The best sites for measuring temperature are those closest to the hypothalamus - the temperature-regulating center - that reflect central or "core" body heat. The temperature in the pulmonary artery (PA), esophagus and bladder are used to measure core values, but these sites involve invasive thermometry and are impractical for routine use.
Traditionally, the oral, rectal, and axillary sites have been used. Many clinicians consider the rectal route to be the "gold standard" for temperature measurement in children (Freed and Fraley, 1992; Schuman, 1993). However, rectal measurements do not respond quickly to induced heat changes in the body and are often higher than the PA temperature. These effects may be due to the relatively poor blood flow to the rectum and the insulating property of the stool (Terndrup and Milewski, 1991).
Since the availability of infrared aural sensors, temperature measurement of the tympanic membrane (TM) has become popular. The ear's proximity to the hypothalamus makes it a desirable area for reflecting true core temperature. Results of studies using aural measurements are conflicting, however. Ferra-Love (1991) found no significant differences between PA and TM measurements in adults. Milewski, Ferguson, and Terndrup (1991) found significantly better correlations between rectal and PA temperatures than those of TM and PA assessments and yet, at the same time, found that PA and TM temperatures were not significantly different while rectal temperatures were significantly warmer. However, another study found that PA and TM temperatures were highly correlated (r=.91), whereas rectal and ear temperatures were only moderately correlated (r=.52) (Klein and others, 1993).
In comparisons with rectal, oral, or axillary temperature assessments in children, some studies have found TM measurements to be fairly insensitive in detecting fevers and recommended caution in use with children less than 3 years of age (Freed and Fraley, 1992; Muma and others, 1991). In contrast, several studies have shown strong positive correlations between TM and rectal temperature measurements (Chamberlain and others, 1991; Davis, 1993; Kenney and others, 1990; Stewart and Webster, 1992; Talo, Macknin, and Medendrop, 1991). However, Chamberlain's and Stewart's studies did not obtain the same findings with infants less than 3 months of age; and Davis found inaccurate readings in children less than 3 years. Yet others have reported reliable ear measurements in newborns and young infants (Johnson, Bhatia, and Bell, 1991; Weiss, 1991).
Obviously from a selected review of the literature, it seems that no one routinely used site for temperature assessment provides unequivocal estimates of core body temperature and that similar kinds of comparison studies can yield contradictory results. What factors might influence the discrepancies? One might be the use of the rectal temperature as the "gold standard" for comparison. Some authorities caution that "gold standards" are rarely achieved because the subject (like temperature measurement) is changing and improving (Duggan, 1992). Such may be the case with TM sensors. The ear drum's anatomic location is superior to the rectal site, and a poor correlation between the two sites may actually indicate more accurate, not less accurate, temperature values from ear thermometry (Terndrup and Milewski, 1991). Perhaps aural temperatures should be considered the "gold standard," and studies showing a poor correlation between ear and rectal temperatures should be used to discourage use of the rectal route (Roscelli, 1993).
Also, most models of ear sensors use "offsets" or internal calculations that transform the ear temperature into supposedly equivalent oral or rectal temperatures. These offsets may be a source of error; for example, each manufacturer uses a different formula to calculate the offset and the formula (usually based on adult data) is applied to all age groups (Tourangeau, MacLeod, and Breakwell, 1993). Johnson, Bhatia, and Bell (1991) found that the actual ear reading, not the offsets, reliably indicated temperature in premature and full-term neonates. In addition, the size of the probe may be too large to be placed correctly in the canal (Treloar and Muma, 1988).
Also, technique must be considered. For the sensor to detect heat from the drum, not from the cooler canals, the ear canal must be straightened as when using an otoscope -- the pinna pulled down and back for children under 3 years and up and back for children above 3 years. With the ear tugged correctly and the probe tip pointing at the midpoint between the eyebrow and sideburn on the opposite side of the face, higher temperature readings are obtained (Terndrup and Rajk, 1992). A review of 19 studies (Wells and others, 1995) concluded that aural thermometers are best used with a standardized ear tug in children older than three months. The agreement between tympanic and referent temperature (oral, rectal, axillary, pulmonary artery, and bladder) was consistently lower, suggesting a difference in site of temperature measurement. Pontious and others (1994) have found that accuracy and reliability of temperature measurement from the rectum, mouth, and axilla were significantly improved when experienced nurses received moderate to intensive education. The researchers poignantly conclude, the single most important implication for nursing is that no procedure performed on patients is routine.
Finally, in deciding which route to use, nurses should provide "atraumatic care." Children are less upset having their temperature measured via the ear route than the rectal route (Alexander and Kelly, 1991; Barber and Kilmon, 1989). Parents may also object to the rectal route. In a British study, 37 of 42 parents who were interviewed expressed concerns that included a fear of hurting their child, anxieties about being accused of sexual abuse, difficulty comforting their child, and concern for the youngster's feelings (Kai, 1993).
In considering all the findings for and against different sites of temperature measurement, nurses need to think critically about why the temperature is needed, how clinically significant a small difference in temperature between routes really is, and how much the procedure upsets the child and caregiver. Remember, we are not even sure what normal body temperature is. The "gold standard" of 37°C (98.6°F) in adults has been questioned with a "new" mean oral temperature reported as 36.8°C (98.2°F) (Mackowiak and others, 1992).
Alexander D, Kelly B: Responses of children, parents, and nurses to tympanic thermometry in the pediatric office, Clinical Pediatrics 30(4, suppl):53-56, 1991.
Barber N, Kilmon CA: Reactions to tympanic temperature measurement in an ambulatory setting, Pediatric Nursing 15(5):477-481, 1989.
Chamberlain JM and others: Comparison of a tympanic thermometer to rectal and oral thermometers in a pediatric emergency room, Clinical Pediatrics 30(suppl. 4):24-29, 1991.
Davis K: The accuracy of tympanic temperature measurement in children, Pediatric Nursing 19(3):267-272, 1993.
Duggan PF: Time to abolish "gold standard," British Medical Journal 304(6841):1568-1569, 1992.
Ferra-Love R: A comparison of tympanic and pulmonary artery measures of core temperature, Journal of Post Anesthesia Nursing 6(3):161-164, 1991.
Freed GL, Fraley JK: Lack of agreement of tympanic membrane temperature assessments with conventional methods in a private practice setting, Pediatrics 89(3):384-386, 1992.
Kai J: Parents' perceptions of taking babies' rectal temperature, British Medical Journal 307:660-662, 1993.
Kenney RD and others: Evaluation of an infrared tympanic membrane thermometer in pediatric patients, Pediatrics 85(5):854-857, 1990.
Klein DG and others: A comparison of pulmonary artery, rectal, and tympanic membrane temperature measurement in the ICU, Heart & Lung 22(5):435-441, 1993.
Johnson KJ, Bhatia P, Bell EF: Infrared thermometry of newborn infants, Pediatrics 87(1):34-38, 1991.
Milewski A, Ferguson KL, Terndrup TE: Comparison of pulmonary artery, rectal, and tympanic membrane temperatures in adult intensive care unit patients, Clinical Pediatrics 30(4, suppl):13-16, 1991.
Muma BK and others: Comparison of rectal, axillary, and tympanic membrane temperatures in infants and young children, Annals of Emergency Medicine 20(1):41-44, 1991.
Pontious S and others: Accuracy and reliability of temperature measurement by measurement instrument and site plus level of nursing inservice education, Journal of Pediatric Nursing, in press, April 1994.
Roscelli JD: Letter to the editor: Aural, oral, or rectal - does it make any real difference? Pediatrics 91(1):166, 1993.
Schuman AJ: The accuracy of infrared auditory canal thermometry in infants and children, Clinical Pediatrics 32(6):347-354, 1993.
Stewart JV, Webster D: Re-evaluation of the tympanic thermometer in the emergency department, Annals of Emergency Medicine 21(2):158-161, 1992.
Talo H, Macknin ML, Medendrop SV: Tympanic membrane temperatures compared to rectal and oral temperatures, Clinical Pediatrics 30(suppl. 4):30-35, 1991.
Terndrup TE, Milewski A: The performance of two tympanic thermometers in a pediatric emergency department, Clinical Pediatrics 30(4, suppl):18-23, 1991.
Terndrup TE, Rajk J: Impact of operator technique and device on infrared emission detection tympanic thermometry, Journal of Emergency Medicine 10:683-687, 1992.
Treloar D, Muma B: Comparison of axillary, tympanic membrane and rectal temperatures in young children, Annals of Emergency Medicine 17(4):435, 1988.
Tourangeau A, MacLeod F, Breakwell M: Tap in on ear thermometry, Canadian Nurse 89(8):24-28, 1993.
Weiss ME: Tympanic infrared thermometry for fullterm and preterm neonates, Clinical Pediatrics 30(4, suppl):42-45, 1991.\\Wells N and others: Does tympanic temperature measure up? MCN 20(2):95-100, 1995.
See Chapter 7 in Nursing Care of Infants and Children, 5th and 6th editions.
See Chapter 7 in Essentials of Pediatric Nursing, 5th edition.
March 15, 2002
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