Chapter 5 Vital Signs
Vital signs reflect the body’s physiologic status and provide information critical to evaluate homeostatic balance. Vital signsinclude four critical assessment areas:temperature, pulse, respiration and blood pressure. These four signs form baseline assessment data necessary for an ongoing evaluation of a client’s condition. If the nurse has established the normal range for a client, deviations can be more easily recognized.
Many factors such as the temperature of the environment, physical exertion, and the effects of illness cause vital signs to change, sometimes outside normal range. Vital signs should be taken at regular intervals. The more critical the client’s condition, the more often these signs need to be taken and evaluated. They are not only indicators of a client’s present condition, but also provide clues to a positive or negative change in status. An alteration in vital signs may signal the need for medical or nursing intervention.
Vital signs are a quick and efficient way of monitoring a client’s condition or identifying problems and evaluating the client’s response to intervention. Vital signs and other physiological measurements are the basis for clinical problem solving. Assessment of vital signs allows the nurse to identify nursing diagnoses, implement planned interventions, and evaluate nursing effect. When the nurse learns the physiological variable values influencing vital signs and recognizes the relationship of vital sign changes to other physical assessment findings, precise determinations of the client’s health problems can be made. Careful measurement techniques ensure accurate findings.
Guidelines for Taking Vital Signs
The nurse assesses vital signs whenever a client enters a health care agency. Vital signs are included in a complete physical assessment or obtained individually to assess a client’s condition. The nurse must be able to measure vital signs correctly, understand and interpret the values, communicate findings appropriately, and begin interventions as needed. The following guidelines assist the nurse to incorporate vital sign measurement into nursing practice:
1. The nurse caring for the client is responsible for vital signs measurement. The nurse should obtain the vital signs, interpret their significance, and make decisions about interventions.
2. Equipment should be functional and appropriate for the size and the age of the client. Equipment should be selected based on the client’s condition and characteristics. For example, an adult-size blood pressure cuff should not be used for a child.
3. The nurse should know the client’s normal range of vital signs. A client’s usual values may differ from the standard range for that age or physical state. The client’s usual values serve as a baseline for comparison with findings taken later. Thus a nurse can detect a change in condition over time.
4. The nurse should know the client’s medical history, therapies, and prescribed medications. Some illnesses or treatments cause predictable vital sign changes. Most medications affect at least one of the vital signs.
5. The nurse should control or minimize environmental factors that may affect vital signs. Measuring the pulse after the client exercises may yield a value that is not a true indicator of the client’s condition.
6. The nurse should use a systematic approach when taking vital signs. Each procedure requires following a step-by-step approach to ensure accuracy.
7. The physician decides the frequency of vital signs assessment according to the client’s condition. In the hospital the physician orders a minimum frequency of vital sign measurements for each client. Following surgery or treatment interventions, vital signs are measured frequently to detect complications.
8. The nurse may use vital sign assessment to determine indications for medication administration. The physician may order certain cardiac drugs to be given only within a range of pulse or blood pressure. The nurse does not administer these drugs if vital sign assessment is outside of these limits. Taking vital signs to determine clinical changes and trends is useful in making therapeutic decisions.
9. The nurse should analyze the results of vital sign measurement. The nurse is often in the best position to assess all clinical findings about a client. Vital signs are not interpreted in isolation. The nurse must also know other physical signs or symptoms and be aware of the client’s ongoing health status.
10. The nurse should verify and communicate significant changes in vital signs. Baseline measurements allow a nurse to identify changes in vital signs. When vital signs appear abnormal, it may help to have another nurse or a physician repeat the measurement. The nurse informs the physician of abnormal vital signs and documents and reports vital sign changes to nurses working the next shift.
SectionⅠBody Temperature
Physiology of Body Temperature
The body temperature reflects the balance between the amount of heat produced by body processes and the amount of heat lost to the external environment. There are two kinds of body temperature: core temperature and surface temperature. The core temperature is the temperature of deep tissues, such as the cranium, thorax, abdominal cavity, and pelvic cavity, and remains relatively constant. The surface temperature is the temperature of the skin, the subcutaneous and the fat tissue. Surface temperature fluctuates depending on blood flow to the skin and the amount of heat lost to the external environment.
Heat Production
Thermoregulation requires the normal function of heat-production processes. Heat is produced in the body through metabolism. Cellular chemical reactions require energy in the form of ATP. The amount of energy used for metabolism is the metabolic rate. Activities requiring additional chemical reactions increase the metabolic rate. As metabolism increases, additional heat is produced. When metabolism decreases, less heat is produced. Heat production occurs during rest, voluntary movements, involuntary shivering, and nonshivering thermogenesis.
Voluntary movements such as muscular activity during exercise require additional energy. The metabolic rate can increase up to 2000 times normal. Heat production can increase up to 50 times normal.
Shivering is an involuntary body response to temperature differences in the body. The skeletal muscle movement during shivering requires significant energy. Shivering can increase heat production 4 to 5 times greater than normal. Heat is produced to equalize body temperature.
Nonshivering thermogenesis occurs primarily in neonates. Vascular brown adipose tissue present at birth is metabolized for heat production.
Heat Loss
Heat loss and heat production occur simultaneously. The skin’s structure and exposure to the environment result in constant, normal heat loss through radiation, conduction, convection, and evaporation.
Radiation is the transfer of heat between two objects without direct contact by electromagnetic waves. Blood flows from the core internal organs carrying heat to skin and surface blood vessels. The amount of heat carried to the surface depends on the extent of vasoconstriction and vasodilation regulated by the hypothalamus. Heat radiates from the skin to any surrounding cooler object. Radiation increases as the temperature difference between the objects increases.
Peripheral vasodilation increases blood flow to the skin to increases radiant heat loss. Peripheral vasoconstriction minimizes radiant heat loss. Up to 85% of the human body’s surface area radiants heat to the environment. However, if the surroundings are warmer than the skin, the body absorbs heat through radiation.
The nurse increases heat loss through radiation by removing clothing or blankets. The client’s position enhances radiation heat loss (e.g., standing exposes a great radiating surface area and lying in a fetal position minimizes heat radiation). Covering the body with dark, closely woven clothing also reduces the amount of radiation heat lost.
Conduction is the transfer of heat from one object to another with direct contact. When the warm skin touches a cooler object, heat is lost. When the temperatures of the two objects are the same, conductive heat loss stops. Heat conducts through solids, gases, and liquids. Conduction normally accounts for a small amount of heat loss. The nurse increases conductive heat loss when applying an ice pack or bathing a client with cool water. Applying several layers of clothing reduces conductive loss. The body gains heat by conduction when contact is made with materials warmer than skin temperature, such as applying a warm pack or bathing a client with warm water.
Convection is the transfer of heat away by air movement. Heat is first transferred to air molecules directly in contact with the skin. Air currents carry away the warmed air. As the air current velocity increases, convective heat loss increases. An electric fan promotes heat loss through convection. Convective heat loss increases when moistened skin comes into contact with slightly moving air.
Evaporation is the transfer of heat energy when a liquid is changed to a gas. During evaporation, approximately 0.6 calorie of heat is lost for each gram of water that evaporates. The body continuously loses heat by evaporation. About 600 to 900 ml a day evaporates from the skin and lungs, resulting in water and heat loss.
By regulating perspiration or sweating, the body promotes additional evaporative heat loss. Millions of sweat glands located in the dermis of the skin secrete sweat through tiny ducts on the skin’s surface. When body temperature rises, the anterior hypothalamus signals the sweat glands to release sweat. During exercise and emotional or mental stress, sweating is one way to lose excessive heat produced by the increased metabolic rate.
People who lack sweat gland function are unable to tolerate warm temperatures because they cannot cool themselves adequately. Diaphoresis is visual perspiration of the forehead and upper thorax. When diaphoresis occurs, the body temperature is reduced. A lowered body temperature inhibits sweat gland secretion.
Evaporation is the main heat loss when environment temperature is higher than body temperature.
Regulation of Body Temperature
Body temperature is precisely regulated by physiological and behavioral mechanisms. For the body temperature to stay constant, and within the normal range, the relationship between heat production and heat loss must be maintained. This relationship is regulated by neurological and cardiovascular mechanisms.
Neural and Vascular Control
The hypothalamus, located between the cerebral hemispheres, controls body temperature the same way a thermostat works in the home. A comfortable temperature is the “set point” at which a heating system operates. In the home a fall in environmental temperature activates the furnace, whereas a rise in temperature shuts the system down. The hypothalamus senses minor changes in body temperature. The anterior hypothalamus controls heat loss, and the posterior hypothalamus controls heat production.
When nerve cells in the hypothalamus become heated beyond the set point, impulses are sent out to reduce body temperature. Mechanisms of heat loss include sweating, vasodilation (widening of blood vessels), and inhibition of heat production. If the hypothalamus senses the body’s temperature lower than set point, signals are sent out to increase heat production by muscle shivering or heat conservation by vasoconstriction (narrowing of blood vessels) of surface blood vessels. Lesions or trauma to the hypothalamus or spinal cord, which carries hypothalamic messages, can cause serious alterations in temperature control.
Behavioral Control
Humans voluntarily act to maintain comfortable body temperature when exposed to temperature extremes. When the environmental temperature falls, a person can add clothing, move to a warmer place, raise the thermostat setting on a furnace, increase muscular activity by running in place, or sit with arms and legs tightly wrapped together. In contrast, when the temperature becomes hot, a person can remove clothing, stop activity, lower the thermostat setting on an air conditioner, seek a cooler place, or take a cool shower. The ability of a person to control body temperature depends on (1)the degree of temperature extreme, (2) the person’s ability to sense feeling comfortable or uncomfortable, (3) thought processes or emotions, and (4) the person’s mobility or ability to remove or add clothes. Body temperature control is difficult if any of these abilities are absent or lost. Infants can sense uncomfortable warm conditions but need assistance in changing their environment. Older adults may need help in detecting cold environments and minimizing heat loss. Illness and decreased level of consciousness or impaired thought processes result in an inability to recognize the need to change behavior for temperature control. When temperature becomes extremely hot or cold, health-promoting behaviors have a limited effect on controlling temperature.
Factors Affecting Body Temperature
The site of temperature measurement (oral, rectal, axillary, tympanic membrane, esophageal, pulmonary artery, or even urinary bladder) is one factor that determines the client’s temperature within a narrow range.For healthy young adults the average oral temperature is 37℃. In clinical practice, nurses learn the temperature range of individual client. No single temperature is normal for all people.
Table 8-1 Average Temperature and Normal Range
Site Average Temperature Normal Range
oral 37℃ 36.3~37.2℃(97.3~99.0℉)
rectal 37.5℃ 36.5~37.7℃(97.7~99.9℉)
axillary 36.5℃ 36.0~37.0℃(96.8~98.6℉)
Many factors affect the body temperature. Changes in body temperature occur when the relationship between heat production and heat loss is altered by physiological or behavioral variables. The nurse must be aware of these factors when assessing temperature variations and evaluating deviations from normal.
Circadian rhythms
Body temperatures normally change 0.5 to 1℃over 24 hours. Temperature drops between 2 and 6 AM and peaks between 1 and 6PM in clients who work days and sleep nignts. Temperature patterns are not automatically reversed in people who work at night and sleep during the day. It takes 1 to 3 weeks for the cycle to reverse. In general, the circadian temperature rhythm does not change with age.
Age
Temperature regulation is labile during infancy because of immature physiological mechanisms. This can continue until puberty. Infant temperature may respond drastically to changes in the environmental. Special care is needed to protect newborns from environmental temperature change.
With aging the normal mean temperature is lower. Thus a temperature that seems normal in ayoung adult may represent a fever in an older adult. The older adult has a narrower range of body temperature than the younger adult. With aging, control mechanisms deteriorate and sensitivity totemperature extremes increases.
Hormone level
Women generally have greater variations in body temperature than men.
Hormone changes during ovulation and menstruation cause body temperature fluctuations. When progesterone level is low, the body temperature is lower than the baseline level. During ovulation, greater amounts of progesterone enter into the circulatory system and raise the body temperature to previous baseline level or by about 0.3℃to 0.6℃above basal temperature.
Body temperature changes also occur in women during menopause. Women who have stopped menstruating may experience period of intense body heat and sweating lasting from 30 seconds to 5 minutes. There may be intermittent increase in skin temperature of up 4℃during these periods, referred to as hot flashes. This is due to the instability of the vasomotor controls for vasodilatation and vasoconstriction.
Exercise
Muscle activity requires an increased blood supply and an increased carbohydrate and fat breakdown. This increased metabolism causes an increase in heat production. Any form of exercise can increase body temperature. Prolonged, strenuous exercise can temporarily raise body temperatures up to 38.3℃to 40℃.
Medication
Some medications can influence temperature, such as anaesthetic and febrifuge.
Stress
Physical or emotional stress, such as anxiety, can raise body temperature through hormonal and neural stimulation. Stimulation of the sympathetic nervous system can increase the production of epinephrine and norepinephrine, thereby increasing metabolic activity and heat production. Nurse may anticipate that a highly stressed or anxious client could have an elevated body temperature.
Environment
Environmental temperature extremes can raise or lower body temperature. The changes depend on the extent of exposure, air humidity, and the presence of convection currents.
Ingestion of hot/cold liquids
Drinking hot or cold liquids can cause slight variations in actual oral temperature readings.
Smoking
Smoking cigarettes or cigars can increase body temperature measurement.
Alterations in Body Temperature
Elevated Body Temperature
Changes in body temperature outside the normal range affect the set point. These changes can be related to excess heat production, excessive heat loss, minimal heat production, minimal heat loss, or any combination of these alterarions. The nature of the change affects the type of clinical problems a client experiences.
Fever
A body temperature above the usual range is called fever or hyperthermia. It occurs because heat loss mechanisms are unable to keep pace with excess heat production, resulting in an abnormal rise in body temperature. A single temperature reading may not indicate a fever, so some people recommend determining a fever based on several temperature reading at different times of the day compared to the normal for that person at that time, in addition to physical signs and symptoms of infection.
A true fever results from an alteration in the hypothalamic set point. Pyrogens such as bacteria cause a rise in body temperature. When they enter the body, pyrogens act as antigens, triggering the immune system. Hormone-like substances are released to promote the body’s defense against infection. These hormones also trigger the hypothalamus to raise the set point. To meet the new higher set point, the body produces and conserves heat. Several hours may pass before the body temperature reaches the new point. During this period the person experiences chills, shivers, and feels cold, even though the body temperature is rising. The chill phase resolves when the new set point, a higher temperature, is achieved. During the next phase, the plateau, the chills subside and a person feels warm and dry. If the new set point has been “over shot” or the pyrogens are removed, the third phase of a febrile episode occurs. The skin becomes warm and flushed because of vasodilation. Diaphoresis assists in evaporative heat loss. When the fever “breaks”, the client becomes afebrile.