PEDIATRIC DENTISTRY/Copyright © 1989 byThe American Academy of Pediatric Dentistry

Volume 11, Number 2

An investigation of capnography and pulse oximetry asmonitors of pediatric patients sedated for dental treatment

John Iwasaki, DDS, MS

Diane C.H. Dilley, DDS

Abstract

Traditional methods of monitoring sedated pediatric den-tal patients have major shortcomings. This study evaluatedthe use of capnography in conjunction with pulse oximetry formonitoring children during conscious sedation for dentaltreatment. The specific purposes of the study were to deter-mine if capnography would: (1) detect ventilatory changesthat subsequently cause an oxyhemoglobin desaturation asdetected by pulse oximetry; and (2) detect an airway obstruc-tion.

Ten pediatric dental patients (mean age 2 years, 10months) were sedated with 75 mg/kg of chloral hydrate instrict accordance with the Guidelines for the Elective Use ofConscious Sedation, Deep Sedation, and General Anesthesiain Pediatric Patients of the American Academy of PediatricDentistry and the American Academy of Pediatrics (1985).All patients were monitored continuously using bothcapnography and pulse oximetry. Analysis of data obtainedusing these monitors revealed that specific end-tidal CO2values were not predictive for subsequent oxyhemoglobindesaturations and that capnography was very accurate indetecting complete obstruction of the airway. Pulse oximetryrevealed that all patients had mild oxyhemoglobin desatura-tions and that 50% had moderate desaturations.

Traditional methods of monitoring sedated patientsinclude observation of tissue color, measurement ofblood pressure, palpation of the pulse, and auscultationof heart and lung sounds using a precordial stetho-scope. In recent years each method has been recognizedas having serious shortcomings, especially for pediatricdental patients. Recently, 2 new instruments have beenadvocated for improved respiratory monitoring ofsedated patients. The pulse oximeter permits noninva-sive monitoring of arterial oxyhemoglobin saturation,pulse rate, and pulse strength. The capnometer permitsquantitative noninvasive monitoring of respired CO2.The overall objective of this investigation was to explorethe potential of using capnography in conjunction with

William F. Vann, Jr., DMD, MS, PhD

Jay A. Anderson, DDS, MD

pulse oximetry during conscious sedation of pediatricdental patients.

Literature Review

When sedating children in the conventional dentaloffice setting, conscious sedation is the desired tech-nique. Even though patients under conscious sedationare sedated at a level less than deep sedation, they are atrisk for respiratory compromise leading to inadequateoxygen content, or hypoxemia. This may result fromairway obstruction or a drug-induced respiratory de-pression. Anderson and Vann (1988) noted that themonitoring recommendations of the Guidelines for theElective Use of Conscious Sedation, Deep Sedation, andGeneral Anesthesia in Pediatric Patients of the AmericanAcademy of Pediatric Dentistry and American Acad-emy of Pediatrics (1985) are essential. They note furtherthat the Guidelines do not fully address hypoxemia, theleading cause of morbidity and mortality in pediatricdental sedations (Goodson and Moore 1983).

Standard monitoring examines only the signs andsymptoms that result from a decrease in the O2 contentof the patient’s blood (hypoxemia). Initially, hypoxemiapresents as increased ventilatory effort, increased heartrate, and increased blood pressure. These symptoms arefollowed by cyanosis (a bluish tint in the nailbed andlips), bradycardia, cardiac dysrhythmia, and cardiovas-cular collapse. Reliance only on signs and symptoms torecognize hypoxemia is very unpredictable in pediatricdental patients. Visual observation of tissue color maybe obscured by dental paraphernalia such as the rubberdam, patient eye protection, and restraints covering thehands and feet. Furthermore, color changes associatedwith hypoxemia are not detectable until dangerouslylow levels have been reached (Comroe and Bethelho1947). Moreover, color change is a subjective variable,affected by hemoglobin composition, tissue pigmenta-

PEDIATRIC DENTISTRY: JUNE, 1989 N VOLUME 11, NUMBER 2 111

tion, and the observer's skill in distinguishing colorchanges (Dripps et al. 1982).

The precordial stethoscope is an excellent diagnosticinstrument for listening to heart and lung sounds, but itseffectiveness is diminished by the noise of high-speedhandpieces (Drummond et al. 1984). Blood pressure isan unreliable indicator of sedation complications be-cause it correlates poorly with changes in O2 saturationduring mild hypoxemia (Mueller et al. 1985). Respira-tion has been found to increase significantly only in thepresence of moderate hypoxemia (Mueller et al. 1985).In summary, even when detected, changes in bloodpressure, heart rate, and respiration are not good earlyindicators of respiratory complications during seda-tion.

Pulse OximetryPulse oximetry is a noninvasive method to monitor

the oxygen content in arterial blood. It measures theamount of O2 carried by the hemoglobin in the bloodstream, or oxyhemoglobin saturation (SaO2). A healthyindividual has an SaO2 of 96-100% while breathing roomair.

Several studies (Yoshiya et al. 1980; Yelderman andNew 1983; Anderson et al. 1988) have shown that inadults, SaO2 values obtained using pulse oximetry cor-relate highly with measured arterial saturation valuesunder a variety of clinical conditions. Pulse oximetryalso has been found to detect hypoxemia in the absenceof clinical signs or symptoms in adult patients. There isconsiderable evidence that pulse oximetry is also accu-rate and rapidly responsive to changes in the oxygena-tion in infants and children (Monaco et al. 1983; Swed-low and Stearn 1983; Cote et al. 1988). Furthermore,studies suggest that pulse oximetry is an excellentmethod of monitoring respiration in children sedatedfor dental procedures (Mueller et al. 1985; Moody et al.1986). Whitehead et al. (1988) found that pulse oximetryprovided early detection of respiratory distress suchthat correction was a relatively simple matter of read-justing head position.

CapnographyCapnography has been advocated as a monitor for

apnea and airway obstruction and to quantify adequacyof ventilation. A small suction tube is placed in or nearthe patient's upper airway for continuous collection ofrespired air that is then analyzed for the CO2 concentra-tion using infrared spectroscopy. The quantity of CO2

expired is displayed as a graphic wave form on hardcopy or an oscilloscope monitor (Fig 1). The upslope ofthe wave correlates with the increasing amount of ex-haled CO2 as dead space gases are exhaled. A plateauoccurs when primarily alveolar gas is being exhaled.

Fie 1. A graphic wave form as displayed on a capnometer'soscilloscope monitor.

The end of the plateau portion of the curve representsthe end-tidal CO2. This concentration of CO, mostclosely reflects alveolar gas and, therefore, arterial CO2

concentration (PaCO2). Inhalation results in a down-slope of the graph as the amount of CO2 decreases.When CO2 is not being exhaled, a flat baseline results(Fig 2). This occurs when a patient is not breathing(apnea) or when there is obstruction of the airway.

••* - &PHE& -

FIG 2. A flat baseline on the capnometer's oscilloscope signalsthat the patient is not breathing (apnea) or that there is an airwayobstruction.

112 MONITORING SEDATED PEDIATRIC PATIENTS: Iwasaki et al.

Kalenda and Kramer (1979) reviewed variousbreathing patterns detected by capnography and dem-onstrated that periods of apnea could be detected, ascould periods of decreased breathing, or hypoventila-tion. Anderson et al. (1987) used a capnometer with amodified sampling tube to monitor respiration of non-intubated adult dental patients undergoing outpatientgeneral anesthesia and concluded that capnographywas an excellent method of monitoring for apnea andairway obstruction. Results suggested that capnogra-phy also could be used to indicate trends for developinghypoventilation. When all of the evidence is considered,capnography has been shown to be useful in monitoringrespiration in nonintubated adults, but it has not beenexamined as a monitor in nonintubated pediatric pa-tients.

In summary, a review of the literature leads to theconclusion that the standard methods of monitoringhave significant shortcomings when used with sedatedpediatric dental patients. Pulse oximetry is an excellentmethod of monitoring blood oxygenation, but it doesnot give an early warning of airway obstruction orhypoventilation. Capnography has the potential tocomplement pulse oximetry because it could give ad-vanced warning of potential respiratory problems. Thepurpose of this study was to answer the followingresearch questions:

1. Will capnography quantitatively detect ventilatorychanges that subsequently cause an arterial oxygendesaturation detected by pulse oximetry in sedatedpediatric dental patients?

2. Will capnography detect airway obstruction in se-dated pediatric dental patients?

Materials and MethodsThe patient sample included 10 child patients. Each

child was 24-60 months old, required sedation toachieve cooperation and safe operating conditions, wasan American Society of Anesthesia (ASA) Class I anes-thesia risk, and received a presedation health evaluationby a physician.

Written parental consent was obtained for all seda-tion procedures, after a full explanation of the proce-dures and risks. Pre- and postappointment instructionswere used for all patients and all sedation appointmentprocedures were carried out in strict accordance withthe Guidelines for the Elective Use of Conscious Sedation,Deep Sedation, and General Anesthesia in Pediatric Patientsof the American Academy of Pediatric Dentistry andAmerican Academy of Pediatrics (1985).

Patients were required to be NPO from midnight ofthe night before the appointment and guardians wereinstructed to give only clear liquids up to 4-6 hr beforethe procedure. Patients were weighed and baseline

measurements were obtained including blood pressure,heart rate, and respiratory rate. Patients were admini-stered 75 mg/kg dose of liquid chloral hydrate orallyvia preloaded syringes, followed by 25 cc of water.Comedicaments and N2O/O2 were not used in an effortto eliminate confounding factors related to multipledrug interactions. This design also allowed collection ofdata from patients who were not supplemented withoxygen.

Administration of chloral hydrate signaled abaseline time for the appointment procedures. Thepatient and guardian waited for 30 min in a quiet room.The patient then was carried to a dental chair and placedin a Papoose Board® restraining device. Cloth towelswere rolled up and placed behind the necks of allpatients to help support their airways and preventphysical airway obstructions during dental treatment.Then, a precordial stethoscope, a pulse oximeter, and acapnometer were attached. The precordial stethoscopewas placed for maximum auscultation of respiratoryand cardiac sounds.

A 15-second period was allowed for the Ohmeda3700 (Ohmeda Corp; Englewood, CO) pulse oximeter(Fig 3) to complete its self-test routines for electronics,battery status, and calibration accuracy. The pulse ox-imeter contained the new "M" version software pro-gram. An Ohmeda 3700 flexible pulse oximeter probewas taped to the great toe of the patient's left foot and alltoes then were taped together to minimize individualtoe movement (Fig 4, next page). A cloth was placedover the sensor to prevent interference from extraneouslight sources. All probe placements resulted in maxi-mum pulse signal strength as demonstrated by the

Fic 3. The Ohmeda 3700 pulse oximeter (top) and the Ohmeda5200 capnometer (bottom).

PEDIATRIC DENTISTRY: JUNE, 1989 ~ VOLUME 11, NUMBER 2 113

ig 4. Flexible pulse oximeter probettached with tape to child patient'sreal toe on the left foot.

oximeter's signalstrength bar graph indi-cator. The pulse oxime-ter was set in the slowresponse mode (6-secSaO2 response time).

The Ohmeda 5200(Ohmeda Corp; Engle-wood, CO) capnometer(Fig 3) was set for a 5-minwarm-up period andcalibrated as recom-mended by the manufac-turer using a standardgas (5% CO2/ 65% N,O,and 30% O2). The sam-pling flow rate was set at150 ml/min and the ap-nea alarm was set for acontinuous tone to signala 30-sec absence of CO2.

A Biomed® (Biochem International Inc; Waukesha,WI) pediatric nasal CO2 sample line was used as thecapnometer sampling tube (Fig 5). Respiratory rate andheart rate were recorded every 5 min and SaO2 andrespired CO2 were recorded continuously using a dualchannel strip recorder (Ohmeda Corp; Englewood,CO).

The operating dentist was shielded from the moni-toring equipment and notified to reposition the pa-tient's head at any time the pulse oximeter revealed asaturation below 96%. The Moore head tilt maneuver(Moore et al. 1984) was performed to assess the level ofsedation at times the patient was in a quiet sleep. If thepatient failed to clear the airway immediately, the headwas repositioned following the first evidence of desatu-ration.

Mechanical monitoring continued throughout thedental appointment and was discontinued after com-pletion of the operative procedures. At that point, allbaseline measurements were repeated. Patients werereleased when they were alert, able to sit up unaided,and walk with minimal assistance.

Data AnalysisDescriptive data analyses were used to answer the

research questions. End-tidal CO2 values were com-pared to SaO2 values that occurred simultaneously be-low 96% SaO2. These end-tidal CO, values also werecompared against SaO2 values above 95% SaO2 to ruleout false positives. Airway obstruction was examinedby assessing capnographic data collected during anyperiod of obstruction or apnea as determined by auscul-tation of the airway.

1

Fie 5. A Biomed pediatric nasal CO2 sample line was used as thecapnometer's sample tube for the child patients.

ResultsThe sample size included 10 patients with a mean age

of 2 years, 10 months (range 2 years, 2 months to 4 years,8 months; 8 females, 2 males). All were healthy ASAClass I patients. The patients' mean weight was 12.6 kg(range 10.5-14.5 kg). The mean dose of chloral hydratewas 920 mg (range 780-1000 mg).

Findings for Pulse OximetryA desaturation period was defined as the period of

time in which the SaO, went below 96% and returned to96%. There was an average of 11.8 desaturation periodsper patient (range 4-23 desaturation periods). Thenumber of mild and moderate desaturations for eachpatient is illustrated in the Table.

Findings for End-Tidal CO2

No predictive value was found between end-tidalCO2 values and specific SaO2 values. The end-tidal CO2values ranged from 5 to 47 mm Hg for SAO2s below 96%and 5 to 45 mm Hg for normal SAO2s. However, therewas a trend of decreasing respiratory rate as detected bycapnography 30 and 20 sec prior to a desaturation.

DiscussionPulse Oximetry Findings

Ten patients (100%) experienced mild desaturationsat 90-95% and 50% experienced moderate desaturationsat 88-89%. This differs from the findings of Mueller et al.(1985), who reported 25% mild desaturations and 10%moderate desaturations, and an overall prevalence of

114 MONITORING SEDATED PEDIATRIC PATIENTS: Iwasaki et al.

TABLE Patient desaturations

#Sa02 90-95% #Sa02 <90%*Patient (mild desaturations) (moderate desaturations)

1 21 02 23 13 18 04 7 05 4 06 8 37 9 18 14 09 9 3

10 5 2Averages 11.8 1.0

* All desaturations < 90% were in the range of 88-89%.

desaturations of 35% using a dosage of 100 mg/kg oralchloral hydrate (a 33% higher dose) with 50% N20/O2.The higher incidence of desaturations in our study wasthought to be due to the lack of 02 supplementation.

All patients experienced periods of crying inter-mixed with periods of quiet sleep. Both the mild andmoderate desaturations occurred during periods ofcrying and in many instances, with breath holding.These desaturations may be associated with a dimin-ished oxygen reserve as a result of accelerated basaloxygen consumption during periods of distress. Nodesaturations thought to be due to motion artifact wereincluded.

Moore Head TiltThe Moore head tilt maneuver was tested during

periods of quiet sleep. Only one patient did not attemptto clear the airway during the head tilt procedure. Bydefinition, this patient was in deep sedation. This inci-dence of deep sedation differs from that reported byMoore et al. (1984), who noted 27% of their patients didnot respond to the head tilt when sedated with 60 mg/kg of chloral hydrate and 50% N202. In that study, allnonresponders were females younger than 36 monthsold. The authors speculated that the young age andfemale sex may render patients more susceptible tochloral hydrate and N20/O 2 sedation. In this study, 80%of the patients were female but only one, aged 2 years,1 month, failed to respond to the head tilt. Five otherfemales younger than 36 months of age responded to thehead tilt. The results of Moore et al. (1984) may, there-fore, reflect a deepening in the level of sedation by theaddition of N20/O2.

The Research QuestionsOur first research question was whether capnogra-

phy would quantitatively detect ventilatory changesthat subsequently cause an arterial 02 desaturation as

detected by pulse oximetry in sedated pediatric dentalpatients. A specific end-tidal CO2 measured bycapnography was not predictive of an SaO2 less than96% as measured by oximetry. This may have resultedfrom irregular and rapid patient breathing patternswhile conscious, because panting and breath holdingduring crying produced variable end-tidal CO2 read-ings at times of no desaturation. However, evaluation ofrespiratory rates suggested that there was a trend of adecrease in respirations within the 30-sec period prior tothe desaturation.

The second question was whether capnographywould detect airway obstruction in sedated pediatricdental patients. Total airway occlusion was revealedreadily by capnography in one sedated child. This wasverified during the Moore head tilt procedure. Whenbreath sounds could not be auscultated, the capnometerrecorded no end-tidal CO2. When the airway was repo-sitioned, there were immediate breath sounds and areturn of CO2. This finding was similar to those reportedby Anderson et al. (1987), who noted an immediate dropin respired CO2 to baseline (zero) when an occlusionoccurred.

Early warning of airway occlusion by the capnome-ter did not give a practical advantage over monitoringwith pulse oximetry in these patients. Oxygen desatura-tions were noted within seconds of an airway occlusion.This was a period of time roughly equivalent to thatnecessary for verification of an occlusion. This shorttime difference may have been related to the young ageof the patients and/or the lack of O2 supplementation.

Advantages and Limitations ofCapnography in this Study

Capnography may be used to detect the presence ofapnea, airway obstruction, and hypoventilation. Apneaor airway obstruction is detected by the absence ofrespired CO2. Increases in end-tidal CO2 indicate thathypoventilation is occurring. If there is an adequaterespired air sample, accurate end-tidal CO2 can be deter-mined. The patients who were sedated lightly some-times became excited and panted, resulting in veryrapid respiratory rates and highly erratic tracings. Theexchange of gases through the nose at these rates proba-bly did not reflect accurate end-tidal CO2 values becauserapid shallow breaths involve air exchange primarilywith anatomic dead spaces. The end-tidal CO2 wouldreflect lower values because anatomic dead spacescontain little CO2. Also, gas sampling flow rates canaffect the accuracy of end-tidal CO2 measurement (Sasse1985). High sampling rates may increase the concentra-tion of room air in the sample, producing erroneouslylow end-tidal CO2 values. However, low sampling flowrates decrease the capnometer’s response time. If respi-

PEDIATRIC DENTISTRY: JUNE, 1989 ~ VOLUME 11, NUMBER 2 115

ratory rates are rapid and tidal volumes are small, thentrue end-tidal CO2 may not be sampled. Fromm andScamman (1988) evaluated 5 capnometers for accuracyduring rapid respiration of pediatric patients and con-cluded that more than 31 respirations/min resulted inan underestimation of end-tidal CO2.

Accuracy of end-tidal CO2 measurements was com-plicated further by the location of the sampling tube.Sampling accuracy would be diminished if nasal air hada different CO2 concentration than air exhaled throughthe mouth. Only expired nasal air was analyzed in thisstudy. Patients who breathed orally, especially duringcrying, decreased nasal air flow, and this resulted inpoor air exchange and possible inaccurate end-tidal CO2readings. Schieber et al. (1985) reported that the accu-racy of peak expired CO2 was affected by the location ofthe sampling site. When a modified circle breathingcircuit was used and air samples were taken at the distalend of an endotracheal tube, expired CO2 and PaCO2correlated. Samples drawn from other locations under-estimated PaCO2. Anderson et al. (1987) used a similarnasal prong probe and found correlation coefficients of0.93-0.99 between end-tidal CO2 and PaCOR in 50% ofthe patients. Twenty per cent of their patients hadcorrelation coefficients of 0.78-0.85. However, thesewere adult patients whose respiratory physiology mayhave differed from the patient population of this study.

The accuracy of the sampling in our study also mayhave been affected by the diameter of the nares. Patientswith nares smaller than 5 mm were subject to possiblenasal obstruction from the sampling tube assembly.Occlusion of either the nares or the sampling prongsoccurred when the prongs were pushed too deeply intothe nostrils. This was observed occasionally when inad-vertent pressure was applied from finger retraction ofthe rubber dam in the anterior maxillary region by theoperator. Excessive pressure by the operator on thenasal prongs can cause suction of either nasal mucosa ormucus into the line. Because the Biomed 5200 pediatricsampling prongs have a smaller diameter than the stan-dard adult lines, this may have increased the likelihoodof line blockage. Line blockage also occurred with exces-sive mucous secretions during crying. When purging bythe monitor failed to clear the sample line of condensedmoisture, a new nasal sample line was applied.

The capnometer was unaffected by patient move-ment, a practical advantage in the monitoring of chil-dren who may alternate between periods of restfulnessand movement during dental sedations.

Conclusions

Based on the findings in this study, the followingconclusions were made:

1. Capnography was an excellent method of monitor-

ing for complete airway occlusions.2. Specific end-tidal CO~ values were not predictive of

specific SaO~ values.3. The end-tidal CO2 readings were not affected by

motion, but were affected by nasal prong placement,mouth breathing, rapid shallow breathing, and ob-struction of the sampling line from nasal tissues ormucous condensation.

4. Although capnography detected airway obstruc-tions prior to changes detected by pulse oximetry,the time difference was too little to provide anypractical advantage in these patients.

5. There appeared to be a trend of decreasing respira-tions 30 sec prior to a desaturation.

6. All sedated patients experienced mild or moderatedesaturations, but only one patient failed to sponta-neously open the airway when the Moore head tiltwas administered.

Directions for Future Research

This was the first study to investigate capnographyfor monitoring sedated pediatric dental patients. It gavepractical insight into the usefulness of capnography asa method of monitoring such patients. Future studiesshould examine the use of blood gas analysis to correlateend-tidal CO2 and respired CO2 in children. Blood gasanalysis would also permit evaluation of the influenceof prong placement, prong length, and prong diameteron the sampling accuracy of respired CO2.

Future controlled clinical studies also should exam-ine N~O/O2 as a comedicament with chloral hydrate. Itseems almost certain that N20/O2 deepens the level ofsedation and thus has the potential to increase thenumber of patients who reach a level of deep sedation.At the same time, N20/O2 may provide a level of 02supplementation sufficient to increase the patient’sPaO2 significantly. If this were true, a pediatric patientsupplemented with N20/O2 might experience fewerdesaturations. Oxygen supplementation also may pro-duce a longer time lag between airway occlusion de-tected by capnography and a desaturation detected bypulse oximetry.

Finally, the influence of age and sex on a child’sresponse to sedation with chloral hydrate is a relation-ship that merits additional study.

Dr. Iwasaki is in the private practice of pediatric dentistry in Boone,North Carolina; Dr. Vann is an associate professor and chairman andDr. Dilley is an associate professor, pediatric dentistry, and Dr.Anderson is an assistant professor, oral and maxillofacial surgery, allat the University of North Carolina. Reprint requests should be sentto: Dr. William F. Vann, Jr., Dept. of Pediatric Dentistry, Universityof North Carolina School of Dentistry, CB #7450, 205 Brauer Hall,Chapel Hill, NC 27599-7450.

American Academy of Pediatric Dentistry: Guidelines for the elec-tive use of conscious sedation, deep sedation, and general anes-

1 1 6 MONITORING SEDATED PEDIATRIC PATIENTS: Iwasaki et al.

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Hostility and the AIDS patient

A quarter of Americans surveyed feel hostility toward persons infected with the AIDS virus, HarvardUniversity researchers found.

After analyzing results from 53 national and international opinion surveys, the researchers concludedthat although the public is relatively aware of the low risks of contracting the disease through casualcontact, education has not been very effective in reducing hostile feelings toward AIDS patients.

In analyzing the surveys, the researchers found that many people thought people with AIDS shouldbe tattooed or quarantined in some way. Twenty per cent said patients with AIDS were "getting theirrightful due,"1 in 12 said AIDS patients should not be treated with compassion, and a quarter said theydidn’t want their child in school with someone who had AIDS.

The researchers believe discrimination against AIDS patients can be prevented only by legislation thatensures confidentiality and such rights as security in employment and housing. Studies of the effects ofanti-racism legislation have shown that even when people maintain hostile attitudes, the threat of legalaction against them will generally prevent them from acting out their aggression.

PEDIATRIC DENTISTRY:JUNE, 1989 ~ VOLUME 11, NUMBER 2 117