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Infrared emission tympanic thermometers cannot be relied upon in a wilderness setting
Wilderness and Environmental Medicine, 10, 201-203 (1999)
Letter to the Editors Infrared emission tympanic thermometers cannot be relied upon in a wilderness setting To the Editors:
Hypo- and hyperthermia are some of the acknowledged risks of participation in wilderness activities. Knowledge of a casualty's core temperature may substantially guide decisions regarding medical management and evacuation in the field. Despite this, conventional teaching has recommended assessing core temperature based on history and limited clinical assessment, without resorting to actual temperature measurement [1]. This recommendation is in part related to the practical issue of temperature measurement, either oral or rectal, in a field setting. The optimal site at which to measure body temperature remains a difficult issue in thermal research. The technical nature of esophageal, pulmonary arterial, and bladder thermometry make these measurements inappropriate in a field setting. A rectal reading may be a valid core temperature measure in the field, but it requires significant patient exposure and discomfort. Oral readings are clearly affected by fluid intake and ventilatory effort, leaving tympanic readings as one of the few potentially viable alternatives. Infrared emission detection (IRED) thermometers are inexpensive, portable, relatively rugged, require minimal patient exposure, and give almost instantaneous readings. Use of IRED tympanic thermometry has now become routine in outpatient settings and for home use. For all of these reasons, it is likely that attempts will be made to use them in a field setting. We made an assessment of two brands of IRED thermometers in a single subject in a broad range of ambient temperatures, replicating different field conditions. The studies were performed in a series of hot and cold environments. These were a van in full sun (52.3°C), outdoors in full sun (40.2°C), outdoors in shade (34.4°C), two offices (24.6°C and 24.2°C), a food preparation area (12.1 0C), a refrigerated storage room (3.8°C) and a freezer (- 22.1 0C). Ambient temperatures were measured using a Fluke 87 True RMS Multimeter (John Fluke Mfg Co, Everett, WA) connected to a YSI 405 air temperature probe (Yellow Springs Instrument Co, Yellow Springs, OH). The subject was examined in order to rule out the presence of local ear pathology and was then prepared by having a rectal thermistor probe placed
and connected to a Propaq Encore monitor. The subject wore normal street clothes without any headgear. The thermometers studied were an IVAC Core Check Model 2090 (IVAC Corporation, San Diego, CA) (specified ambient operating range 18.3°C-32.2°C) and a First Temp Genius Model 3000A (Sherwood Medical, Watertown, NY) (range 15.6°C-35°C). Both thermometers were calibrated to manufacturer's instructions and were set to the core equivalent mode (in which the reading is calibrated to that of the pulmonary artery by means of a mathematical offset). In each setting, the subject and the thermometers were placed into the environment 10 min before readings commenced. Each of the two operators (one left-handed and one right-handed operator) took two readings in each of the subjects' ears, using the dominant hand for each device. Simultaneous rectal and tympanic temperatures were recorded (see the Figure). A total of 112 recorded pairs of simultaneous rectal and tympanic temperature measurements were available for analysis. The Core-Check thermometer displayed an error code only at 3.8°C and at -22.1°C. The Genius thermometer gave readings at these temperatures but with a small arrow in one comer of the display indicating an ambient temperature below the specified operating range. Both devices gave readings in all of the hot ambient environments. The mean temperature :±: standard deviation for each thermometer in each environment is shown in the Table. The IRED thermometers gave readings that were commensurately higher in hotter environments and lower in colder environments than the simultaneous rectal measurements; at times, the readings were significantly different from each other. There was no significant difference between the median temperature measured in the left ear (36SC) and the right ear (36.7°C) (p = 0.935). The median temperature measured by operator 1 was 36SC and by operator 2, 36.7°C (P = 0.635). Infrared emission detection thermometers have won widespread acceptance in primary care settings despite some debate over their accuracy [2-7]. The thermometers work by detecting infrared emissions from the tympanic membrane and nearby tissues. Implicit in this design is the notion that tympanic membrane temperature accurately reflects core body temperature [8]. Previous studies of temperature measurement in ambient temper-
202
Letter to the editors
Genius 3000A (left) and Core-Check 2090 (right). atures well above or below room temperature or in field environments [9-13] have shown substantial variations in readings, particularly when IRED thermometers were used. Our study has tested two representative IRED devices across a very broad range of ambient temperatures in a controlled manner. The increasingly significant Temperatures recorded in various environmentst Ambient temperature
Rectal temperature
-22.1 3.8 12.1 24.2 24.6 34.4 40.2 52.3
37.1 37.3 37.4 37.2 37.2 37.4 37.6 37.7
Genius 3000A Mean (SD) 28.9 33.9 35.7 36.4 36.8 37.6 39.3 40.7
(1.2)* (0.6)* (0.25)* (0.22)* (0.25)*+ (0.32)+ (0.19)*:j: (0.3)*:j:
Core-Check Mean (SD)
35.9 (0.16)* 36.3 (0.17)* 36.4 (0.12)*+ 36.8 (0.21)*+ 37.6 (0.09):j: 38.3 (0.13)*:j:
t All temperatures are in dc. *p < 0.01 compared with rectal measure. :j:p < 0.01 compared with the other IRED thermometer.
overreading and underreading we observed in high and low ambient temperatures, respectively, suggests that ambient warming and cooling of the ear canal and tympanic membrane may substantially affect the results of IRED thermometers. It is also likely that low and high ambient temperatures magnify inaccuracies in the linearizing coefficient algorithm that converts the relationship between infrared emission and temperature to a straight line. Further inaccuracies may be introduced by the devices' use of mathematical offsets to convert the measured temperature to that at another site (such as the core equivalent in our study). One should always be wary of generalizing the results of a study on a single subject to a larger group. We feel these results can be generalized because we have previously shown that these same two thermometers showed the same tendency when several subjects were studied in a cold environment [14]. We chose an equilibration time of 10 min for the subject and the thermometer on the basis of one manufacturer's product manual, because the other manual did not specify a time. One could argue that shorter or longer times should have been tested, but every wilderness situation is unique, and
203
Letter to the editors
it is impossible to recreate all possible field scenarios. The good agreement between our two operators suggests that technique and the effects of handedness did not play a part in the results we observed. We have quite deliberately tested these IRED thermometers in simulated field conditions well outside their manufacturers' recommended ambient operating range. Our study has shown that the temperature readings they give when used outside approved ranges give an unreliable measure of core temperature that could lead to highly inappropriate medical decisions. We conclude that the currently available devices are not suitable for field use. Technological advances may increase the reliability of IRED thermometers in different ambient temperatures, but tympanic membrane temperature measurement will continue to be influenced by the surroundings. Ian R. Rogers, FACEM Debra L. O'Brien, FACEM Chung Wee, MBBS Alison Smith, PhD Derrick Lopez, M Med Sci Perth, Western Australia References 1. Forgey WW (ed). Wilderness Medical Society Practice Guidelines for Wilderness Emergency Care. Merrillville, IN: ICS Books; 1995. 2. Temdrup TE. An appraisal of temperature assessment by infrared emission detection tympanic thermometry. Ann Emerg Med. 1992;21:1483-1492. 3. Rotello LC, Crawford L, Temdrup TE. Comparison of infrared ear thermometer derived and equilibrated rectal
temperatures in estimating pulmonary artery temperatures. Crit Care Med. 1996;24:1501-1506. 4. Yaron M, Lowenstein SR, Koziol-McLain J. Measuring accuracy of the infrared tympanic thermometer: Correlation does not signify agreement. J Emerg Med. 1995;13: 617-621. 5. Manian FA, Griesanauer S. Lack of agreement between tympanic and oral temperature measurements in adult hospitalised patients. Am J Infect Control. 1998;26:428-430. 6. Brennan DF, Falk J, Rothrock SG, Kerr RB. Reliability of infrared tympanic thermometry in the detection of rectal fever in children. Ann Emerg Med. 1995;25:21-30. 7. Jaffe DM. What's hot and what's not: The gold standard for thermometry in emergency medicine. Ann Emerg Med. 1995;25:97-99. 8. Temdrup TE, Crofton DJ, Morelliti AJ, Kelley R, Rajk 1. Estimation of contact tympanic membrane temperature with a noncontact infrared thermometer. Ann Emerg Med. 1997;30:171-175. 9. Livingstone SD, Grayson J, Frim J, Allen CL, Limmer RE. Effect of cold exposure on various sites of core temperature measurements. J Appl Physiol. 1983;54:10251031. 10. Doyle F, Zehner WJ, Temdrup TE. The effect of ambient temperature extremes on tympanic and oral temperatures. Am J Emerg Med. 1992;10:285-289. 11. Weiss SJ, Hanhart EJ, Mcbride R, Johnson H, Denninghof K, Johnson WD. Tympanic thermometry in out-of-hospital patients. Ann Emerg Med. 1995;25:41-47. 12. Roth RN, Verdile Vp, Grollman LJ, Stone DA. Agreement between rectal and tympanic membrane temperatures in marathon runners. Ann Emerg Med. 1996;28:414-417. 13. Hansen RD, Amos D, Leake B. Infrared tympanic membrane temperature as a predictor of rectal temperature in warm and hot conditions. Aviat Space Environ Med. 1996; 67:1048-1052. 14. O'Brien DL, Rogers IR, Smith A, Lopez D. Infrared typanic thermometers are unreliable in low ambient temperatures. Emerg Med. 1998;10:313-316.
Letter to the Editors Infrared emission tympanic thermometers cannot be relied upon in a wilderness setting To the Editors:
Hypo- and hyperthermia are some of the acknowledged risks of participation in wilderness activities. Knowledge of a casualty's core temperature may substantially guide decisions regarding medical management and evacuation in the field. Despite this, conventional teaching has recommended assessing core temperature based on history and limited clinical assessment, without resorting to actual temperature measurement [1]. This recommendation is in part related to the practical issue of temperature measurement, either oral or rectal, in a field setting. The optimal site at which to measure body temperature remains a difficult issue in thermal research. The technical nature of esophageal, pulmonary arterial, and bladder thermometry make these measurements inappropriate in a field setting. A rectal reading may be a valid core temperature measure in the field, but it requires significant patient exposure and discomfort. Oral readings are clearly affected by fluid intake and ventilatory effort, leaving tympanic readings as one of the few potentially viable alternatives. Infrared emission detection (IRED) thermometers are inexpensive, portable, relatively rugged, require minimal patient exposure, and give almost instantaneous readings. Use of IRED tympanic thermometry has now become routine in outpatient settings and for home use. For all of these reasons, it is likely that attempts will be made to use them in a field setting. We made an assessment of two brands of IRED thermometers in a single subject in a broad range of ambient temperatures, replicating different field conditions. The studies were performed in a series of hot and cold environments. These were a van in full sun (52.3°C), outdoors in full sun (40.2°C), outdoors in shade (34.4°C), two offices (24.6°C and 24.2°C), a food preparation area (12.1 0C), a refrigerated storage room (3.8°C) and a freezer (- 22.1 0C). Ambient temperatures were measured using a Fluke 87 True RMS Multimeter (John Fluke Mfg Co, Everett, WA) connected to a YSI 405 air temperature probe (Yellow Springs Instrument Co, Yellow Springs, OH). The subject was examined in order to rule out the presence of local ear pathology and was then prepared by having a rectal thermistor probe placed
and connected to a Propaq Encore monitor. The subject wore normal street clothes without any headgear. The thermometers studied were an IVAC Core Check Model 2090 (IVAC Corporation, San Diego, CA) (specified ambient operating range 18.3°C-32.2°C) and a First Temp Genius Model 3000A (Sherwood Medical, Watertown, NY) (range 15.6°C-35°C). Both thermometers were calibrated to manufacturer's instructions and were set to the core equivalent mode (in which the reading is calibrated to that of the pulmonary artery by means of a mathematical offset). In each setting, the subject and the thermometers were placed into the environment 10 min before readings commenced. Each of the two operators (one left-handed and one right-handed operator) took two readings in each of the subjects' ears, using the dominant hand for each device. Simultaneous rectal and tympanic temperatures were recorded (see the Figure). A total of 112 recorded pairs of simultaneous rectal and tympanic temperature measurements were available for analysis. The Core-Check thermometer displayed an error code only at 3.8°C and at -22.1°C. The Genius thermometer gave readings at these temperatures but with a small arrow in one comer of the display indicating an ambient temperature below the specified operating range. Both devices gave readings in all of the hot ambient environments. The mean temperature :±: standard deviation for each thermometer in each environment is shown in the Table. The IRED thermometers gave readings that were commensurately higher in hotter environments and lower in colder environments than the simultaneous rectal measurements; at times, the readings were significantly different from each other. There was no significant difference between the median temperature measured in the left ear (36SC) and the right ear (36.7°C) (p = 0.935). The median temperature measured by operator 1 was 36SC and by operator 2, 36.7°C (P = 0.635). Infrared emission detection thermometers have won widespread acceptance in primary care settings despite some debate over their accuracy [2-7]. The thermometers work by detecting infrared emissions from the tympanic membrane and nearby tissues. Implicit in this design is the notion that tympanic membrane temperature accurately reflects core body temperature [8]. Previous studies of temperature measurement in ambient temper-
202
Letter to the editors
Genius 3000A (left) and Core-Check 2090 (right). atures well above or below room temperature or in field environments [9-13] have shown substantial variations in readings, particularly when IRED thermometers were used. Our study has tested two representative IRED devices across a very broad range of ambient temperatures in a controlled manner. The increasingly significant Temperatures recorded in various environmentst Ambient temperature
Rectal temperature
-22.1 3.8 12.1 24.2 24.6 34.4 40.2 52.3
37.1 37.3 37.4 37.2 37.2 37.4 37.6 37.7
Genius 3000A Mean (SD) 28.9 33.9 35.7 36.4 36.8 37.6 39.3 40.7
(1.2)* (0.6)* (0.25)* (0.22)* (0.25)*+ (0.32)+ (0.19)*:j: (0.3)*:j:
Core-Check Mean (SD)
35.9 (0.16)* 36.3 (0.17)* 36.4 (0.12)*+ 36.8 (0.21)*+ 37.6 (0.09):j: 38.3 (0.13)*:j:
t All temperatures are in dc. *p < 0.01 compared with rectal measure. :j:p < 0.01 compared with the other IRED thermometer.
overreading and underreading we observed in high and low ambient temperatures, respectively, suggests that ambient warming and cooling of the ear canal and tympanic membrane may substantially affect the results of IRED thermometers. It is also likely that low and high ambient temperatures magnify inaccuracies in the linearizing coefficient algorithm that converts the relationship between infrared emission and temperature to a straight line. Further inaccuracies may be introduced by the devices' use of mathematical offsets to convert the measured temperature to that at another site (such as the core equivalent in our study). One should always be wary of generalizing the results of a study on a single subject to a larger group. We feel these results can be generalized because we have previously shown that these same two thermometers showed the same tendency when several subjects were studied in a cold environment [14]. We chose an equilibration time of 10 min for the subject and the thermometer on the basis of one manufacturer's product manual, because the other manual did not specify a time. One could argue that shorter or longer times should have been tested, but every wilderness situation is unique, and
203
Letter to the editors
it is impossible to recreate all possible field scenarios. The good agreement between our two operators suggests that technique and the effects of handedness did not play a part in the results we observed. We have quite deliberately tested these IRED thermometers in simulated field conditions well outside their manufacturers' recommended ambient operating range. Our study has shown that the temperature readings they give when used outside approved ranges give an unreliable measure of core temperature that could lead to highly inappropriate medical decisions. We conclude that the currently available devices are not suitable for field use. Technological advances may increase the reliability of IRED thermometers in different ambient temperatures, but tympanic membrane temperature measurement will continue to be influenced by the surroundings. Ian R. Rogers, FACEM Debra L. O'Brien, FACEM Chung Wee, MBBS Alison Smith, PhD Derrick Lopez, M Med Sci Perth, Western Australia References 1. Forgey WW (ed). Wilderness Medical Society Practice Guidelines for Wilderness Emergency Care. Merrillville, IN: ICS Books; 1995. 2. Temdrup TE. An appraisal of temperature assessment by infrared emission detection tympanic thermometry. Ann Emerg Med. 1992;21:1483-1492. 3. Rotello LC, Crawford L, Temdrup TE. Comparison of infrared ear thermometer derived and equilibrated rectal
temperatures in estimating pulmonary artery temperatures. Crit Care Med. 1996;24:1501-1506. 4. Yaron M, Lowenstein SR, Koziol-McLain J. Measuring accuracy of the infrared tympanic thermometer: Correlation does not signify agreement. J Emerg Med. 1995;13: 617-621. 5. Manian FA, Griesanauer S. Lack of agreement between tympanic and oral temperature measurements in adult hospitalised patients. Am J Infect Control. 1998;26:428-430. 6. Brennan DF, Falk J, Rothrock SG, Kerr RB. Reliability of infrared tympanic thermometry in the detection of rectal fever in children. Ann Emerg Med. 1995;25:21-30. 7. Jaffe DM. What's hot and what's not: The gold standard for thermometry in emergency medicine. Ann Emerg Med. 1995;25:97-99. 8. Temdrup TE, Crofton DJ, Morelliti AJ, Kelley R, Rajk 1. Estimation of contact tympanic membrane temperature with a noncontact infrared thermometer. Ann Emerg Med. 1997;30:171-175. 9. Livingstone SD, Grayson J, Frim J, Allen CL, Limmer RE. Effect of cold exposure on various sites of core temperature measurements. J Appl Physiol. 1983;54:10251031. 10. Doyle F, Zehner WJ, Temdrup TE. The effect of ambient temperature extremes on tympanic and oral temperatures. Am J Emerg Med. 1992;10:285-289. 11. Weiss SJ, Hanhart EJ, Mcbride R, Johnson H, Denninghof K, Johnson WD. Tympanic thermometry in out-of-hospital patients. Ann Emerg Med. 1995;25:41-47. 12. Roth RN, Verdile Vp, Grollman LJ, Stone DA. Agreement between rectal and tympanic membrane temperatures in marathon runners. Ann Emerg Med. 1996;28:414-417. 13. Hansen RD, Amos D, Leake B. Infrared tympanic membrane temperature as a predictor of rectal temperature in warm and hot conditions. Aviat Space Environ Med. 1996; 67:1048-1052. 14. O'Brien DL, Rogers IR, Smith A, Lopez D. Infrared typanic thermometers are unreliable in low ambient temperatures. Emerg Med. 1998;10:313-316.