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While humans maintain a consistent internal body (core) temperature independent of the outside environment, the body’s surface or skin temperature can vary widely with environmental conditions and physical activity. Despite these fluctuations, the core temperature remains relatively constant, unless febrile illness or exposure to extremes in external temperature occurs. The body’s cells, tissues, and organs require this constant internal temperature and function optimally within a relatively narrow temperature range. When measured orally, body temperature in adults usually ranges from 36.2°C to 37.9°C (97°F to 100°F). This state of normal body temperature in a patient is termed afebrile. When oral temperature exceeds 38°C (100.4°F), this is termed hyperthermia, fever, or pyrexia. Infants are considered to have a fever with a rectal temperature of 38°C (100.4°F) or an oral temperature of 37.2°C (99°F) (American Academy of Pediatrics [AAP], 2020). In general, oral, temporal, and tympanic temperatures tend to read similarly and are slightly lower than rectal temperatures, which most accurately reflect core temperature; axillary temperatures read slightly lower than do oral temperatures (Harding et al., 2020). Refer to Table 19-2, which lists reference ranges for adult temperatures at diƯerent body sites. TABLE 19- REFERENCE RANGES FOR ADULT TEMPERATURE FROM DIFFERENT BODY SITES Oral Axillary Rectal Tympanic 97°F–100°F 96°F–99°F 98°F–101°F 97°F–100°F 36.2°C–37.9°C
35.6°C–37.8°C
36.7°C–38.3°C
36.2°C–37.9°C
Regulation of Body Temperature Body temperature regulation requires the coordination of many body systems. For the core temperature to remain steady, heat production must equal heat loss. The thermoregulatory center in the anterior hypothalamus is the body’s built-in thermostat. It senses small changes in body temperature and stimulates the necessary responses in the nervous system, circulatory system, skin, and sweat glands to maintain homeostasis (state of dynamic equilibrium) (Hill & Mitchell, 2021). HEAT PRODUCTION The body continually produces heat as a by-product of metabolism, chemical reactions that occur in body cells. The process of thermoregulation keeps core temperature fairly constant regardless of where the heat is being produced. The basal metabolic rate (BMR) reflects the amount of energy the body uses, and thus the amount of heat produced, during absolute rest in an awake state. Physical exercise, increased production of thyroid hormones, and stimulation of the sympathetic nervous system can increase heat production. HEAT LOSS Just as the body is continually producing heat, it is also continuously losing heat through the skin and lungs. Heat is lost through four processes: radiation, conduction, convection, and evaporation. p. 374
processes, which are usually lowest in the early morning during sleep. This occurs to an even greater degree in infants and children. EXERCISE Body temperature increases with exercise because of increased breakdown of carbohydrates and fats to provide energy. Strenuous exercise, such as running a marathon, can temporarily raise the temperature to as high as 40°C (104°F). STRESS Emotional or physical stress can elevate body temperature. When stress stimulates the sympathetic nervous system, circulating levels of epinephrine and norepinephrine increase. As a result, the metabolic rate increases, which, in turn, increases heat production. Patients who have stress or anxiety may have an elevated temperature with no underlying pathology. HORMONES People assigned female at birth usually have greater variations in their temperature than do people assigned male at birth. Progesterone, a hormone secreted at ovulation, increases body temperature 0.3°C to 0.6°C (0.5°F to 1°F) above baseline. By measuring temperature daily, people can determine when they ovulate, which is the basis for the natural family planning method of birth control (see Chapter 40). After menopause, mean temperature norms are the same for all genders. Thyroxine, epinephrine, and norepinephrine also elevate body temperature by increasing heat production. Factors AƯecting Body Temperature Measurement External factors can lead to false temperature readings. Small alterations in oral temperature readings can occur after smoking or chewing gum or when oxygen is administered by mask or cannula. Hot or cold drinks may also cause variations in oral temperature readings. Diaphoresis or air blowing over the face may aƯect temporal artery measurements; stool in the rectum can aƯect rectal temperatures.
Assessing Body Temperature Temperature measurement establishes a baseline for comparison as a disease progresses or therapies are instituted. The accuracy of a temperature value depends on the site used and adherence to the correct procedure for the site and device. Accurate measurement using appropriate technique is especially important since it will aƯect diagnosis and treatment (Fitzwater et al., 2019; Pecoraro et al., 2021). When repeated measurements are evaluated on the same patient, the same device and site should be used (Dante et al., 2020). SITES Core body temperature is measured most accurately using invasive devices in sites such as the bladder or esophagus (Jevon, 2020); however, these sites require special probes. More easily accessed sites are the rectum, mouth, forehead (temporal artery), axilla, and ear (tympanic). While rectal and oral temperature measurement routes are most accurate and recommended, other routes will be described in this section, as some facilities still use them, and appropriate route may diƯer based on the setting. Because body temperature can vary due to many factors, a baseline should be obtained and used to evaluate subsequent changes for the individual. Refer to Table 19-2 for reference ranges for various sites. p. 375 p. 376 Rectal Rectal temperature is the peripheral route that most closely approximates core temperature and is therefore the most accurate (Pecoraro et al., 2021). It is the only recommended route for infants younger than 3 months of age (American Academy of Pediatrics [AAP], 2020). The rectal route is not appropriate for all patients in all situations, so use clinical judgment when selecting the route to measure temperature. If this route is used, position the thermometer away from fecal material, which may falsely elevate the temperature reading.
Axillary Axillary temperature readings are always lower than rectal readings, but the exact diƯerence in clinical practice is inconsistent (Teller et al., 2019). Bathing, diaphoresis, and ambient air temperature may influence the reading, so consider this when interpreting the result. While measurement by the axillary route is useful for screening for fever, especially among pediatric patients, it should not be relied upon for accurate measurements and should be interpreted in the context of the patient’s condition (AAP, 2020; Teller et al., 2019). Ear Since the development of the tympanic membrane thermometer, the ear has been added to the list of sites where temperature can be measured. While this route has not been recommended in the past, technological innovations to devices have again made this route a viable option (Dante et al., 2020; Jevon, 2020; Shi et al., 2020). It may be used on adults and children over 6 months of age (AAP, 2020). Reading and accuracy of the result can be aƯected by the presence of cerumen, patient position (lying on the side of temperature measurement), and ear canal size that cannot accommodate the device (Hill & Mitchell, 2021; Jevon, 2020). EQUIPMENT Equipment used for temperature measurement includes electronic thermometers, tympanic membrane thermometers, temporal artery thermometers, noncontact infrared thermometers (NCITs), and disposable paper thermometers. Disposable paper thermometers, which are thin strips of chemically treated paper used to measure oral and axillary temperature, are available but are not commonly used. Mercury thermometers, no longer used due to the dangers of exposure to mercury, may still be found in homes and should be replaced with other equipment and properly disposed of. Thermometers are considered medical devices by the U.S. Food and Drug Administration (FDA, 2022) and therefore must adhere to standards for safety and eƯicacy. Tympanic Membrane Thermometers
The tympanic membrane thermometer is a portable, handheld device resembling an otoscope that recharges using a battery pack. It records temperature through a sensor probe placed in the ear canal to detect infrared radiation from the eardrum. It is noninvasive and fast to use but should not be used on people with ear drainage or scarred tympanic membranes. These thermometers are especially useful in assessing children for fever when the rectal or oral routes are not appropriate (Dante et al., 2020; Jevon, 2020; Shi et al., 2020). Temporal Artery Thermometers The temporal artery thermometer is a handheld device that scans the forehead and measures temperature over the temporal artery (Fig. 19-1). Measurement of temperature over the temporal artery requires contact with skin but not mucous membranes. For accuracy, the head must be uncovered since bandages or clothing will trap heat. Measurement of temperature using this method is one of the least accurate and is not recommended (Fitzwater et al., 2019; Kiekkas et al., 2019; Nygaard et al., 2020). p. 376 p. 377 Outcome-Based Teaching Plans Sylvia Yantes, 26 years old, has just given birth to her first child, a boy weighing 5 lb, 10 oz. Her son had three elevated temperature readings during the first 24 hours of life. Before Sylvia and her son can go home, she needs to be able to monitor his temperature. OUTCOME Before discharge, Sylvia (the mother) will be able to demonstrate accurate assessment of rectal temperature.
STRATEGIES
Provide the mother with a log indicating date and times and a place to fill in the temperatures obtained. Provide the mother with appointment information requesting that she bring the temperature log to that baby visit. When viewing the log at the first baby visit, provide positive feedback to the mother. Stress that the mother reports any temperature elevation above 38°C (100.4°F), which could indicate infection. Electronic Thermometers Healthcare organizations use electronic thermometers extensively for measuring oral, rectal, and axillary temperatures. The thermometer consists of a battery-powered display unit and a temperature-sensitive probe connected to the display unit by a thin cord. A disposable plastic sheath covers the probe to prevent the transmission of infection. Electronic thermometers provide readings in less than 60 seconds. The electronic thermometer is ideally suited for use with children because the sheath is unbreakable and the time necessary for accurate measurement is relatively short. A separate probe (often red) must be used for rectal temperature measurement. Noncontact Infrared Thermometers NCITs measure skin temperature by detecting infrared radiant energy that is emitted by the body (Sullivan et al., 2021). In most cases, the forehead is chosen as the site of measurement. Advantages of NCIT include speed of result, reduced patient discomfort, decreased cross contamination between patients due to no contact with skin or mucous membranes, and lack of need for plastic covers as is necessary with other devices (Aggarwal et al., 2020). Readings can be falsely elevated if the patient is wearing excessive clothing at the site; readings can be falsely decreased by use of makeup on the site, perspiration, or use of antipyretics (Aggarwal et al., 2020). Environmental conditions, such as wind, sun, or humidity, can also aƯect the accuracy of measurement (Spindel et al., 2021). Because of these factors and due to inconsistent data to support its accuracy, use
NCIT cautiously in the context of care delivery and consider the resulting temperature reading in combination with a thorough assessment of the patient (Aggarwal et al., 2021; Pecoraro et al., 2020; Spindel et al., 2021; Sullivan et al., 2021). Scales Temperature can be measured on the Celsius or Fahrenheit scale (Fig. 19-2). The scale used varies among organizations. Nurses do not routinely have to convert from one scale to the other; however, if conversion is necessary, use the simple conversion guide provided in Figure 19-2.
