The purpose of this article is to explore the pathogeneses, appropriate history and physical assessment techniques, and nursing interventions of orthostatic hypotension. Orthostatic hypotension is a sustained drop in blood pressure that may occur when moving from a supine or sitting position to a standing position. This phenomenon is common among elderly individuals, in particular in institutionalized elderly individuals, and has implications for their mobility, mental activity, and maintenance of consciousness. If blood pressure is not being maintained within normal limits, it must be assumed that those physiological factors which are responsible for the regulation of blood pressure are dysfunctional.
REGULATION OF ARTERIAL BLOOD PRESSURE
Blood flow to the tissues is dependent on adequate arterial blood pressure. Therefore, arterial pressure, which is directly related to cardiac output and total peripheral resistance, is a closely regulated physiological phenomenon and protected by a number of mechanisms that are part of a negative feedback system that responds to cardiovascular changes.
When an individual changes position from supine or sitting to standing, 10% of the total blood volume is shifted from the thorax to dependent parts of the body which results in a decrease in cardiac output and, therefore, blood pressure. These changes activate mechanisms that instantaneously increase cardiac output and blood pressure (Smith & Ebert, 1990).
Figure 1 summarizes the cardiovascular responses to a change in position and the compensatory mechanisms stimulated to return blood pressure to normal. In a healthy young individual, these mechanisms have reestablished a normal blood volume distribution and cardiac output within 3 to 5 seconds after assuming an upright posture.
The baroreceptor reflex is a neurological response to changes in pressure and volume sensed by stretch receptors in the aorta and carotid arteries. A decrease in stretch of these receptors stimulates the sympathetic nervous system that increases cardiac output and total peripheral resistance. The skeletal muscle pump also plays a critical role in reestablishing normal arterial pressure. Muscular contractions of the lower calf collapse the veins of the lower leg. Because these veins have valves that do not allow retrograde flow, venous blood volume is displaced toward the heart increasing venous return and, thus, cardiac output. There is also a change in secretion of hormones, such as antidiuretic hormone, aldosterone, and atrial natriuretic hormone that influences the rate of renal reabsorption of sodium and water, thus regulating total body fluid volume (Weems & Downey, 1992).
The ability to maintain an adequate mean arterial pressure depends on the coordination of all these physiological systems. If any individual system is impaired, the ability to maintain an adequate blood pressure will be hampered and blood pressure will fall with a change in position, resulting in a decrease in coronary and cerebral perfusion and tissue ischemia. How efficiently the system operates is dependent on a number of factors such as age, gender, general health, and physical fitness. The remainder of this discussion will focus on the diagnostic definition of orthostatic hypotension, the influence of aging on the occurrence of orthostatic hypotension, the possible causes of orthostatic intolerance, and finally, nursing implications.
PATHOGENESIS, DIAGNOSIS, AND INCIDENCE OF ORTHOSTATIC HYPOTENSION
Orthostatic hypotension is a disorder of the mechanisms by which arterial pressure is maintained within normal limits in the short term. The most widely used diagnostic criteria for orthostatic hypotension is a drop of > 20mmHg in systolic pressure or a fall of > 10mmHg in diastolic pressure on assumption of the upright posture from supine. Some investigators consider the presence of symptoms of orthostatic hypotension (dizziness and fainting) to be more clinically important than a change in pressure reading. Therefore, their definition of orthostatic hypotension includes evidence of these symptoms with a change in position. Kochar (1990) combines both in a classification system from Class I to IV, depending on the degree to which the postural hypotension is accompanied by symptoms, from a drop in blood pressure with no symptoms (Class I) to a drop in blood pressure associated with syncope (Class IV). Similarly, in a prospective study of a random population of elderly individuals, the classifications ranged from postural hypotension I to III depending on whether symptoms were present and whether there was an isolated decrease in one of the readings or if both diastolic and systolic pressure decreased (Tilvis, Hakala, Valvanne, & Erkinjuntti, 1996).
The reported incidence of orthostatic hypotension among elderly individuals varies from a low of 6% to a high of 35%. The wide range of reported prevalence is probably because of a number of factors including differences in experimental design, measurement techniques, and the population studied (Mader, 1989). In two separate studies in which large random populations of elderly individuals were studied (n = 5,201 and ? = 521) the reported incidence of asymptomatic orthostatic hypotension was 16.2% in the first and 30.3% in the second (Rutan et al., 1992; Tilvis et al., 1996). Even taking into consideration the differences in studies, it would be difficult to dispute that orthostatic hypotension is a significant occurrence among elderly individuals with a lot of possibly damaging clinical sequelae.
However, it is difficult to isolate the causes of orthostatic hypotension that may be purely a result of aging and those that may be because of the presence of concomitant cardiovascular or neurological diseases. In fact, the higher prevalence of orthostatic hypotension reported in some studies may be because of a greater number of study participants with those problems. However, in a 4year prospective study in which 521 individuals were studied for a 4-year period, of the 90 participants who were classified as healthy (absence of cardiovascular and cerebrovascular diseases, no hypertension, diabetes, or dementia), 33.2% were reported to have PH-I or PH-II defined as a change in blood pressure without symptoms, and 17.3% had dizziness on postural testing (Tilvis et al., 1996). In The Cardiovascular Health Study, in which 5,201 men and women age 65 and older participated, 16.2% had asymptomatic orthostatic hypotension defined as a drop in systolic or diastolic pressure without dizziness or fainting (Rutan et al., 1992). In this study, the older the participant, the greater the chance of having orthostatic hypotension, from a prevalence of 14.8% for those age 65 to 69 to 26% for those age 85 and older. Therefore, regardless of whether the orthostatic hypotension is purely a result of aging or concomitant diseases, the reality is that among elderly individuals there is a high prevalence of it and clinicians must pay heed.
Orthostatic intolerance in elderly individuals is at least theoretically because of dysfunction in one or all of the following: the response of the baroreceptor system, the cardiac response to sympathetic stimulation, the amount of volume ejected by the heart per beat, the tone of the blood vessels, the efficiency of the skeletal pump, or thoracic blood volume (Smith, Porth, & Erickson, 1994). It is highly likely that intolerance to orthostatic stress in elderly individuals is multifactorial. Studies in both humans and animals suggest there is a tendency for negative changes in all of these variables proportional to age. Tonkin, Wing, Morris, and Kapoor (1991) report a study of 37 elderly individuals, comparing responses to orthostatic stress among those who had age-related orthostatic hypotension (AOH-otherwise healthy elderly individuals, n = 13), orthostatic hypotension related to disease of the autonomic system (n = 9), and 15 elderly control individuals (Tonkin et al., 1991). Those participants who were AOH had appropriate neural responses to stresses which were not baroreceptor mediated but had an attenuated response to local pressure and volume changes. In contrast, those with an autonomic neuropathology could not respond at all to any stimuli. According to the investigators, their results suggest the cause of the decreased adaptation to position changes in those with AOH is decreased sensitivity of the baroreceptors to pressure and volume changes.
There is also experimental evidence that with aging there is a decreased cardiac response to sympathetic antagonists and agonists, an overall increase in total peripheral resistance, a decrease in supine thoracic blood volume, and a decrease in the efficiency of the skeletal muscle pump as a result of deconditioning of the antigravity muscles (Smith & Porth, 1990). In response to postural stress testing, older subjects have less of an increase in heart rate, more of an increase in total peripheral resistance, and more of a decrease in thoracic blood volume after a change in position from supine to sitting or standing than younger subjects (Frey, Tomaselli, & Hoffler, 1994; Smith et al., 1994).
In addition, any systemic disorder which affects the cardiovascular or neurological systems will increase the chances the affected individual will experience chronic orthostatic intolerance. For example, an individual with diabetes is more susceptible to an associated orthostatic hypotension most likely because of peripheral neuropathy which is a common chronic complication of that disorder. Some other causes include antihypertensive and psychotropic drugs, endocrine disorders which influence water and sodium balance, multiple sclerosis, Parkinson disease, or any condition which may cause a reduction in cardiac output, such as mitral valve prolapse. All of these disorders tend to have a higher incidence among the elderly population.
Other factors besides systemic disease may influence the incidence of orthostatic intolerance in elderly individuals. An increase in ambient temperature tends to increase the incidence of orthostatic hypotension regardless of age. This is probably related to the vasodilation that occurs in rise of body temperature. If an elderly individual has a decreased ability to regulate body temperature because of systemic disease, medications, or age-related changes, the effect of increased ambient temperature would be intensified. There is also some evidence that the incidence of orthostatic hypotension is positively correlated with that of systolic hypertension. The incidence of systolic hypertension tends to increase with age, which suggests a possible reason for the higher occurrence of orthostatic hypotension in this group. Postprandial drops in blood pressure, particularly after breakfast, also have been found in both healthy and frail elderly individuals. A proposed mechanism for this is the sequestration of blood volume in the circulation of the digestive tract, which would tend to reduce venous return and, thus, cardiac output. Finally, some experimental results suggest even healthy elderly individuals are not as able to compensate for mild sodium and water deficits as younger individuals, making them more vulnerable to orthostatic hypotension because of decreased total blood volume (Mader, 1989; Smith & Porth, 1990).
It is essential to include an assessment of orthostatic tolerance in all elderly clients. Most elderly clients who require nursing care either in the home or in an institution have some chronic or acute illness which can impair their ability to regulate blood pressure. Close attention to this possible problem may prevent life-threatening falls and enhance quality of life by increasing independence. A client history should include questions about symptoms such as dizziness, lightheadedness, loss of balance, or fainting with changes in position. It also should elicit information regarding any chronic illness such as diabetes, alcoholism, renal disease, or neurological disease which can increase the likelihood of orthostatic intolerance. Any alterations in fluid and electrolyte balance should be considered, and medications should be evaluated for their potential to cause orthostatic hypotension. In particular, the history should document whether the client is taking medications that tend to cause vasodilation, volume decrease, impairment of autonomic reflexes, or depression of the central nervous system.
To determine whether a client has orthostatic hypotension, blood pressure is measured after changes in position. The first blood pressure reading should be taken after the client has been supine for at least 10 minutes. Then, a blood pressure reading should be taken when the client sits up, and again 1 minute and 3 minutes after standing. A last reading may be taken after the client has been walking for 5 minutes. Make note of any complaints of dizziness, lightheadedness, or fainting. A drop of 20 mmHg or more in systolic or diastolic pressure is considered significant by most clinicians and deserves further follow up, even if there are no accompanying symptoms. Of course, a nurse practitioner or physician also should evaluate the presence of symptoms without a fall in blood pressure because these may be indicative of decreased flow to the brain.
It is important to note that, as in the diagnosis of hypertension, one reading is not sufficient to determine whether or not an individual has orthostatic hypotension. In a study by Ward and Kenny (1996), for 32.5% of 40 outpatients evaluated for symptomatic orthostatic hypotension, the drop in blood pressure documented at a first visit was not reproducible at two subsequent visits. In this same study, the drop in blood pressure was more likely to be reproducible in the morning than in the afternoon, which suggests that evaluations be made in the morning (Ward & Kenny, 1996).
Figure 2. Instruction sheet for orthostatic hypotension.
If a client does have a drop in blood pressure with changes in position, follow up is warranted with the possibility of pharmacological treatment to enhance the client's homeostatic mechanisms and increase their blood pressure. Nonpharmacological methods also can be used to increase blood pressure and prevent the injuries that can occur as a result of an acute drop in blood pressure. One of the most important is adequate hydration to avoid volume depletion. An evaluation of the client should always include an assessment of fluid balance and nutritional status. The amount of water and other noncaffeinated drinks the client is drinking should be balanced against the amount of fluid loss. If the output is greater than the intake, the client may have a fluid deficit. Does the client have an increased amount of insensible fluid loss or loss of fluid through vomiting, diarrhea, or respiratory problems? Is the client taking medications that tend to increase loss of fluid either through urine or stool? The water content of food comprises the greater portion of fluid intake per day. Therefore, if a client is not eating properly or enough this could reduce water intake as well. Is the client taking any medications which have a tendency to cause orthostatic hypotension? These medications include antihypertensives such as calcium channel blockers, diuretics, vasodilators, and ACE inhibitors; antidepressants; and sedatives.
Other nonpharmacological methods include sleeping with the head of the bed elevated, which adapts the cerebral blood vessels to lower perfusion pressures and avoids the sudden dislocation of large volumes of blood to the legs when rising. It also stimulates the reninangiotensin-aldosterone and vasopressin systems resulting in vasoconstriction and sodium-water retention (Kochar, 1990). In addition, clients should be encouraged to sit on the edge of the bed for a few minutes before standing. While they are sitting at the edge of the bed, they should exercise the calf muscles to assist in return of blood to the heart. After standing, the client should walk in place for a few moments before walking away from the bed. Knee-length elastic stockings may also prove useful in reducing the drop in blood pressure by reducing the amount of blood which can be sequestered in the veins of the calf muscles. Clients also should be advised to avoid standing up quickly after bending to pick something off the floor or to look at a bottom shelf of a cabinet or bookshelf. Advise clients to bend at the knees if possible and keep the head above heart level (squatting posture). Eating smaller meals more frequently and avoiding any major chores for the first hour after a meal would be helpful to those who are prone to postprandial orthostatic hypotension. For example, gardening, housework, or shopping should not be scheduled immediately after a meal. Clients who get up at night to use the bathroom should be advised to consider a bedside commode or urinal to avoid night-time episodes of orthostatic hypotension.
Orthostatic hypotension is a significant clinical problem among elderly individuals with the potential for severe personal injuries and loss of independence. It should be highly suspected as a possible cause of dizziness or unexplained falls reported by a client. An evaluation for orthostatic intolerance should be a part of a regular history and physical assessment of any elderly client, particularly those older than age 70 or those using any medications associated with this disorder.
Orthostatic hypotension can be treated and the possible problems prevented with diligent nursing and health care. Figure 2 is an example of an instruction sheet that may be used as a teaching tool with clients who have or potentially have orthostatic hypotension. Old age alone is not a sufficient explanation for the increased incidence of orthostatic hypotension. The causes of orthostatic intolerance in elderly individuals still are unclear and more basic and clinical research is needed to elucidate its origins.
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