dioxide levels. The clinical importance of this is, first, that the patient is significantly more sensitive to respiratory depressant drugs (including the benzodiazepines used in intravenous sedation) and, second, that high levels of oxygen, as used in inhalation sedation, may also cause the patient to stop breathing as hypoxic drive is reduced.
Severe psychological/psychiatric problems
Patients suffering from delusional states such as psychoses or schizophrenia are notoriously difficult and unpredictable in their response to sedation. This relates to the frequently unpredictable reaction of the patient to the feelings of being sedated. Most of these patients are also taking heavy-duty antipsychotic drugs, which may interact with the sedatives that they are being given as part of their dental treatment. Consequently, only experienced sedationists should treat these patients.
Thyroid dysfunction
Individuals who suffer from hypothyroidism are significantly more susceptible to the effects of central nervous system depressant drugs. Sedation should be avoided in this group.
Hyperthyroid patients may be difficult to sedate and care has to be taken with the use of vasoconstrictors in local analgesic solutions.
Pregnancy and lactation
It is wise to carry out as little treatment as possible for pregnant patients. Almost any drug that is given to the mother will cross the placenta and enter the fetal circulation. While the effects on the mother are easily observed, the effects on the fetus are masked from direct observation. The use of sedation during pregnancy should be restricted to the absolute minimum. It is, however, permissible to use sedation to provide emergency dental care, perhaps in the situation where the fetus would be at greater risk from the repeated administration of antibiotics than from a single visit for treatment under sedation.
Inhalation sedation should be avoided during the first 3 months of pregnancy when there is the greatest risk of damage to the fetus. After this point, there is no evidence of any problem in the use of inhalation sedation with nitrous oxide. Common sense indicates that this will be the case, given the regular use of nitrous oxide as an obstetric analgesic.
There is no evidence that intravenous midazolam causes any fetal abnormalities. It can be used during the first 6 months of pregnancy if required. There is evidence that intravenous midazolam can cause hypotonia in the older fetus and, therefore, it should not be used during the last 3 months of pregnancy.
Contraindications to inhalation sedation with nitrous oxide
In addition to the general contraindications above, a blocked nasal airway is a specific contraindication for the use of nitrous oxide sedation. Inhalation sedation will not work when a patient cannot breathe through the nose. Some blockages are temporary, such as hay fever or the common cold, and treatment may merely have to be postponed. Other blockages of the nasal airway are permanent. These could include enlarged adenoids or a deviated nasal septum. Alternative means of anxiety control may have to be used unless surgical correction is planned.
Contraindications to sedation with midazolam
The following conditions are contraindications to the use of benzodiazepine sedation (in addition to those described in the general section above).
Hepatic insufficiency
Midazolam is detoxified in the liver. If hepatic function is greatly reduced, then its metabolism is also reduced. Because there is considerable extrahepatic metabolism of midazolam, it is generally accepted that a clinically significant decrease in the metabolism of midazolam would only occur when other hepatic functions, such as the production of blood clotting factors, are also significantly reduced.
Porphyria
In this condition, the use of certain drugs sensitises the sufferer to the effects of sunlight. The most notable drugs that cause these effects are barbiturates, although the benzodiazepines have also been implicated.
Myasthenia gravis
This autoimmune condition causes impairment of transmission at the neuromuscular junction. The resultant decrease in impulse transmission makes the sufferer very susceptible to the effects of other muscle relaxant drugs, including the benzodiazepines. Administration of benzodiazepine can lead to the patient being paralysed but awake.
Allergy to the benzodiazepine group of drugs
Although very rare, this must be considered as an absolute contraindication to the use of intravenous midazolam.
Dental contraindications
The dental contraindications to sedation fall into two groups:
All forms of dental treatment may be carried out under sedation. The judgement as to whether it is appropriate to carry out any particular treatment must be made on a patient-to-patient basis.
Patient assessment
This section covers the areas of assessment which are specific to assessing patients for sedation.
The aims of patient assessment are to discover what sedation is required and suitable.
Patient’s psychological ability to tolerate dental treatment
There are many patients who find dentistry difficult to cope with. Some of those are so phobic of dental treatment that they avoid attending at all costs, unless driven by intractable pain. It is important to find out what the patient’s specific fears are, and what their previous experiences of dental treatment have been. This also ensures that basic mistakes, such as suggesting that claustrophobic patients have inhalational sedation, are avoided.
Patient’s physiological ability to tolerate dental treatment
If a patient suffers from any of the medical conditions highlighted above, it is important to establish how well they have tolerated receiving dental treatment previously. A history of aggravation of the medical condition in the dental setting should be taken as an indication for sedation.
The type and amount of dental treatment required
It is important to establish that the patient actually requires dental treatment prior to the administration of sedation. It is also impossible for the patient to give informed consent (see below) if the dental treatment has not been explained.
Is the treatment practical under sedation?
It must be established that the treatment needed can be carried out under sedation.
Does the patient need sedation?
Information in the above areas will allow an informed decision as to whether or not the patient requires sedation. As in all areas, the provision of treatment should not be complicated unnecessarily. Sedation should only be used where there is a definite indication.
Are there any contraindications to sedation?
It is important to ensure that there are no reasons to avoid sedation prior to offering it to a patient.
The assessment process
The assessment process follows similar lines to the history taking and examination of all dental patients.
Dental history
In addition to the current dental history, it is important to establish the patient’s pattern of attendance, and any specific fears. This will aid in treatment planning and will also give an indication of the potential co-operation once sedated. Those who are phobic of anything in their mouths tend to co-operate less well than those with a specific fear (e.g. needles or drills). There are specially designed questionnaires available for this purpose, but many tend to pose their questions in a threatening way. It is often better to ask the patient to say in their own words what they find difficult to cope with.
Medical history
In addition to the standard questions, it is important to establish if there has been a previous history of sedation, and how the patient coped. Other factors that are of importance in sedation terms are:
Dental examination
It is frequently not possible to carry out a full dental examination. Anxious patients do not tolerate the use of probes (even periodontal) well. The reaction to the examination helps in the assessment of the level of anxiety. It also allows appropriate radiographs to be prescribed.
Physical examination
All adult patients should have their blood pressure recorded as part of the assessment for sedation. Patients who are found to be hypertensive (systolic pressure more than 160 mmHg or diastolic more than 100 mmHg) should be referred for investigation.
If inhalational sedation is proposed, then the patency of the nasal airway should be confirmed. If intravenous sedation is proposed, it is important to establish if there are visible veins, along with ascertaining if there have been previous problems with having cannulae sited.
Establish rapport with the patient and deal with misconceptions
The importance of this process cannot be overstated. Most patients needing sedation will relate tales of a previous bad experience at the dentist. The most important part of building a rapport is to try (difficult as it is) to persuade the patient that you are different from the previous dentists. It is also important to deal with any misconceptions such as the difference between amnesia, as induced by sedation, and unconsciousness.
The patient should also give written informed consent at the assessment appointment.
6.2 Pharmacology of sedative agents
The two groups of drug to be considered are the benzodiazepines for oral and intravenous sedation and nitrous oxide for inhalation sedation. Many other agents have been used for sedation but are either now obsolete or are not recommended for basic sedation techniques.
The benzodiazepines
The benzodiazepines form a large group of drugs comprising over 50 marketed preparations. All of the group have basically the same effects on the body system (they are pharmacodynamically the same). Differences between the drugs primarily relate to the potency of the drug, which is a measure of affinity the drug has for its receptor, the strength of effect that it has on the receptor and also the length of time required to eliminate the drug from the body (pharmacokinetic properties). The pharmacokinetic differences relate to two areas:
1. The length of time it takes to eliminate the parent drug (the elimination half-life).
2. Whether the elimination process produces metabolites that are themselves pharmacologically active.
The principal pharmacological effects of the benzodiazepines, listed as seen with increasing dose (with anxiolysis occurring with the lowest dose), are:
• amnesia
Mechanism of action
Benzodiazepines have two distinct mechanisms of action. In higher centres of the brain, benzodiazepines bind to a receptor that controls sodium ion movement. The receptor is closely associated with a receptor for the endogenous, inhibitory neurotransmitter gamma-aminobutyric acid (GABA). The action of GABA allows chloride ions from the extracellular fluid to enter the cell. This makes the cell more negatively charged and, therefore, less likely to fire. The benzodiazepines increase the affinity of the GABA receptor for its transmitter and, thus, increase the inhibitory action of GABA. This action of the benzodiazepines is responsible for the sedative and anticonvulsant properties of this group of drugs.
The second mechanism of action is seen at lower centres in the brain stem and spinal cord. Here the benzodiazepines mimic the action of another inhibitory neurotransmitter, glycine. This action of the benzodiazepines is responsible for the anxiolytic and muscle relaxant actions.
Repeated administration of benzodiazepines (e.g. when used as oral anxiolytic agents) produces tolerance to the effects that are mediated via GABA. The effects produced by mimicking glycine are, however, largely unaltered.
The amnesic actions of benzodiazepines are poorly understood. The administration causes anterograde amnesia (i.e. from the point of administration forwards in time). Long-term memory is affected more than short-term memory, and therefore patients remember less the week after the appointment than at the point of discharge.
Side-effects of intravenous benzodiazepines
The principal side-effect of intravenous benzodiazepine administration is respiratory depression. This is produced by two mechanisms. First, the muscle relaxant actions of the drugs affect the respiratory muscles, namely the intercostal muscles and the diaphragm. This reduces the efficiency of the contractions. Second, as with all drugs that depress the central nervous system (CNS), the carbon dioxide receptors in the brain are affected, resulting in a lesser response to changes in blood carbon dioxide. Consequently, although the patient can breathe and will take deep breaths with suitable encouragement, they do not feel the need to breathe.
The second notable side-effect is that of sexual fantasy production. Such fantasies have been described in the literature, although again the mechanism is unclear. It is also unclear why patients may remember the fantasy but yet have no memory of any treatment that has been carried out. The incidence is unknown, but it appears to be dose related with a threshold for midazolam of 0.1 mg/kg body weight. No member of the dental team must ever be left alone with a sedated patient, in case this should result in an allegation being made.
Available benzodiazepines for sedation
Diazepam
Diazepam is a non-water-soluble benzodiazepine. It is available as either a solution in propylene glycol or as a soya-based emulsion. The solution is irritant to inject and is associated with pain and thrombophlebitis. Both the solution and the emulsion contain 5 mg/ml.
Pharmacokinetic properties
Diazepam is a long-acting drug. Its elimination half-life is 48 hours. It is metabolised to active metabolites with an elimination half-life in excess of 3 days.
Its use as an intravenous sedative is associated with rebound sedation, occurring 4–6 hours after administration. This occurs after the patient has been discharged and, consequently, is not under professional supervision.
Midazolam
Midazolam is a water-soluble imadazobenzodiazepine, which is painless on intravenous injection. It is available in three concentrations: 5 mg in 5 ml, 10 mg in 5 ml or 10 mg in 2 ml. Since the publication of the Rapid Response Report by the National Patient Safety Agency in December 2008, the use of the lowest concentration (5 mg in 5 ml has been advised for intravenous sedation. The 10 mg in 2 ml preparation is still used for oral sedation.
Pharmacokinetic properties
Midazolam is a short-acting drug with an elimination half-life of about 90 minutes. Its metabolites are largely inactive.
The metabolism of midazolam occurs both in the liver and extrahepatically. The half-life of midazolam is less affected by liver disease than any of the other benzodiazepines.
The effects of a single titrated dose are not prolonged by renal disease.
Midazolam is between two and five times as potent as diazepam.
Midazolam is currently becoming more popular as an oral sedative, despite the lack of a product licence for this use in the UK and the availability of an oral preparation. Midazolam tablets are available in other countries.
Other benzodiazepines
Although there are in excess of 50 benzodiazepines currently available, no others are commonly used for dental sedation.
Benzodiazepine antagonist drugs
Flumazenil
Flumazenil was the first benzodiazepine antagonist drug to be marketed commercially. It is an imadazobenzodiazepine that has a structure very similar to that of midazolam.
Flumazenil acts competitively to displace the active benzodiazepine molecule from the receptor site, thus blocking any potential action.
Pharmacokinetics
Flumazenil is a very short-acting drug. Its elimination half-life is 53 minutes, which is significantly shorter than that of any of the sedatives it may be used to reverse.
Contraindications to the administration of flumazenil
Flumazenil is a non-selective antagonist that will block the effects of all benzodiazepines. It should not be given to patients who are taking protracted courses of oral benzodiazepines as it may produce an acute withdrawal reaction. Where oral benzodiazepines are used to control epilepsy, the administration of the antagonist will antagonise the anticonvulsant action of the benzodiazepine, potentially leading to fitting.
Flumazenil is a benzodiazepine and must not be administered if an allergic reaction to the sedative is suspected.
Propofol
Propofol (2,6-diisopropylenol) is a synthetic sedative hypnotic, which was introduced for the induction and maintenance of general anaesthesia. In common with other anaesthetic agents, it will produce sedation when given in lower doses.
Propofol is lipid soluble and thus is presented in a 1% (10 mg/ml) emulsion.
Clinical effects of propofol
The action of propofol is to enhance the effect of GABA. This is accomplished via a different mechanism from the benzodiazepines, allowing its use in regular benzodiazepine users.
Sedative doses of propofol produce a different quality of sedation from benzodiazepines. The effect is closer to a pure anxiolysis. This can be associated with patients becoming more talkative.
The amnesic actions of propofol are less predictable than those of benzodiazepines.
Side-effects of propofol
Propofol causes depressant effects on the cardiovascular system. It will cause a fall in arterial blood pressure and heart rate. Falls of 25–35% in systolic blood pressure have been recorded, but are of little clinical significance to young, fit and healthy patients treated in the supine position.
Although propofol does produce profound respiratory depression in anaesthetic doses, it would appear that in sedative doses less respiratory depression is seen with propofol than with midazolam.
Pain on injection (especially when small veins are used) is the most common cause of complaint from patients. Mixing a small amount of plain lidocaine with the solution can prevent this.
As with the other sedatives described, sexual fantasies have been described by patients receiving propofol sedation.
The distribution and elimination of propofol
Propofol has an extremely short redistribution half-life. This accounts for the rapid patient recovery from sedation. The elimination from the body takes longer, and thus patients may have residual effects that they fail to appreciate.
Nitrous oxide
Nitrous oxide is the oldest sedative currently in use in clinical dentistry. It is the only drug that is in general use for inhalational sedation in dentistry.
Physical properties of nitrous oxide
Nitrous oxide is a gas at room temperature and pressure. It is colourless and is sometimes described as having a sweet odour. It is 1.5 times as heavy as air and tends to collect at floor level. Pressurised nitrous oxide will liquefy, as its critical temperature (the temperature above which it cannot exist as a liquid) is 36.5°C. Nitrous oxide cylinders contain a mixture of gaseous and liquid nitrous oxide at a pressure of approximately 640 psi.
Anaesthetic and analgesic properties
Nitrous oxide is a weak anaesthetic agent. The MAC50 value (i.e. the theoretical value that would provide surgical anaesthesia for 50% of the population) is 110%. This can be contrasted with isoflurane at 1.15%. Nitrous oxide is insoluble in blood (blood:gas partition 0.47), which means that there is a rapid equilibration between the concentration of nitrous oxide in the alveoli and that in the blood, and induction of and recovery from sedation is extremely rapid.
The main effects of nitrous oxide are mood alteration, particularly euphoria, and analgesia. An inspired concentration of 50% nitrous oxide equates to approximately 15 mg morphine, particularly when considering ischaemic muscle pain.
Effects of chronic exposure to nitrous oxide
It should be emphasised that there are virtually no problems of acute exposure for patients, provided that physiological concentrations of oxygen are administered with the nitrous oxide. There are, however, a number of potential problems with chronic exposure:
• Decreased fertility in female staff.
• Increased rate of miscarriage in staff and partners of staff.
• Combination with cobalt-containing vitamins:
• impairment of DNA synthesis.
• Depression of haematopoiesis.
All of these effects tend only to be seen when there is not active scavenging of waste gases.
6.3 Current sedation techniques
Basic sedation techniques
Inhalation sedation
Techniques of inhalation sedation tend to fluctuate in popularity. It has also been described by a number of names such as relative analgesia, inhalational sedation or inhalation psychosedation. All the widely available techniques involve the use of mixtures of nitrous oxide and oxygen.
Advantages of inhalation sedation
Rapid onset of sedation
The relative insolubility of nitrous oxide in blood results in the peak levels of nitrous oxide being attained within 3–5 minutes of inhalation.
Rapid recovery
There is effectively no metabolism of nitrous oxide, recovery being effected by exhalation of the gas via the lungs. The same factors that produce rapid induction of sedation lead to rapid recovery.
Recovery is independent of treatment time
Once a stable level of sedation is achieved, the continued administration of nitrous oxide merely maintains the equilibrium of blood:alveolar concentration. Consequently, patients recover as rapidly whether they have been treated for 10 minutes or 2 hours.
Absence of metabolism
Only 0.0004% of the inspired nitrous oxide is absorbed. The almost total absence of metabolism accounts for the safety of nitrous oxide and its ability to be used in a wide range of patients.
The technique does not involve an injection
Many patients are frightened of needles and the fact that nitrous oxide administration does not require an invasive technique is an advantage.
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