Dental Anesthesia and Pediatric Dentistry

Joseph

A.

Giovannitti,

Jr.,

DMD

Division ofOral andMaxillofacial Surgery andPharmacologicalSciences, BaylorCollegeofDentistry, Dallas, Texas

Pediatric patients between the ages of 18moand 6 yr are someof themostdifficult patientstomanagein

dentistry. Theyare oftenanxiousand fearful duetolack of past experiences, and are commonly influenced by parental feelings aboutdentistry. Coping skills areeither

underdevelopedornonexistent, and thereis noincentive to cooperate. Unlike an adult, the child neither under-stands nor cares thatcooperation during treatment may produce a favorable cosmetic or functional result. Den-tistry is filled with potential dangers to the young child. Fear ofthe unknown, surprise, pain, "shots," and

phys-ical restraint can all be debilitating to their developing

psyche. Scores of adults have become dental phobics

because ofone or twobad experiencesaschildreninthe dental office. Pediatric dentists adeptly manage many seemingly difficult patients. However, successful treat-ment is dependent upon adequate localanesthesia, and even then many young patients can only be managed

with sedation or general anesthesia.

GOALS OF PEDIATRIC ANESTHESIA

The goal ofpediatric management is to accomplish the necessary dental treatment and yet maintain the child's comfort and cooperation. Unfortunately, these goals do not gohand-in-hand. Comfort is directly related to anx-ietycontrol, which can beachievedwithorwithoutdrugs. However, acomfortable child is not always a cooperative one. Oftentimes, cooperation will be gained only when levels of sedation are deepened and the child becomes obtunded. Thus pediatric sedation is not without risk. Drug responses are varied and unpredictable, and most sedatives cannotreadily induce cooperation. Overdosage may occur, especially when opioids are used, when

re-dosing occurs, or when drug combinations are

em-ployed.1-3

The lack of titratability of nonintravenous techniques increases the riskassociated with fixed dosing. Although advances in monitoring technology and better training have dramatically enhanced the safety of

pedi-ReceivedJanuary15, 1995;accepted forpublication March 27, 1995. Address correspondence to Dr. Joseph Giovannitti,Jr., 4514 Cole Avenue, Suite 905, Dallas, TX 75205.

AnesthProg 42:95-99 1995

C 1995by the American Dental Society of Anesthesiology

atric

sedation,

it should

only

be attempted by

properly

trained

individuals,

with appropriate monitoring, andwith

resuscitative equipment

readily

available.

PEDIATRIC ANATOMY AND PHYSIOLOGY

Therearemany anatomicaland

physiological

differences thatinfluence

pediatric

anesthetic management. Pediatric patients have large heads, short necks, relatively

large

tongues, tonsilsandadenoids,andnarrownasal passages that are

readily

blocked

by

secretions or edema. The

larynx

ismore cephaladandanterior in achild, with the

glottis at C3-4 as opposed to C4-5 in the adult. The

epiglottis

is

long

and stiff and protrudes posteriorly ata

450 angle.

Thenarrowestportionof the upper airwayisat

thecricoid ring, makingthe pediatricpatientmoreprone

toobstruction from edema

following

intubation. The

tra-chea extends 4 to 6 cm from the glottis to the carina,

compared

with6to8cmintheadult,and theanglesthat the

right

and leftmainstembronchi makewith the trachea

are equal. Therefore, the chance ofendobronchial

intu-bation is greater. Finally, pediatric patients have fewer

lung alveoli;

the 20 million present at birth increase to

300 millionby age 8.

A highermetabolic rate in infants and children results

in a proportionally greater alveolar ventilation than in

adults: 100to150mL/kg-min compared with 60

mL/kg-min.Thefunctional residual capacity (FRC)isthe sum of the expiratoryreservevolume and the residual volume. It

acts as a buffer to maintain arterial oxygenation

during

inspiration and expiration. In an adult, the ratio of alve-olarventilationtoFRCis1.5to 1. Inthe infant, thisratio

is5to 1.Moreover,the supine position required for den-taltreatmentfurtherdecreases the FRC by 20% to 30%. Since the metabolic demand for oxygen is 60% greater thanintheadult, and the alveolar ventilation to FRC ratio

issohigh, hypoxemiacandevelop rapidlyinthepediatric

patient. Bradycardia is apremorbid response to

hypox-emia, soanyunexplainedbradycardia should be treated immediately with 100% oxygen.4

DISSOCIATIVE SEDATION

The high cost of malpractice insurance for general anes-thesia and regulation conceming the hospitalization of dental patients has motivated the dental profession to

ISSN0003-3006/95/$9.50 SSDI0003-3006(95)00068-2

seek altemative pain and anxiety control methods.

Tra-ditional forms ofconscious sedation have certain limita-tions in pediatric patients, in the mentally handicapped,

and in certain adult patients. A technique described by Bennett,5 called dissociative sedation, offers a safe and reliable alternative to traditional conscious sedation and general anesthesia. Using ketamine astheprimary seda-tive agent, this technique is marked by consciousness

(assuming the patientisof normal intellect and sufficient age), cooperation, occasional roboticbehavior, amnesia, andanalgesia. Unlike otherdrugsused for this purpose, ketaminedoes notdepressthecardiorespiratory system, but will eithermaintain orslightlystimulateit. Respiratory depression does not occur, oxygen saturation remains

adequatewithoutsupplementaloxygenation, and the air-wayismaintained along with theabilitytospontaneously

cough, swallow, and otherwise clear secretionsordebris.

Clinicalexperience with ketamine has been extensive, and thedrughasdemonstratedawide range of

applica-tions and an exceptional margin of safety. Green and

Johnson6conductedaliterature reviewofboth prospec-tive and retrospective reports concerning the use of ke-tamine as the primary sedative in unintubated pediatric

patients over a20-yr period. Procedurescompletedwith ketamineincludedbronchoscopy, dressingchanges, car-diaccatheterization, dentistry, ear, nose, and throat

pro-cedures, gastroenterology procedures, ophthalmology

procedures, and minor or major surgical procedures. They reviewed 97 papers describing 17,550 administra-tions, 11,598 of which involved pediatric patients. Of note wasthe relative lack of monitoringinthislarge sam-pling of patients. Most of the monitoring was done by clinicalobservation; pulse and cardiacmonitors were not regularly used, and vital signs were only occasionally measured. Despite this lack of diligence in monitoring, there was a relative absence of respiratory or cardiac

complications. Although the low complication rate in these reports maynotdirectly support the needfor

man-datorymonitoring during ketamine sedation, monitoring

during any sedative or anesthetic procedure is now the standard ofcare. Nevertheless, sincemonitoring maybe difficultorimpossiblein the combativeoruncooperative

patient,itmaysometimes bedelayed until the patient has been induced withan appropriate amount of ketamine. Even with its remarkable record of safety, efficacy, and reliability, a dentist or physician administering ketamine should have in-depth anesthesia knowledge and skill, and be proficient in treating airwaycomplications. Pharmacologyand Clinical Effects

Ketamine, aderivative of the hallucinogen phencyclidine, wasfirstsynthesizedin 1963. Its racemic form, containing equal amounts ofthe dextro- and levo-isomers, is used

clinically. Its high degree of lipid solubility enables it to enter the central nervous system rapidly. Ketamine is thought toproduceitsunique clinical state by inducinga dissociation between the thalamoneocortical and limbic systems, thus preventing the higher centers from perceiv-ing visual,auditory, and painful stimuli.7 Thisproduces a patient with the classic "ketamine stare" in which the patientlooks vacantly offintospace withglassy eyes and horizontal nystagmus. When ketamine has been admin-istered in a low dose, the patient may appear to be re-moved or detachedfrom his/herphysicalbeing, but may still respond to command. These effects may be due to thebinding of ketamine toN-methyl-D-aspartate (NMDA) receptors in the central nervous system. Itisthought that these receptors may be a subgroup of sigma opioid re-ceptors, andthat this may account for theanalgesic effect of ketamine.8 This mechanism remains controversial in light of conflicting reports of the partial reversal of the effects of ketamine with naloxone.9

Ketamine is veryrapidly acting when injected intrave-nously or intramuscularly. Peak plasma concentrations are achieved in about 1 min after intravenous adminis-tration and in about 5 min after intramuscular adminis-tration. Thepharmacokineticprofile of ketamine is similar inboth adults and children, conforming to a classic two-compartment model. Ketamine, being a highly lipid-soluble compound, rapidly enters the central nervous system andexertsitsclinicaleffect. Its termination of ac-tivity occursthroughredistribution to the peripheral com-partment. Thus, the clinical effects of ketamine begin to wane in about 15 min after intravenous administration andassoon as30min afterintramuscular injection. The elimination half-life of ketamine is 2 to 3 hr in adults. Children metabolize the drug more rapidly, resulting in an elimination half-life of only 1 to 2 hr. Ketamine is metabolizedinthe liverby the cytochrome P450 system to norketamine, an active metabolite with one-third the dissociative potency of ketamine itself. The concomitant administration ofdrugs thatare metabolized in the liver may extend thehalf-life of ketamine and prolong recov-erytime.

RespiratoryEffects. Patients are able to maintain an airwayindependently,because ketamine preserves spon-taneous respiration and enhances muscular tone of the upper airway. Protective reflexes remain intact, making

endotracheal intubation unnecessary. Respiratory de-pression is rarely associated with ketamine administra-tion, althoughitmay occur afterrapid intravenous bolus injection. A patient breathing room air will maintain the oxygen saturation at least at preoperative levels. In-creases in oxygen saturation may occasionally be seen afterketamine administration. This is due to bronchodi-lation and decreased airway resistance caused by direct

smooth musclerelaxation, increasedcirculating catechol-amines, andinhibition of vagal oufflowby ketamine. The effect of ketamine onventilation isclinically insignificant, although the carbon dioxide (CO2) response curve is shifted to the right. The slope of the curve, however, remains unchanged, indicating that hypercarbic respira-torystimulation remains intactbutmay requirea slightly higher arterial CO2 tension for a given ventilatory

re-sponse.'1 Ketamine stimulatessalivaryand tracheobron-chial secretions, which may induce laryngospasm. These effects canbe adequatelycontrolledbythe concomitant administration of an antisialogogue. Although laryngos-pasm isa possible side effect of ketamine administration and may be potentially life threatening, the literature re-view conducted by Green andJohnson6 revealed only

two cases of laryngospasm in 11,589 pediatric patients. Also, since upper airway protective reflexesremainintact, there appears to be minimal risk of aspiration of gastric contents. Inthe20 yr of ketamine usestudiedby Green andJohnson, only twocases of aspiration were found.

Cardiovascular Effects. Ketamine has a stimulatory

effect on the cardiovascular system, which resultsinmildto moderateincreases in blood pressure, heart rate, and car-diac output Ketamine inhibits the reuptake of catechol-amines attheadrenergicnerveterminal,withresultant sym-pathomimetic effects. Anincrease incoronaryperfusion oc-curs in response to increased myocardial oxygen consumption. Ketamine is therefore relatively contraindi-cated in patients with uncontrolled hypertension, athero-sclerotic heartdisease, and severe congestive heart failure. Hypertensive responses to ketamine may be exaggerated

byrapidintravenousbolus injection and may be minimized

byslowadministration of low doses of ketamine.

Neuromuscular Effects. Ketamine produces skeletal musclehypertonicityandrigidity,whichmaysometimes in-terferewith dental procedures because ofinability toopen themouth; this appears to be a dose-related phenomenon. Random movement unrelated to surgical or painfulstimuli

often occurs with ketamine administration. This random movementmaybe mistaken foraninadequate level of se-dation wheninfactitisunrelatedtothe dentalprocedure.

Myoclonus,twitching,andjerking movements are common

followingketamine administration. When these movements have been extensive, they have been mistaken for seizure activity. This may have led to reports of ketamine as a sei-zure-inducing medication and recommendations against its use inpatients with seizure disorders. However, ketamine has been shown to have anticonvulsive properties and has been used without

complication

in patients with seizure problems. Therefore ketamine is not contraindicated in the seizurepatient.

Other Effects. It should be noted that ketamine causesanelevationinintracranial pressurebyproducing cerebralvasodilation and increased perfusion

pressure.'2

Ketamine is therefore relatively contraindicated in pa-tientswith serious head trauma, hydrocephalus, and in-tracranial lesions, since medullary compression may cause

apnea.13

Increased intraocular pressure may also occur.Finally, ataxia and dizziness may persist for up to 4 hr after ketamine administration. Therefore, rapid inde-pendent ambulation is not recommended following the useofketamine.

Emergence Phenomenon. Psychic reactions associ-ated with ketaminemay result from the disconnection of external stimuli from higher cerebral function. The inci-dence of psychic phenomena with ketamine has been reported to bebetween 0% and 50% in adults and 0% and 10% inchildren.6 These experiences havebeen de-scribed as detachment, floating or bodilysuspension, out of body experiences, and strange thoughts or dreams. Factors thatmay place patients atincreased risk for these reactions may include age greater than 10 yr, female patients, rapidintravenousadministration ofhigh doses, personality disorders, and excessive noiseorstimulation during recovery, although this latter point has notbeen demonstrated in controlled studies. Not all psychic re-sponses to ketamine are unpleasant. In fact, Blankstein and

Anderson,14

in acomparison of low-dose ketamine with methohexital in adults undergoing oral surgery, found that ketaminewas notassociatedwith unpleasant

dreaming, whereas some methohexital subjects experi-enced horrifying dreams. Adverse psychic reactions to ketamine may occur,but reactions of this nature seem to beeasilyattenuatedwith theconcomitantadministration ofbenzodiazepines, opioids, orpropofol. Also, agradual tapering of the ketamine dose and its cessation 15 min before the end of the procedure will aid in minimizing adverse emergence phenomena.

Anotheremergencephenomenon ofconcern isnausea and vomiting. Although reports indicate that the inci-dence of nausea and vomiting may range from 0% to 43%, the incidenceinpediatric patients is somewhat less than 10%.6 When vomiting does occur, it is almost al-ways latein the recovery phase when the patient is alert and the airway may be cleared without assistance. Vom-iting can be successfully controlled with the administra-tion of0.625 mg droperidol intraoperatively.

Technique of Administration

Dissociative sedation may be induced either intrave-nouslyorintramuscularly. If intravenous access is permit-ted, 0.25 mg/kg of ketamine is administered. Intramus-cular induction may be achieved with 2 to 4 mg/kg of

ketamine mixed with 5pug/kgglycopyrrolate for salivation control. Maintenance may be with either a continuous infusion ofa0.1% ketamine solution at a rate of 50

pg/

kg-min, orby 2- to 5-mg boluses givenintermittently as needed. Midazolam maybe administratedin 1-mg incre-ments to provide background sedation and to control possible psychotomimetic effects.

A dissociative sedation technique has been described for adults in which sedation is achieved with an opioid (meperidine, 50 mg) and a benzodiazepine (diazepam,

10mg).15Ketamine, 25 mg, isthenadministeredshortly

before local anesthetic administration. Less

variability

in patient response to the injectionswas reported with ke-tamine ascompared with methohexital used ina similar manner. Thistechnique may be modified foruseinolder pediatric patients or in those who will cooperate with intravenouscatheterplacement. Midazolam isgiven toa clinical end-point, atwhich time an opioid may or may notbe added at the anesthetist's discretion. Ketamineis then administered slowlyin 5 to 10 mg increments until the desired effect has beenachieved, and local anesthet-ics are injected. The success of dissociative sedation, as with all sedation techniques, is dependentuponthe pro-duction ofadequatelocal anesthesia.

Possible side effects ofconcern with thistechnique

in-clude nausea, vomiting, andlaryngospasm.Aspreviously

discussed, vomiting is rare during the intraoperative pe-riod and is mostlikely tooccurlateinthe recoveryphase. Therefore, the risk of aspirationis minimal, and this side effect may besuccessfully controlled with the intraoper-ative administration of droperidol. Laryngospasm rarely occurs during dissociative sedation. It has been the au-thor's experience that when laryngospasm does occur, it is almost always associated with excessive salivation or the indiscriminent use of water during the dental proce-dure. Ifantisialogogues areused,and proper attention is

paidto operatortechnique, this potentially serious com-plication canvirtually be eliminated.

Our medicalcolleagues have been usingdissociative se-dation for pediatric patientsin the hospitalemergency set-ting inplace of traditional sedative techniques or physical

restraint16

Aseriesof 112pediatric patients received 4 mg/ kg ketamine for analgesia andsedation for emergency room treatment. The success rate was97%, nightmares were not

reported,and parental acceptance was high. Parents appre-ciated the fact that separation anxiety waseliminated, phys-icalrestraintwasunnecessary, and thatthere was no need forhospitalization or traumatic preoperative testing. PROPOFOL

Propofol, or2,6-diisopropylphenol, is anintravenous an-esthetic that may be used for sedation or general anes-thesia. Itis marketed as a whiteemulsion containing

soy-beanoil, egg lecithin, and glycerol. Because it is preser-vative free and its vehicle is capable of supporting the rapid growth ofmicroorganisms, strict aseptic technique must be adhered to in the preparation of the drug for administration. The drug should be discarded 6 hr after preparation to avoid contamination.

Pharmacokinetically, propofol has two distribution phases: a rapid phase with a distribution half-life of 1.8 to 8.3 min andaslower distribution phase withahalf-life of 34 to 64 min. The terminal elimination half-life of propo-fol is 300 to 700 min. The termination of activity of propofol is largely through rapid redistribution from the central nervous system to peripheral tissues. Although propofol has a highmetabolicclearance, the termination ofactivity is not dependent upon the elimination half-life of thedrug. Patientsareusually responsive within 8to10 min following cessation ofpropofol infusion. The dose requirementforpropofol isdecreasedinelderly patients, since higher peak plasma concentrations occur per unit dose. However, the dose requirement is increasedin chil-dren by 1.5timesdueto the shorterelimination half-life in thepediatric patient.

Cardiorespiratory effectsofpropofol include systemic hypotension, apnea, airway obstruction, and respiratory depression. These effects occur in a dose-dependent fashion and are more likelyto occur after a rapid intra-venous bolus injection. Because of drug-induced de-creases in mean arterial pressure and cerebral perfusion pressure, contraindications for propofol include patients with increased intracranial pressure and impaired cere-bralcirculation.

TechniqueofAdministration

Propofol may be used as an adjunct to the previously described dissociativesedationtechniqueinanattemptto

speedthe recovery ofpediatric patients. Ketamine accu-mulates with increasing doses andsignificantly prolongs recovery time. Because propofol is associated with a rapid recovery time, it can easily be incorporated into a

pediatric sedation technique. There are a considerable number ofpublished studies describing the use of propo-folin children.17-20

Inpatientsunwilling or unable to cooperate with intra-venouscatheter placement, intramuscular inductionwith ketamineisperformed as before. Once thei.v.is in place, propofol may be given in 10 to 20 mg intermittent bo-luses as needed, or as a continuous infusion. When ad-ministering a continuous infusion, an infusion pump should beused, or a0.2% solution of propofol should be prepared in 5% dextrose. This is the maximal dilution recommended forpropofol, since dilution to less than 2

mg/mLmay breakthe emulsion. Thispreparation is then infused at arate of 50 to 150 ,ug/kg-min for maintenance

of sedation. Arousaloccurs within 10 min after the infu-sion has beendiscontinued. This technique provides ex-cellent behavior management and spontaneous ventila-tion ismaintained. Oxygen saturationremainsat

preop-erative levels without the routine use of supplemental

oxygen. When patients allow the placement of an i.v.

catheter,sedation is achievedby titrationofmidazolamto a clinicalendpoint, the use of a narcotic if indicated, and the administration of low-dose ketamine prior to local

anesthetic administration. Sedation is then maintained with intermittent boluses of propofol, or

with

a continu-ous infusion. Again, recovery is greatly enhanced and emergence is smooth.

CONCLUSION

Ofallthepediatric sedation techniques, itisthis author's opinion thatdissociative sedation produces the most re-liable cooperation without obtunding the patient. In trainedhands, dissociative sedation is extremely safe and highly effective. Patientand parental acceptance is high. The addition of propofol has made a good technique evenbetter.

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