نبض یکی از علائم حیاتی مهم
The pulse is examined primarily to establish cardiac rate and rhythm. However, palpation of peripheral pulses yields clues to cardiac disease, such as aortic insufficiency, and information about the integrity of the peripheral vascular supply. Doppler ultrasound provides a noninvasive method of assessing blood flow in the ED. It has utility in the location of a pulse, in the assessment of fetal heart tones beyond the first trimester, for evaluation of peripheral lower extremity vascular insufficiency, and for the evaluation of blood pressure in infants or in patients with low-flow states.
Blood flowing into the aorta with each cardiac cycle initiates a pressure wave. Blood flows through the vasculature at approximately 0.5 m/sec; however, pressure waves in the aorta move at 3 to 5 m/sec. Therefore, palpated peripheral pulses represent pressure waves, not blood flow.
Indications and Contraindications
The evaluation of pulse presence and rate is indicated in most patients who present to the ED. Patients with minor complaints, believed unlikely to be related to a circulatory problem, do not require this measurement. The necessity of repeated evaluations is dictated by the clinical complaint and status of the patient. Detailed pulse assessment is essential in all patients with potential peripheral vascular insufficiency. Although an association between the absence of a radial pulse (or the absence of both radial and femoral pulses) and hypotension has been demonstrated for hypovolemic trauma patients, the variability in individual response prohibits the use of this parameter as an absolute gauge of blood pressure. No contraindications exist to assessment of pulse, but a few cautionary notes about the examination of the carotid pulse should be kept in mind: Concurrent bilateral carotid artery palpation should be avoided, as this maneuver could endanger cerebral blood flow. In addition, massage of the carotid sinus, found at the bifurcation of the external and internal carotid arteries at the level of mandible angle, may result in reflex slowing of the heart rate (see Chapter 11 ). To avoid inadvertent carotid sinus massage, the carotid pulse should be palpated at or below the level of the thyroid cartilage. A rare risk of precipitating a cerebrovascular event by vigorous palpation of the carotid artery is present in adults with atherosclerotic disease. This risk may be minimized by prior auscultation of the carotid artery. If a bruit is present, the carotid pulse may be gently palpated, but avoid vigorous palpation.
Assessment of the pulse may be performed by the clinician at the bedside with any timepiece that has a second-hand display. This allows simultaneous assessment of all characteristics of the pulse: its rate, rhythm, gross perfusion pressure, and upstroke. If continuous monitoring is deemed necessary, bedside cardiac monitors can constantly monitor heart rate and rhythm and may be more accurate indicators of a perfusing rhythm than cardiac auscultation. Pulse oximetry (see Chapter 2 ), although primarily intended to measure oxygen saturation, also may be used to monitor the pulse rate. In a critical care situation, more sophisticated invasive monitoring techniques are available (see Chapter 20 ) for arterial pressure measurement and rate assessment.
Pulses are palpable at numerous sites, although for convenience the radial pulse at the wrist is routinely used. The examiner should use the tips of the first and second fingers to palpate the pulse. The two advantages to this technique are (1) the fingertips are quite sensitive, enabling the pulse to be easily located and counted, and (2) the examiner's own pulse may be erroneously counted if the thumb is used instead of the first and second fingers. Pulses are also easily palpated at the carotid, brachial, femoral, posterior tibial, and dorsalis pedis arteries. Palpation of the pulse at the brachial artery may facilitate the appreciation of pulse contour and amplitude. It is located at the medial aspect of the elbow and is more easily palpated when the elbow is held slightly flexed. Pulse rate is ideally determined by counting the pulse for 1 minute, particularly if any abnormality is present. Common convention in acute care settings is the counting of a regular pulse for 15 seconds and multiplying the resultant number by 4 to determine beats/min.
In newborns, direct heart auscultation and umbilical palpation are the methods of choice to determine heart rate. Instantaneous changes in newborn heart rates are best indicated for the resuscitation team by the examiner tapping out each heartbeat. In unstable children, palpation of central arteries, particularly femoral and brachial pulses, is recommended over palpation of more peripheral arteries.
In most circumstances the palpated heart rate will approximate the actual heart rate within 2%.
Individual physiology must be considered in pulse interpretation. In infants and children, pulse rate must be interpreted with reference to age. Pulse varies with respiration, increasing with inspiration and slowing with expiration. This is known as a sinus dysrhythmia and is physiologic.
Although bradycardia is defined as a heart rate of <60 beats/min in adults, a well-conditioned athlete may have a normal resting heart rate of 30 to 40 beats/min. As discussed earlier, a redefinition of bradycardia to <50 beats/min and tachycardia to >90 beats/min has been proposed based on a normal healthy population. These definitions of normal represent the 95% of a population and do not speak to an individual's normal baseline rate.
The clinician must consider whether an abnormal pulse rate is a primary or secondary condition. The examination of the entire set of vital signs is instrumental in discerning the cause for the abnormal rate. For example, hyperthermia causes a sinus tachycardia. Drug fever, typhoid fever, and central neurogenic fever are suggested when no corresponding tachycardia is found in a patient with elevated body temperature. Hypothermia, with its reduced metabolic demands, may be associated with bradycardia.
Clinical evaluation of the patient with an abnormal pulse rate dictates a consideration of medications the patient may be taking or the presence of a mechanical pacemaker. Digitalis compounds, β-blockers, and antidysrhythmics may alter the normal heart rate and the ability of this vital sign to respond to a new physiologic stress. These cardioactive medications may be causing the patient's heart rate abnormality.
In addition to determining the pulse rate, information about the regularity of the pulse is obtained during palpation. An irregular pulse suggests atrial fibrillation or flutter with variable block, and accurate assessment of the pulse should be obtained by auscultation of apical cardiac sounds. The apical pulse is frequently greater than the peripheral pulse, reflecting inadequate filling time and stroke volume, with resultant non-transmitted beats. A greater pulse deficit generally reflects more severe disease.
Pulse Amplitude and Contour
Amplitude and contour of the pulse are generally assessed simultaneously. Figure 1-1 compares normal and abnormal pulse amplitudes and contours. Accurate examination and description provide additional clinical information. Superimposition of one pathophysiologic state on another may modify the pulse. For example, sepsis may manifest with variable pulse amplitude, depending on the stage in the development of the disease at which the patient presents. Early in sepsis, cardiac output increases and vascular resistance decreases, causing bounding pulses. In advanced sepsis or septic shock, falling cardiac output and increased vascular resistance are seen, and pulses are diminished.
Figure 1-1 Examples of abnormalities of the arterial pulse compared with the normal pulse. The normal pulse pressure is approximately 30 to 40 mm Hg. The pulse contour is smooth and rounded. (The notch on the descending slope of the pulse wave is not palpable.) (From Bates B: A Guide to Physical Examination and History Taking, 4th ed. Philadelphia, JB Lippincott, 1987.)
Definable age-related pulse amplitude and contour changes can be identified. Aging changes in the arterial pulse are explained by both an increase in arterial stiffness with increased pulse wave velocity and progressively earlier wave reflection. This leads to increased pulse amplitude in the elderly in all commonly measured sites (carotid, femoral, and radial). In addition to these age-related changes, pulse wave analysis may be useful in determining arterial stiffness and the likelihood of atherosclerotic disease. Although intriguing, the routine measurement of pulse amplitude is not reproducible by simple palpation but instead requires instrumentation not available in EDs.
Pulses During Cardiopulmonary Resuscitation
Palpated "femoral pulses" during chest compression may represent either forward arterial blood flow or "to-and-fro" movement of blood from the right heart to the venous system. A carotid pulse is preferred when assessing the adequacy of chest compressions during cardiopulmonary resuscitation (see Chapter 17 ).