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n
Sufficient space/clearance interaction with occlusion.
n
Sufficient bone to implant into:
n
Ridge mapping
n
Computer simulation.
n
Available site to harvest bone and willingness to
undergo grafting procedures if there is insufficient
bone.
n
Relationship of ideal tooth position to the potential
underlying implant placement:
n
Diagnostic wax-up
n
Production of custom surgical guides.
Restoration factors:
n
Relative dimensions of the restoration to the remaining dentition:
n
Loss of space
n
Drifting/tipping/rotation of teeth.
n
Choice of abutments:
n
‘off-the-shelf’; prefabricated
5 • Restorative Management of Dental Implants
n
Bespoke custom
n
Type of material.
n
Use of screw- or cement-retained definitive restorations.
n
Excessive spacing between teeth, therefore no support
for papilla creation/augmentation.
n
Emergence of profile of restoration and soft tissue
aesthetic consideration.
n
Thickness of tissue and impact of abutment materials
(titanium will show through thin biotype gingival
tissue).
SINGLE BEST ANSWER QUESTIONS ANSWERS
1. E
2. C
3. B
147
6
Conscious Sedation in Dentistry
CHAPTER OUTLINE
Introduction, 148
6.1 Conscious Sedation, 148
6.2 Pharmacology of Sedative Agents, 151
6.3 Current Conscious Sedation
Techniques, 154
Introduction
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 has fluctuated
in popularity since Horace Wells first discovered the potential of nitrous oxide in 1844. The administration of centrally acting drugs by dentists has attracted some concerns
over safety; however, dentistry has an excellent record in
this regard when compared with other medical specialties.
The excellent safety record is built on the twin foundations
of good quality education and adherence to appropriate
clinical guidelines and standards of practice.
The techniques described in this chapter are safe and
amenable to use by suitably trained dentists working in a
clinical setting that is suitably equipped and meets the
required standards.
6.1 Conscious Sedation
LEARNING OBJECTIVES
You should:
• understand what conscious sedation means
• know the indications for conscious sedation
• know when not to use conscious sedation
• be able to assess a patient’s suitability to receive
conscious sedation.
6.4 Dental Treatment Planning, 161
6.5 Medicolegal Aspects, 162
Self-Assessment: Questions, 163
Self-Assessment: Answers, 165
patient is maintained throughout the period of sedation.
The drugs and techniques used to provide conscious sedation for dental treatment should carry a margin of safety
wide enough to render loss of consciousness unlikely’.
Techniques for producing conscious sedation are frequently considered as falling into two groups – basic and
advanced. The basic techniques are:
n
inhalation sedation using nitrous oxide/oxygen
n
intravenous sedation using midazolam alone
n
oral/transmucosal benzodiazepine, which has been
demonstrated to provide adequate competence in intravenous techniques.
The advanced techniques are:
n
any form of conscious sedation for patients under
the age of 12 years other than nitrous oxide/oxygen inhalation sedation
n
benzodiazepine 1 any other agent, for example, opioid,
propofol and ketamine
n
propofol either alone or with any other agent, for example, benzodiazepine, opioid and ketamine
n
inhalation sedation using any agent other than nitrous
oxide/oxygen alone
n
combined (non-sequential) routes, for example, intravenous 1 inhalation agent (except for the use of nitrous
oxide/oxygen during cannulation, which is discontinued
prior to the administration of the intravenous agent).
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.
There have been many definitions of conscious sedation put
forward over the years. The current definition that must be
accepted in the United Kingdom is found in the Intercollegiate Advisory Committee for Sedation in Dentistry’s report
‘Standards for Conscious Sedation in the Provision of
Dental Care’ and the Scottish Dental Clinical Effectiveness
Programme’s document ‘Conscious Sedation in Dentistry’.
The definition is: ‘Conscious Sedation is a technique in
which the use of a drug or drugs produces a state of depression of the central nervous system enabling treatment to
be carried out, but during which verbal contact with the
148
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:
n
phobias
n
specific: drills, needles, extractions
n
general: things in mouth, all dental procedures
n
gagging: inability to tolerate objects intraorally without
retching
n
persistent fainting during procedures, often associated
with the administration of local analgesics
n
idiosyncrasy to local analgesics: patients who have a
problem where local analgesics appear not to work;
the cause of the failure is psychological rather than
anatomical or pharmacological.
Medical Indications
Some conditions may be aggravated by the stress of undergoing dental treatment. These include:
n
ischaemic heart disease
n
hypertension
n
asthma
n
epilepsy
n
psychosomatic illnesses.
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 including:
n
mild-to-moderate mental and physical disability
n
spasticity disorders
n
Parkinson’s disease.
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 to 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 from being able to treat the patient.
6 • Conscious Sedation in Dentistry
149
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 receiving inhalation sedation with nitrous
oxide and oxygen, who may be allowed to attend without
an escort, provided that the dentist feels it is appropriate.
Normally such patients will be asked to bring an escort to
the first appointment so their response and recovery can
be assessed. 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.
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, in theory, 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
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
III Patient with moderate intercurrent disease that does
IV Patient with severe intercurrent disease that is a constant
V Patient who is unlikely to survive 24 hours with or without
VI A clinically brain-dead patient awaiting organ harvest
and does not affect lifestyle
affect lifestyle
threat to life
medical intervention
150
Master Dentistry
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 a 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.
There is a balance to be reached between ensuring that
the patient receives appropriate dental care, including the
prevention of complications such as pregnancy gingivitis
and management of risk to the fetus. Each patient must be
individually assessed, and an individual-specific treatment
plan devised.
Contraindications to Intravenous Sedation With Midazolam
The following conditions are contraindications to the use of
benzodiazepine sedation (in addition to those described in
the general section earlier).
Needle phobia. Siting an intravenous cannula is a prereq-
uisite for intravenous sedation. If the patient cannot
consent to and accept intravenous cannulation (with or
without inhalation sedation or premedication), intravenous sedation cannot be carried out.
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, precluding many types of dental
treatment.
Porphyria. In this condition, the use of certain drugs sen-
sitises 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:
n
those procedures considered too long or too difficult to be
carried out under local analgesia
n
where the presence of spreading infection in the floor
of the mouth threatens the airway; in such cases, the
airway must be secured under general anaesthesia (GA).
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.
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 successful. In such cases, patients may
have become so accustomed to mouth-breathing that it is
difficult to re-establish nasal breathing,
PATIENT ASSESSMENT
This section will cover the areas of assessment which are
specific to assessing patients for sedation.
The aim of patient assessment is 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.
6 • Conscious Sedation in Dentistry
151
This also ensures that basic mistakes, such as suggesting
that claustrophobic patients have inhalational sedation,
are avoided.
Patient’s physiological ability to tolerate dental treat-
ment. 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 es-
tablished that the treatment needed can be carried out
under sedation.
Will any treatment provided be maintained? In many
cases, patients attending for sedation may have a poor
attendance record. The author has seen many patients
who have had extensive treatment carried out under sedation and not returned until many restorations have
been lost or there is extensive caries and periodontal disease. As with all patients, advanced treatment should not
be provided unless the patient demonstrates the ability
and motivation to maintain their oral health.
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 im-
portant to ensure that there are no reasons to avoid sedation prior to offering it to a patient.
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. The airway should also be assessed to determine if there are likely to be problems maintaining patency
during dental treatment under sedation.
If inhalational sedation is proposed, then the patency of
the nasal airway and patient’s nasal breathing 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 a written informed consent
form at the assessment appointment.
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. This may include sedation for
medical procedures. Other factors that are of importance
in sedation terms are:
n
current drug history
n
past drug history
n
allergies (including to sticking plaster).
6.2 Pharmacology of Sedative Agents
LEARNING OBJECTIVES
You should:
• understand the clinical effects of the sedative agents
used in dentistry
• understand the side-effects of the sedative agents used
in dentistry
• appreciate the hazards of occupational exposure to
nitrous oxide.
The main drugs used for sedation are considered here. A
number of other agents are known to be used, but their use
is rare, and thus they are not included here.
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
152
Master Dentistry
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 degrees Celsius. 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 of 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:
n
decreased fertility in female staff
n
increased rate of miscarriage in staff and partners of
staff
n
combination with cobalt-containing vitamins
n
oxidation of vitamin B
n
impairment of DNA synthesis
n
depression of haematopoiesis
n
neurological effects: central nervous system (CNS)
12
degeneration
n
liver disease
n
malignancy, especially cervical carcinoma.
All these effects tend only to be seen when there is no
active scavenging of waste gases.
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:
n
the length of time it takes to eliminate the parent drug
(the elimination half-life)
n
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 as follows:
n
anxiolysis
n
anticonvulsive
n
mild sedation
n
decreased attention
n
amnesia
n
more profound sedation
n
muscle relaxation
n
anaesthesia or hypnosis.
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
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 have
no memory of any treatment that has been carried out. The
incidence is unknown, but it appears to be dose related with
6 • Conscious Sedation in Dentistry
153
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
Midazolam
Midazolam is a water-soluble imiadazobenzodiazepine,
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. The lowest concentration (5 mg in 5 mL) is the
standard preparation for intravenous sedation. The 10 mg in
2 mL preparation is still used for oral sedation.
Pharmacokinetic properties. Midazolam is a shortacting 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 the first choice of oral and transmucosal
sedative, despite the lack of a product licence for its use in
the United Kingdom or 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.
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 adminis-
tered if an allergic reaction to the sedative is suspected.
OPIOIDS
Opioids are used in combination with other agents where
single agents fail to produce an adequate level of anxiolysis
to allow dental treatment to proceed. Opioids are centrally
acting analgesics, which in addition produce other clinical
effects including euphoria and sedation. Opioids have a
number of side-effects. The most relevant to conscious sedation are respiratory depression, nausea and vomiting and
depression of the cardiovascular system.
Fentanyl is the most commonly used opioid in the practice of sedation. It is presented as a 0.05 mg/mL solution.
The standard adult dose of conscious sedation is 0.05 mg,
and thus the 2-mL ampule is the most appropriate of the
available preparations. A rare side-effect of fentanyl is chest
wall rigidity. This is described at anaesthetic rather than
sedative doses. The clinical effect of intravenous fentanyl is
almost instantaneous and lasts for between 30 and 60 minutes. Nausea and vomiting are most likely if the patient is
moved prior to the effects of fentanyl wearing off.
Shorter acting agents, such as remifentanil, have been
described for use by infusion, usually in combination with
propofol.
The future
Remimiazolam
Remimiazolam is related to midazolam but has a significantly shorter duration of action, as it is broken down by
tissue esterases rather than cytochrome-dependent hepatic
pathways. As such, this agent is administered by continuous intravenous infusion rather than titration. Currently,
this agent is at the clinical trial stage of development. Initial
results indicate that it has significant advantages in terms
of increased flexibility of treatment time and decreased recovery time.
Benzodiazepine Antagonist Drugs
Flumazenil
Flumazenil was the first benzodiazepine antagonist drug to
be marketed commercially. It is an imiadazobenzodiazepine
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 sig-
nificantly 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
Opioid Antagonist Drugs
Naloxone
Naloxone is an opioid antagonist. It reverses the clinical effects of the opioids including sedation, analgesia, respiratory depression and nausea and vomiting.
Naloxone acts by competitively displacing opioid agonists.
It is an opioid.
There are marked parallels with flumazenil:
n
both are competitive antagonists
n
shorter duration of action than the agonist leading to
the possibility of residual sedation
n
structurally similar to the agonists, so allergy to agonist
likely to mean allergy to antagonist
n
must be readily available in the dental environment
where agonists are used for sedation.
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
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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 lignocaine 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.
KETAMINE
Ketamine is described as a dissociative anaesthetic agent. It
produces effective analgesia, amnesia and sedation in subanaesthetic doses. Unlike all other sedative agents, ketamine
stimulates the cardiovascular system and may stimulate the
respiratory system.
The main disadvantage of ketamine is that it is associated
with hallucinations in about 25% of patients. The incidence is said to be reduced when midazolam is used in
combination with ketamine.
There is emerging evidence that ketamine may be more
effective for paediatric sedation than midazolam, but it is
not currently in general use.
6.3 Current Conscious Sedation Techniques
LEARNING OBJECTIVES
You should:
• know the advantages and disadvantages of each type of
sedation
• be aware of the techniques involved
• appreciate the need for postgraduate training prior to
independent practice of sedation
• appreciate the differences between basic and advanced
sedation techniques
• understand the principles of monitoring patients under
sedation
• understand clinical and electromechanical monitoring.
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 pa-
tients are frightened of needles, and the fact that nitrous
oxide administration does not require an invasive technique is an advantage.
A degree of analgesia is produced. Although the use of
inhalation sedation will not provide sufficient analgesia
to allow dental treatment to be carried out, it will make
the administration of local anaesthetic injections easier.
Inhalation sedation can be used on virtually all patients.
Inhalation sedation has very few contraindications and is
the only technique currently recommended for patients
of all ages.
Disadvantages of Inhalation Sedation
Bulk of equipment. The equipment required for the ad-
ministration of inhalational sedation is bulky and can
cause problems in a small surgery.
Expense of equipment. The equipment that is to be used
must be a dedicated inhalational sedation machine. It is
not acceptable to have a general anaesthetic machine
that is used for both types of treatment. This is because
general anaesthetic machines do not have the same
safety features as relative analgesia machines. In addition to the equipment for drug administration, a scavenging system to remove expired gases is required.
Finally, once in use, the costs of the gases must be taken
into account.
Intrusion of nosepiece into the operating field. This can
be a problem when treating upper anterior teeth (Fig. 6.1).
Fig. 6.1 The nosepiece of the MAC1 Inhalation Sedation Machine
adapts against the upper lip, impairing access to the upper anterior
teeth.
Disruption of the seal in this area will result in both a
decrease in the effectiveness of sedation and an increase in
chronic exposure of staff.
Patient’s perception of equipment. Patients who have
had a previous bad experience associated with general
anaesthesia may find that the nosepiece reminds them of
the GA mask.
Chronic exposure of staff. The major health problems that
may be associated with the use of nitrous oxide will affect
staff, not patients. Measures must be taken to ensure that
occupational exposure is kept to a minimum.
Potential addiction. Nitrous oxide is an addictive drug;
dentists should be aware of the risks to both their staff
and themselves.
Technique for Inhalation Sedation
The technique described (Box 6.1) is based on the use of the
McKesson MAC1 Inhalation Sedation Machine, which
is one of the most widely used machines for this type of
sedation (Fig. 6.2).
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Box 6.1 Technique for Inhalation Sedation.
1. Preprocedural machine checks. It is vital for the patient’s wellbeing that all equipment is in working order and that there is
a sufficient supply of nitrous oxide and, more importantly,
oxygen for the session. The manufacturer’s instructions for
checking and servicing equipment should be followed.
2. The correct size of nosepiece for the patient should be selected.
This is often best done at an assessment appointment as part of
introducing the patient to the process of sedation.
3. The patient is brought into the surgery, and pre-treatment
discussions completed.
4. The relative analgesia machine is turned on, with 100%
oxygen at a flow rate of 6 L/min.
5. The nosepiece is fitted to the patient, and the flow rate titrated
until the reservoir bag on the machine can be seen to move
with each breath but does not fully collapse when the patient
breathes in.
6. Nitrous oxide is introduced. The initial introduction is 10%
increments at 1-minute intervals. After an inspired concentration of 20% has been reached, the increments are reduced to
5%. Throughout the process, the patient must be reassured
and encouraged. The most important part of sedation is the
patient management. Inhalational sedation will not work
without the hypnotic suggestions of the operator.
7. Once adequate sedation has been achieved, dental treatment
can commence.
8. The patient’s level of sedation and breathing pattern should
be monitored during treatment. The concentration of nitrous
oxide and flow rate of gases should be adjusted as required
to maintain patient comfort.
9. Reassurance and positive suggestions should be maintained
throughout the procedure.
10. Once the treatment has been completed, the nitrous oxide
should be reduced to 0%.
11. The patient should be encouraged to breathe 100% oxygen for
a minimum of 2 minutes, or until recovered prior to removal of
the nosepiece.
12. Turn off the flow of oxygen.
13. Reinforce postoperative instructions and discharge the patient.
Signs and Symptoms of Adequate Sedation With Nitrous Oxide
Signs. The signs are what the operator sees:
n
The patient is awake.
n
The patient is relaxed and comfortable.
n
Vital signs are within normal limits: heart rate, respiration rate and blood pressure (if measured) will all be
normal.
n
Blink rate is reduced.
n
Mouth remains open on request: in this respect, inhalational sedation is very different from intravenous sedation.
n
Protective reflexes are normal.
n
Hyperactive gag reflexes are reduced, allowing dental
treatment.
n
Decreased response to painful stimuli.
Symptoms. The symptoms are what the patient feels:
n
Relaxed and comfortable.
n
Lessened awareness of pain.
n
Paraesthesia/tingling.
n
Mild intoxication.
n
Euphoria.
Fig. 6.2 The McKesson MC1 RA Machine. (Image courtesy of Cestradent
McKesson.)
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n
n
n
n
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Detachment.
Warmth.
Indifference to the passage of time.
Dreaming.
Patients will not necessarily show all the signs, or experience all the symptoms of sedation that are listed here. It is
a matter of judgement as to when adequate sedation has
been achieved. The majority of patients will require between 25% and 40% nitrous oxide to achieve sedation. It is
very important to avoid oversedation, as patients find overdoses of nitrous oxide unpleasant.
Signs and Symptoms of Oversedation
Oversedation can cause:
n
persistent mouth closing
n
spontaneous mouth-breathing
n
complaints of unpleasant feelings
n
lack of co-operation
n
nausea and vomiting.
The treatment of a patient who is oversedated involves
reducing the concentration of inspired nitrous oxide by
5–10% and reassuring the patient that things will improve.
Recovery From Sedation
Once dental treatment has been completed, the patient is
allowed to breathe 100% oxygen for 2 minutes. This allows
the nitrous oxide to be exhaled via the scavenging system
rather than into the surgery. It can also prevent a phenomenon called diffusion hypoxia, which may arise owing to
the rapid release of nitrous oxide from blood when it is removed from the inspired air.
After recovery, a child patient must be discharged into
the care of a responsible adult. Adults may be discharged
alone, and it is the dentist’s responsibility to decide if the
patient needs to be accompanied or not.
Dental Professionals Who Can Administer Inhalation Sedation
In addition to appropriately trained dentists, dental hygienists
and therapists who have undergone postregistration training
in inhalation sedation are able to administer this type of sedation. All who administer inhalation sedation must be assisted
by an appropriately trained dental nurse. In addition, for hygienists and therapists, there must be a dentist on the premises, but not necessarily in the surgery (treatment room) in
case the dental treatment unexpectedly moves beyond the
competence of the treating Dental Care Professional ( DCP).
Intravenous Sedation
Intravenous sedation is normally used for anxious adult
patients. It is particularly useful for the extremely anxious
or for those who feel claustrophobic when undergoing dental treatment. The basic technique for intravenous sedation
involves a titrated dose of midazolam.
Advantages of Intravenous Sedation
Speed of onset of sedation. The hand-to-brain circulation
time is of the order of 20 seconds; as a result, the onset
of sedation is very rapid. This prevents an increase in
anxiety while waiting in the dental environment.
The dose of sedative can be titrated against the pa-
tient’s response. The patient receives the correct dose of
sedative for their needs.
Administration is comfortable. Once venous access is
achieved, the patient is not troubled (unlike intramuscular or subcutaneous injections).
Intravenous access is preserved. This allows the adminis-
tration of other agents if required (as in the case of a
medical incident).
Recovery. This is shorter than for drugs administered via
the oral or intramuscular route.
Disadvantages of Intravenous Sedation
The establishment of intravenous access. Many patients
find the process of having an intravenous cannula sited
unpleasant. It is, however, amazing how many patients
find that it is acceptable to have an injection in the hand
but will not tolerate intraoral injections.
Rapid onset. The rapid onset of the effects of intravenous
drugs means that care must be taken to ensure that patients are not oversedated.
Adverse reactions. Any adverse reactions to the drugs
tend to be more severe if the drugs are administered by
injection rather than orally.
No easy reversal is possible. There is no way to recover
the drug once it has been administered. The only way to
reverse sedation is by the use of antagonist drugs.
Technique of Intravenous Sedation
The primary prerequisite for the use of intravenous sedation
is that all those involved in the patient’s treatment have received the appropriate training and the surgery is equipped
with the appropriate scale of equipment for administering
the sedation, monitoring the patient and dealing with any
emergencies. Both dentist and dental nurse should have attended relevant postgraduate/postcertification courses.
Equipment Required for Intravenous Sedation
Administration
n
Surgical wipe to disinfect skin
n
Gauge intravenous cannula
n
Surgical tape to fix cannula
n
Syringes
n
10 mL to administer the sedative
n
20 mL for the saline flush
n
Gauge needle to draw up drug
n
Labels to distinguish syringes
n
Tourniquet
n
Disposable tray
Monitoring equipment
n
Stop watch
n
Non-invasive blood pressure recording facility
n
Pulse oximeter
Emergency equipment
As for all dental surgeries and
n
Flumazenil
n
Facility to give supplemental oxygen at a flow of 2 L/min
(most emergency cylinders are set to a minimum of 5 L/min)
Special dental equipment
n
Mouth props
n
Dental chair with a fast prone facility that will work in
the event of power failure