An appraisal of temperature assessment by infrared emission detection tympanic thermometry

COLLECTIVE REVIEW tympanic thermometry

An Appraisal of Temperature Assessment by Infrared Emission Detection Tympanic Thermometry From the Departments of Emergency Medicine and Pediatrics, State University of New York Health Science Center at Syracuse. Received for publication December 4, 1991. Revision received March 16, 1992. Accepted for publication April 2, 1992. This study was supported in part by Thermoscan Inc, San Diego, California.

Thomas E Terndrup, MD, FACEP

[Terndrup TE: An appraisal of temperature assessment by infrared emission detection tympanic thermometry. Ann EmergMed December 1992;21:1483-1492.] INTRODUCTION Emergency physicians depend on the ability to accurately measure body t e m p e r a t u r e in their patients. The ability to rapidly and reliably detect abnormalities in body temperature facilitates p r o p e r diagnosis and the evaluation of patient complaints. Recent developments in the technology of thermometry allow assessment of body temperature by measuring i n f r a r e d emissions from the auditory canal, including the tympanic membrane. I n f r a r e d emission detection (IRED) thermometers offer significant advantages over traditional thermometers because they do not require contact with the tissue of interest or equilibration time for temperature measurement. Clinical trials of IRED thermometry using tympanic membrane/auditory canal emissions are being published with increasing frequency and with encouraging, yet occasionally conflicting, results. We examine the rationale for IRED tympanic/auditory canal thermometry and compare it with traditional methods of temperature assessment. This review focuses on the factors that are i m p o r t a n t in deciding on a site and method of temp e r a t u r e measurement, the advantages and disadvantages of IRED tympanic thermometry compared with traditional sites and techniques, and the results of recent trials using IRED devices. In addition, p r o d u c t information for available IRED tympanic/ear devices is included. S I T E OF T E M P E R A T U R E MEASUREMENT Body t e m p e r a t u r e is neither homogeneous nor constant. 1,2 Under normal conditions, core body t e m p e r a t u r e varies as much as + 0.7 C from 37.0 C from diurinal variation, exercise, and ambient temperature stress. 3 At 22 C, or typical ambient conditions, a t e m p e r a t u r e gradient exists from skin temperature to core areas, such as central vessels, mediastinum, and organs.4, s This gradient is larger in colder and smaller in warmer ambient conditions. 6 The temperature of local tissues is a balance between heat production (ie, blood temperature and local metabolism) and heat elimination (ie, the temperature gradient between arterial and venous blood and surface

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contact with the ambient temperature). 7 The best measurement sites should be relatively devoid of local tissue changes that produce spurious elevation or depression of temperature readings. The temperature of the arterial blood perfusing the preoptic area of the hypothalamus, or t e m p e r a t u r e control center, dictates the body's physiologic response to t e m p e r a t u r e stresses in maintaining homeostasis. 5,74o More than 30 years ago, measurements from various body sites taken with sensitive thermocouples and calorimetry showed that the hypothalamus controls sweating and p e r i p h e r a l vasodilation in response to warm stress. 8-]o Cold stress responses (ie, vasoconstriction and increased heat production) are evoked by both p e r i p h e r a l (skin t e m p e r a t u r e less than 33 C) and central thermoreceptors.3, 5 Therefore, body sites at which the temperature most closely approximates and changes with that of the hypothalamus provide the most accurate temperature information on which physiologic responses are based. Although estimates of body t e m p e r a t u r e can be obtained with traditional thermometers by equilibrating with oral, rectal, bladder, or vascular tissues, these sites are subject to multiple influences that make them inaccurate in assessing hypothalamic temperature.2,a, ~ 4 9 Both external (eg, ambient temperature, probe placement technique) and internal (eg, phase lag in rectal tissue during r a p i d body t e m p e r a t u r e changes, blood t e m p e r a t u r e that decreases dramatically in distal vascular segments such as the extremities from increases in vascular resistance and heat loss through arterioles perfusing the skin) factors spuriously influence these measures. F o r example, oral t e m p e r a t u r e may vary up to 0.6 C in various sublingual regions unless probes are accurately placed in the posterior sublinguat pocket (Figure 1).13 Temperatures of the esophagus and tympanic membrane are Figure 1. Mean temperature differences and ranges among three sublingual sites and between closed-mouth and open-mouth positions ~z Temperature difference (F) 1.8

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largely not influenced by these factors. 2°-23 Temperatures taken at each of these sites serve as reliable estimates of the hypothalamic arterial blood temperature.24, 2s Investigators also have determined that some tissue sites are not in sync with physiologic responses to alterations in t e m p e r a t u r e homeostasis.4,5, ]8 F o r example, sweating responses are related directly to tympanic or b r a i n temperature and inversely to skin t e m p e r a t u r e during warm ambient exposure (Figure 2). 5 There are no described temperature receptors or effector organs in sites commonly used for temp e r a t u r e measurement, such as the sublingual area or the rectal vault. 16 In addition, the rectal temperature may change opposite that of the brain during warming o r cooling 26 (Figure 3) s or fail to detect r a p i d temperature changes ( F i g u r e 4), 3 whereas tympanic t e m p e r a t u r e closely approximates b r a i n temperature (Figure 5). 27-30 When body temperature is not changing rapidly, mean body temperature may be assessed accurately in a variety of locations. These include mouth, rectum, esophagus, bladder, central vessels, and tympanic membrane. Less accurate screening sites include the axilla and skin. 31-33 However, when body temperature is changing, rectal and b l a d d e r temperatures have a distinct lag in temperature r e s p o n s e . 29,3° Rectal responses to rapidly increasing or decreasing body t e m p e r a t u r e are slow and may both over- and underestimate actual t e m p e r a t u r e (Figure 5). Although average body temperature is reflected in traditional monitoring sites, the actual temperature of arterial blood perfusing the b r a i n may be substantially warmer or colder than average. 15~18,26 For

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TEMPERATURE ASSESSMENT Terndrup

clinical purposes, an accurate site of t e m p e r a t u r e measurement should be able to identify a b n o r m a l temperatures reliably. Small measurement errors are generally acceptable for clinical practice, as long as patients with h y p e r t h e r m i a or hypothermia are detected. Other than accuracy, factors that are important in considering body site selection for temperature measurement are convenience, placement of temperature probes noninvasively, patient discomfort, patient modesty, patient cooperation, time requirements, exposure of staff to mucous membranes, exposure of staff to infectious diseases, costs, and contraindications to use of this site. 34,35 The auditory canal is a readily accessible, yet somewhat protected, cavity formed by a 25- to 35-ram-long curvilinear tube. Importantly, the hypothalamus and tympanic membrane both receive arterial blood supply from branches of the carotid artery.2a,zs, 28 Tympanic membrane temperature, measured with contact bead thermistors, has been shown to accurately assess b r a i n , aortic, and p u l m o n a r y a r t e r y temperatures.24,28,30, 36 Recently published information shows that the temperature of the anterior, inferior one third of the tympanic membrane is equivalent to core body t e m p e r a t u r e in human beings. 37 Therefore, if tympanic membrane temp e r a t u r e can be assessed with IRED thermometers, accurate body t e m p e r a t u r e can be obtained.

Figure 3. Deviations o f rectal f r o m cranial internal temperature on entering and leaving a bath of 40 C (upper panel) and during exercise (lower panel) s

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METHOD OF TEMPERATURE MEASUREMENT Thermometry methods include mercury-in-glass, thermophototrophic or liquid crystal cells, thermistors, and thermoelectric and IRED devices. Traditional mercury-in-glass thermometers are still p o p u l a r despite requiring longer equilibration times for accuracy, a 25% rate of inaccuracy, and recent regulations proposing excluding mercury from public schools (state of California). al-aa Thermophototrophic cells produce a graded color change over varying temperature ranges. Their use is restricted to skin and oral measurements, which have demonstrated inaccuracies.33,34045 Thermistors and thermocouples are used in electronic digital and other invasive monitors, such as esophageal probes.46 Although quite accurate, they require p r o p e r placement techniques and adequate equilibration times and are influenced by both patient and o p e r a t o r variability. 11-15,17,24 Traditional thermometers require transfer of heat energy from local tissues to the t e m p e r a t u r e probe. This heat transfer causes expansion of mercury, activation of photochemical

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If a noncontact IRED thermometer is used, contraindications to tympanic thermometry are r a r e , such as in the patient who has active hemorrhage or possible cerebrospinal fluid r h i n o r r h e a . Local inflammatory processes do not spuriously influence IRED readings in the auditory canal, 38,39 whereas oral and rectal temperatures may be factitiously elevated.14,18,24,35,40 Placement of esophageal, vascular, or b l a d d e r thermistors requires a cooperative or sedated patient, and these sites generally are unsuitable for many patients.35,39 Insertion of a noneontact probe requires a minimum of patient cooperation, no undressing, and no contact with mucous membranes. With the availability of IRED devices, the tympanic membrane may be the current ideal site for t e m p e r a t u r e measurement.

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ANNALS OF EMERGENCY MEDICINE 21:12 DECEMBER1992

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compounds, or a response of a thermistor or thermocouple. Implicit in this heat transfer is a requirement for equilibration time and tissue contact with the body site of interest. 1,5 Equilibration times are critical for accuracy with mercuryin-glass thermometers. 13 Adequate equilibration times for oral, rectal, and axillary readings are seven, three, and ten minutes, respectively. 13,14,35,42 Used in the predictive mode, electronic digital thermometers generally require 30 seconds for oral or rectal t e m p e r a t u r e measurement.36, 42 By plotting temperature versus time points, this method estimates the equilibration point and thus predicts temperature. The pre¢lictive mode may yield less accurate t e m p e r a t u r e readings because it assumes an idealized model of heat transfer between the probe and tissue sites. The more accurate monitoring mode is frequently avoided in clinical practice because of the additional equilibration time required. Placing thermocouples against the tympanic membrane provides a very accurate measure of the t e m p e r a t u r e of arterial blood supplying the hypothalamus 5,20,22,24,28,37,47,48 However, largely because of patient discomfort and the risk of tympanic membrane perforation, this method remains in limited use in anesthesia and t e m p e r a t u r e research. Devices using IRED thermometers do not require equilibration or tissue contact because their sensors collect sufficient infrared emissions from the site of interest in seconds. Infrared emission detection devices that can accurately measure tympanic membrane temperature may soon replace other thermometry methods because of their advantages over traditional methods.

Figure 5. Effect of cooling to 5 C, upper panel, and 15 C, middle panel, and warming to 50 C, lower panel, both common carotid arteries on temperatures of the brain, tympanic membrane, and rectum. 27

The body dissipates heat by conduction, evaporation, convection, and radiation. Radiation of electromagnetic waves in the form of infrared emissions is responsible for approximately 60% of the body's heat 10ss.6,49, 5° The tympanic membrane, like other body sites, emits infrared radiation in proportion to its temperature. Enough infrared energy can be detected in a fraction of a second to allow a determination of temperature. Clinical studies have demonstrated a linear relationship between IRED tympanic readings and body t e m p e r a t u r e measured with thermistors or mercuryin-glass thermometers at rectal, 51-56 pulmonary arterial,Z1, 52 sublingual,S3, 57 and axillary sites.58, 59 The various operational components of a typical, current IRED tympanic thermometer are illustrated (Figure 6). I n f r a r e d emissions pass through a probe cover, window, and b a r r e l , or wave guide, after a pushbutton is activated. The infrared sensor detects heat flow or level by collecting emissions in a short time. The signal passes to an analog-to-digital converter, then a microprocessor, and finally a digital display. There are considerable variations in how manufacturers have designed the field-of-view of the sensor, the size of the front window, and the mathematical algorithm that determines the digital display value. Some manufacturers

Figure 6. Diagram of representative infrared (IR) emission detection thermometer. A/D is analog-to-digital converter and F~Pis microprocessor.

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TEMPERATURE ASSESSMENT Terndrup

adjust IRED readings for ambient temperature effects by incorporating a sensor output into the algorithm. The advantages to IRED devices over traditional thermometers are rapidity of results, efficiency, patient comfort, lack of external influence (eg, hot or cold liquid ingestion, tachypnea, gum chewing), no mucous membrane contact, minimal contraindications, noninvasive procedure, preservation of patient modesty, and a minimal risk of disease transmission.S0,61 When nurses' time, diaper changes, and gloves are considered in the cost of rectal temperature measurement, the costs of IRED tympanic thermometery are considerably less than rectal. 58 In one study, 62 nurses' time alone was more expensive with either mercury-in-glass or digital electronic methods compared with all costs for IRED tympanic temperature measurements during one year. Current disadvantages of IRED devices are that many health professionals are unfamiliar with their use and the interpretation of results. Similar to other methods, current devices are operator dependent, requiring careful placement for acceptable accuracy. 57 Definition of normal and abnormal IRED tympanic temperature ranges has not been done, requiring conversion of readings to an oral, rectal, or core equivalent value. Attempts to use these "offsets" (ie, a value added to actual IRED readings), linear regression, and other mathematical derivatives of IRED tympanic readings have led to some problems with accuracy when related to a reference temperature value. 59,63,64 It is presently unclear if the inaccuracy lies in the reference or in the IRED tympanic temperature, or if both are acceptably accurate and the d/f-

ferences are difficult to interpret. As use of IRED devices becomes more widespread and clinical experience increases, these limitations should become less problematic. SIGNIFICANCE

OF T E M P E R A T U R E

ELEVATION

Fever is an abnormal elevation of body temperature. Through various chemical mediators, the hypothalamic thermostat is reset to a higher level. 3 Clinicians generally recognize the importance of detecting fever and that there is no absolute temperature value to represent it. The presence or absence of fever and its significance rest both in the patient's clinical condition and the site of temperature measurement. Oral temperatures of more than 37.6 C and rectal temperatures of more than 38.3 C are generally accepted cutoffs for fever.l, 65,66 Esophageal, central vascular, and tympanic temperatures probably represent core temperature, but these temperatures may still vary by as much as + 0.7 C from 37.0 C during d/urinal changes. 1,3,5 Abnormal values represent physiologic and statistical deviations from acceptable norms, as well as abnormalities from disease processes. 66 Elevation of body temperature can be caused by nonpathologic factors, including exercise, d/urinal variation, ovulation, pregnancy, inflammation at the site of body temperature measurement, and ingestion of hot liquids. 3,6,46 Depression of body temperature readings may be caused by cool ambient temperature exposure, poor probe placement technique, inadequate equilibration times, and poorly calibrated thermometers. Patients who appear to be well with an abnormally elevated or depressed body temperature must

Table 1. Clinical studies of~RED tympanic thermometers Setting*

No.

Age G r o u p

Reference t

Correlation

Sensitivity

OP50 140 Children R 0.80 92% ICU51 260 Adults R, PA 0.98 NR~ Ward 58 107 Adults R 0.90 NR OP58 22 Adults R, 0 NR NR EDe3 1t3 Children R, 0 0.77/0.75 29% EDe4 102 Children R/OIl 0.76 NR ED54 411 Adults R, 0 0.90/0.78 NR 0P TM 62 Children T 0.91 NR OP53 964 Children R/0 NR 79% ED39 251 Children R 0.79 NR NUR76 31 Newborns R, A, T NR NR ED59 224 Children R, A 0.81 55% ICU52 190 Adults R, PA 0.74 NR EDso 303 Child ren R 0.70 68/83% ED5s 184 Children R 0.87 80% 0P 5e 137 Children R, 0 0.77 NR OP57 151 Children O, A NR 84/84% NUR el 22 Newborns A 0.70 NR OP72 21 Adults R, 0 NR NR Ward 60 Adults 0 0.85 NR *Ward, hospital ward; OP, outpatient; NUR, nursery. tTemperature used as reference: R, rectal, PA, pulmonaryartery thermistor; 0, oral; A, axillary; T, tympanic. *Equals averagevalues for reference minus IREDtemperatures, in calibration mode, C. Values in brackets have no IREDthermometer mode reported. §Not reported. IITwo instrumentswere compared.

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Reported Site Difference* [+0.3], [+0.3] -0.2 [+0.3], [-1.0] [+0.76], [+0.53] [-0.31] [+0.005] NR [+0.08] +0.4 -0.25, +0.26, +0.35 [+0.61], [-0.81] +0.5, +0.1 + 0.4/0.0 NR +1.1, +0.2 +0.9/+0.77, +0.2/+0.07 +0.15 +1.5, +0.8 +0.67

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TEMPERATURE A S S E S S M E N T Terndrup

be queried for the presence of one or more of the above factors. Elevation of body temperature also may represent the presence of disease, both benign and serious. Determining whether it is benign or serious is a frequent clinical problem requiring thoughtful evaluation. Likewise, both normal and abnormal body temperatures can be measured with IRED tympanic thermometers. At present, little information is available about normal, unadjusted IRED tympanic temperature. Most clinical studies using these devices have used mathematical offsets added to actual IRED readings in order to predict body temperature at more traditional locations, such as the mouth and rectum. Data on normal tympanic temperatures in various age groups using actual IRED readings are urgently needed. This information will eliminate the need for the addition of offsets to actual IRED readings, which probably are not the same for all age groups or individuals (Table 1). Prediction of abnormal body temperature using tympanic IRED measurements then can be done without dependence on interpretation of derived oral, rectal, or core body temperature estimates. CLINICAL STUDIES THERMOMETERS

OF

IRED

TYMPANIC

Many clinical studies of IRED tympanic thermometers have been published (Table 1). Unfortunately, many published studies have failed to report equipment calibration, s t a n d a r d ization of thermometer operation (including the mode of operation, duration, and placement of thermometer probes), training of personnel, and use of a potentially inaccurate reference or "gold s t a n d a r d " temperature. Most studies have been unblinded or uncontrolled, introducing o p e r a t o r and investigator bias in interpreting results. In studies using

IRED thermometers to detect fever, various cutoffs for lower limits of fever have been used, with some studies not adjusting for normal body site temperature differences. In reporting results, investigators have used correlation, linear regression, sensitivity, specificity, predictive values, receiver operating characteristic curves, and offsets to describe their data. Despite the limitations in design, most studies have shown a linear relationship between IRED thermometry and reference temperatures, with correlation coefficients of approximately 0.75 for children and 0.95 for adults (Table 1). Unfortunately, when the mode of IRED thermometer operation is not r e p o r t e d , it is impossible to compare studies. The mode of IRED thermometer operation is important because adjustments or offsets generally are a d d e d to the actual tympanic IRED readings to estimate body temperature elsewhere, such as in the mouth or rectum. These offsets vary considerably among manufacturers, from + 0.3 to 0.78 C for oral to + 0.72 to 1.15 C for rectal, and may be a source of systematic e r r o r if offsets have been determined arbitrarily. 67 If offsets are used, it is imperative that they be based on trials that include various clinical settings, age groups, and reference temperatures. F u t u r e trials of IRED thermometers should r e p o r t u n a d j u s t e d readings (ie, with no offset) to facilitate comparison of results. In evaluating clinical trials in which adequate information is available on equilibration times and mode of thermometer operation, results indicate a very good relationship between various reference and IRED thermometers. Kenney et a153 found little or no difference in temperature measurement by IRED thermometers compared with glass-mercury thermometers in 964 pediatric patients. This was true for both oral (mean difference, 0.08 C) and rectal (0.05 C) measure-

Table 2. Current/RED tympanic~ear thermometers

Manufacturer Temperature range* Read modes+ Response time Repeat temperature time Continuous mode Charge use time

lsffemp2000A ®

Genius®~

Diatek7000®~

Ototemp+M3000~

ThermoscanProl T M

CoreCheck+M~

Intelligent Medical Systems 20-44 C 0, R, C, Cal, S 2 sec 20 sec Yes 10 hr

IMS

Diatek

Exergen

Thermoscan

IVAC

16-44 C 24-42 C 16-54 C 26-42 C 25-43 C 0, R, C, Cal, S O, R, T, S T O, R, C, T C 1-2 sec 2 sec 5 sec < 2 sec 3 sec 10 sec 8 sec 6 sec 10 sec Immediate Yes Yes No No No 5,000 20,000 5,000 10,000 8,000 temperatures temperatures temperatures temperatures temperatures Warranty (yr) 1 1 1 1-3 1 3 Antitheft No No No No Yes Yes List price $595 $495 $595 $699 $425 $695 Probe covers* $75 $75 $50 $40 $69 $75 Offsets§ O, 0.4; R, 0.8; 0, 0.8; R, 1.4; O, 0.44; None 0, 03; R, 1.15; --II C, 0.94 C, 1.3 R, 0.74 C = 0.74 *All thermometers listed meet American Society for Testing and Materials standards + 0.1 C. tO, oral; R, rectal; C, core; Cal, calibration; T, tympanic; S, surface. ~Price per thousand. {Numerical value added to unadjusted tympanic membrane reading, in C. II Manufacturer restricts availability of this information and uses a variable offset. ~6eniua® (Intelligent Medical Systems); Diatek700O® (Biatek Corporation, San Diego, California); 0toternpT%000(Exergen Corporation, Boston, Massachusetts); CoreCheck (IVAC Corporation, San Diego, California). TM

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ments. Similarly for aduhs, Green et a154 found nearly no difference between rectal and IRED tympanic (0.005 C) measurements. Although equilibration times are not reported, Muma et a159 found much larger differences between rectal and IRED tympanic measurements in 224 children younger than 3 years old. Their reported sensitivity for fever detection of 55% and specificity of 100% suggest that the rectal offset was too low or that operators were poorly trained. Emergency physicians are more inclined to use a test with better sensitivity and are more willing to sacrifice some specificity. The sensitivity of fever screening studies would be improved to much more appealing values by the use of a larger offset. Several investigators have observed that o p e r a t o r technique has a significant influence on results.ST,S8,68 Unless operators p e r f o r m IRED readings in a s t a n d a r d fashion, comparison is difficult. Because ambient t e m p e r a t u r e affects auditory canal 69-71 and IRED readings, 72,73 u n r e p o r t e d ambient variance is also confounding. When patients have rapidly increasing body temperatures, using a rectal measurement as the reference t e m p e r a t u r e may underestimate actual body t e m p e r a t u r e and lead to falsely low sensitivity for fever detection and reduced correlation. Also, when body t e m p e r a t u r e is changing, if temperatures to be compared are obtained at different times, additional errors are introduced. Now that new IRED thermometers are being introduced, additional difficulty in comparing performance occurs. These thermometers may use different methods of calibration, offsets for body site equivalence, and I R E D sensors, and their microprocessors handle IRED readings in different ways (Table 2). F o r example, the lstTemp2000A ® (Intelligent Medical Systems, Carlsbad, California) probe tip is preheated to a constant t e m p e r a t u r e before each I R E D reading, whereas the T h e r m o s c a n P r o l (Thermoscan, Inc, San Diego, California) p r o b e tip is calibrated against ambient temperature. In addition, offsets for the different manufacturers and devices vary considerably. Comparison of performance of devices for fever screening may be accomplished by using receiver operating characteristic curves with the devices in the same operating mode against a common reference temperature. 6° The device with the best performance is suggested by a larger area u n d e r the curve when sensitivity is plotted against 1-specificity. Other factors, such as ease of operation, on-screen directions, short repeat time between measurements, cost, and technical support, p r o b a b l y will dictate purchase choices as well. Several investigators have examined the impact of acute otitis media and cerumen on the accuracy of IRED tympanic thermometry. In an unblinded, uncontrolled study of 62 children with unilateral acute otitis media, infected ears were an average of 0.09 C warmer than uninfected ears. 74 A larger single-blind trial found that differences between the IRED temperatures of infected and uninfected ears (0.1 C) were not large enough to interfere with accuracy. 39 Other authors also have concluded that acute otitis media does not TM

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significantly influence IRED thermometry.S3,ss,s6, s9,Ts Similarly, the presence of nonobstructive cerumen does not h a m p e r accuracy of tympanic thermometry with IRED devices.55,58,59,68 Newborns a p p e a r to have a smaller difference between IRED tympanic and oral, rectal, and axillary temperatures (Table 1). P a r t i c u l a r l y in newborns, the smaller differences in t e m p e r a t u r e readings among different body sites may be due in p a r t to the thermally protected enviromnent in which the studies normally are completed and a more homogeneous body temperature.61, 76 In addition, the correlation between IRED tympanic temperatures and those at other body sites is smaller in children than in adult subjects. Relatively large probe tip size may increase the likelihood of cooler auditory canal emission contamination of IRED tympanic readings in smaller patients. The "gold s t a n d a r d " or reference temperature used to assess accuracy is critical to interpretation of clinical studies of IRED tympanic t e m p e r a t u r e measurements. If reference temperatures are inaccurate, then spurious sensitivity and specificity values for IRED tympanic measurements of actual body t e m p e r a t u r e will be reported. If more than one reference t e m p e r a t u r e site is used, then correction for normal differences in sites must be done before data can be pooled. 53 The reference t e m p e r a t u r e of choice for IRED tympanic studies is obtained with a p r o p e r l y calibrated tympanic thermistor. This eliminates the impact of using two different sites of t e m p e r a t u r e measurement when comparing IRED readings to a reference. The only such study published to date is one of 31 newborns, 76 which found that IRED tympanic (lstTemp2000A ®, calibration mode) measurements were 0.35 C less than thermistor tympanic. Additional studies with tympanic thermistors are required for further validation of IRED thermometry with various age groups and thermometers. By using the same body site as a reference temperature, comparison of devices is performed more reliably, because the confounding influence of local site effects is eliminated. The p r o p e r conceptual technique of IRED thermometers is to aim at the warmest area of the tympanic membrane, the anterior, inferior third. 37 Detection of infrared emissions from the cooler areas of the auditory canal 23,48,71 p r o b a b l y will lead to falsely low values. Investigators have demonstrated the importance of o p e r a t o r handedness and an ear "tug" in reproducibility.58,61, 68 Right-handed operators should take right-sided IRED tympanic measurements. By gently retracting the external ear superiorly and posteriorly while aiming the probe at the midpoint between the ear and the eyebrow, consistent results can be obtained. If ear retraction is not used, the likelihood of contamination by cool air from the auditory canal is increased and IRED readings may be falsely low. IRED tympanic thermometers have been shown to be easy to use with excellent reproducibility and good acceptance by children and parents, to be unaffected by factors influencing oral temperatures, and to be a better indicator of rectal t e m p e r a t u r e than oral thermometers in adnhs. 53-58,77-79

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I

CURRENT

IRED

TYMPANIC

MEMBRANE

THERMOMETERS

At the time of this writing there are six marketed IRED tympanic membrane devices available in the United States (Table 2). Various features of the instruments are presented for comparison, including temperature range, mode of operation, response times, and some special features. A recent comparison of these devices showed that significant increases in IRED tympanic temperatures occur when standard otoscopic technique is used to straighten the auditory canal. 80 In addition, substantial differences in measured tympanic infrared emissions between devices were shown when they were used in an unadjusted mode. Thus, performance of IRED thermometers is dependent on both operator technique and device. It is likely that additional models will become available and that current models will be improved as clinical experience widens. It is crucial to the development of IRED tympanic thermometry that controlled, well-designed studies are done with calibrated, properly placed thermometers. Performance cannot be compared unless investigators and manufacturers demand that controlled, clinical trials be performed. FUTURE

OF

IRED

TYMPANIC

MEMBRANE

THERMOMETRY

Clinicians should expect increasing lay and professional use. Emergency department visits from parents wielding overthe-counter IRED thermometers on sleeping or sick children will be increasingly common. Estimates that up to 60% of temperatures will be obtained with IRED technology by the mid-1990s have been made (Lyman LW, Diatek Corporation news release). A model recently has been released for home use and apparently met with considerable interest. Knowledgeable clinicians familiar with the advantages and limitations of IRED thermometers will be well positioned to provide professional guidance. Increasing demands from patients for convenience, modesty, and cleanliness, as well as nursing demands for rapidity of results, noninvasiveness, and safety, will drive thermometry choices. Controlling practice costs will consider not only instrumentation but also nursing time, gloving, diaper changes, and other factors implicit in traditional temperature measurement techniques. Furthermore, IRED devices will be improved for human thermometry. Modification of infrared emission sensors and microprocessors that enhance tympanic membrane IRED measurements, while restricting the impact of nontympanic membrane infrared emissions on the final digital readout, may become possible. Uncontaminated tympanic membrane IRED readings probably will enhance sensitivity, specificity, and predictive values for fever detection because auditory canal signals dampen IRED flux. Normative data for healthy, afebrile subjects of various age groups on unadjusted IRED tympanic membrane read-

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ings will be available soon from a large, multicenter trial. These data will allow direct use of tympanic membrane IRED readings to determine normal or abnormal body temperature without using correction factors or other mathematical derivatives of IRED readings to determine an estimate of body temperature at more traditional locations. Bioengineering guidelines also have recently suggested that chnicians learn the normal ear temperature instead of relying on an offset to relate the measurement to a more familiar temperature. 79 Devices will become less operator dependent and will be configured to display continuous or frequent repeat IRED readings. Clinical settings in which IRED thermometers will become increasingly valuable include physicians' offices, hospital wards, anesthesia suites, outpatient surgery centers, nursing homes, day care facilities, EDs, ICUs, and virtually anywhere temperatures are monitored. Perhaps the largest market for the future use of IRED thermometers is in the home, where parents and their children will enjoy the advantages and convenience of IRED tympanic tbermometry. REFERENCES 1. DuBois EF: The many different temperatures of the human body and its par~s. WestJ Surg 1951;59:476-490. 2. Bazett HC, Love L, Newton M, et ah Temperature changes in blood flowing in arteries and veins in man. JApplPhysio11948;1:3-19. 3. Cranston Wh Temperature regulation. Br Med J 1966;2:69-75. 4. Gerbrandy J, Snell ES, Cranston WI: Oral, rectal, and esophagealtemperatures in relation te central temperature control in man. Clin Sci 1954;13:615-624. 5. Banzinger TH: Heat regulation: Homeostasis of central temperature in man. Physiol Rev 1969;49:671-759. 6. Hardy JD, DuBois EF: Basal metabolism, radiation, convection, and vaporization at temperatures of 22-35%. J Nutr 1938;15:477-497. 7. Hayward JN, Baker MA: Role of cerebral arterial blood in the regulation of brain tern perature in a monkey. Am J Physiel 1988;215:389-403. 8. Benzinger TH: Peripheral cold and central warm reception, main origins of human thermal discomfort. Proc Nail Acad Sci1953;49:832-839. 9. Banzinger TH: The dimunitJon of therrnoregulatory sweating during cold reception of the skin. Proc Natl Acad Sci1961;47:1683-1688. 10. Benzinger TH, Pratt AW, Kitzenger C: The thermostatic control of human metabolic heat production. Proc Natl Acad Sci1961;47:730-739. 11. Sugarek NJ: Temperature lowering after ice water: Enhanced effects in the elderly. JAm Geriat Soc 1986;34:526-529. 12. Tandberg D, Sklar D: Effect of tachypnea on the estimation of body temperature by an oral thermometer. N Engl J Mad 1983;308:945-946. 13. Erickson R: Thermometer placement for oral temperature measurement in febrile adults. Int J Nuts Stud 1976;13:199-208. 14. Erickson R: 0ral temperature differences in relation to thermometer and technique. Nuts Res 1980;29:157-164. 15. Buck SH, Zaritsky AL: Occult core hyperthermia complicating cardiogenic shock. Pediatrics 1989;83:782-784. 16. Mead J, Bonmarito CL: Reliability of rectal temperatures as an index of internal body temperature. J App/ Physio/1949;2:97-109. 17. Graysen J: Observations on the temperature of the human rectum. BrMed J 1951;2:1379-1392.

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19. Eichna LW, Berger AR, Rader B, et ah Comparison of intracardiac and intravascular temperatures with rectal temperatures in man. J Clin Invest 1951;30:353-359.

46. Lewinter JR, Terndrup TE: Assessment of vital signs, in Roberts JR, Hedges JR (eds): Clinical Procedures in EmergencyMedicine, ed 2. Philadelphia, WB Saunders, 1991, p 432-444.

20. Nadel ER, Horvath SM: Comparison of tympanic membrane and deep body temperatures in man. Life Sci1970;9:869-875. 21. Whitby JD, Duncan LJ: Cerebral, esophageal, and nasopharyngeal temperatures. Br J Anesth 1971;43:673-676. 22. Nicholson RW, Iserson KB: Core temperature measurement in hypovelemic resuscitation. Ann Emerg Med 1991;20:62-65.

47. Cabanac M, Germain M, Birnel H: Tympanic temperatures during hemiface cooling. Eur J Appl Physio11987;56:534-539. 48. Greenleaf JE, Castle BL: External auditory canal temperature as an estimate of core temperature. J Appl Physio11972;32:194-198. 49. Wilson RD, Knapp C, Draper DL, et al: Tympanic thermography: A clinical and research evaluation of a newtechnique. South MedJ 1971;64:1452-1455.

23. Sharkey A, Elliett P, Lipton JM, et ah The temperature of the air within the external auditory canal compared with esophageal temperature during anesthesia and surgery. J Therm Bio11987;12:11-13.

50. Hughes w-r, Patterson GG, Thornton D, et el: Detection of fever with infrared thermometry: A feasability study. J InfDis 1985;152:301-306.

24. Benzinger M, Benzinger PH: Tympanic clinical temperature. Presented atthe Fifth International Symposium on Temperature, Washington, DC, June 1971, p 2089-2102.

51. Shinozaki T, Dean R, Perkins FM: Infrared tympanic thermometer: Evaluation of a new clinical thermometer. CritCare Med1988;16:148-150.

25. Benzinger M: Tympanic thermometry in surgery and anesthesia. JAMA 1969;209:1207-1211.

52. Milewski A, Ferguson KL, Terndrup TE: Comparison of pulmonary artery, rectal, and tympanic membrane temperatures in adult intensive care unit patients. Clin Pediatr 1991;S:13-16.

26. Molnar GW, Read RC: Studies during open heart surgery on the special characteristics of rectal temperature. J Appl Physio11974;36:333-336. 27. Tanabe K, Takaori S: Effects of cooling and warming of the common carotid arteries on the brain and tympanic membrane temperatures in the rabbit. Jpn J Pharmacol 1964;14:67-79. 28. Shiraki K, Konda N, Sagawa S: Esophageal and tympanic temperature responses to core blood temperature changes during hyperthermia. JAppl Physio11986;61:98-102. 29. Martin PA, Robins HI, Dennis WH: Monitoring body site temperatures during systemic hyperthermia. Crit Care Med 1987;15:163-164. 30. Webb GE: Comparison of esophageal and tympanic temperature monitoring during cardiopulmonary bypass, J Int Anesth Res Soc 1973;52:729-733.

53. Kenney RD, Fortenberry JD, Surratt SS, et al: Evaluation of an infrared tympanic membrane thermometer in pediatric patients. Pediatrics 1990;85:854-858. 54. Green NM, Danzl DF, Praszkier H: Infrared tympanic thermegraphy in the emergency department. J Emerg Med 1989;7:437-440. 55. Chamberlain JM, Grandner J, Rubinoff JL, et ah Comparison of a tympanic thermometer to rectal and oral thermometers in a pediatric emergency department. Clin Pediatr 1991;S:24-29. 56. Tale H, Macknin ML, Medendorp SV: Tympanic membrane temperatures compared to rectal and oral temperatures. Clin Pediatr1991;S:30-33.

31. Schiffman RF: Temperature monitoring in the neonate: A comparison of axillary and rectal temperatures. Nuts Res 1982;131:274-277.

57. Shenep JL, Adair JR, Hughes WT, et al: Infrared, thermistor, and glass-mercury thermometry for measurement of body temperature in children with cancer. Clin Pediatr 1991;S:36-41.

32. Kresch M J: Axillary temperatures, a screening test for fever in children. J Pediatr 1984;104:596-599.

58. Weiss ME: Tympanic infrared thermometry for full-terrn and pre-term neonates. Clin Pediatr 1991;S:40-45.

33. Lawit EM, Marshall CL, Salzer JE: An evaluation of a plastic strip thermometer. JAMA 1982;247:321-325.

59. Muma DK, Treloar DJ, Wurmlinger K, etal: Comparison of rectal, axillary, and tympanic membrane temperatures in infants and young children. Ann Emerg Med 1991;20:41-44.

34. Ilsley AH, Ruten A J, Runciman WB: An evaluation of body temperature measurement. Anesth Intens Care 1983;11:31-39. 35. Norris J: Taking temperatures: Changing state of the art. Contemp Pediatr1985;2:22-39.

60. Terndrup TE, Milewski A: The performance of two tympanic thermometers in a pediatric emergency department. Clin Pediatr 1991;S:18-23.

36. Hirata K, Nagasaka T, Noda Y, et al: Finger vasodilation correlates better with tympanic than esophageal temperature. EurJApplPhysio11988;57:735-739.

61. Terndrup TE, Allegra JR, Kealy JA: A comparison of oral, rectal, and tympanic membrane derived temperature changes after ingestion of liquids and smoking. Am J Emerg Med 1989;7:150-154.

37. Brinnel H, Cabanac M: Tympanic temperature is a core temperature in humans. J Therm Bio11989;14:47-53.

62. Alexander DT, Kelly BA: Cost effectiveness of tympanic thermometry in the pediatric office setting. Clin Pediatr 1991;S:57-61.

38. Fisch RO, Eaton BG, Giebink 6S: Tympanic membrane temperature during experimental etitis media due to streptococcus pneumonia in chinchillas. LabAnimal Sci1982;32:278-279.

63. Rhoades FA, Grandner J: Assessment of aural infrared sensor for body temperature measurement in children. Clin Pediatr1990;29:112-115.

39. Terndrup TE, Wong A: Influence of otitis media on the correlation between rectal and auditory canal temperatures. Am J Dis Child 1991;145:75-78. 40. Smith L, Prince HN, Johnson E: Bacteriologic study on electronic hospital thermometers. J Infect Cent 1981;2:315-316. 41. Greenbaum El, Carson M, Kincannon WN, etal: Rectal thermometer induced pneumoperitoneum in the newborn: Report of 2 cases. Pediatrics 1969;44:539-542. 42. Knapp HA: Accuracy of glass clinical thermometers compared to electronic thermometers. Am J Surg 1966;112:139-141. 43. Abbey JC, Anderson AS, Close EL, et al: How ]ong is that thermometer accurate? Am J Nurs 1978;78:1375-1376. 44. Valenti WM, Takacs KM: Infection control in clinical thermometry: Perforation of soft plastic thermometer sheaths during temperature measurement. Am J Infect Cent 1981;9:1-5.

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64. Ros SP: Evaluation of a tympanic membrane thermometer in an outpatient clinical setting. Ann Emerg Med 1989;18:1004-1006. 65. van der Bogert F, Moravec CL: Body temperature variations in apparently healthy children. J Pediatr1937;IO:466-471. 66. Ivy AC: What is normal or normalit,/? Q Bull N Univ Med Sch 1944;18:22-32. 67. Nierman DM: Core temperature measurement in the intensive care unit. Crit Care Med 1991;19:818-823. 68. Pransky SM: The impact of technique and conditions of tympanic membrane upon infrared tympanic thermometry. Clln Pediatr 1991;S:50-52. 69. McCaffrey TV, McCook RD, Worster RD: Effect of head skin temperature on tympanic and oral temperature in man. JApplPhysio11975;39:114-118. 70. McCaffrey TV, Geiss GS, Chung JM, et al: Effect of isolated head heating and cooling on sweating in man. AviatSpace Environ Mad 1975;46:1353-1357.

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71. Morgans LF, Nunnelly SA, Stribley RF: Influence of ambient and core temperatures on the auditory canal temperature. AviatSpace Environ Meal 1981;52:291-293. 72. Zehner W J, Terndrup TE: The impact of moderate ambient temperature variance on the relationship between oral, rectal, and tyrnpanic membrane temperatures, Olin Pediatr 1991;S:62-64. 73. Fraden J, Lackey RP: Estimation of body site's temperatures from tympanic measurements. Clin Pediatr 1991;S:65-70.

Address for reprints: Thomas E Terndrup, MD, FACEP Department of Emergency Medicine SUNY Health Science Center at Syracuse 750 East Adams Street Syracuse, New York 13210

74. Weir M R, Weir TE: Are "hot" ears really hot? Am J Dis Child 1989;143:763-764. 75. Kelly B, Alexander D: Effect of otitis media on infrared tympanic thermometry. Clin Pediatr 1991;S:46-48. 76. Johnson KJ, Bhatia P, Bell EF: Infrared thermometry of newborn infants. Pediatrics 1991;87:34-38. 77. Barber N, Kilmon CA: Reactions to tympanic temperature measurement in an ambulatory setting. Pediatr Nurs 1989;15:477-481. 78. Alexander D, Kelly B: Responses of children, parents, and nurses to tympanic thermometry in the pediatric office. Clin Pediatr1991;S:53-56. 79. Anonymous: Infrared ear thermometry. Health Devices 1991;20:431-436. 80. Terndrup TE, Rajk J: Impact of operator technique and device on infrared emission detection tympanic thermometry. J Emerg Med 1992 (in press). 81. Erickson RS, Yaunt ST: Comparison of tympanic and oral temperature in surgical patients. Nurs Res 1991;40:90-93.

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