Measurement of body temperature is essential to the evaluation of health status of animals in both clinical and research settings.1 Body temperature can be measured by several methods that are typically classified according to the invasiveness of the procedure, thermometer location, the extent of contact between the probe and the patient, and thermometer type.2–5 Invasive methods of temperature monitoring include arterial catheterization, urinary bladder catheterization, and insertion of esophageal probes.2,6,7 These methods require adequate patient sedation or restraint and technical skills to obtain temperature measurements.4,5 Whereas these invasive techniques provide the most accurate measurements of core body temperature, they are not practical for routine temperature measurement and are typically reserved for monitoring of critical patients and research settings.2,7
Rectal thermometry is currently the most clinically acceptable and relatively noninvasive method to obtain body temperature measurements in animals. Glass mercury thermometers, digital thermometers, or predictive thermometers that are in contact with the rectal mucosa for various time periods are routinely used.2,7 Glass thermometers are used less often and require a longer time to equilibrate to body temperature. Digital thermometers require less time than glass thermometers, but still typically require 45 to 60 seconds to measure rectal temperatures. Digital predictive thermometers require the shortest measurement time because they use the initial rate of temperature change to predict the final temperature reading.2,3
In veterinary medicine, rectal temperature measurement is the typical method used to estimate core body temperature.3–6,8,9 However, measurement of rectal temperature requires adequate manual restraint and, therefore, can cause stress to animals, particularly those not accustomed to manual restraint.10,11 This effect may be amplified in a research setting,8 where a study protocol may require frequent measurements.8 Furthermore, stress associated with restraint and temperature measurement may have negative physiologic effects on the animal, increasing core body temperature and potentially leading to false assumptions regarding the overall health status of the animal.7–10 A study12 of hospitalized dogs indicated that the magnitude of tachycardia and other behavioral indicators of stress were greater when temperature was measured with rectal thermometry versus other methods. Furthermore, gastrointestinal variables (eg, peristalsis and volume of fecal material) may affect temperature measurements obtained with a rectal thermometer.3–5 Because of these factors, there has been increasing interest in noncontact, noninvasive measurement techniques for estimating core body temperature in animals.
The use of infrared tympanic thermometers has been investigated.4,5 This method provides for relatively rapid acquisition of a temperature measurement from a relatively easily accessible anatomic site.2,6,9 Infrared thermometers measure the amount of radiation emitted from the tympanic membrane via a sensor probe.13 The probe detects the thermal source, and the infrared radiation is converted to an electric signal and calibrated to display a temperature reading.6,14 Because the tympanic membrane shares its blood supply with the hypothalamus via the carotid artery, core body temperature can be approximated from this measurement.2,9,15 However, because tympanic membrane temperature is variably cooler than core body (hypothalamic) temperature, tympanic thermometers have a built-in offset that converts the measured temperature to core body or rectal temperature to compensate for this difference.15,16
Tympanic thermometry is currently widely used in human patients because of the ease and rapidity of use.13,14,16,17 Tympanic thermometry in veterinary medicine has been evaluated in several species, including cats,5,8 dogs,2–4,12,18 rabbits,6 guinea pigs,7 monkeys,9 goats,19 sheep,19 cows,20 and horses.19 However, results have varied greatly between species and between studies, with some studies2,5,9,18,19 finding close agreement between tympanic and rectal temperature measurements, whereas other studies3,4,6,7,19 report a lack of agreement. Aside from species differences, various studies have also compared tympanic thermometer measurements with various gold standards. Although some investigators have used invasive methods as the gold standard,2,3,8 others have used commercial rectal thermometers with various rectal insertion depths.4–7,9,18 Therefore, differences in the procedures and methods of comparison may also have affected the conclusions of previous studies.
Tympanic thermometers designed for human use have been studied and used in veterinary medicine.4–6,9 However, because of the differences in the anatomy of the ear canal between veterinary species, tympanic thermometers specifically designed for companion animals have recently been developed.3,6,9,18 The latter devices have a smaller probe, allowing for more precise placement into the ear canal.9,18 The ear canal in dogs and cats consists of horizontal and vertical canals that need to be traversed to reach the tympanic membrane.9 This differs from the relatively straight ear canal in human patients, which generally allows for easier positioning of the tympanic thermometer probe when recording tympanic temperature.21 The ear canal in chinchillas lies in a dorsal to ventral direction, parallel to the tympanic membrane.22,23
We are not aware of prior studies evaluating the use of tympanic thermometers in chinchillas. In addition to being pets, chinchillas are used extensively in experimental studies of otitis media and hearing loss and as an experimental model of ototoxicosis.23–29 Because measurement of rectal temperature can be time consuming and stressful, tympanic thermometry may offer a suitable alternative for measurement of body temperature in chinchillas. Therefore, the objectives of the study reported here were to assess the clinical practicality and reliability of tympanic thermometry in chinchillas, evaluate the effects of restraint time and thermometer insertion depth on rectal temperature measurements, and determine the extent of agreement between temperature measured with 2 tympanic and a rectal thermometer. It was our hypothesis that there would be good agreement between the results of tympanic and rectal thermometry in chinchillas.
R & R Chinchilla Inc, Jenera, Ohio.
Vet-Temp Rapid Digital Thermometer DT-10, Advanced Monitors Corp, San Diego, Calif.
Traceable Digital Thermometer 15-077-8, Fisher Scientific, Pittsburgh, Pa.
Thermoscan IRT 4520, Braun, Southborough, Mass.
Vet-Temp VT-150, Advanced Monitors Corp, San Diego, Calif.
Research Randomizer, version 4.0, Geoffrey C. Urbaniak and Scott Plous, Middletown, Conn. Available at: www.randomizer.org. Accessed Nov 5, 2015.
R: a language and environment for statistical computing, R Foundation for Statistical Computing, Vienna, Austria. Available at: www.r-project.org. Accessed Nov 5, 2015.
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