Clinical thermometry: An update and review

When I opened my first practice in 1986, I was intrigued by an advertisement in Contemporary Pediatrics that caught my attention, and days later I was the proud owner of a FirstTemp tympanic thermometer. The manufacturer (Intelligent Medical Systems; Carlsbad, California) promised the device’s measurements were as accurate as oral and rectal temperatures taken with glass thermometers. I was initially skeptical of this high-tech thermometer, but within weeks it proved to be a very popular device among staff, providers, and patients. The reason it was successful was that it required little patient cooperation and took temperatures in seconds, and it produced measurements comparable to those obtained with our digital oral and rectal thermometers. This month’s Peds v2.0 provides an overview of the history of clinical thermometry and reviews some of the thermometers that are currently available for home and office use.

A brief history of clinical thermometry

Early physicians recognized that illness often was associated with fever, but it took centuries for scientists to develop the means to actually measure body temperature. Although Galileo in 1592 was the first to fashion a crude thermometer, it was another Italian scientist, Santorio Santorio, who was the first to take oral temperatures in 1625.¹ His thermoscope, as it was called, was large and cumbersome, and took hours to perform a single measurement.

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It was not until the mid-1800s that the German physician Carl Wunderlich developed a foot-long thermometer that could take clinical temperatures.¹ In 1868, he published his data of more than 1 million axillary readings from more than 25,000 patients. He determined that there was a diurnal variation in daily body temperatures ranging from 97.3°F in the morning to 99.5°F in the evening. He also originated the standard of 98.6°F as “normal body temperature” that we use today. His readings took 20 minutes to perform, and for anyone but the most patient of physicians, this was not a practical device.

It was a contemporary of Carl Wunderlich, Thomas Clifford Allbutt, an Englishman, who introduced the first portable 6-inch thermometer in 1866 that could record a temperature in 5 minutes.¹ His thermometer could be transported in a pocket. Subsequently, temperature measurement became a routine vital sign. (You can view one of Allbutt’s thermometers by visiting https://museumofhstm.wordpress.com/2012/08/31/allbutts-clinical-thermometer/.) Allbutt eventually received a knighthood for his achievement and service to medicine.

NEXT: Fever and children

Fever and children

Before the Haemophilus influenzae type b vaccine first became available in 1985 and the first pediatric conjugate pneumococcal vaccine became available in 2000, pediatricians routinely encountered severe illnesses in patients that included meningitis, septic arthritis, osteomyelitis, and sepsis. These were so common that blood cultures and spinal taps were routine office procedures. Before the introduction of the H influenzae and pneumococcal vaccines, 3% of young febrile children without a focus of infection had positive blood cultures for H influenzae, Streptococcus pneumoniae, or Neisseria meningitides. Six percent of those patients positive for pneumococcus also were discovered to have meningitis, while up to 20% of positive blood cultures for H influenzae were associated with meningitis.^2,3 Today, the incidence of occult bacteremia is 0.5%, and we rarely perform blood cultures or spinal taps in the workup of infections, except in febrile young infants.⁴ The key point is that, just 2 decades ago in the last century, parents and pediatricians were alerted to the possibility of severe pediatric illness by the presence of fever, and they were comforted by its absence. Today, documentation of a fever alerts physicians regarding the cause of the associated symptoms. In most situations, there is an infectious cause with rheumatologic illnesses, malignancy-related fevers, and period fevers being much less common.⁵

Fever in young infants

Even today, when an infant in the first 2 month of life presents with fever, we proceed to evaluate that child for sepsis, meningitis, pneumonia, or a urinary tract infection. In most circumstances, this warrants admission of young infants for empiric antibiotic therapy pending results of cultures. Therefore, identification of fever in young infants is very important with most protocols identifying “fever” as a rectal temperature of 100.4°F or higher.

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Studies have repeatedly shown that parents overdiagnose fever when they rely on touch alone. There are also a wide variety of home thermometers available for use in infants including pacifier thermometers, forehead thermometers, ear thermometers, and digital thermometers that can be used either orally or rectally. When parents report an elevated temperature in a young infant above the threshold of 100.4°F degrees, it often is followed by the recommendation for the parent to take the baby to the emergency department for a septic workup. Emergency department physicians, erring on the side of caution, often will do this workup if the infant has no fever on arrival, and even when an antipyretic has not been given. It is therefore important for pediatricians to instruct new parents regarding how to take a temperature, as well as recommend a thermometer for home use and recommend an age-dependent site for temperature measurement.

NEXT: Are tympanic temperatures reliable?

Tympanic temperatures: Reliable or not?

Fever and its measurement was a popular topic in the pediatric literature during the 1980s through 2000 when infrared “tympanic” thermometers (the FirstTemp was introduced in 1984) became available, and pediatricians published study after study comparing this device’s measurement to those taken by more traditional means. The tympanic membrane was an attractive site for temperature measurement because of its shared blood supply with the hypothalamus, the body’s thermoregulatory center. Many arguments ensued regarding the appropriateness of the use of tympanic thermometers in clinical practice, with some studies showing good correlation and others showing poor correlation between temperatures taken from the ear canal and oral, axillary, and rectal sites.^6,7

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Many other companies introduced their own ear thermometers. All the devices had 1 thing in common: They did not really measure temperatures of the tympanic membrane, but measured the temperature of the ear canal. To present measurements with which physicians were more familiar, all these devices added a “fudge factor” called an “offset” to the actual ear canal measurement to present an equivalent oral or rectal temperature. Although these temperatures were not influenced by the presence of cerumen or otitis media, measurements were affected by the size of the ear canal and how deep the probe could be inserted comfortably. Overall, because of their speed and ease of use, ear thermometers became an office staple to screen children aged older than 2 years for the presence or absence of fever.

Temporal artery thermometry

It was Exergen (Watertown, Massachusetts) that introduced the next innovation in infrared temperature measurement. Forehead temperatures have been taken by concerned mothers since the dawn of time, and Francesco Pompei, the founder and chief executive officer of Exergen, suspected that the superficial branch of the temporal artery was an ideal site for reliable and reproducible temperature measurement. Exergen introduced its clinical temporal artery thermometer, the TAT-5000, in 2000. Now nearly 16 years later, the company has sold more than 400,000 devices and the thermometer is being used by over half of pediatric practices in the United States.

The device measures the patient’s core body temperature, which is about 1°F or 0.5°C higher than oral readings. The TAT-5000 thermometer uses dual scanners, one that measures ambient environmental temperature and another that gauges the arterial temperature of the patient’s skin. The thermometer records over 1000 readings per second, producing an audible click as the device registers a higher reading. After taking 3000 readings, an internal “heat balance” algorithm determines the arterial temperature, which is displayed on the unit’s LED screen. Best of all, although the thermometer lists for over $400, Exergen frequently puts the device on sale for $200. One reason the device is so popular in the medical community is that it carries a lifetime warranty.

Parents also can purchase a home forehead thermometer manufactured by Exergen for less than $30. This is the Exergen consumer TAT-2000C. It uses the same technology as the TAT-5000, but it can store up to 8 temperatures, has an illuminated screen, and can be silenced so it doesn’t wake a child. The device has a warranty of 1 year. Exergen worked with Dr. Keith Powell and 15 pediatric practices affiliated with the Children’s Hospital Medical Center of Akron, Ohio, to establish a normal upper limit of measurements for its temporal artery thermometers. Powell recorded 2300 temperatures from children to determine the “threshold” for fever as displayed in the Table.⁸

NEXT: Home thermometers

Home thermometers

If you view the thermometers available for home use displayed at any pharmacy, you will see a wide variety of thermometers for taking temperatures on children. Consumer sites such as Consumer Search (www.consumersearch.com/digital-thermometers/best-temporal-thermometers) list thermometers that they recommend for home use. These include the Kinsa Smart Thermometer (New York, New York) that I reviewed in “What’s new in ‘connected’ medical devices” that appeared in the November 2015 issue of Contemporary Pediatrics. Other Consumer Search favorite models include the Vicks V934 digital thermometer (Kaz Inc; Southborough, Massachusetts) for rectal temps; the Braun Thermoscan 5 (Kronberg, Germany) for ear temperatures; and the Exergen TAT-2000C for forehead temperatures. Please note that pacifier thermometers should be avoided because they are not believed to be accurate.

Newest clinical thermometers

The latest innovation in clinical thermometry is the noncontact, infrared forehead thermometer. One model sold for use in pandemics (eg, Ebola, influenza) is the Thermofocus 01500A3, manufactured by Tecnimed (Varese, Italy). It is placed a few inches from the center of the forehead and positioned so that 2 beams of light emanating from the device overlap. A button is depressed and the temperature is displayed seconds later. Tecnimed states that the device’s reading is as accurate as an axillary temperature. The Thermofocus can store up to 9 measurements, and it sells for about $80 on Amazon.com.

Thermomedics (Delray Beach, Florida) released its Caregiver clinical-grade, noncontact infrared thermometer last year. The device is very rugged, and takes a measurement when placed 0.5 inches to 2 inches from the forehead. It can store up to 30 readings. Like the Thermofocus, the Caregiver can be used to measure environmental objects (eg, heated baby formula in a bottle) as well. The Caregiver sells for $357 and comes with a 2-year warranty, with a lifetime warranty optional. According to the manufacturer, the device displays a reading that should be interpreted as an oral temperature.

Note that I’m not aware of any peer-reviewed articles evaluating noncontact, clinical- grade thermometers such as the Caregiver and the Thermofocus. I’ve used both devices in my clinic on dozens of children, both febrile and afebrile, and I have found the readings to closely correlate with temperatures taken by our TAT-5000.

Next: Expediting medical documentation

In conclusion

As clinicians, we often take our tools for granted. We are able to record one of our most important vital signs because of the efforts of scientists and physicians centuries ago. Our readings are displayed in seconds, but it remains up to the pediatrician to determine the cause, treatment, and consequences of the illness associated with the fever.

REFERENCES

1. Pearce JM. A brief history of the clinical thermometer. QJM. 2002;95(4):251-252.

2. Avner JR, Baker MD. Management of fever in infants and children. Emerg Med Clin North Am. 2002;20(1):49-67.

3. Baraff LJ. Management of fever without source in infants and children. Ann Emerg Med. 2000;36(6):602-614.

4. Carstairs KL, Tanen DA, Johnson AS, Kailes SB, Riffenburgh RH. Pneumococcal bacteremia in febrile infants presenting to the emergency department before and after the introduction of the heptavalent pneumococcal vaccine. Ann Emerg Med. 2007;49(6):772-777.

5. Majeed HA. Differential diagnosis of fever of unknown origin in children. Curr Opin Rheumatol. 2000;12(5):439-444.

6. Kenney, RD, Fortenberry JD, Surratt SS, Ribbeck BM, Thomas WJ. Evaluation of an infrared tympanic membrane thermometer in pediatric patients. Pediatrics. 1990;85(5):854-858.

7. Freed, GL, Fraley JK. Lack of agreement of tympanic membrane temperature assessments with conventional methods in a private practice setting. Pediatrics. 1992;89(3):384-386.

8. Exergen Corp. Temporal artery thermometer instructions for use. TemporalScanner 2000C. Available at: http://www.exergen.com/medical/PDFs/tat2000c manual 818621r5 artwork.pdf. 2005. Accessed February 16, 2016.

Dr Schuman, section editor for Peds v2.0, is adjunct assistant professor of pediatrics, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire, and editorial advisory board member of Contemporary Pediatrics. He has nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article.