Vital Signs
Introduction to Vital Signs
Vital signs are objective guideposts that provide data to determine a person’s state of health. Vital signs include temperature, pulse, respiration (collectively called TPR), and blood pressure (BP). Another indicator of a patient’s health status is pulse oximetry. Although some physicians order this measurement routinely on all patients as part of the patient workup, most physicians order this vital sign only when the patient complains of respiratory problems (e.g., shortness of breath).
The normal ranges of the vital signs are finely adjusted, and any deviation from normal may indicate disease. During the course of an illness, variations in the vital signs may occur. The medical assistant should be alert to any significant changes and report them to the physician because they indicate a change in the patient’s condition. When patients visit the medical office, vital signs are routinely checked to establish each patient’s usual state of health and to establish baseline measurements against which future measurements can be compared. The medical assistant should have a thorough knowledge of the vital signs and should attain proficiency in taking them to ensure accurate findings.
General guidelines that the medical assistant should follow when measuring the vital signs are as follows:
1. Be familiar with the normal ranges for all vital signs. Keep in mind that normal ranges vary based on the different age groups (infant, child, adult, elder).
2. Make sure that all equipment for measuring vital signs is in proper working condition to ensure accurate findings.
3. Eliminate or minimize factors that affect the vital signs, such as exercise, food and beverage consumption, smoking, and emotional state.
4. Use an organized approach when measuring the vital signs. If all of the vital signs are ordered, they are usually measured starting with temperature, followed by pulse, respiration, blood pressure, and pulse oximetry.
Temperature
Regulation of Body Temperature
Body temperature is maintained within a fairly constant range by the hypothalamus, which is located in the brain. The hypothalamus functions as the body’s thermostat. It normally allows the body temperature to vary by only about 1° to 2° Fahrenheit (F) throughout the day.
Body temperature is maintained through a balance of the heat produced in the body and the heat lost from the body (Figure 19-1). A constant temperature range must be maintained for the body to function properly. When minor changes in the temperature of the body occur, the hypothalamus senses this and makes adjustments as necessary to ensure that the body temperature stays within a normal and safe range. If an individual is playing tennis on a hot day, the body’s heat-cooling mechanism is activated to remove excess heat from the body through perspiration.

Heat Production
Most of the heat produced in the body is through voluntary and involuntary muscle contractions. Voluntary muscle contractions involve the muscles over which a person has control, for example, the moving of legs or arms. Involuntary muscle contractions involve the muscles over which a person has no control; examples are physiologic processes such as digestion, the beating of the heart, and shivering.
Body heat also is produced by cell metabolism. Heat is produced when nutrients are broken down in the cells. Fever and strong emotional states also can increase heat production in the body.
Heat Loss
Heat is lost from the body through the urine and feces and in water vapor from the lungs. Perspiration also contributes to heat loss. Perspiration is the excretion of moisture through the pores of the skin. When the moisture evaporates, heat is released and the body is cooled.
Radiation, conduction, and convection all cause loss of heat from the body. Radiation is the transfer of heat in the form of waves; body heat is continually radiating into cooler surroundings. Conduction is the transfer of heat from one object to another by direct contact; heat can be transferred by conduction from the body to a cooler object it touches. Convection is the transfer of heat through air currents; cool air currents can cause the body to lose heat. These processes are illustrated in Figure 19-2.
Body Temperature Range
The purposes of measuring body temperature are to establish the patient’s baseline temperature and to monitor an abnormally high or low body temperature. The normal body temperature range is 97° F to 99° F (36.1° C to 37.2° C), the average temperature being 98.6° F (37° C). Body temperature is usually recorded using the Fahrenheit system of measurement. Table 19-1 lists comparable Fahrenheit and Celsius temperatures and explains how to convert temperatures from one scale to the other.
Table 19-1
Equivalent Fahrenheit and Celsius Temperatures
Fahrenheit | Celsius |
93.2 | 34 |
95 | 35 |
96.8 | 36 |
97.7 | 36.5 |
98.6 | 37 |
99.5 | 37.5 |
100.4 | 38 |
101.3 | 38.5 |
102.2 | 39 |
104 | 40 |
105.8 | 41 |
107.6 | 42 |
109.4 | 43 |
111.2 | 44 |
Temperature Conversion | |
From Bonewit-West K: Clinical procedures for medical assistants, ed 8, St Louis, 2011, Saunders.
Alterations in Body Temperature
A body temperature greater than 100.4° F (38° C) indicates a fever, or pyrexia. If the body temperature falls between 99° F (37.2° C) and 100.4° F (38° C), this is called a low-grade fever. When an individual has a fever, the heat the body is producing is greater than the heat the body is losing. A temperature reading greater than 105.8° F (41° C) is known as hyperpyrexia. Hyperpyrexia is a serious condition, and a temperature greater than 109.4° F (43° C) is generally fatal.
A body temperature less than 97° F (36.1° C) is classified as subnormal, or hypothermia. This means that the heat the body is losing is greater than the heat it is producing. A person usually cannot survive with a temperature less than 93.2° F (34° C). Terms used to describe alterations in body temperature are illustrated in Figure 19-3.
Variations in Body Temperature
During the day-to-day activities of an individual, normal fluctuations occur in the body temperature. The body temperature rarely stays the same throughout the course of a day. The medical assistant should take the following points into consideration when evaluating a patient’s temperature.
1. Age. Infants and young children normally have a higher body temperature than adults because their thermoregulatory system is not yet fully established. Elderly individuals usually have a lower body temperature owing to factors such as loss of subcutaneous fat, lack of exercise, and loss of thermoregulatory control. Table 19-2 shows the normal ranges of body temperature according to age group.
Table 19-2
Variations in Body Temperature by Age
Age | Site | Average Temperature | |
Newborn | Axillary | 97° F-100° F | 36.1° C-37.8° C |
1 yr | Oral | 99.7° F | 37.6° C |
5 yr | Oral | 98.6° F | 37° C |
Adult | Oral | 98.6° F | 37° C |
Rectal | 99.6° F | 37.5° C | |
Axillary | 97.6° F | 36.4° C | |
Aural | 98.6° F | 37° C | |
Elderly (over 70 yr) | Oral | 96.8° F | 36° C |
From Bonewit-West K: Clinical procedures for medical assistants, ed 8, St Louis, 2011, Saunders.
2. Diurnal variations. During sleep, body metabolism slows down, as do muscle contractions. The body’s temperature is lowest in the morning before metabolism and muscle contractions begin increasing.
3. Emotional states. Strong emotions, such as crying and extreme anger, can increase the body temperature. This is important to consider when working with young children, who frequently cry during examination procedures or when they are ill.
4. Environment. Cold weather tends to decrease the body temperature, whereas hot weather increases it.
5. Exercise. Vigorous physical exercise causes an increase in voluntary muscle contractions, which elevates the body temperature.
6. Patient’s normal body temperature. Some patients normally run a low or high temperature. The medical assistant should review the patient’s past vital sign recordings.
7. Pregnancy. Cell metabolism increases during pregnancy, and this elevates body temperature.
Fever
Fever, or pyrexia, denotes that a patient’s temperature has increased to greater than 100.4° F (38° C). An individual who has a fever is said to be febrile; one who does not have a fever is afebrile.
Fever is a common symptom of illness, particularly inflammation and infection. When there is an infection in the body, the invading pathogen functions as a pyrogen, which is any substance that produces fever. Pyrogens reset the hypothalamus, causing the body temperature to increase to above normal. Fever is not an illness itself, but rather a sign that the body may have an infection. Most fevers are self-limited, that is, the body temperature returns to normal after the disease process is complete.
Stages of a Fever
A fever can be divided into the following three stages:
1. The onset is when the temperature first begins to increase. This increase may be slow or sudden, the patient often experiences coldness and chills, and the pulse and respiratory rate increase.
2. During the course of a fever, the temperature rises and falls in one of the following three fever patterns: continuous, intermittent, or remittent. Fever patterns are described and illustrated in Table 19-3. During this stage the patient has an increased pulse and respiratory rate and feels warm to the touch. The patient also may experience one or more of the following: flushed appearance, increased thirst, loss of appetite, headache, and malaise. Malaise refers to a vague sense of body discomfort, weakness, and fatigue.
3. During the subsiding stage, the temperature returns to normal. It can return to normal gradually or suddenly (known as a crisis). As the body temperature is returning to normal, the patient usually perspires and may become dehydrated.
Assessment of Body Temperature
Assessment Sites
There are five sites for measuring body temperature: mouth, axilla, rectum, ear, and forehead. The locations in which temperatures are taken should have an abundant blood supply so that the temperature of the entire body is obtained, not the temperature of only a part of the body. In addition, the site must be as closed as possible to prevent air currents from interfering with the temperature reading. The site chosen for measuring a patient’s temperature depends on the patient’s age, condition, and state of consciousness; the type of thermometer available; and the medical office policy.
Oral Temperature
The oral method is a convenient and one of the most common means for measuring body temperature. When the medical assistant records a temperature, the physician assumes it has been taken through the oral route, unless it is otherwise noted. There is a rich blood supply under the tongue in the area on either side of the frenulum linguae. The thermometer should be placed in this area to receive the most accurate reading. The patient must keep the mouth closed during the procedure to provide a closed space for the thermometer.
Axillary Temperature
Axillary temperature is recommended as a site for measuring temperature in toddlers and preschoolers. The axillary site also should be used for mouth-breathing patients and for patients with oral inflammation or who have had oral surgery.
The temperature obtained through the axillary method measures approximately 1° F lower than the same person’s temperature taken through the oral route (see Table 19-2). The medical assistant should make a notation to tell the physician that the temperature was taken through the axillary route.
Rectal Temperature
The rectal temperature provides an extremely accurate measurement of body temperature because few factors can alter the results. The rectum is highly vascular and, of the five sites, provides the most closed cavity. The temperature obtained through the rectal route measures approximately 1° F higher than the same person’s temperature taken through the oral route (see Table 19-2). The medical assistant should make a notation on the patient’s chart if the temperature has been taken rectally.
Aural Temperature
The aural (ear) site is used with the tympanic membrane thermometer. The ear provides a closed cavity that is easily accessible. Tympanic membrane thermometers provide instantaneous results, are easy to use, and are comfortable for the patient. They make it easier to measure the temperature of children younger than 6 years, uncooperative patients, and patients who are unable to have their temperatures taken orally.
Forehead Temperature
The temporal artery is a major artery of the head that runs laterally across the forehead and down the side of the neck. In the area of the forehead, it is located approximately 2 mm below the surface of the skin. Because the temporal artery is located so close to the skin surface and is easily accessible, the forehead provides an ideal site for obtaining a body temperature measurement. In addition, the temporal artery has a constant steady flow of blood, which assists in providing an accurate measurement of the patient’s body temperature.
The forehead site can be used to measure body temperature using a temporal artery thermometer in individuals of all ages (newborns, infants, children, adults, elderly). The results compare in accuracy with other methods used to measure body temperature. The temperature obtained through the forehead site is about the same as a rectal temperature measurement. The temporal artery reading measures approximately 1° higher than oral body temperature and 2° higher than axillary temperature on the Fahrenheit scale.
Types of Thermometers
The four types of thermometers available for measuring body temperature are electronic thermometers, tympanic membrane thermometers, temporal artery thermometers, and chemical thermometers. Mercury glass thermometers are no longer used in the medical office because they break easily and release mercury. Mercury is a chemical that is dangerous to the human body because it can cause damage to the nervous system. If mercury is released into the environment, it can be harmful to wildlife. Many cities have banned the sale or use of mercury because of its potential hazards.
Electronic Thermometer
An electronic thermometer is often used in the medical office to measure body temperature. Electronic thermometers are portable and measure oral, axillary, and rectal temperatures ranging from 84° F to 108° F (28.9° C to 42.2° C).
An electronic thermometer measures body temperature in a brief time, which varies between 4 and 20 seconds, depending on the brand of thermometer used. The temperature results are digitally displayed on an LCD screen. An electronic thermometer consists of interchangeable oral and rectal probes attached to a battery-operated portable unit (Figure 19-4). The probes are color-coded for ease in identifying them. The oral probe is color-coded with blue on its collar and is used to take oral and axillary temperatures; the rectal probe is color-coded with red on its collar and is used to take rectal temperatures only.

A disposable plastic cover is placed over the probe to prevent the transmission of microorganisms among patients. Depending on the method of taking the temperature, the probe may be inserted into the mouth, axilla, or rectum and is left in place until an audible tone is emitted from the thermometer. When the tone sounds, the patient’s temperature in degrees Fahrenheit is displayed on the screen. The medical assistant ejects the plastic probe cover into a regular waste container.
The casing, probes, and attached cords of the electronic thermometer should be periodically cleaned with a soft cloth slightly dampened with a solution of warm water and a disinfectant cleaner.
Procedures 19-1, 19-2, and 19-3 outline the methods for measuring oral, axillary, and rectal temperatures using an electronic thermometer.
Tympanic Membrane Thermometer
The tympanic membrane thermometer is used at the aural site. The tympanic membrane thermometer functions by detecting thermal energy that is naturally radiated from the body. As with the rest of the body, the tympanic membrane gives off heat waves known as infrared waves. The tympanic thermometer functions like a camera by taking a “picture” of these infrared waves, which are considered a documented indicator of body temperature (Figure 19-5). The thermometer calculates the body temperature from the energy generated by the waves and converts it to an oral or rectal equivalent.

The tympanic membrane thermometer is battery operated and consists of a small handheld device with a sensor probe (Figure 19-6). To operate the thermometer, the probe is covered with a disposable soft plastic cover and is placed in the outer third of the external ear canal. An activation button is depressed momentarily, and the results are displayed in 1 to 2 seconds on a digital screen. The probe cover is ejected into a regular waste container. The procedure for taking aural body temperature using a tympanic membrane thermometer is presented in Procedure 19-4.
Temporal Artery Thermometer
Measuring temperature using a temporal artery thermometer is the newest method for assessing body temperature. A temporal artery thermometer is an electronic device consisting of a probe attached to a portable unit (Figure 19-7).

To perform the procedure, a scan button is continually depressed while the probe is gently and slowly moved across the patient’s forehead. During this process, the probe sensor scans the forehead for the infrared heat given off by the temporal artery. The probe sensor captures the highest temperature or peak temperature in the area being scanned. The peak temperature represents the temperature given off by the temporal artery, or body temperature.
Along with measuring the peak temperature, the probe sensor automatically measures the ambient temperature, which is the surrounding air temperature. This is done because there is a small heat loss from the forehead that occurs as a result of cooling by ambient temperature. The thermometer’s computer determines and automatically corrects for any effect from ambient temperature. An accurate body temperature reading is digitally displayed on the screen on the thermometer. The procedure for measuring temperature using a temporal artery thermometer is presented in Procedure 19-5.

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