AUGUST, 1979 Volume 24 :: Number 4

Sedation for dental treatment of infants. 1. Physiology and pharmacology

Robin Woods

ABSTRACT-The principal functions of the central nervous system, the pharmacology, and the effect on the central nervous system, of a number of drugs used for a sedation technique for young children are described. This information is presented as a foundation for the application of clinical procedures.

(Received for publication September, 1978)

Introduction The reduced amount of dental caries now experienced

in the Australian community' makes it possible to care for the dental needs of some of the very young patients who formerly would have been untreated. Lesions need to be detected early and most rudimentary lesions appear in the fissures of deciduous teeth in the child's third year, although some occur as early as 18 months of age. Simple restorations inserted in fissures, when lesions are first noticed, and coupled with a caries prevention pro- gramme are usually sufficient to avoid unnatural loss of the deciduous teeth; frequently there is no need for any further restorations.

When conservative treatment is needed for infants it is essential thai.an appropriate and regular preventive dentistry programme is also commenced. Identification of the particular cause of the dental caries is necessary as well as the means to restore diseased teeth if an appropriate treatment plan is to be developed.

As placing of effective restorations for infants can produce stress leading to restlessness, sedation may be a

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Barnard, P. D., and Clements, F. W.-Oral health care in Australia. Internat. D. J . , 26: 3, 320-326 (Sept.) 1976.

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necessary adjunct to allow treatment for the very young, those needing extensive treatment, and those otherwise unable to accept treatment. However, this may be necessary only for a small proportion of patients. In the past, treatment of the very young has often needed a general anaesthetic, or treatment has been avoided.

A sedation technique for these children will be described, but, in order to apply the technique, an appreciation of some functions of the central nervous system and the effects on it of the drugs used is essential.

Throughout the proceedings the patient must be able to respond to aural communication and local anaesthesia is always used. The technique is consistent with the definition for sedation adopted by the Australian Dental Association New South Wales Branch.z

It is also necessary to appreciate other aspects of the pharmacology of drugs used in order to apply this knowledge to the clinical situation.

Hession, R. W., Woods, R. G., and Newland, R. B. -The policy of the Australian Dental Association New South Wales Branch on the administration of sedative, anaesthetic, and analgesic drugs with particular reference to the intra- venous route of administration. Sydney, The Australian Dental Association New South Wales Branch, 1971.

214 Australian Dental Journal, August, 1979

TABLE I Symptoms of the planes of analgesia when sedation is induced with a narcotic plus nitrous oxide and oxygen

Symptom Guedel's first stage of anaesthesia

First plane Second plane Third plane

Respiration . . . . Normal Normal Normal

Pulse* and blood pressure Normal Normal Normal

Muscle tone . . . . Normal Normal Usually normal occasionally mandible becomes rigid

Response to directions Normal (aural response)

Slow, but patient responds Markedly diminished although patient can be aroused

Amnesia . . . . . . Slight Moderate to complete Complete

Analgesiat . . . . Slight Moderate but insufficient for Marked but not sufficient for other than simple treatment deep cavity preparations

Effect on fear . . . , Fear is reduced if patient is not Fear eliminated, patient relaxed Fear eliminated although patient stimulated or aroused will tolerate painless pro- may have hallucinations and

Comments . . . . Suitable for treatment of older Ideal for treatment of infants and Too deep for treatment. Patient or experienced children from children, treatment accepted unable to keep mouth open. age 4 yrs. Good local anacs- with no fear or resistance. Suppressionofmandiblecould thetic essential Local anaesthetic essential. occlude airway. Patient will

Will respond to pain with respond to pain with disorien- disorientation and panic

cedures well become restless

tation and panic

Pulse rate may slow in response to diminishing fear and relaxation. t Other than from local anaesthetics.

Tbe ceatrd nervm system

The principles of consciousness, the functions of the central nervous system, and the importance of oxygen are discussed to facilitate understanding of the technique to be described and its effect on the central nervous system.

c- Uld SCd8tiW

Awareness of surroundings and the ability to respond to them or to stimulation are the principal criteria of consciousness. Awareness depends on the senses and the appreciation by the sensory gyrus of the cerebral cortex of information from surroundings conveyed from peripheral sensory organs through sensory nerves.

Depression of the activity of the sensory cortex or diminution of the sensory stimulation gradually dimini- shes awareness and, where conditions exist preventing a person from voluntarily reversing this state, a condition of sedation or ultimately general anaesthesia occurs. During sedation, although cortical activity is reduced, vital reflexes controlling respiration, the cardiovascular system, and the protection of the patient's airway must always remain functional. Four stages of anaesthesia have been described by

Guedel-analgesia, delerium or excitement, surgical

' Langa, H. - Relative analgesia in dental practice. Philadelphia, W. B. Saunders Company, 1958 (p. 42).

anaesthesia, and respiratory paralysis. Langa' has studied the stage of analgesia, and has divided it into three planes. These planes should be recognized clinically as they are an accurate means of determining the level of sedation achieved.

A summary of the symptoms of the planes of anal- gesia adapted from Langa3 is presented in Table I . Signs and symptoms of sedation vary with the agents used, for instance, barbiturates or diazepam sedation does not produce any analgesia at all. The symptoms set out in Table 1 are consistent with those where sedation is produced by means of a narcotic plus nitrous oxide and oxygen.

Sedation for infants should be at the level of the second plane of analgesia. In this plane they will respond to directions, their mouths will remain open facilitating treatment, and they are relaxed with no evidence of fear. Blood pressure and respiration should remain un- changed but breathing should always be monitored.

The seasory newws system

Stimulation of receptors by light, sound, odour, taste or touch is conveyed by sensory nerves entering the central nervous system either as part of one of the cranial nerves or through the posterior horn of the spinal cord. The sensory tracts ascend the central nervous system, exchange sides and enter the thalamus where they are

Australian Dental Journal, August, 1979

relayed to the appropriate section of the sensory cortex. The sensory pathways are summarized in Fig. 1.

The motor nervous system

cortex often from responses conveyed to it from the sensory cortex. Motor nerve fibres descend the central

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protect the airway, control coughing, salivation, sneez- ing, crying, blinking, and the size of the iris of the eye. The hypothalamic centres control body temperature and water balance, they also mediate control, usually emotional and initiated in the cortex, of respiration and ~rdiovascular activity.

Voluntary activity is initiated in the

Thalamus

Fig. 1 . -Diagrammatic coronal section of the central nervous system showing the principal sensory

pathways.

Fig. 2. -Diagrammatic coronal section of the central nervous system showing the principal motor

pathways.

nervous system in bundles described anatomically as Afferent nerves

Efferent nerves - - - - - - pyramidal tracts. These tracts cross and elements emerge within the cranial nerves or descend in the cord to emerge in the spinal nerves through the anterior horn. The motor system mediates the voluntary control of skeletal muscle, activity is initiated in the cortex and terminates in the neuromuscular end plate of a muscle cell. Figure 2 is a simplified diagram of the motor nervous system.

The sutoaomic nervous system The autonomic nervous system regulates the body’s

vital functions, in particular respiration and cardio- vascular activity. The system is supplied with information regarding blood pressure, oxygen and carbon dioxide concentrations in blood, muscle tension as well as other functions from receptors through the network of autonomic afferent nerve fibres. Autonomic receptors are widely distributed through the body, some of the main sites are located in the carotid and aortic sinuses. Afferent fibres enter the central nervous system through the posterior horn of the cord or as part of a cranial nerve, they ascend, exchange sides and terminate in the autonomic reflex centres of the medulla or the hypo-

Fig. 3. -Diagrammatic coronal section of the central nervous system showing principal autonomic path-

ways both afferent and efferent.

thalamus. The medulla contains reflexes controlling respiration

and cardiovascular activity. In addition, other reflexes

216 Australian Dental Journal, August, 1979

medical histories taken over several years in private p r a ~ t i c e . ~

Narcotics produce some peripheral vasodilatation which is probably due to a local rather than a central effect, this could result in some hypotension although not noticeable generally in children. Although narcotics have an analgesic effect the analgesia produced is in- sufficient to suppress deliberate painful stimulation. There is no appreciable direct effect on the heart or cardiovascular system.

To permit a precise dose, and to eliminate variable absorption factors, narcotics are best administered intramuscularly.

Narcotic antagonists A simple molecular change in the structure of

narcotics produces new substances not unlike narcotics in some respects but which antagonize or reverse some of their effects. Used alone, narcotic antagonists may display effects such as sedation and analgesia and even respiratory depression very similar to the effects pro- duced by narcotics. Administered with narcotics, antagonists such as nalorphine hydrobromide antago- nize respiratory depression caused by narcotics. They are not respiratory stimulants and do not antagonize respiratory depression caused by drugs other than nar- cotics. Although their action is relatively rapid, used intramuscularly they may take up to 30 minutes to be effective and during this period ventilation of the patient’s lungs may have to be performed.

Control of autonomic function is initiated in the medullary or hypothalamic autonomic centres as a reflex response to afferent stimulation. Efferent fibres from these centres descend the central nervous system and emerge either with the cranial nerves or in the spinal nerves through the anterior horn of the cord and enter the sympathetic or parasympathetic nervous reticulation which innervates all organs. A diagrammatic summary is presented in Fig. 3.

oxygen An adequate supply of oxygen is essential to the

orderly function of the central nervous system. Nerve tissues are particularly susceptible to reduced oxygen tension which, in the area of the medullary reflexes, may cause an unpredictable response from the respiratory or cardiovascular reflexes and in the cortex can produce restlessness, hallucinations, unco-ordinated motor activity, and other sensory or motor irregularities.

Symptoms of cortical disturbances should never be attributed to insufficient sedation but are often the first signs of cerebral hypoxia due either to respiratory depression or an airway blockage. Hypoxia is a grave hazard to a patient. Restlessness and twitching is often the first symptom of cerebral hypoxia and if allowed to continue myocardial anoxia and cardiac arrest can be dangerous sequelae. Therefore, at all times when a patient is under sedation an adequate supply of oxygen should be ensured.

Pharmacology In addition to understanding the relevant functions

of the central nervous system, it is necessary to under- stand the pharmacological properties of drugs used for the sedation technique and particularly their effects o i

the central nervous system.

Narcotics Narcotics are well-established, effective and reliable

drugs which produce sedation and some analgesia. Although the precise nature of their action is still unknown, they are central nervous system depressants. They are especially effective at clinical doses, depressing activity of the cerebral cortex, producing sedation and relaxation by reducing anxiety. Doses used for sedation are generally less than required to produce transient euphoria.

By affecting the medullary autonomic centres, nar- cotics can produce respiratory depression and diminish those reflexes which protect the airway. Although, in calculated doses used for sedation, respiratory depres- sion is unlikely, patient idiosyncracies could bring about respiratory depression and therefore, breathing should always be monitored. A history of narcotic hyper- sensitivity was recorded in 11 of the 2,800 patients of all ages (approximately 0.4 per cent) in a survey of patients’

Belladonna alkaloids Belladonna alkaloids are anticholinergic agents which

act primarily on the peripheral nervous system. By blocking the cholinergic effects of the vagus nerve which tends to reduce heart rate, belladonna alkaloids strengthen and increase the pulse rate and slightly elevate the blood pressure. The smooth muscles of the bronchi are also relaxed, pulmonary secretions reduced, facilitating respiration, and gaseous exchange. Drying of the oral and nasal mucosa associated with these alkaloids appears to cause some itching of the nose; cerebral effects including amnesia and hallucinations can occur but are not usual with clinical doses.

Nitrous oxide Nitrous oxide has been used in dentistry to produce

anaesthesia and analgesia ever since the first demon- stration by Horace Wells in 1844. Even so, the manner in which it produces its effect is not fully understood.

Woods, R.-Pyogenic dental infections: a ten year review. Austral. D. J., 23: I , 107-1 I I (Feb.) 1978.

’ Jaffe, J. H.-Narcotic analgesics. In, The pharmacological basis of therapeutics. Goodman, L. S., and Gilman, A,, Edits. New York, Macmillan Company, 4th edn., 1970 (p. 266).

Australian Dental Journal, August, 1979 211

TABLE 2 Summary of relevant effects of drugs and oxygen used with sedation techniques

Agent and effect

Region affected Oxygen Narcotics Nitrous oxide Local anaesthetics Catecholamines

Cerebral cortex . . Orderly function Depression of Depression of In high concentra- Stimulation lead- Hypoxia leads to function function tions leads to ing to restless-

(II ness and g transient restlessness and Sedation and Sedation and E hallucinations relaxation relaxation stimulation, anxiety 3 occur occur restlessness,

8 muscle spasm z

3 Autonomic reflexes.. Orderly function Respiratory de- Little effect at In high concen- Little direct c Hypoxia leads to pression with clinical conccn- trations may effect e unpredictable large doses trations used lead to unpre- V

Heart , . . . . . Improves rhythm No direct effect No marked effect Transient brady- Adrenaline

responses in dentistry dictable changes

and function cardia rhythm increases rate Anoxia leads to becomes more and stroke

irregular regular volume function Noradrenaline myocardial reflex irritability and tachycardia cardiac arrest

Blood pressure . , . . No effect, can raise No direct effect No direct effect Transient reduc- Adrenaline raises blood pressure tion both systolic lowers lowered during systolic and diastolic treatment diastolic Noradrenaline

raises both systolic and diastolic

The gas is easily administered by inhalation, taking approximately seven to ten minutes for an effective blood level to be reached. It is removed by exhalation and most of the gas is exhaled within ten minutes after cessation of administration.

Activity of the cerebral cortex is depressed by nitrous oxide producing sedation*. The autonomic reflexes of the medulla can be affected producing nausea and hiccoughs, but respiratory depression does not occur at the concentrations usually employed in dentistry. Nitrous oxide also provides some analgesia similar in degree to that provided by therapeutic doses of narcotics.

Nitrous oxide has no appreciable effect on the normal cardiovascular system although there appears to be some peripheral vasodilation, blood pressure remains unchanged and there is sometimes a slowing of the pulse. The peripheral vasodilation which occurs increases the chance of intravascular injection of local anaesthetics. Arrhythmias have been reported' during dental anaes-

When administered in high concentrations in a pressure chamber at 1 .2 atmospheres nitrous oxide can produce general anaesthesia."

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Price, H. L., and Dripps, R. D.-General anaesthetics. In, The pharmacological basis of therapeutics. Ibid., p. 71.

' Martindale-The extra pharmacopoeia. Norman W. Blacow, Edit. London, The Pharmaceutical Press, 26th edn., 1972 (p. 843).

thesia with nitrous oxide. Although they were not serious and all were resolved, such reactions in the presence of a degenerative heart lesion and hypoxia could initiate a serious complication.

Although achieving their effects by different routes, nitrous oxide and narcotics affect similar areas of the central nervous system ; used together for sedation they appear to complement each other.

Local anaesthetics Analgesia is essential for sedation in children but

that provided by nitrous oxide or narcotics is not sufficient for other than simple procedures.

Like nitrous oxide and narcotics, local anaesthetics affect nerves, they reversibly block conduction along nerve trunks by preventing movement of sodium ions across the cell membrane.8 Additionally, local anaes- thetics have a direct effect on the heartt and are able to stimulate or depress central nervous system activity.

Because their effect is local, the dose of local anaesthetic used is not proportional to the patient's body weight but related to the nature of the tissues at the

t Local anaesthetics tend to reduce cardiac excitability and promote a regular heart rhythm. This is of greater significance when treating adults.

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Walton, J. G., and Thompson, J. W.-Pharmacology for the dental practitioner. London, The British Dental Association, 1970 (p. 69).

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injection site. Infants certainly require less local anaes- thetic to produce analgesia than do adults, however, the toxicity of local anaesthetics is proportional to the patient’s body weight.

Excessive doses of prilocaine may produce methaemo- globinaemia, a condition which reduces the oxygen carrying capacity of haemoglobin. Where oxygen tension is crucial methaemoglobinaemia can reduce the avail- able oxygen to a critical level. Where there is a history of anaemia any interference in oxygen transport by haemoglobin will be more serious.

When local anaesthetics are administered in relatively large doses there appears to be a reduction in blood pressure and the pulse may be slowed. For instance, in high concentrations following an intravenous injection, some cortical stimulation may be manifested as muscle spasm, restlessness, or hallucinations.

Whether it is due to transient reduction in blood pressure or to the loss of stimulation from an important sensory area of the face, sedation often appears to deepen following administration of local anaesthetics.

Australian Dental Journal, August, 1979

blood pressure and is associated with bradycardia produced indirectly by reflex action. Both catechol- amines are satisfactory vasoconstrictors and are effective in increasing depth and prolonging dental anaesthesia.

The cerebral cortex is stimulated by both adrenaline and noradrenaline which can produce motor and sensory symptoms. This can occur in young children after an injection of two ml of a local anaesthetic solution containing catecholamines.

Felypressin Felypressin is an alternative vasoconstrictor for dental

local anaesthetics. Available with three per cent prilo- caine, felypressin 0.03 IU per ml is a relatively effective preparation especially for children. It is a posterior pituitary hormone derivative and appears to have no marked effect on the central nervous system or the heart.

Catechdamiw vlsoeonstridors Adrenaline and noradrenaline, vasoconstrictors used

with many dental local anaesthetics, can directly affect the cardiovascular system. Although their effects are similar there are some differences. Adrenaline tends to increase heart rate and output and produces a transient rise in systolic blood pressure. Noradrenaline tends to produce a transient rise in both systolic and diastolic

Summary

Effective sedation is needed to permit young patients to receive proper dental treatment. A knowledge of the central nervous system and the pharmacology of the drugs employed is essential for safe and competent sedation. Some of the principles of sedation have been presented. A summary of the physiological effects of the drugs described is set out in Table 2. The clinical application of these principles will be published subsequently.

P.O. Box 22, Yass, N.S.W., 2582.