Accuracy of Core Temperature Measurement with the IVAC® CORE.CHECKT Tympanic Thermometer System
Roberta Erickson, PhD, RN
Assistant Professor, Department of Adult Health and Illness
School of Nursing, Oregon Health Sciences University
Linda DiBenedetto, R.N.
Senior Clinical Study Associate
Review of the medical literature and recently completed research shows that the ear canal is a useful site for clinical measurement of body temperature. This paper describes why the ear canal is an appropriate site and provides information about the accuracy of readings with the CORE.CHECK tympanic thermometer.
The best sites for temperature measurement are near vital organs in the central core of the body. The pulmonary artery is considered the optimal core site1, but it requires a special invasive catheter and monitoring system found only in intensive care units. For everyday temperature taking, however, more practical methods are needed that estimate core temperature with reasonable accuracy. The mouth, rectum, and axilla are the traditional sites, although each has certain disadvantages.2, 3 The mouth is affected by eating, drinking and smoking; the rectum involves cross contamination risks; and the axilla is much lower than core temperature and is more variable than other sites. The tympanic membrane has been identified as an ideal location for temperature measurement.4 The tympanic membrane temperature has been shown to be close to temperature in the brain and the pulmonary artery.5, 6, 7 The CORE.CHECK tympanic thermometer offers a new technique, which is to take a "tympanic-based" temperature in the ear canal, by measuring natural infrared energy emitted by the tympanic membrane and nearby tissue and processing it to give an estimate of core temperature, all within a few seconds.
During the development of the CORE.CHECK tympanic thermometer, IVAC conducted extensive clinical work to derive a statistically valid correlation between pulmonary artery catheter temperature and tympanic temperature. The study subjects were critically ill adult patients in four types of critical care units: Surgical Intensive Care, Medical Intensive Care, Coronary Intensive Care and a Burn Unit. After statistical analysis on 299 comparison data points, a mathematical formula was developed to best approximate pulmonary artery core temperature with the CORE.CHECK tympanic thermometer.
Validation of the final algorithm is very important. A recent clinical study8 was conducted in which tympanic temperatures taken with the CORE.CHECK tympanic thermometer were evaluated for accuracy by comparing them to readings made directly in the pulmonary artery. The study subjects were 38 critically ill adult patients (27 men and 11 women), including 33 who had cardiac surgery, 4 with nonsurgical cardiac illnesses, and 1 who had vascular surgery. The average age was 64 ± 9 years, with a range of 39 to 78 years. In most cases, temperature measurements were made every 20 minutes over a 4-hour period. A total of 347 sets of measurements were obtained. The mean difference between tympanic temperatures with the CORE.CHECK tympanic thermometer and pulmonary artery temperatures was only 0.07°C (0.13°F). The standard deviation was ±0.41°C (00.74°F), indicating that the difference varied to a moderate extent, as has been noted with other infrared thermometers, perhaps due to variations in ear anatomy or positioning of the thermometer probe in the ear canal.
In conclusion, temperatures measured with the CORE.CHECK tympanic thermometer provide accurate determinations of core temperature along with the advantage of nearly instantaneous readings.
REFERENCES
- 1. Brongelmann GL: Dilemma of body temperature measurement. In: Man in stressful environments: Thermal and work Physiology. Shiraki K, Yousef MK, editors. Springfield: Charles C Thomas, 1987:5-22.
- 2. Erickson, R: A sourcebook for temperature taking. San Diego: IVAC Corporation, 1980.
- 3. Terndorf TE, Allegra JR, Keally J: 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.
- 4. 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.
- 5. Shiraki K, Sagawa S, Tajima F, Yokata A, Hashimoto M, Brengelmann GL: Independence of brain and tympanic temperatures in an unanesthetized human. J Appl Physiol 1988; 65:482-486.
- 6. Hayward JS, Eckerson JD, Kemna D: Thermal and cardiovascular changes during three methods of resuscitation from mild hypothermia. Resuscitation 1984; 11:21-33.
- 7. Shiraki K, Konda N, Sagawa S: Esophageal and tympanic temperature responses to core blood temperature changes during hyperthermia. J Appl Physiol 1986, 61:98-102.
- 8. Erickson, RS, & Kirklin, SK: Comparison of tympanic-based oral, and axillary methods for core temperature measurement. Manuscript submitted for publication, 1991.
10/31/91
