Ashley Moore-Gibbs Hypotension, or low blood pressure, is defined as a systolic blood pressure of 90 mm Hg or less. Blood pressure readings should always be interpreted in the context of the patient’s prior measurements. In patients with preexisting hypertension, a significant reduction from baseline with accompanying symptoms may represent relative hypotension, despite a reading above 90 mm Hg. The causes of hypotension are numerous, ranging from relatively benign to life-threatening. It is important for health care providers in the ambulatory setting to develop a methodical approach to the evaluation, treatment, and referral of patients with hypotension. Orthostatic hypotension is defined by a sustained reduction in systolic blood pressure of more than 20 mm Hg or in diastolic blood pressure of more than 10 mm Hg within 3 minutes of standing.1 Orthostatic hypotension is common in older adults, and its incidence is highest in those with Parkinson disease and those taking vasoactive medications.2 When hypotension occurs, there is an alteration in one or more of the three components necessary for the maintenance of normal blood pressure. The first component is the state of contraction of the muscles in the blood vessel wall. Vasodilator medications, sepsis, anaphylaxis, autonomic nervous system dysfunction, and certain endocrine disorders may cause abnormal blood vessel relaxation and a decrease in blood pressure. The second component is intravascular volume. When intravascular volume is reduced as a result of bleeding, vomiting, diarrhea, or inadequate fluid intake, hypotension may result. The third component is the adequacy of cardiopulmonary function. A decrease in cardiac function resulting from pump failure or dysrhythmia will cause a reduction in cardiac output and blood pressure. Understanding of these three fundamental mechanisms of hypotension will help generate a differential diagnosis. Abnormalities of more than one of these three components may occur simultaneously in the same patient. Orthostatic hypotension is a sustained reduction in systolic blood pressure of more than 20 mm Hg or in diastolic blood pressure of more than 10 mm Hg within 3 minutes of standing.1 Common in older adults, orthostatic hypotension occurs most frequently in those with Parkinson disease and those taking vasoactive medications.2 Orthostatic hypotension may result from either neurogenic or non-neurogenic causes. In turn, neurogenic orthostatic hypotension can be caused by abnormalities of either the central or peripheral nervous system. Peripheral autonomic dysfunction is the most frequent cause of orthostatic hypotension in the elderly.3 With aging, there is a decrease in baroreflex sensitivity. This blunts the normal physiologic response to standing (i.e., vasoconstriction and a modest increase in heart rate), with a resultant drop in blood pressure. In addition to decreased baroreflex sensitivity, older individuals have diminished heart rate responses and impaired alpha1-adrenergic vasoconstriction.2 Age-related reductions in parasympathetic tone also occur and result in less cardioacceleration during vagal withdrawal on standing.2 Orthostatic hypotension is more common in patients with degenerative neurologic diseases and some peripheral neuropathic syndromes.2 Medications, including diuretics, antihypertensives, alpha blockers, nitrates, calcium channel blockers, antidepressants, and opiates, may provoke or worsen orthostatic hypotension.2 Neurogenic orthostatic hypotension involves the central nervous system and is well associated with increased mortality rates in patients with diabetes, hypertension, or Parkinson disease and those receiving dialysis.4 Patients with neurogenic orthostatic hypotension may be symptomatic or asymptomatic during episodes of orthostatic hypotension. Symptoms emerge during postural changes, after prolonged standing, with dehydration, after alcohol ingestion, after carbohydrate-heavy meals, with heat exposure or fever, during stressful events, or with Valsalva maneuvers from straining.4 Non-neurogenic causes of orthostatic hypotension include cardiac functional impairment, dehydration, and vasodilation. A transient drop in blood pressure occurring with an abrupt change in position and resolving rapidly suggests a non-neurogenic cause.1 Postprandial hypotension is another potential cause of hypotension in the elderly. It should be suspected when there is a decrease in blood pressure within 2 hours after eating.3 The mechanism of postprandial hypotension is poorly understood. Current evidence suggests that the cause of postprandial hypotension is multifactorial, including autonomic and neural dysfunction, changes in gastrointestinal hormones, meal composition, gastric distention, and the rate of delivery of nutrients to the small intestine.3 Multiple factors contribute to a postprandial fall in blood pressure, and this manifests with inadequate cardiovascular compensation for meal-induced splanchnic blood pooling.3 Postprandial changes in diastolic blood pressure are not as marked as systolic blood pressure changes. Typically there is a fall in systolic blood pressure of more than 20 mm Hg, or a decrease to 90 mm Hg or lower when the preprandial blood pressure is 100 mm Hg or higher within 2 hours of a meal.3 Although the symptoms of hypotension vary greatly, those related to the brain and heart predominate. Lightheadedness and dizziness are common symptoms of orthostatic hypotension. In addition, some individuals may experience blurred or tunnel vision and a dull pain in the back of the neck and shoulders.1 Symptoms are more pronounced with positional changes such as standing and do not occur while the patient is supine.1 Neurologic symptoms of hypotension include lightheadedness, dizziness, confusion, focal neurologic deficits, and loss of consciousness.4 Cardiopulmonary symptoms of hypotension include shortness of breath, dyspnea on exertion, chest pain, palpitations, and syncope.1 In addition to identification of the physical symptoms that result from hypotension, careful attention should be paid to symptoms that may reveal the underlying cause. Inquiry should be made about fluid intake, nausea and vomiting, diarrhea, rectal bleeding or melena, polyuria, and any antecedent cardiopulmonary symptoms. Hypotension may be evident on simple blood pressure measurement or after an assessment of orthostatic vital signs. A decrease in systolic blood pressure of 20 mm Hg and/or a decrease in diastolic blood pressure of 10 mm Hg when the patient changes position from lying to standing is diagnostic of orthostatic hypotension.1 Pulse and blood pressure measurements are performed with the patient in the supine, sitting, and standing positions (if the patient’s response allows for this) when the patient has been supine at least 5 minutes and ideally at both 1 and 3 minutes of standing.1 Detection of orthostatic hypotension may require multiple measurements performed on different days and at different times. Orthostatic measurements are more sensitive early in the morning when the patient awakens, because of nighttime pressure natriuresis.1 Ambulatory automated blood pressure monitors may be useful in detecting orthostatic changes, but the patient must be able to recall specific times symptoms were noted with a change in posture. A low blood pressure, absolute or in comparison with the patient’s normal pressure when the patient is supine, confirms the diagnosis, particularly if the decrease is associated with dizziness, lightheadedness, or tachycardia when the patient is in the standing position.1 In those with hypertension, a reduction of systolic blood pressure readings of 30 mm Hg may be more appropriate when determining a diagnosis of orthostatic hypotension, depending on the patient’s baseline.1 Prospective studies have demonstrated that a reduction in systolic blood pressure of more than 20 mm Hg is a risk factor for falls, especially in older patients with hypertension.1 Measurement of heart rate concomitantly with blood pressure is important because failure of the pulse to increase with a decrease in blood pressure is indicative of neurogenic hypotension or central or peripheral nervous system diseases resulting in autonomic failure.1 Tachycardic heart rates that are exaggerated suggest underlying volume depletion such as dehydration.1 In elders, age-related reduction in baroreflex sensitivity decreases the ability for an appropriate heart rate response and is less useful as a diagnostic tool for measurement of heart rate.1 However, younger patients experiencing symptoms concerning for hypotension may maintain their systolic blood pressure and exhibit an increased pulse with a position change in conjunction with symptoms of cerebral hypoperfusion (fatigue, lightheadedness, exercise intolerance, or cognitive impairment); this represents postural orthostatic tachycardia syndrome (POTS).5 There is an absence of orthostatic hypotension; however, the standing heart rate is often 120 beats per minute or higher.5 POTS is more common in women aged 15 to 25 years. Up to half of those diagnosed with POTS have antecedent viral illness, and 25% have a family history of similar complaints.5 Pathophysiologic mechanisms of POTS are multifactorial and include hypovolemia, venous pooling, hyperadrenergic states, and restricted adrenergic neuropathies in the lower limbs.5 When hypotension is identified, diagnostic testing is guided by the patient’s history and physical examination findings. Relatively simple bedside tests with a high diagnostic yield include electrocardiography (ECG), serum hemoglobin, serum electrolytes, stool testing for occult blood, and urine pregnancy test in women of childbearing age. A careful review of the patient’s medical regimen is fundamental because numerous drugs may cause or worsen hypotension. Additional testing should be based on the differential diagnosis. If cardiac dysfunction is suspected, additional studies (e.g., echocardiography, cardiac monitoring) may be indicated. When a pulmonary embolus is suspected, a D-dimer test and, if positive, a computed tomography (CT) scan of the chest should be performed. If intra-abdominal bleeding is the presumed cause, a CT scan of the abdomen may be required.
Hypotension
Definition and Epidemiology
Pathophysiology
Clinical Presentation and Physical Examination
Diagnostics
Hypotension
Chapter 33
