The Effect of Ambient Temperature Extremes on Tympanic and Oral Temperatures FRANCES DOYLE, MD,* W. JOHN ZEHNER, MD,t THOMAS E. TERNDRUP, MD* Exposure to ambient temperature extremes immediately preceding emergency department triage may affect tympanic membrane temperatures taken with infrared emission detection thermometers. In a prospective, unblinded study, 20 healthy subjects, on 2 separate days, underwent lbminute exposures to hot (43.5%) and cold (-5°C) temperature extremes In an environmental control room (Et%). Tympanic and oral temperatures were taken at baseline and at r-minute intervals for 20 minutes after exiting the ECR. Rectal temperatures remained stable during the exposures. Oral temperatures rose significantly after hot exposure (P < .05; max 0.4%) and briefly decreased alter cold exposure (max 0.5%). Tympanic temperatures were elevated for 20 minutes after hot exposure (max 0.8%) and decreased briefly only in male subjects after cold exposure (max 0.7%). Individuals demonstrated wide variability in their temperature responses. Tympanic and oral temperatures taken within the first 20 minutes after exposure to outdoor temperature extremes may fall to accurately reflect the patient’s true temperature. (Am J Emerp Med 1992;10:285-289. Copyright 0 1992 by W.8. Saunders Company) Accurate temperature measurement is necessary for patient assessment.“’ Abnormalities of body temperature serve as independent predictors of disease severity and frequently dictate the need for further evaluation and treatment.3 In outpatients, temperature measurements are most commonly obtained from oral or rectal sites using mercuryin-glass or electronic thermistor probes. However, oral temperatures are spuriously affected by recent liquid ingestion4 probe placement,5*6 equilibration time,’ ambient temperature,8V9 smoking, and tachypnea.“,” Rectal temperatures, while indicative of core under stable body temperature conditions, may be inaccurate when body temperature is changing rapidly. ” In addition, patient issues such as convenience, modesty, rectal perforation, and invasiveness, as well as nursing staff issues such as exposure to rectal microorganisms, added time required for undressing, contraindications, and mucous membrane exposure limit the applicability of rectal temperature measurement.2.4 A thermistor in contact with the tympanic membrane accurately reflects brain temperature because the preoptic area of the hypothalamus, or temperature control center, shares a common blood supply with the tympanic membrane from branches of the internal carotid artery.12*13 Multiple studies From the “Department of Emergency Medicine, St Joseph’s Hospital and Health Center, Syracuse, NY; and the Departments of TEmergency Medicine and *Pediatrics, State University of New York Health Science Center at Syracuse, Syracuse, NY. Manuscript received September 10, 1991; revision accepted January 8, 1992. Supported in part by Thermoscan Inc, San Diego, CA. No reprints available. Key Words: Tympanic temperature, ambient temperature, body temperature measurement, emergency department triage. Copyright 0 1992 by W.B. Saunders Company 0735-8757/92/l 004-0003$5.00/O
have indicated that tympanic membrane temperature is a better indicator of brain temperature than rectal14,15 or esophageal temperature. I5316Previous studies using tympanic thermistors show an excellent correlation with esophageal temperatures, 12,17-19but tympanic measures are generally lower than esophageal. Recent studies have shown that noncontact infrared emission detection (IRED) tympanic thermometers correlate in a linear fashion with temperature measurements from ora1,3*15~20‘23 recta1,20-22.24-26 pulmonary artery,26.27 and axillary3 sites. Tympanic IRED thermometers do not require mucous membrane contact or equilibration times since only seconds are required to obtain sufficient information for a reading. Although IRED readings are unaffected by recent liquid ingestions,4 respiration,’ and smoking,4 ambient temperatures influence auditory canal measurements28-32 and thermistor tympanic measurements33-35 and thus may influence IRED readings. In many emergency departments (EDs), initial temperature measurements are performed in triage, usually shortly after arrival. If the patient comes inside from an ambient temperature that is either excessively warm or cold, IRED tympanic thermometry may be spuriously affected. The purpose of this study was to determine if a brief exposure to ambient temperature extremes would significantly influence oral thermistor or IRED tympanic temperature readings, compared with baseline values. We performed a prospective, unblinded trial in healthy adult subjects to examine the influence of cold (- YC) and hot (43.X) ambient temperature extremes on oral and IRED tympanic temperatures. In this way we attempted to determine the amount of and duration of effect on oral or tympanic temperatures. METHODS
Healthy subjects were remunerated for their participation. Subjects were excluded for fever, cerumen occlusion of the auditory canal, nonsteroidal antiinflammatory or acetaminophen use, and upper respiratory tract infections within the preceding 24 hours. In general, resting subjects equilibrated at normal ambient temperature for at least 15 minutes prior to baseline recordings. On cold exposure days, subjects wore slacks, a shirt, and shoes. They were provided with gloves and a winter coat that came below the buttocks during the extreme cold exposure. On hot exposure days, they wore shorts, a T-shirt, and shoes. The study was approved by the Institutional Review Board for the Protection of Human Subjects, and all subjects gave written informed consent. All subjects were health care workers and thus obtained their own rectal and oral temperatures. They were instructed to insert the lubricated, covered, rectal probe approximately 2 inches into the rectum, and to record their temperature from the predictive mode. The sublingual posterior fold was 285
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used for all oral temperatures, and oral temperatures were obtained in either the predictive or monitor mode. Time constraints demanded that the predictive mode be used for baseline temperatures and those taken immediately after leaving the environmental control room (ECR). The investigators were experienced with IRED tympanic thermometry from a previous study. To minimize operator variability, tympanic IRED temperatures were obtained by a single investigator for individual subjects. All IRED tympanic temperatures were obtained using posterior and superior external ear retraction. Right-handed operators used the right auditory canal and left-handed operators the left. Tympanic temperatures were taken in the calibration mode. Digital electronic thermometers (Diatek 600, San Diego, CA) were used for oral and rectal measurements. An IRED device (Pro-l, Thermoscan, San Diego, CA) was used for tympanic membrane temperatures. Calibrations against a water bath over a range of 35 to 40°C demonstrated an accuracy of *O.l”C for the electronic thermometer. Calibration against a black-body (IR-3000, Thermoscan) demonstrated an accuracy of +O.l”C at 37 and 40°C for the IRED tympanic. The ECR was equilibrated overnight at either 435°C for the hot experiment or - 5°C for the cold experiment, and was validated against a mercury column thermometer. Following baseline temperature recordings, the subjects sat in the ECR at hot and then cold extreme temperature for 15 minutes for each experimental period on 2 separate days. Immediately upon leaving the ECR, subjects recorded a rectal, tympanic, and oral temperature. Subjects then recorded oral temperature and underwent tympanic IRED recordings every 2 minutes for 20 minutes. At the end of each experimental period, subjects recorded another rectal temperature. If investigators suspected spurious IRED tympanic readings, or error messages occurred, temperatures were repeated. Comparison of rectal or oral and tympanic temperatures was performed using the paired, two-tailed Student’s t-test. Comparison of the temperature at each site between baseline and experimental conditions was examined using repeat measures analysis of variance (ANOVA), with isolation of significant differences based upon Scheffe’s F test. Comparison of male and female responses was performed for oral and tympanic measures following both exposures, using repeat measures ANOVA. Significance was considered to be achieved for P < .05. RESULTS
The subjects averaged 31 -C 6.8 (mean f SD) years of age (range, 21 to 46 years). Twenty-one subjects participated in the hot experiment (11 men and 10 women) and 20 (10 men and 10 women) in the cold. All experiments were performed on March 5 and 7, 1991. Room temperature was stable during the experiment periods (20.5”C 2 0.05.) There were no complications during the study and no shivering was observed. Occasional discomfort from the prolonged insertion of the oral and repeated use of the tympanic probe were reported. At baseline, rectal temperature (37.7”C 2 0.4) was significantly greater than oral (P = .OOOl, t = 6.75; 36.9”C 2 0.5), which were both greater than tympanic (P = .OOOl, t = 12.17; 36.1”C 2 0.6). Rectal temperature changed little dur-
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ing either experimental period. No change in rectal temperature occurred following hot exposure. Rectal temperatures 20 minutes after cold exposure showed a statistically significant decrease of 0.16”C (P < .05). After hot exposure, oral temperatures were significantly elevated compared with baseline, from 8 to 20 minutes after exposure (P = .OOOl, F = 9.338; Figure 1). A transient decrease in oral temperature was observed 2 minutes after exiting the ECR. Individual responses to hot exposure varied widely. The range of oral temperatures was greatest at 8 minutes after exiting the ECR, 1.6”C (36.1 to 37.7”C). One subject’s oral temperature increased 1.2”C. and did not return to baseline at the end of 15 minutes, while another had a decrease of 0.7”C and returned to baseline within 10 minutes. Two subjects never varied their temperatures by more than O.l”C. After hot exposure, IRED tympanic temperatures increased significantly from baseline (P = .0039, F = 2.71; Figure 1) and persisted for 20 minutes. The greatest increase was immediately after leaving the ECR, +0.8”C + 0.5; range, 35.2 to 37.3”C. Individual data showed no temperature decreases at 2 minutes after exiting the ECR, as is seen with the oral temperatures. All subjects showed at least a 0.5”C increase in temperature at some time during the recording period. One subject showed a delayed temperature elevation, eventually increasing above baseline by 2°C. After cold exposure, oral temperature, compared with baseline, was significantly decreased from 2 to 4 minutes after leaving the ECR (P = .OOOl, F = 10.055; Figure 2). The greatest decrease was seen at 2 minutes after exiting the ECR, 0.5”C ? 0.5; range, 35.5 to 37.3”C. Individual data showed the greatest decrease in a female subject, - 1.3”C from baseline at 2 minutes after exiting the ECR. At 15 minutes after leaving the ECR, she was still 0.5”C below baseline. Seven subjects showed a 0.1 to 0.4”C initial increase in oral temperature before decreasing. Five subjects showed a 0.2 to 0.7”C increase in their oral temperatures, compared with baseline, at 15 minutes. Tympanic IRED temperatures were not significantly changed after cold exposure (P = .OOOl, F = 8.123: Figure 2). The greatest individual decrease in temperature was 1.7”C upon exiting the ECR. The range of tympanic IRED temperatures after cold (2.6”C) was greatest at 8 minutes.
1 36.9-
35.4! :. , baseline 0
.
I 2
, 4
.
, 6
.
, 8
, 10
, 12
.
, 14
,
, 16
, , , 18 20
Time, baseline and min after exposure
FIGURE I. Oral (circles) and tympanic (squares) temperatures, mean -t SD, at baseline and after exiting the “hot” ECR. *P < .05 compared with baseline.
DOYLE ET AL m TEMPERATURE
0 UY +I
37.0 -
E
35.5 -
EXTREMES
AND TYMPANIC
READINGS
E c
36.0 -
3 E g
35.5 -
E
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.
, 2
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~ , 6
_ ( 8
, , * , 10 12
, 14
.
, 16
~ , 18
_ , 20
1
Time, baseline and min after exposure
(circles) and tympanic (squares) temperatures, baseline and after exiting the “cold” ECR. *P < .05 compared with baseline. FIGURE 2. mean 2 SD,
Oral
at
Fourteen subjects went above their baseline at some time; one subject by 1.2”C. Male, but not female, subjects had significant reductions in tympanic IRED from 0 to 8 minutes after exiting the ECR (P = .OOOl, F = 7.011; Figure 3). In comparing males and femaIes, no differences were present for either exposure using oral responses. No differences between male and female responses were measurable for tympanic responses following hot exposure. During oral measurements, no differences were observed between temperatures taken in the monitor versus the ptedictive mode. While measuring tympanic temperatures, occasional results appeared to be spurious values. However, these measures were all repeated and confirmed to be the same reading. DISCUSSION In heaithy subjects, exposure to ambient temperature extremes results in substantial intersubject variability compared with baseline. After hot exposure both tympanic and oral temperatures rise significantly, and some temperature elevations persist for 20 minutes. Tympanic temperature demonstrates a greater initial elevation than oral temperature. Cold exposure results in decreases in oral temperature in all subjects, and tympanic temperature in males.
35.0! , . baseline 0
_ . , . 1, . , . 1, . , , 2
4
6
8
10
.
. 12
14
. , . 16
10
1 20
Time, basellne and mln after exposure
FIGURE 3. Tympanic temperatures after cold (-ST) exposure for females (open squares) and males (closed squares), mean + SD. *P < .OS compared with baseline.
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Little information is available on the effect of ambient temperature extremes on the measurement of tympanic temperature using the IRED devices. In 21 healthy adults, moderate increases in ambient temperature (ie, 35°C) elevated IRED tympanic membrane readings by 0.7”C compared with baseline (ie, temperatures taken at a room temperature of 20°C). 36 Consistent with the present study, no change in IRED tympanic temperature occurred at moderate decreases in ambient temperature (ie, 18.3”C). Temperatures were taken during the exposure in this earlier study. Tympanic thermometry using thermistors has been widely studied, and the results are in agreement with and help to explain our findings. Thermistor studies involve the placement of a bead in direct contact with the tympanic membrane, and occlusion of the auditory canal to isolate the tympanum from the environment. Isolated cooling and heating of the head, or total body exposure to cold, significantly affect thermistor tympanic temperatures37*38 with little or no effect on esophageal temperature.3g-41 Marcus showed that tympanic changes are most affected by the supraauricular scalp temperature on the side of the temperature change,34*35 and that temperature changes of the pinna do not affect thermistor tympanic readings.34 Cabanac et al showed that heating the body while cooling one side of the face with fanning causes a greater rise in the esophageal temperature compared with both tympanic temperatures.33 These results support the hypothesis of a countercurrent temperature exchange in the head, and the concept of isolated brain cooling under thermal stress.42 Arterial blood in proximity to environmentally heated or cooled venous blood sets up a countercurrent temperature exchange, which in turn affects the tympanic temperature. 33*35V3g The lack of vasoconstriction of scalp vessels may explain the diminished effect of cold exposure compared with hot exposure.33*43,44 In our study, during hot exposures we found a small but statistically significant elevation in the tympanic and oral temperatures which persisted for 20 minutes. The initial tympanic elevation was greater than the oral. After hot exposure, elevation of tympanic thermistor temperatures were also greater for tympanic than oral temperatures.31*4’945 Thermistor tympanic temperature studies also showed considerable individual variation. The early decrease in oral temperatures in our study may be explained by mouth breathing while exiting the ECR or inadequate equilibration time using the monitor mode. As in the thermistor studies, during severe cold exposure there was a decrease in oral and male tympanic temperatures. The effect was less than that seen with the hot extreme. Scalp vessels ate known to have less vasoconstrictive than vasodilatative capabilities.43’” During hot exposure vasodilation may increase local blood flow and thus temperature in the tympanic membrane, whereas cold has less influence on scalp blood flow. Infrared emission detection tympanic temperatures decreased in male, but not female subjects. Since subjects did not wear hats, the female subjects’ hair may have played a protective role in decreasing heat loss in the external auditory canal and supraauricular area. Additionally this may be a reflection of the decreased conductance of females compared with males.46 Subjects demonstrated a late increase in IRED tympanic temperature after cold exposure. Benzinger has also noted such an over-
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shoot phenomenon in thermistor studies4’ This may be due to a reflex vasodilation after the cold stress is removed. The decrease in rectal temperature, while unanticipated,48 may be explained by the cooling of the blood in the thighs and buttocks in our seated subjects.’ This difference of 0.16”C is clinically of little consequence. Tympanic thermometers using IRED have a wide angle of view even when inserted properly. This likely results in contamination of tympanic temperature measurement by auditory canal infrared emissions.49 Brinnel and Cabanac” showed that tympanic temperatures taken precisely in the anterior, inferior quarter of the tympanic membrane were unaffected by skin temperature. Previous studies using thermistors show that, while auditory canal temperatures correlate well when measuring body temperature changes, the absolute canal temperature is location-dependent.28-32 The IRED device we used controls for ambient temperature of the thermometer and corrects for auditory canal resistance, but not for canal temperature. Current IRED devices are operator-dependent.5’ The technique which produces greatest precision requires retraction of the external ear and the operator using his/her dominant hand in the same ear of the subject.3.5’ By using a single investigator to take all IRED temperatures on each subject, we minimized measurement, but not systematic, error. Temperatures taken in both ears by a single operator correlate extremely well in multiple studies.20,21,23,27 Chamberlain et al demonstrated the best linear regression fit using the maximum of three IRED tympanic temperatures.*’ We chose to take one temperature to simulate clinical IRED device operation. Frequent IRED tympanic measurements are unlikely to affect tympanic readings.3 Our study concentrates on tympanic temperature measurement as it relates to routine ED patient care. Thus, we chose not to study oral or tympanic measurements while being exposed to hot or cold temperatures. We arbitrarily chose a 15-minute exposure time to represent a typical travel time to the ED in a metropolitan area. We measured temperatures after exposure for 15 to 20 minutes to reflect the time period in which an initial triage temperature might be taken. As no significant difference between mercury in glass and electronic thermometers has been shown,‘2*53 electronic thermometers were chosen for their speed, convenience, and common clinical use. Measurements of rectal temperature were limited to baseline, time 0, and completion of the study, based on previous data that the rectal temperature should remain stable during these ambient temperature ranges.36 This study was unblinded and no exclusions were performed for medications acting as vasodilators or constrictors. This may have effected the results of one study subject. Inadequate equilibration time during oral readings after exiting the ECR may have led to falsely low initial values.337 The time of day54 and the effect of shift work on diurinal temperature was not examined in this study. The lack of acclimatization of subjects to warm temperatures may have falsely increased the temperature changes and duration of observed effects55 with hot exposure. Given a standard deviation of 0.4”C and 10 subjects in each group, with CY= 0.05 and p = 0.2, we would have needed differences of 0.5”C between males and females to reliably determine no statis-
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tical difference.56 Further studies are needed to characterize younger and older patient populations after exposure to temperature extremes.’ The effect of thermal protection afforded by a hat and acclimatization may be significant when temperature is measured using IRED tympanic thermometers. CONCLUSION This study shows substantial intersubject variability in oral and tympanic temperatures after exposure to ambient temperature extremes. Thus, during a typical ED triage time of 15 to 20 minutes, tympanic and oral temperatures may fail to accurately reflect the patient’s baseline temperature and may require repeat measurement later in the patient’s ED visit. The authors thank Thermoscan Inc for their support of this project, and Andre Pennardt, MD for help in data collection.
REFERENCES 1. Cranston WI: Temperature regulation. Br Med J 1966;2: 69-75 2. Lewinter JR, Terndrup TE: Assessment of vital signs. In Roberts JR, Hedges JR (eds): Clinical Procedures in Emergency Medicine (ed 2). Philadelphia, PA, Saunders, 1991, pp 432-444 3. Shenep JL, Adair JR, Hughes WT: Infrared, thermistor, and glass-mercury thermometry for measurement of body temperature in children with cancer. Clin Pediatr 1991;30:36-41 (SUPPI) 4. 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 5. Neff J, Ayoub J, Longman A, et al: Effect of respiratory rate, respiratory depth, and open versus closed mouth breathing on sublingual temperature. Res Nurs Health 1989;12:195-202 6. Erickson R: Oral temperature differences in relationship to thermometer technique. Nurs Res 1980;29:157-164 7. Hardy JD: Body temperature regulation. In Mountcastle VB (ed): Medical Physiology. St Louis, MO, Mosby, 1980, pp 14-18 8. Sloan REG, Keatinge WR: Depression of sublingual temperature by cold saliva. Br Med J 1975;1:718-720 9. Howell TH: Oral temperature range in old age. Gerontol Clin 1975;17:133-136 10. Tandberg WD, Sklar D: Effect of tachypnea on the estimation of body temperature by an oral thermometer. New Engl J Med 1983;308:945-946 11. Cranston WI, Gerbrandy J, Snell ES: Oral, rectal and oesophageal temperatures and some factors affecting them in man. J Physiol 1954;126:347-358 12. Benzinger M: Tympanic thermometry in surgery and anesthesia. JAMA 1969;209:1207-1211 13. Benzinger TH: On physical heat regulation and the sense of temperature in man. Physiology: Proc Natl Acad Sci USA 1959;45:645-659 14. Mellergard P, Nordstrom C: Epidural temperature and possible intracerebral temperature gradients in man. Br J Neurosurg 1990;4:31-38 15. Nicholson RW, lserson KV: Core temperature measurement in hypovelemic resuscitation. Ann Emerg Med 1991;20:8588 16. Davis FM, Barnes PK, Bailey JS: Aural thermometry during profound hypothermia. Anesth lntens Care 1981;9:124-128 17. Molnar GW, Read RC: Studies during open-heart surgery on the special characteristics of rectal temperature. J Appl Physiol 1974;36:333-336 18. Wilson RD, Knapp C, Traber DL, et al: Tympanic thermography: A clinical and research evaluation of a new technique. South Med J 1971;64:1452-1455 19. Webb GE: Comparison of esophageal and tympanic tem-
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perature monitoring during cardiopulmonarv bypass. Anesth Analg 1973;52:729-732 _ _20. Talo H. Macknin ML. Medendoro SV: Tamoanic membrane temperature compared to rectal ‘and oral temperatures. Clin Pediatr 1991;30-33 (suppl) 21. Chamberlain JM, Grandner J, Bubinoff JL, et al: Comparison of a tympanic thermometer to rectal and oral thermometers in a pediatric emergency department. Clin Pediatr 1991;24-29 (SUPPI) 22. Kenney RD, Fortenberry JD, Surratt SS, et al: Evaluation of an infrared tympanic membrane thermometer in pediatric patients. Pediatrics 1990;85:854-858 23. Weiss ME, Pue AF, Smith J: Laboratory and hospital testing of new infrared tympanic thermometers. J Clin Engin 1991; 16:137-144 24. Ward L, Kaplan RM, Paris PM: A comparison of tympanic and rectal temperatures in the emergency department. Ann Emerg Med 1988;17:435 (abstr) 25. Green MM, Danzl DF: Infrared tympanic thermography in the emergency department. J Emerg Med 1989;7:437-440 26. Milewski A, Ferguson KL, Terndrup TE: Comparison of pulmonary artery, rectal, and tympanic membrane temperatures in adult intensive care unit patients. Clin Pediatr 1991;13-16 (SUPPI) 27. Shinozaki T, Deane R, Perkins FM: Infrared tympanic thermometer: Evaluation of a new clinical thermometer. Crit Care Med 1988;16:148-149 28. Greenleaf JE, Castle BL: External auditory canal temperature as an estimate of core temperature. J Appl Physiol 1972; 32:194-198 29. Edwards RJ, Belyavin AJ, Harrison MH: Core temperature measurement in man. Aviat Space Environ Med 1978;49:12891294 30. Cooper KE, Cranston WI, Snell ES: Temperature in the external auditory meatus as an index of central temperature changes. J Appl Physiol 1964;19:1032-1035 31. Gibbons LV: Body temperature monitoring in the external auditory meatus. Aerospace Med 1967;38:671-675 32. Sharkey A, Elliott P, Lipton JM, et al: The temperature of the air within the external auditory meatus compared with esophageal temperature during anaesthesia and surgery. J Therm Biol 1987;12:11-13 33. Cabanac M, Germain M, Brinnel H: Tympanic temperatures during hemiface cooling. Eur J Appl Physiol 1987;56:534539 34. Marcus P: Some effects of radiant heating of the head on body temperature measurements at the ear. Aerospace Med 1973;44:403-406 35. Marcus P: Some effects of cooling and heating areas of the head and neck on body temperature measurement at the ear. Aerospace Med 1973;44:397-403 36. Zehner WJ, Terndrup TE: The impact of moderate ambient temperature variance on the relationship between oral, rectal, and tympanic membrane temperature. Clin Pediatr 1991;61-64 (SUPPI) 37. Livingstone SD, Grayson J, Frim J, et al: Effect of cold
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exposure on various sites of core temperature measurements. J Appl Physiol 1983;54:1025-1031 38. Nadel ER, Horvath .%I: Comparison of tympanic membrane and deep body temperatures in man. Life Sci 1970;9:869875 39. Nielsen B: Natural cooling of the brain during outdoor bicycling? Eur J Physiol 1988;411:456-461 40. McCaffrey TV, Geis GS, Chung JM: Effect of isolated head heating and cooling on sweating in man. Aviat Space Environ Med 1975;46:1353-1357 41. McCaffrey TV, McCook RD, Wurster RD: Effect of head skin temperature on tympanic and oral temperature in man. J Appl Physiol 1975;37:114-118 42. Brinnel H, Nagasaka T, Cabanac M: Enhanced brain protection during passive hyperthermia in humans. Eur J Appl Physiol 1987;56:540-545 43. Nunneley SA, Troutman SJ, Webb P: Head cooling in work and heat stress. Aerospace Med 1971;42:64-68 44. Fox RH, Goldsmith R, Kidd DJ: Cutaneous vasomotor control in the human head, neck, and upper chest. J Physiol 1962; 161:298-312 45. McCook RD, Wurster RD, Randall WC: Pseudomotor and vasomotor responses to changing environmental temperature. J Appl Physiol 1965;20:371-378 46. Hardy JD: Body temperature regulation. In Mountcastle VB (ed): Medical Physiology. St Louis, MO, Mosby, 1981, pp 1417-1456 47. Benzinger TH: Peripheral cold and central warmreception: Main origins of human thermal discomfort. Physiology: Proc Natl Acad Sci USA 1963;49:832-839 48. Gerbrandy J, Snell ES, Cranston WI: Oral, rectal, and oesophageal temperatures in relation to central temperature control in man. Clin Sci 1954;13:615-624 49. Fraden J, Lackey RP: Estimation of body sites temperature from tympanic measurements. Clin Pediatr 1991;65-70 (SUPPI) 50. Brinnel H, Cabanac M: Tympanic temperature is a core temperature in humans. J Therm Biol 1989;14:47-53 51. Pransky SM: The impact of technique and conditions of the tympanic membrane upon infrared tympanic thermometry. Clin Pediatr 1991;50-52 (suppl) 52. Riyadh Al Kharj Hospital Programme: Comparison of accuracy of digital and standard mercury thermometers. Br Med J 1983;287:1263 (abstr) 53. Knapp HA: Accuracy of glass clinical thermometers compared to electronic thermometers. Am J Surg 1966;112:139-141 54. Jeong WS, Tokura H: Circadian rhythm of rectal temperature in man with two different types of clothing. Int Arch Occup Environ Health 1990;62:295-298 55. Mitchell D, Senay LC, Wyndham CH, et al: Acclimatization in a hot, humid environment: Energy exchange, body temperature, and sweating. J Appl Physiol 1976;40:768-778 56. Young MJ, Bresnitz EA, Strom BL: Sample size nomograms for interpreting negative clinical studies. Am Intern Med 1983;99:248-251
have indicated that tympanic membrane temperature is a better indicator of brain temperature than rectal14,15 or esophageal temperature. I5316Previous studies using tympanic thermistors show an excellent correlation with esophageal temperatures, 12,17-19but tympanic measures are generally lower than esophageal. Recent studies have shown that noncontact infrared emission detection (IRED) tympanic thermometers correlate in a linear fashion with temperature measurements from ora1,3*15~20‘23 recta1,20-22.24-26 pulmonary artery,26.27 and axillary3 sites. Tympanic IRED thermometers do not require mucous membrane contact or equilibration times since only seconds are required to obtain sufficient information for a reading. Although IRED readings are unaffected by recent liquid ingestions,4 respiration,’ and smoking,4 ambient temperatures influence auditory canal measurements28-32 and thermistor tympanic measurements33-35 and thus may influence IRED readings. In many emergency departments (EDs), initial temperature measurements are performed in triage, usually shortly after arrival. If the patient comes inside from an ambient temperature that is either excessively warm or cold, IRED tympanic thermometry may be spuriously affected. The purpose of this study was to determine if a brief exposure to ambient temperature extremes would significantly influence oral thermistor or IRED tympanic temperature readings, compared with baseline values. We performed a prospective, unblinded trial in healthy adult subjects to examine the influence of cold (- YC) and hot (43.X) ambient temperature extremes on oral and IRED tympanic temperatures. In this way we attempted to determine the amount of and duration of effect on oral or tympanic temperatures. METHODS
Healthy subjects were remunerated for their participation. Subjects were excluded for fever, cerumen occlusion of the auditory canal, nonsteroidal antiinflammatory or acetaminophen use, and upper respiratory tract infections within the preceding 24 hours. In general, resting subjects equilibrated at normal ambient temperature for at least 15 minutes prior to baseline recordings. On cold exposure days, subjects wore slacks, a shirt, and shoes. They were provided with gloves and a winter coat that came below the buttocks during the extreme cold exposure. On hot exposure days, they wore shorts, a T-shirt, and shoes. The study was approved by the Institutional Review Board for the Protection of Human Subjects, and all subjects gave written informed consent. All subjects were health care workers and thus obtained their own rectal and oral temperatures. They were instructed to insert the lubricated, covered, rectal probe approximately 2 inches into the rectum, and to record their temperature from the predictive mode. The sublingual posterior fold was 285
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used for all oral temperatures, and oral temperatures were obtained in either the predictive or monitor mode. Time constraints demanded that the predictive mode be used for baseline temperatures and those taken immediately after leaving the environmental control room (ECR). The investigators were experienced with IRED tympanic thermometry from a previous study. To minimize operator variability, tympanic IRED temperatures were obtained by a single investigator for individual subjects. All IRED tympanic temperatures were obtained using posterior and superior external ear retraction. Right-handed operators used the right auditory canal and left-handed operators the left. Tympanic temperatures were taken in the calibration mode. Digital electronic thermometers (Diatek 600, San Diego, CA) were used for oral and rectal measurements. An IRED device (Pro-l, Thermoscan, San Diego, CA) was used for tympanic membrane temperatures. Calibrations against a water bath over a range of 35 to 40°C demonstrated an accuracy of *O.l”C for the electronic thermometer. Calibration against a black-body (IR-3000, Thermoscan) demonstrated an accuracy of +O.l”C at 37 and 40°C for the IRED tympanic. The ECR was equilibrated overnight at either 435°C for the hot experiment or - 5°C for the cold experiment, and was validated against a mercury column thermometer. Following baseline temperature recordings, the subjects sat in the ECR at hot and then cold extreme temperature for 15 minutes for each experimental period on 2 separate days. Immediately upon leaving the ECR, subjects recorded a rectal, tympanic, and oral temperature. Subjects then recorded oral temperature and underwent tympanic IRED recordings every 2 minutes for 20 minutes. At the end of each experimental period, subjects recorded another rectal temperature. If investigators suspected spurious IRED tympanic readings, or error messages occurred, temperatures were repeated. Comparison of rectal or oral and tympanic temperatures was performed using the paired, two-tailed Student’s t-test. Comparison of the temperature at each site between baseline and experimental conditions was examined using repeat measures analysis of variance (ANOVA), with isolation of significant differences based upon Scheffe’s F test. Comparison of male and female responses was performed for oral and tympanic measures following both exposures, using repeat measures ANOVA. Significance was considered to be achieved for P < .05. RESULTS
The subjects averaged 31 -C 6.8 (mean f SD) years of age (range, 21 to 46 years). Twenty-one subjects participated in the hot experiment (11 men and 10 women) and 20 (10 men and 10 women) in the cold. All experiments were performed on March 5 and 7, 1991. Room temperature was stable during the experiment periods (20.5”C 2 0.05.) There were no complications during the study and no shivering was observed. Occasional discomfort from the prolonged insertion of the oral and repeated use of the tympanic probe were reported. At baseline, rectal temperature (37.7”C 2 0.4) was significantly greater than oral (P = .OOOl, t = 6.75; 36.9”C 2 0.5), which were both greater than tympanic (P = .OOOl, t = 12.17; 36.1”C 2 0.6). Rectal temperature changed little dur-
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ing either experimental period. No change in rectal temperature occurred following hot exposure. Rectal temperatures 20 minutes after cold exposure showed a statistically significant decrease of 0.16”C (P < .05). After hot exposure, oral temperatures were significantly elevated compared with baseline, from 8 to 20 minutes after exposure (P = .OOOl, F = 9.338; Figure 1). A transient decrease in oral temperature was observed 2 minutes after exiting the ECR. Individual responses to hot exposure varied widely. The range of oral temperatures was greatest at 8 minutes after exiting the ECR, 1.6”C (36.1 to 37.7”C). One subject’s oral temperature increased 1.2”C. and did not return to baseline at the end of 15 minutes, while another had a decrease of 0.7”C and returned to baseline within 10 minutes. Two subjects never varied their temperatures by more than O.l”C. After hot exposure, IRED tympanic temperatures increased significantly from baseline (P = .0039, F = 2.71; Figure 1) and persisted for 20 minutes. The greatest increase was immediately after leaving the ECR, +0.8”C + 0.5; range, 35.2 to 37.3”C. Individual data showed no temperature decreases at 2 minutes after exiting the ECR, as is seen with the oral temperatures. All subjects showed at least a 0.5”C increase in temperature at some time during the recording period. One subject showed a delayed temperature elevation, eventually increasing above baseline by 2°C. After cold exposure, oral temperature, compared with baseline, was significantly decreased from 2 to 4 minutes after leaving the ECR (P = .OOOl, F = 10.055; Figure 2). The greatest decrease was seen at 2 minutes after exiting the ECR, 0.5”C ? 0.5; range, 35.5 to 37.3”C. Individual data showed the greatest decrease in a female subject, - 1.3”C from baseline at 2 minutes after exiting the ECR. At 15 minutes after leaving the ECR, she was still 0.5”C below baseline. Seven subjects showed a 0.1 to 0.4”C initial increase in oral temperature before decreasing. Five subjects showed a 0.2 to 0.7”C increase in their oral temperatures, compared with baseline, at 15 minutes. Tympanic IRED temperatures were not significantly changed after cold exposure (P = .OOOl, F = 8.123: Figure 2). The greatest individual decrease in temperature was 1.7”C upon exiting the ECR. The range of tympanic IRED temperatures after cold (2.6”C) was greatest at 8 minutes.
1 36.9-
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FIGURE I. Oral (circles) and tympanic (squares) temperatures, mean -t SD, at baseline and after exiting the “hot” ECR. *P < .05 compared with baseline.
DOYLE ET AL m TEMPERATURE
0 UY +I
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EXTREMES
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(circles) and tympanic (squares) temperatures, baseline and after exiting the “cold” ECR. *P < .05 compared with baseline. FIGURE 2. mean 2 SD,
Oral
at
Fourteen subjects went above their baseline at some time; one subject by 1.2”C. Male, but not female, subjects had significant reductions in tympanic IRED from 0 to 8 minutes after exiting the ECR (P = .OOOl, F = 7.011; Figure 3). In comparing males and femaIes, no differences were present for either exposure using oral responses. No differences between male and female responses were measurable for tympanic responses following hot exposure. During oral measurements, no differences were observed between temperatures taken in the monitor versus the ptedictive mode. While measuring tympanic temperatures, occasional results appeared to be spurious values. However, these measures were all repeated and confirmed to be the same reading. DISCUSSION In heaithy subjects, exposure to ambient temperature extremes results in substantial intersubject variability compared with baseline. After hot exposure both tympanic and oral temperatures rise significantly, and some temperature elevations persist for 20 minutes. Tympanic temperature demonstrates a greater initial elevation than oral temperature. Cold exposure results in decreases in oral temperature in all subjects, and tympanic temperature in males.
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. 12
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FIGURE 3. Tympanic temperatures after cold (-ST) exposure for females (open squares) and males (closed squares), mean + SD. *P < .OS compared with baseline.
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Little information is available on the effect of ambient temperature extremes on the measurement of tympanic temperature using the IRED devices. In 21 healthy adults, moderate increases in ambient temperature (ie, 35°C) elevated IRED tympanic membrane readings by 0.7”C compared with baseline (ie, temperatures taken at a room temperature of 20°C). 36 Consistent with the present study, no change in IRED tympanic temperature occurred at moderate decreases in ambient temperature (ie, 18.3”C). Temperatures were taken during the exposure in this earlier study. Tympanic thermometry using thermistors has been widely studied, and the results are in agreement with and help to explain our findings. Thermistor studies involve the placement of a bead in direct contact with the tympanic membrane, and occlusion of the auditory canal to isolate the tympanum from the environment. Isolated cooling and heating of the head, or total body exposure to cold, significantly affect thermistor tympanic temperatures37*38 with little or no effect on esophageal temperature.3g-41 Marcus showed that tympanic changes are most affected by the supraauricular scalp temperature on the side of the temperature change,34*35 and that temperature changes of the pinna do not affect thermistor tympanic readings.34 Cabanac et al showed that heating the body while cooling one side of the face with fanning causes a greater rise in the esophageal temperature compared with both tympanic temperatures.33 These results support the hypothesis of a countercurrent temperature exchange in the head, and the concept of isolated brain cooling under thermal stress.42 Arterial blood in proximity to environmentally heated or cooled venous blood sets up a countercurrent temperature exchange, which in turn affects the tympanic temperature. 33*35V3g The lack of vasoconstriction of scalp vessels may explain the diminished effect of cold exposure compared with hot exposure.33*43,44 In our study, during hot exposures we found a small but statistically significant elevation in the tympanic and oral temperatures which persisted for 20 minutes. The initial tympanic elevation was greater than the oral. After hot exposure, elevation of tympanic thermistor temperatures were also greater for tympanic than oral temperatures.31*4’945 Thermistor tympanic temperature studies also showed considerable individual variation. The early decrease in oral temperatures in our study may be explained by mouth breathing while exiting the ECR or inadequate equilibration time using the monitor mode. As in the thermistor studies, during severe cold exposure there was a decrease in oral and male tympanic temperatures. The effect was less than that seen with the hot extreme. Scalp vessels ate known to have less vasoconstrictive than vasodilatative capabilities.43’” During hot exposure vasodilation may increase local blood flow and thus temperature in the tympanic membrane, whereas cold has less influence on scalp blood flow. Infrared emission detection tympanic temperatures decreased in male, but not female subjects. Since subjects did not wear hats, the female subjects’ hair may have played a protective role in decreasing heat loss in the external auditory canal and supraauricular area. Additionally this may be a reflection of the decreased conductance of females compared with males.46 Subjects demonstrated a late increase in IRED tympanic temperature after cold exposure. Benzinger has also noted such an over-
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shoot phenomenon in thermistor studies4’ This may be due to a reflex vasodilation after the cold stress is removed. The decrease in rectal temperature, while unanticipated,48 may be explained by the cooling of the blood in the thighs and buttocks in our seated subjects.’ This difference of 0.16”C is clinically of little consequence. Tympanic thermometers using IRED have a wide angle of view even when inserted properly. This likely results in contamination of tympanic temperature measurement by auditory canal infrared emissions.49 Brinnel and Cabanac” showed that tympanic temperatures taken precisely in the anterior, inferior quarter of the tympanic membrane were unaffected by skin temperature. Previous studies using thermistors show that, while auditory canal temperatures correlate well when measuring body temperature changes, the absolute canal temperature is location-dependent.28-32 The IRED device we used controls for ambient temperature of the thermometer and corrects for auditory canal resistance, but not for canal temperature. Current IRED devices are operator-dependent.5’ The technique which produces greatest precision requires retraction of the external ear and the operator using his/her dominant hand in the same ear of the subject.3.5’ By using a single investigator to take all IRED temperatures on each subject, we minimized measurement, but not systematic, error. Temperatures taken in both ears by a single operator correlate extremely well in multiple studies.20,21,23,27 Chamberlain et al demonstrated the best linear regression fit using the maximum of three IRED tympanic temperatures.*’ We chose to take one temperature to simulate clinical IRED device operation. Frequent IRED tympanic measurements are unlikely to affect tympanic readings.3 Our study concentrates on tympanic temperature measurement as it relates to routine ED patient care. Thus, we chose not to study oral or tympanic measurements while being exposed to hot or cold temperatures. We arbitrarily chose a 15-minute exposure time to represent a typical travel time to the ED in a metropolitan area. We measured temperatures after exposure for 15 to 20 minutes to reflect the time period in which an initial triage temperature might be taken. As no significant difference between mercury in glass and electronic thermometers has been shown,‘2*53 electronic thermometers were chosen for their speed, convenience, and common clinical use. Measurements of rectal temperature were limited to baseline, time 0, and completion of the study, based on previous data that the rectal temperature should remain stable during these ambient temperature ranges.36 This study was unblinded and no exclusions were performed for medications acting as vasodilators or constrictors. This may have effected the results of one study subject. Inadequate equilibration time during oral readings after exiting the ECR may have led to falsely low initial values.337 The time of day54 and the effect of shift work on diurinal temperature was not examined in this study. The lack of acclimatization of subjects to warm temperatures may have falsely increased the temperature changes and duration of observed effects55 with hot exposure. Given a standard deviation of 0.4”C and 10 subjects in each group, with CY= 0.05 and p = 0.2, we would have needed differences of 0.5”C between males and females to reliably determine no statis-
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tical difference.56 Further studies are needed to characterize younger and older patient populations after exposure to temperature extremes.’ The effect of thermal protection afforded by a hat and acclimatization may be significant when temperature is measured using IRED tympanic thermometers. CONCLUSION This study shows substantial intersubject variability in oral and tympanic temperatures after exposure to ambient temperature extremes. Thus, during a typical ED triage time of 15 to 20 minutes, tympanic and oral temperatures may fail to accurately reflect the patient’s baseline temperature and may require repeat measurement later in the patient’s ED visit. The authors thank Thermoscan Inc for their support of this project, and Andre Pennardt, MD for help in data collection.
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