15.4: Temperature
By the end of this section, you will be able to:
- Differentiate optimal from other temperature ranges for patients
- Describe the types of thermometers used to obtain patient temperature
- Identify factors affecting patient temperature
Body temperature reflects the balance between heat produced and heat lost. Heat is produced in the body during muscle movement and the normal physical and chemical process, called metabolism. A patient’s temperature is one of the four main measurements routinely monitored to determine function of the body, along with heart rate, respiratory rate, and blood pressure (Johns Hopkins Medicine, 2023). A patient’s body temperature is considered a vital sign, meaning that it can provide the nurse with critical or vital information. Temperature provides clues to other body systems, and or processes for maintaining homeostasis, such as the presence or absence of an infection, a functioning hypothalamus, and an effective integumentary system. Temperature is measured in either degrees Fahrenheit (°F) or degrees Celsius (°C). In the United States, the Fahrenheit scale is mostly used, and patients are most familiar with thinking of temperature in terms of Fahrenheit degrees. In health care, both Fahrenheit and Celsius measurements are documented (Table 15.5).
| Fahrenheit | Celsius |
|---|---|
| 97° | 36.1° |
| 98.6° | 37° |
| 99° | 37.2° |
| 100.4° | 38° |
| 102° | 38.9° |
| 104° | 40° |
The body is able to maintain a normal temperature through a variety of governing biochemical mechanisms, but at times, these mechanisms may behave in ways that cause abnormalities that require treatment. Intact skin, metabolism, and brain function all aid in temperature regulation . When one of these features becomes impaired or stretched beyond its limits, temperature maintenance, among other processes, is lost. To determine if the temperature is in the normal range, the nurse uses a thermometer to obtain a reading. Because of the variety of thermometers available, the nurse can choose the best one for the patient.
A nurse is caring for a patient in the emergency department who had wisdom teeth extracted a week ago. The patient came to the emergency department for a two-day history of fevers, chills, and drainage from oral wounds. The nurse is preparing to obtain the initial set of vital signs. After analyzing the presenting symptoms, the nurse obtains the axillary thermometer rather than the more commonly used oral thermometer because of the patient’s recent procedure and oral complications.
Temperature Ranges
Targeted temperature management is an average overall scale with normal fluctuations, which can range between 97ºF and 99ºF (36.1°C and 37.2°C). The targeted range for body temperature is referred to as normothermia. Fluctuations occur within normothermia due to circadian rhythm, metabolism, and hormones. For instance, circadian rhythm refers to the body’s natural ability to lose heat in the extremities due to naturally occurring vasodilatation of the cutaneous vasculature during sleep-wake cycles. Changes in body temperature naturally drop between the hours of 3 and 5 a.m. and again between 1 and 4 p.m. Times of high metabolic activity increase temperature because of the increase in chemical reactions producing heat within the body. Exercise, infection, and hyperthyroidism are all examples of increased metabolic needs. Fluctuations of the thyroid hormone affect metabolic activity as well, meaning that an increase in thyroid hormone will increase the temperature (Whitmer, 2021).
The body’s ability to maintain its temperature within normal ranges is called thermoregulation. The hypothalamus is responsible for thermoregulation and is an endogenous, or internal, mechanism of heat regulation. For example, if the body’s temperature is increasing, the hypothalamus will detect this change and increase blood flow to the body’s surface, which in turn activates the sweat glands, inducing perspiration. If the body’s temperature is decreasing, the hypothalamus will induce shivering to create more heat (Figure 15.15).
When temperatures are markedly outside of normal ranges, they are considered either hyperthermia or hypothermia . When the core body temperature is more than 105.8°F (41°C), hyperthermia occurs. When the temperature is less than 95°F (35°C), it is known as hypothermia. These conditions are the result of exogenous factors (variables outside the body’s control), such as the environment, not the result of the hypothalamus. Cold water and very cold or very hot air temperatures are just some examples of exogenous (outside the body) environmental factors that affect temperature.
Mechanisms of Heat Transfer
Heat is transferred from areas of higher temperatures to lower temperatures. When heat is transferred, it may affect temperature. For example, after exercising, which causes a small increase in body temperature, an individual may take a cool shower, which can lower the temperature due to heat transfer. Figure 15.16 illustrates the four methods of heat transfer, using a newborn as an example: conduction, convection, radiation, and evaporation (Whitmer, 2021).
Conduction
When heat is transferred between two objects in direct contact, conduction occurs. Heat is given off in waves through the surface of the body. An example of conduction is when a heating pad is used to warm muscles, or when the body transfers internal heat to an ice pack and melts the ice. Conduction is an important process in heat transfer because it allows instant lowering of the body temperature but only allows approximately 3 percent of heat loss. This means the body can transfer excessive heat from one selected area to another. For example, a burned hand with an ice pack placed on it allows heat to be transferred, not losing more than 3 percent of the body’s overall heat. Nurses can alter the environment to increase heat transfer through conduction by providing interventions such as cool or tepid sponge baths, cool packs, and cooling blankets.
Convection
Another mechanism of heat transfer is convection . It occurs through air or water currents. An example of convection is the internal heat lost using a ceiling fan, which circulates air currents. Heat is also lost through this method by cold and windy environmental conditions. Convection permits heat loss of as much as 15 percent. Nurses may use convection to alter the patient’s environment through the use of a fan, air conditioner, or heater.
Scenario: An experienced nurse is precepting a nursing student in the emergency department when emergency medical services brings in a hypothermic patient found passed out at the bus stop at 2 a.m. It is early spring, and the temperature that night dipped to 47°F (8.3°C). The patient is unconscious and only wearing an undershirt and pants. The patient’s jacket was found on the bench. The blood alcohol level is extremely elevated at 0.27, while the core body temperature is 92°F (33.3°C).
Nurse: Do you know that alcohol intoxication can actually make a person more susceptible to hypothermia?
Student Nurse: I thought it made you warmer.
Nurse: It does make a person feel warmer which is actually dangerous. People feel so warm that they remove their clothing, even when it is too cold outside.
Student Nurse: Okay, yes, that makes sense, and then they lose heat due to convection. I was just studying that for the NCLEX.
Scenario follow-up: From this conversation, the nurse was able to educate the student nurse on the life-threatening nature of convection heat loss that occurred because of the removal of clothing in cold weather.
Radiation
Heat transfer through infrared waves is called radiation . It can account for as much as 60 percent of heat loss, the most of the heat transfer methods. For example, an individual may be outside on a warm day but, due to radiation, have vastly different experiences depending on, for example, where they are situated. For instance, standing in the sun allows the sun’s infrared rays to transfer heat to the individual and increase body temperature. In contrast, standing in the shade prevents these infrared rays from reaching the individual, causing the temperature to remain the same. Radiators are an example of radiation used to provide heat in homes. Nurses can alter the environment in clinical settings by utilizing a heat lamp or placing a newborn under a radiant warmer (Figure 15.17).
Evaporation
The transfer of heat through the change of water from a liquid to vapor is evaporation , another method of heat transfer that people experience daily. The human body utilizes this mechanism through perspiration. Other examples of its use to lower temperature are stepping out of a pool or shower and needing to reach for a warm towel. The rate of evaporation and subsequent cooling is often related to the environmental humidity. For example, when comparing moderate temperatures and air humidity in a very humid environment, the rate of evaporation and cooling is decreased, whereas in a dry environment, the rate is increased. Evaporation accounts for as much as 20 percent of heat loss (White, 2021).
Fever Processes
Fever, also known as pyrexia , is defined as an elevated body temperature triggered by the hypothalamus . It is a sign of disease. Infection, inflammation, malignancy, and autoimmune conditions cause fever through a pyrogen , or fever-inducing substance. Once a pyrogen is detected, the hypothalamus triggers a fever to defend the body. With an increase of just 33.8°F (1°C), the body increases the metabolic rate by 10 to 12 percent. This increased metabolic rate, in turn, requires an increase in the oxygen demand that increases the heart and respiratory rate . Protein, instead of bacteria-loving glucose, is the preferred source of energy. The immune system also is bolstered, evidenced by increased white blood cell activity, interferon production, and T-cell activation. This elevated temperature also discourages the growth of microbes, which grow best at normal body temperature s. Pyrexia may also occur due to exercise, and an elevated temperature may be affected by the patient’s gender, age, or emotions. Time of day also correlates to temperature changes.
Scenario: A nurse, working at an urgent care clinic, escorts a patient who has been complaining of daily low-grade fevers.
Nurse: What brings you in today?
Patient: Well, I haven’t felt sick, but I’ve been having low-grade fevers every day for over a week.
Nurse: Anything else going on?
Patient: No, nothing I can think of.
Nurse: How high did your temperature get?
Patient: 100.8°F (38.2°C).
Nurse: What prompted you to take your temperature?
Patient: Well, one day after my run I was feeling kind of shaky, and my temperature reached 100°F (37.8°C). It kind of scared me, but when I took it later that day, it was fine. Then I took it the next day, and it was still up. So, I started taking it every morning just to check. I don’t know, it got me worried. My sister said fevers could be a sign of cancer, so I wanted to get it checked out, just in case.
Nurse: Have you still been running every day?
Patient: Yes, I have been feeling okay.
Nurse: And do you usually take your temperature after you run?
Patient: Yes, that’s when I remember.
Nurse: I will be sure to let the healthcare provider know about your concern. She should be in shortly to examine you, but I did want to point out that sometimes your temperature will rise when your metabolic rate increases, or the speed at which your body converts energy. Running, really any kind of exercise, will increase your metabolic rate and your temperature.
Scenario follow-up: From this conversation, the nurse was able to educate the patient about the direct relationship between the metabolic rate and temperature.
Although fevers increase the survival rate from infections, they are quite uncomfortable due to the body aches, chills, and diaphoresis (sweating) that they cause. Because of the increased metabolism seen when fevers develop, tachycardia (elevated heart rate), piloerection (goosebumps), and flushed skin also occur (Table 15.6). A severely elevated fever, although rare, can be lethal.
| Subjective Findings of Fever (Symptoms) | Objective Findings of Fever (Signs) |
|---|---|
| Night sweats | Diaphoresis |
| Shivering or shaking | Tachycardia |
| Achiness | Piloerection (goosebumps) |
| Warm, flushed skin |
A medication that alleviates a fever is called antipyretic . Common antipyretics are acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs), such as acetylsalicylic acid (aspirin) and ibuprofen . Although these medications do lower a fever, that might not always be desired since the presence of a fever means that the body is fighting off the pyrogen , but when a fever becomes uncomfortable or very elevated, an antipyretic should be administered. Acetaminophen is safe to administer every four to six hours, even in infancy. Aspirin and other NSAIDs should not be administered during pregnancy. Aspirin should be avoided in children under 12 years of age because of the risk of Reye syndrome, and NSAIDs should be avoided in infants younger than 6 months of age. Long-term or excessive use of acetaminophen should be avoided since it can cause liver failure, while long-term or excessive use of ibuprofen should be avoided since it can cause kidney injury. In cases of pediatric or maternal fever, it is best to contact the healthcare provider to determine the best antipyretic to alleviate symptoms (see Table 15.6).
Stages of Fever
A fever naturally passes through stages as the cause of the infection is eliminated. These stages are the onset, duration, and resolution. The onset of a fever occurs when a temperature of 100°F (37.8°C) is attained. The onset can occur suddenly or gradually depending on the infectious agent. The typical duration of a fever is a few days and is followed by its resolution. During the fever, antipyretic medications may be administered but do not always eliminate the fever. The medications are working if they lower the fever and increase comfort.
Types of Thermometers
Thermometers are instruments that measure temperature. A variety of thermometer styles, including both noninvasive and invasive, are available. Glass thermometers, which contain mercury, were one of the first tools to measure temperature. These types of thermometers are no longer in use because of the danger posed by both the glass housing and the toxic element mercury. The most popular thermometers in homes and healthcare settings are digital, providing a near automatic result on a digital screen. A variety of digital thermometer types are available, for various routes, such as oral, rectal, tympanic, and axillary. The COVID-19 pandemic also played a role in the advent of newer thermometer technology due to the need to assess an individual’s temperature rapidly and accurately. One of the more popular thermometers introduced during this time was the no-contact thermal scan thermometers. The type of thermometer used is dependent on the individual and the situation.
See the competency checklist for Vital Signs: Temperature with Digital Thermometer. You can find the checklists on the Student resources tab of your book page on openstax.org.
Oral
The oral thermometer is the most common type used to measure temperature and yields an average normal result of 98.6°F (37°C). Historically, the oral thermometer was a glass mercury thermometer, but since these were found to be dangerous, they are no longer in use. Currently, oral thermometers are digital, providing a reading within seconds of their use. These thermometers measures temperature through contact with the sublingual region, under the tongue (Figure 15.18).
Although the oral thermometer is the most widely used, it does have some limitations. To be able to use the oral route, the patient must be able to understand and follow directions. If they cannot hold it in place, an inaccurate reading will be obtained. Most children will be able to begin using this route around the age of 5 years. Food and drink consumption and smoking can also lead to inaccurate results. Waiting twenty-five minutes after drinking a hot or cold beverage and waiting five minutes after smoking or chewing gum is best practice. Patients who breathe through their mouths have also been found to have lower oral temperature s. Oral thermometers should also be avoided in individuals with oral trauma . Figure 15.19 shows an oral thermometer.
Rectal
The rectal thermometer is considered the gold standard for infants (less than 1 year old) (Johns Hopkins Medicine, 2023). It is the most accurate but also the most invasive type of thermometer. For this reason, it is generally only used for infants and in critical situations. Also, a rectal temperature would be contraindicated with anorectal surgeries and procedures and for those with a low red blood cell count because of the risk of bleeding for those patients. The average rectal reading is approximately 0.5°F (0.3°C) to 1°F (0.6°C) higher than an oral reading. Because of its mode of insertion, into the rectum, the rectal thermometer is denoted by a red color and is only meant to be used rectally (Figure 15.20).
A wide variety of thermometers are commonly available on pediatric units. The reason for this variety is that the pediatric unit often cares for neonates through adolescents, requiring different types of thermometers. For infants through the age of 5 years, the axillary thermometer is often the preferred method of obtaining a temperature. If the reading is considerably low or high in an infant or toddler, a rectal thermometer may be used to verify the results. Most older preschoolers through adolescents are able to use the oral thermometer properly, making it the preferred method in this age group. For those children who are developmentally delayed or unable to follow directions, the axillary thermometer is used.
Another type of thermometer, the temporal thermometer, is becoming readily available on pediatric units because of its minimally invasive nature (Figure 15.21). Using the temporal thermometer, a nurse can obtain a temperature on a sleeping child without disrupting sleep. The temporal thermometer could be used on children older than 6 months old.
Axillary
Obtaining an axillary temperature is minimally invasive since it only requires contact with the skin of the axilla region under the arm, but its results are generally 1°F (0.6°C) lower than the oral route. Because it is minimally invasive, it is the preferred route of obtaining temperature in young children and those who are unable to follow directions.
Tympanic
The tympanic thermometer obtains a temperature through a probe inserted in the ear (Figure 15.22), and its results are slightly higher than an oral reading because of its proximity to an artery that feeds the hypothalamus . Although it is generally easy to obtain and minimally invasive, it should not be done in those patients with a suspected or known ear infection or facial or ear trauma.
Factors Affecting Temperature
As previously mentioned, internal temperature regulation is controlled by the hypothalamus. Factors affecting the ability of the hypothalamus to regulate temperature include age, gender, exercise, emotions, and even the time of day. Neonates, particularly preterm infants, have a difficult time maintaining temperature because of their immaturity and inability to shiver. Brown fat, which is developed during the last months of gestation, aids in neonate thermoregulation . Consequently, lack of brown fat in preterm babies compromises their ability to regulate their temperature. A low temperature in these age extremes may be more serious than a high temperature.
Body temperature is not statistically different in men and women, even though females tend to feel cooler (Parkinson et al., 2021). This difference may be attributed to a slightly more rapid metabolism and increased muscle mass in men. Females also experience temperature changes in relation to their menstrual cycle. For instance, the female’s body temperature drops just prior to ovulation and then increases following ovulation. Increased metabolic activity, such as exercising, has been found to increase body temperature. The human body’s circadian rhythm also affects temperature as the day progresses, with a peak between 10 a.m. and 1 p.m. Times of high metabolic activity increase temperature because of the increase in chemical reactions producing heat within the body (National Institute of General Medical Sciences, 2022). Interestingly, feelings of excitement or love can also increase temperature (Escobar, 2021).
When the body system is assaulted by an infectious agent, the body temperature plummets since all the resources are now targeted on the infection and not on thermoregulation. Because of this, a temperature below 97°F (36.1°C) requires immediate intervention to rule out a life-threatening infection. Very young and very old patients will have consistent temperatures slightly below the “normal range.” For example, the range 97.5°F to 98.5°F (36.4°C to 36.9°C) is considered normal for neonates and geriatric patients. However, it is important to remember these age groups react differently to drastic changes in temperature. For drastically high or low temperatures, an infant may become less active to stimuli and not want to eat, while an older adult patient may become confused and disoriented, or even agitated.
Physiological disorders may also cause fevers or the inability to thermoregulate. Certain cancers are known to cause fevers for reasons not fully understood, but because of the high-risk nature of this group, it is always imperative to rule out infectious causes of fever. Autoimmune disorders may also cause fevers through activation of the immune system . A traumatic brain injury can also affect thermoregulation because of damage to the hypothalamus .
Exposure to extreme or prolonged temperature extremes may also affect a person’s temperature. Being exposed to cold temperatures may lead to hypothermia , particularly if it is prolonged or if the person is underdressed or becomes wet. Hyperthermia may develop in the heat, particularly if the person is doing strenuous activity. Heat exhaustion occurs when the body temperature reaches higher than 100°F (38°C) due to the environment. Heat stroke occurs when the body temperature is greater than 104°F (40°C). Signs and symptoms of the progression to heat stroke are dry and hot skin with no sweating, high heart rate , and confusion or delirium. It can progress rapidly to convulsions and coma and may be fatal.
A temperature reading may also be inaccurate due to incorrect technique. If an abnormal result is obtained, it is best practice to repeat the reading. It may be necessary to check the accuracy of the results using a rectal thermometer if the condition warrants. For oral thermometers, verify that the patient has not eaten, drank, or smoked recently and that the thermometer is in the correct location in the mouth. For rectal thermometers, verify that the tip is inserted enough and that an excessive amount of lubricant was not used. For axillary thermometers, double-check that the tip of the probe is deep within the axillary region. For tympanic thermometers, straightening the ear canal could help obtain a more accurate reading.