to 5 minutes. Tympanic temperatures are obtained by placing a tympanic membrane thermometer in the ear (Fig. 15-2, A). A stable reading is displayed within 3 seconds. In any case, for infection control reasons, the thermometer is covered with a disposable protective sheath, and proper hand washing before and after patient contact is also essential.
In the past, tympanic and rectal temperatures were the preferred assessments for all infants, as well as for adults when oral measures were not feasible. Even today, rectal thermometry is believed to be the most accurate reflection of core body temperature; however, temporal artery (TA) thermometers have been introduced (see Fig. 15-2, B). The TA lies superficial in the temporal region of the skull. A noninvasive swipe of the thermometer along the forehead and across the temporal region provides immediate, accurate measures closely correlating to core body temperature. Today, TA thermometry is popular.
In addition, infrared digital thermometers have gained popularity for identifying subtle skin temperature variations associated with vascular diseases (see Fig. 15-2, C). The thermographic unit conveniently scans and measures skin temperatures and is especially useful in wound management and with patients potential for diabetic foot neuropathies producing diminished blood supplies. It is important to recognize that infrared digital thermometers are not useful for measuring core body temperature and are strictly used to detect superficial skin temperature variations.
Body temperature readings may be measured in either degrees Fahrenheit (°F) or degrees Celsius (°C). Oral temperature readings in healthy adults and children are within the narrow range of 97.7° to 99.5° F (36.5° to 37.5° C) (Table 15-1). Tympanic measurements range from 95.9° to 99.5° F (35.5° to 37.5° C). Axillary temperatures register slightly lower, and rectal and TA temperatures register approximately 1° F higher than oral readings.
Normal Vital Signs
|Temperature (Varies With Meter Type)||97.6°-100° F (36.5°-37.8° C) (method of measurement is also charted as follows)|
|Average oral||98.6° O|
|Average tympanic||97.6° T|
|Average temporal artery||100° TA|
|Average rectal||99.6° R|
|Average axillary||97.6° A|
|Systolic||<120 mm Hg|
|Diastolic||<80 mm Hg|
Significance of Abnormalities
When the oral temperature is higher than 99.5° F, a fever exists (hyperthermia). A patient with a fever is said to be febrile. When the body temperature falls outside the normal range—for example, with an illness or a head injury—the metabolic rate changes accordingly, and the demands on the cardiopulmonary system also change. For example, when the body temperature increases, the metabolic rate also increases, resulting in increased oxygen consumption and carbon dioxide production at the cellular level. As the metabolic rate increases, the cardiopulmonary system must work harder to meet the additional cellular demands by providing more oxygen and eliminating carbon dioxide. As a result of increased body temperature, an increase in cellular metabolism occurs; therefore any event that increases cellular metabolism also increases body temperature.
Conversely, when the patient’s temperature falls below the normal range, hypothermia is said to be present. Although not common, hypothermia may be present in patients exposed to cold environmental temperatures and in those with trauma to the hypothalamus. In addition, medically induced hypothermia is used during heart surgery to decrease the metabolic demands, thereby decreasing the demand on the cardiopulmonary system.
Fevers are common with viral and bacterial infections as a natural response of the human body to increase cellular activity to combat the invading organism. Similarly, a patient may become febrile for a day or two after a surgical procedure as the body responds to initiate healing. Prolonged fever in these patients is evidence of postoperative infection. The culprit is often an infection in the wound, lungs, or urinary tract. Patients having a myocardial infarction might be febrile because of increased cellular activity. Hyperthermia also may result from injury to the temperature-regulating center of the hypothalamus, causing it to set the thermostat at a higher level. This injury may occur as a result of a cerebrovascular accident, cerebral edema (swelling), or tumor.
Despite the increased body temperature in some disease states, cellular function is optimal within only a narrow temperature range. Prolonged hyperthermia can lead to serious complications and resultant cellular damage. Patients with hyperthermia may become confused, dizzy, and even comatose. Conversely, hypothermia may be medically induced or the consequence of accidental exposure. Medically induced hypothermia is performed to therapeutically decrease the body’s need for oxygen. Because temperature is an easily measured indicator of the presence of disease, it is routinely followed as a yardstick of response to therapy for many conditions.
Adequate breathing (minute ventilation) is predicated on respiratory rate and depth of the breath. The depth of breath determines tidal volume. At rest, minute ventilation will generally be adequate provided the respiratory rates are at least 10 to 12 breaths per minute.
While assessing a patient’s respiratory rate, the health care professional obtains a general impression of the functional status of the respiratory system. The respiratory system is responsible for delivering oxygen (O2) from the environment to the tissues and eliminating carbon dioxide from the tissues to the environment. The cells of the body require a constant supply of oxygen for cellular metabolism. As a result of cellular metabolism, the waste product carbon dioxide is produced. Unless oxygen is continually supplied and carbon dioxide is continually eliminated, death will occur. Consequently, failure of the respiratory system is a life-threatening event.
The major muscle of ventilation is the diaphragm. During inspiration the diaphragm contracts, moving downward in the abdominal cavity and pushing the abdominal contents outward. The downward movement of the diaphragm causes an expansion of the chest cavity, along with a decrease in chest cavity pressure. With decreased internal pressure, air moves into the lungs. Expiration is achieved by simple relaxation of the diaphragm. As the diaphragm relaxes, it returns to its original position at the floor of the chest cavity. This action causes an increase of pressure, and subsequently air flows out of the lungs to the environment (Fig. 15-3).
In a healthy adult, a single respiration consists of an inspiratory phase and an expiratory phase. Because the diaphragm is responsible for the movement of air in and out of the lungs, respirations often are counted by observing the movement of the abdomen. A respiratory rate is also assessed by observing the rise (inspiration) and fall (expiration) of the chest; however, abdominal and chest wall movement may be difficult to detect by observation alone, particularly in patients who are breathing shallowly. In these cases, the hand of the health care professional may be placed on the patient’s abdomen or chest to assist in assessing each ventilation. However, obtaining a patient’s respiratory rate without the patient’s knowledge is best because, when aware, patients often alter their breathing rate and pattern. Therefore, after obtaining a pulse rate, many health care professionals leave their hand on the patient’s wrist and count the respiratory rate; the patient assumes that a pulse rate is still being assessed.
In the healthy adult, normal respirations are silent and effortless, automatically occurring at regular intervals. Respiratory rates are measured as the number of breaths per minute; normal range at rest is 12 to 20 breaths per minute (see Table 15-1). Children under the age of 10 years have slightly increased rates, averaging 20 to 30 breaths per minute. Newborns’ respiratory rates average 30 to 60 breaths per minute. Because respiratory rates are higher in children than in adults, counting respirations for a minimum of 1 minute is important to obtain an accurate measurement. In addition, while counting respirations the health care professional assesses the depth (shallow, normal, or deep) and pattern (regular or irregular) of ventilation. Therefore, by assessing the rate, depth, and pattern, an overall impression of the respiratory system can be obtained.
Significance of Abnormalities
Any deviation from normal indicates a change in the status of the respiratory system. If cellular metabolism increases, then the demand for oxygen increases, as does the production of carbon dioxide. The respiratory system responds by increasing the respiratory rate to deliver additional oxygen to the blood. Similarly, with increasing respiratory rates, more carbon dioxide will be exhaled by the lungs. Tachypnea is the term used to describe respiratory rates greater than 20 breaths per minute in the case of an adult patient. Common causes of tachypnea include exercise, fever, anxiety, pain, infection, heart failure, chest trauma, decreased oxygen in the blood, and central nervous system disease.
Bradypnea is the term used to describe a decrease in the respiratory rate. Bradypnea occurs much less frequently than tachypnea. Bradypnea results from depression of the respiratory center of the brain—common with drug overdoses, head trauma, and hypothermia. Dyspnea is a common term used to describe difficult breathing. Orthopnea refers to difficulty breathing (dyspnea) unless sitting up or standing erect. Apnea is the term used to identify the absence of spontaneous ventilation; it is an ominous sign.
The cardiovascular system is a closed fluid system composed of a pump (the heart) and many blood vessels. When the left ventricle of the heart contracts, blood is pumped out of the heart into the aorta and throughout the arteries of the body. The function of the cardiovascular system is to transport oxygenated blood from the lungs to the cells of the body and to return deoxygenated blood back to the heart and lungs to become reoxygenated. In addition, the cardiovascular system transports carbon dioxide from the cells to the lungs for removal.
As previously stated, the cells of the human body require a constant supply of oxygen to effectively function, and any impairment to the cardiovascular system will result in decreased oxygen to the cells and injury; furthermore, if the heart stops beating, death is imminent.
Under normal conditions, the pulse can be palpated at superficially located arteries. Three common sites are used for measuring pulse rate: (1) the radial artery on the thumb side of the wrist, (2) the brachial artery in the antecubital fossa of adults and the upper arm of infants, and (3) the carotid artery in the neck (Fig. 15-4). In addition, listening to the chest with a stethoscope placed over the heart (auscultation) and counting each heartbeat can be used to measure the pulse rate. Pulses obtained in this manner are called apical pulses (Fig. 15-5). When measuring the pulse rate, the second and third digits are placed over the pulse point; the pulse should be counted for 60 seconds for the most accurate assessment. In addition to the rate, the strength and regularity of the beat should be assessed.
During cardiopulmonary resuscitation, the pulse is routinely assessed at the carotid artery; however, peripheral pulse points—the femoral, pedal, and radial arteries—also may be assessed to verify the effectiveness of chest compressions. Presence of a peripheral pulse indicates a systolic blood pressure of at least 80 mm Hg and verifies effective chest compressions.
Pulse rates reflect the rapidity of each heart contraction and are recorded as the number of beats per minute (BPM). Counting the pulse rate for 1 minute is important for an accurate measurement. Resting pulse rates in the normal adult vary from 60 to 100 BPM (see Table 15-1). A normal pulse range for children under the age of 10 years is 70 to 120 BPM.
In critical care settings, patients’ arterial oxygen saturation (Sao2 and Spo2), respiratory rate, and pulse rate are monitored. Arterial oxygen saturation levels (Sao2) are measured through periodically performed blood gas analyses. However, some devices may be used for continuous vital sign monitoring, including electrocardiographs, arterial lines, and pulse oximeters. Electrocardiographs, discussed in more detail in the next chapter, continually monitor the patient’s heart rate and rhythm. Electrodes placed on the patient’s chest monitor the electrical activity of the heart and transform this electrical activity to rate values and waveforms visible on a monitor (Fig. 15-6).
An arterial line is a catheter that is inserted into an artery. The catheter is connected to a pressure transducer that is attached to a monitor. A continual measurement of the patient’s heart rate and blood pressure is visible on the monitor.
A pulse oximeter is a noninvasive device used to provide ongoing assessment of the hemoglobin oxygen saturation of arterial blood as well as the patient’s pulse rate. A light-emitting probe is placed on the finger, foot, toe, earlobe, temple, nose, or forehead of the patient. Hemoglobin oxygen saturation (Spo2) and pulse rate are determined by measuring absorption of selected wavelengths of light by the circulating blood. When the heart pulses, the oximeter converts the light intensity information into hemoglobin oxygen saturation and pulse rate values (Fig. 15-7). Normal pulse oximeter (Spo2) values for a healthy person would be 95% to 100%.
Several factors can affect the accuracy of electronic devices used to monitor pulse rates. For example, patient movement can give rise to inaccurate readings. In addition, misplaced or loose electrodes, lines, or probes also yield inaccurate values. Poor peripheral perfusion caused by low blood pressure, nail polish, and acrylic nails are common causes of pulse oximetry inaccuracies. However, when the factors or situations that limit the device’s precision are corrected, these monitoring instruments provide reliable, continual, and rapid assessment of patients.
Significance of Abnormalities
Because the cardiovascular system is responsible for delivering oxygenated blood to the cells, when cellular demand for oxygen increases, the heart responds by sending more blood to the tissues. The heart accomplishes this task by increasing the number or force of each myocardial contraction. When heart contractions, and therefore pulse rates, increase by more than 20 BPM in the resting adult or reach a rate greater than 100 BPM, the patient is said to be experiencing tachycardia. Exercise, fever, anemia, respiratory disorders, congestive heart failure, hypoxemia, and shock can cause a patient to become tachycardic because of the increased cellular demands for oxygen. Pain, anger, fear, anxiety, and medications may also induce tachycardia, but the stimulus is through the nervous system, not through an increased demand for oxygen.
Bradycardia refers to a decrease in heart rate. Although initially pain can cause tachycardia, unrelieved, severe pain in fact can lead to bradycardia, subsequent heart problems, and even heart failure. Bradycardia also may be seen in hypothermia and in physically fit athletes.
If no pulse can be felt at the wrist, or if cardiac arrest is thought to occur, the pulse should be assessed at the carotid artery for a full 5 seconds while emergency help is summoned. If pulse irregularities are accompanied by patient reports of palpitations, dizziness, or faintness, a physician should be notified because these irregularities can be life-threatening.
Blood pressure is a measure of the force exerted by blood on the arterial walls during contraction and relaxation of the heart. An analogy can be made to water being pumped through a hose. A constant pressure is exerted on the inner surface of the hose by the water. When pumping occurs, the pressure increases as more water is added to the system, causing the water to flow. A similar situation exists in the human body. The pump is the heart, arterial blood vessels are analogous to the hose, and the fluid component is blood instead of water. A constant pressure is exerted on the arterial vessels by the blood when the heart is relaxed. This pressure is called the diastolic pressure. During a contraction of the heart, blood is ejected from the ventricles into the arterial blood vessels, creating an increase in pressure. The peak pressure present during contraction of the heart is known as the systolic pressure.
Blood pressure readings are obtained with the use of a sphygmomanometer and stethoscope. The sphygmomanometer consists of a cuff, tubing, a valve, a bulb, and a manometer attached to the cuff (Fig. 15-8). The two commonly used types of sphygmomanometers are mercury and aneroid (more common). Regardless of which type is used, the cuff of the sphygmomanometer is typically placed on the upper arm midway between the elbow and shoulder. It is important that the proper size cuff, depending on the size of the arm, be used. The bulb is used to inflate the cuff with air. Inflation of the cuff above the patient’s systolic pressure stops blood flow to the arm by collapsing the brachial artery. With the stethoscope placed over the brachial artery in the antecubital fossa of the elbow, opening the valve slowly deflates the cuff of the sphygmomanometer. When cuff pressure no longer exceeds the internal pressure of blood in the brachial artery, blood flow returns and can be heard through the stethoscope. The first sound of blood flow (turbulence of blood flow through the artery) corresponds to the values (numbers) observed on the manometer and indicates the systolic pressure. When the sound of blood flowing through the arm can no longer be heard, the corresponding values on the manometer indicate that the diastolic pressure is reached. The turbulent sound of blood flow through the arteries during blood pressure measurement is called Korotkoff sounds, named for the Russian physician who first described them. Blood pressures are recorded in millimeters of mercury (mm Hg) read from the manometer, with systolic measurements recorded over diastolic measurements (systolic/diastolic).
Blood pressure also may be measured and displayed through a cardiac or vital signs monitor. The cuff is placed around the patient’s arm and may be inflated manually by a health care professional or through an automatic, timed sequence controlled through the monitor. Once the cuff inflates and deflates, blood pressure values electronically display on the monitor (Fig. 15-9).
Normal blood pressure in the healthy adult includes a systolic pressure of less than 120 mm Hg and diastolic pressure of less than 80 mm Hg (see Table 15-1). Pressures are most often recorded with the patient in a sitting position and the arm at approximately the level of the heart. Variations in these conditions can cause some difference in blood pressure readings.
Significance of Abnormalities
The persistent elevation of blood pressure above 140/90 mm Hg is known as hypertension. Hypertension is further categorized. Prehypertension involves consistent systolic pressure of 120 to 139 mm Hg or when consistent diastolic pressures measure between 80 and 89 mm Hg. Stage 1 hypertension is diagnosed when the systolic pressure is consistently recorded at 140 to 149 mm Hg or when diastolic pressure is consistently between 90 and 99 mm Hg. Stage 2 hypertension involves consistent systolic pressures of 160 mm Hg or greater or when diastolic pressures fall to 100 mm Hg or greater.
Hypertension is common, but patients are usually unaware of its presence because no symptoms exist. Hypertension causes a significant increase on the workload of the heart. Extreme elevations in the blood pressure can damage the brain within minutes. Moderate degrees of hypertension can cause damage to the heart, brain, kidneys, lungs, and other organ systems. In addition to various disease states, stress, medications, obesity, and smoking can contribute to hypertension. The incidence of hypertension is higher in men than in women, and it is more common in African-Americans than in whites.
Hypotension is defined as low blood pressure and may be identified by a blood pressure of less than 95/60 mm Hg. Low blood pressure is generally desirable and is usually not problematic unless it produces symptoms (e.g., syncope). In other words, in a healthy adult without any accompanying symptoms, hypotension presents no cause for alarm. A hypotensive patient reporting dizziness, confusion, or blurred vision may have an inadequate circulating blood volume, and further evaluation needs to be initiated immediately. A patient in shock from severe bleeding, burns, vomiting, diarrhea, trauma, or heat exhaustion is hypotensive as a result of a decrease in total blood volume. These persons require immediate care.
The moment-to-moment sustenance of human life depends on a single external substance. This substance is so important that its absence in the environment causes irreversible damage to the brain in approximately 6 minutes. In its absence, production of cellular metabolism is grossly inadequate and death ultimately occurs. This substance is, of course, oxygen, which is essential to each of the billions of cells making up the human body. Oxygen is a colorless, tasteless, and odorless gas that plays a critical role in efficient cellular metabolism. Although oxygen is not flammable, it does support combustion and constitutes 21% of atmospheric gases.
The need for oxygen becomes critical to patients when the internal environment of the body is not consistent. Normally, the 21% of oxygen supplied in room air maintains homeostasis; however, when oxygenation levels become low, the metabolic rate is compromised and the patient’s homeostasis is altered. Accordingly, the patient’s cardiopulmonary system has to adapt to maintain homeostasis caused by hypoxemia. Approximately one third of all patients in acute care settings receive oxygen therapy of some type. The overall goal of oxygen therapy is to maintain adequate tissue oxygenation while minimizing cardiopulmonary work.
Indications for Oxygen Therapy
The primary clinical indications for oxygen administration are to correct hypoxemia or possible tissue hypoxia and prevent or minimize the increased cardiopulmonary workload (increased heart rate, blood pressure, and respiratory rate). Tissue hypoxia is a term used to describe an inadequate amount of oxygen at the cellular (tissue) level. The tissues most sensitive to hypoxia are the brain, heart, lungs, and liver. When hypoxia is present, the metabolic rate of the body is compromised, resulting in altered homeostasis.
To compensate for hypoxia, respiratory rates, depth of breathing, blood pressure, and heart rates increase. A patient with hypoxia feels short of breath and has to work harder to breathe, thereby allowing the body’s adaptive response mechanisms to maintain homeostasis. During this event, oxygen therapy is administered to alleviate the cardiopulmonary work. As a result, blood pressure, heart rate, and respiratory rate and depth may return toward normal.