Learning Supplement
Vital Signs – Body Temperature
Definition
Body temperature is the balance between heat produced in the body and heat
loss from the body.
Temperature-Regulating System
The balance between heat produced in the body and heat loss from the body is
maintained by the process of thermoregulation. Thermoregulation is psychological or
physiological.
 Psychological
Psychological regulation occurs when an individual perceives he is hot or cold.
If a person perceives he is cold, he then puts on a sweater.
 Physiological
The main physiological system regulating temperature is the autonomic
nervous system. Receptors in the skin, abdomen, and spinal cord send messages
to the autonomic nervous system that then sends it to the hypothalamus. The
hypothalamus acts as a central thermostat, receiving input from sensors that
detect hot or cold temperatures. When an individual’s set-point temperature
(temperature that thermoregulatory mechanisms attempt to maintain) increases,
a message is relayed to the hypothalamus, which initiates body responses that
decrease heat production and increase heat loss.
Heat Loss
The four main avenues of heat loss are: Radiation, Conduction, Evaporation, and
Convection.
1. Radiation
Transfer of heat from the surface of one object to the surface of another
without contact. Blood flows from the core internal organs carrying heat
to skin and surface blood vessels. Amount of heat carried to the surface
depends on the extent of vasoconstriction and vasodilation regulated by
the hypothalamus. About 85% of the bodies’ heat is loss via radiation to
the environment when heat leaves the body going to a cooler surface in
the environment.
2. Conduction
Transfer of heat from one object to another with direct contact. When the
warm skin touches a cooler object, the heat leaves the body to the cooler
surface. The amount of heat conducted from the body can be increased by
applying an ice pack or bathing with cool water. The opposite can take
place, a person can decrease the amount of heat loss by applying warm
blankets and not allow the body to come into direct contact with a cooler
surface. The body can actually gain heat via conduction when contact is
made with a warmer object.
3. Evaporation
Transfer of heat when a liquid is changed to a gas. When the body
temperature rises, hypothalamus signals the sweat glands to release
sweat. Sweat evaporates from the skin, resulting in heat loss. Same
principle applies with bathing. Heat is loss with water on the skin.
4. Convection
Transfer of heat away by air movements. Heat leaves the body to cooler
air currents that carry away the heat. An electric fan promotes heat loss
through convection.
Heat Conservation
The body conserves heat via Vasoconstriction. If there is a decrease in the
amount of blood that reaches the surface of the body, then there is not as much heat
that can be released or lost.
Heat Production
Heat is produced in the body by:
a. Increase Basal Metabolism Rate
b. Muscle contraction
c. Shivering
Average Ranges
Normal values of body temperature differ with age groups. Children, adults, and
older adults all have average ranges for each of these groups.
Children:
98.6 – 99.6 degrees F, oral
Adults:
98.6 +/- 1 degree F, oral
Older Adults: 97.6 +/- 1 degree F, oral
Normal values for rectal body temperature is usually 1 degree higher than the
oral and an axillary body temperature is 1 degree lower than the oral temperature.
Terms Related to Temperature
An elevation in body temperature is known a pyrexia, hyperthermia, or fever. A
very high fever (105.8 F) is called hyperprexia. The patient who has a fever is
referred to as febrile; the one without a fever is afebrile. A decreased body
temperature below normal ranges is known as hypothermia.
Interpreting the Temperature
After taking the temperature, the nurse needs to analyze the data and make a
nursing decision. The decision does not come from a single value. Rather, the nurse
needs to look at the relationship of the vital signs to each other, to previous findings,
and to other assessment findings.
If the temperature is above or below the normal range, the nurse should notify
the physician. They should also reassess the temperature more often than ordered.
Usually a patient has orders that specify the frequency to measure temperature and
parameters in which to notify the physician. If a patient’s temperature changes, you
may need to reassess more often than the order requires. This is a nursing
intervention.
Factors that Affect an Individual’s Temperature
1. Age
2. Activity / Exercise/ Sleep
3. Hormones
4. Stress
5. Environment
6. Medication
7. Illness
Sites / Method for Measuring Body Temperature
There are a number of sites for measuring body temperature. The four most
common methods are oral, rectal, axillary, and tympanic.
Oral – it is the most common and convenient site with large vascular supply.
The sublingual pocket under the tongue responds very quickly to changes in core
temperature. A disadvantage is the temperature can be inaccurate if the patient has
just ingested hot or cold food, is smoking, chewing gum, or if the patient breathes
through the mouth. Oral thermometers are not considered safe for infants, children,
elderly, disoriented, epileptic, or unconscious patients.
Rectal – is the most reliable measurement. The major disadvantages are it is
more unpleasant for the patient and inconvenient to gain access to the site. Rectal
temperatures do not respond to body temperature changes quickly, it cannot be
used with rectal surgery, and stool in the rectum can interfere with thermometer
placement that can lead to an inaccurate temperate reading.
Axillary – is the safest, most noninvasive, and easily accessible. The major
disadvantage is that a glass thermometer must be left in place for a long time to
obtain an accurate measurement. Does not always give a true reading of core
temperature. It is used for infants, children, patients, with oral problems, patients
breathing through their mouths, and irrational patients.
Tympanic – is readily accessible, minimal discomfort, and reflects the core
temperature. Major disadvantage is the cost of the equipment and inaccurate
reading related to incorrect positioning of the instrument.
Types of Thermometers
There is a wide variety of thermometers available today. The most commonly
used in the clinical setting is the electronic probe.
Electronic probe – battery operated unit with an attached heat sensitive probe
and disposable probe cover. This thermometer has a more rapid reading of the body
temperature. Can be used in all methods of assessing temperature.
Tympanic Thermometer – infrared light reflectance thermometer determines the
temperature of the tympanic membrane by measuring heat radiated as infrared
energy from that site. Because the hypothalamus and the tympanic membrane
share the same vasculature, the temperature measured reflects the core
temperature. Accuracy depends on placement of the probe in the ear.
Temperature sensitive tape – provides a generalization of body temperature and
is not an accurate measurement of the body temperature. If a temperature
elevation is noted, a more accurate measurement can then be obtained. Should be
placed on dry skin, the forehead is the most common site. A color change on the
tape is used to indicate the approximate body temperature.
Chemical in glass thermometer - measures the temperature by the movement
of chemical through the calibrated glass. This type of thermometer is no longer in
general use, but may still be found in some health care settings.
IV.
Student Activity in the Lab
1.
Practice taking a temperature with electronic thermometer on
classmates following correct procedure. Refer to the procedure in your
textbook.
2.
Chart the temperature on a graphic record and in the descriptive notes.
3.
Participate in simulated experiences.