US Pharm. 2008;33(2):14-17.
Blood pressure measurement is critical in diagnosing hypertension and managing the efficacy of antihypertensive medications.1 Home blood pressure monitoring (HBPM) is a useful tool to allow consumers to participate in their health care. Its popularity has risen in the past decade for a number of reasons. However, its use is not free of risk. There are many precautions patients should observe in taking their blood pressure at home. If done carefully, however, HBPM can provide physicians and other health care providers with compelling information about their patients' health status.
The Gold Standard
For many years, the gold standard to which all other methods were compared was blood pressure taken in the office by a trained health care provider using a mercury sphygmomanometer and the auscultatory technique.1-4 This method, generally credited to Riva-Rocci/Korotkoff, yields a pair of numbers (systolic and diastolic).3,5 It was an inexpensive, simple, and reliable method, and the equipment did not have to be periodically readjusted.3,6 In addition, research on the prognosis of hypertension (e.g., the risk of cardiovascular events) has been based largely on readings taken in a physician's office, using mercury or nonmercury methods.3
Inadequacies of the Office Method
Growing concern over the toxic effects of mercury in the environment has led to apprehension about mercury in sphygmomanometers. The drive to replace them in the United States began in 1998, pursuant to an agreement between the Environmental Protection Agency and the American Hospital Association to limit mercury waste issued from hospitals to the greatest extent possible by 2005.7 Their use is decreasing in the U.S., and they are banned in several European countries.3,6,8
Office blood pressure measurement is subject to a high degree of variation.3 To increase accuracy of office measurement, operators should be regularly retrained in the methods, and patients must be properly prepared and positioned.
However, concerns about mercury and operator error or inconsistency aside, there are other criticisms of office blood pressure measurement. They are of such gravity that office readings are characterized as "poorly reproducible and unable to diagnose hypertension."2 Office readings yield inaccurate results in one half of attempts and may not justify the time and effort needed to take them.2
Office readings do not detect patients with nocturnal hypertension, a common occurrence in posttransplant patients and those undergoing dialysis.9 They are also associated with problems in patients with white-coat hypertension and masked hypertension.
White-Coat Hypertension: A major concern with office blood pressure measurement revolves around the phenomenon of white-coat hypertension, also referred to as the white-coat effect or as isolated clinic hypertension.2,3,6,10 Investigators have long recognized that blood pressure measurements taken in medical offices are higher than those taken at home or at work, perhaps due to an exaggerated stress response to physicians and other medical personnel.9,11 Systolic blood pressure measurements can be 9 to 23 mmHg higher and diastolic readings can be 3 to 10 mmHg higher than those obtained at home or with the use of ambulatory blood pressure measurement.11 An estimated 15% to 20% of patients with stage 1 hypertension may experience white-coat hypertension.4
White-coat hypertension does not occur with equal frequency in all patients. Men exhibit higher readings in the office than women, and patients not taking antihypertensive medications show more elevated readings than those who are on a regimen of antihypertensives.11 Increasing age raises the likelihood of white-coat hypertension, as does anxiety.
White-coat hypertension can be identified if a patient has had persistently elevated clinic blood pressure readings of 140/90 mmHg or higher on three or more visits, while having obtained two or more readings less than 135/85 when awake in settings outside of the clinic.4,12 The patient must not have had target organ damage.
It is vital to identify patients whose hypertension is triggered by blood pressure readings being taken in a clinic setting. This is because such patients are at low risk for sequelae from the apparent high blood pressure readings and are not generally considered candidates for antihypertensive medications, as their ambulatory blood pressure is actually normal.12 In fact, administration of antihypertensives has been demonstrated to lower the blood pressure in the office, but does not affect the normal, ambulatory blood pressure.4
Masked Hypertension: Masked hypertension has received increased recognition in recent years. This occurs in patients who experience the reverse of white-coat hypertension.4 That is, readings taken in the clinic are normal, but those taken in nonclinic settings are abnormal.12 The dangers of this are readily apparent. Patients remain undiagnosed, or the severity of their condition is underestimated. As a result, they experience a relative risk of cardiac events that is 2.3 times higher than patients who receive adequate treatment, increasing the risk of target organ damage.12 The percentage of patients with masked hypertension may be as high as 10%.12
The reasons for masked hypertension are somewhat obscure. However, when trained clinic observers take blood pressures correctly, they are instructed to prepare patients by asking that they refrain from caffeine, exercise, and smoking for at least 30 minutes before measurements are taken.8 Further, patients are seated quietly in a chair for at least five minutes with their feet on the floor. At home, patients may not comply with these instructions. Thus patients' lifestyle choices (i.e., their level of physical activity or alcohol, tobacco, and caffeine use) may not follow clinical recommendations.4 These patients are at increased risk of target organ damage, as they may remain undiagnosed and untreated for longer periods than patients whose clinic readings are more reflective of the actual blood pressures.
Advantages of Home Measurement
HBPM has several advantages over office methods. It is inexpensive, more reproducible, and may help negate white-coat hypertension.13 When the values obtained are compared to office measurements, HBPM may detect masked hypertension, allowing those patients to be treated appropriately.14 It also compensates for the paucity of clinic or office measurements by providing information for a variety of time windows.5,15 When patients are placed on an antihypertensive regimen, performing HBPM can improve their compliance and increase the data needed to guide the physician's decision in modifying the regimen.14 HBPM is superior to clinic measurements in predicting sustained hypertension in borderline patients and in identifying patients at risk of target organ damage and cardiovascular mortality.11 There is often a memory in home devices, increasing the quality of information gained.3 Because of its many advantages, HBPM is characterized as the "optimal method for long-term follow-up of treated hypertension." 13
Types of Monitors
Aneroid Home Monitors: HBPM monitors come in a variety of choices. The first generation consisted of aneroid sphygmomanometers with a pressure-registering gauge, now commonly used in offices and clinics. The patient was required to use a stethoscope to hear the Korotkoff sounds.7 These devices require patient instruction and are poorly suited for patients who have difficulty hearing the subtle Korotkoff sounds.
Electronic Home Monitors: Electronic devices comprise the majority of today's market. Product lines include HoMedics, Invacare, LifeSource, Lumiscope, Mabis, and Omron. Patients should be encouraged to purchase devices with accuracy validated through an agency such as the American National Standards Institute, British Hypertension Society, or the Association for the Advancement of Medical Instrumentation. 16 The advertisement or package insert for each monitor usually mentions its validation status. If it does not, a note or call to the manufacturer before purchase should reveal its status. Web sites can also provide this information. For example, Omron Healthcare's Web site lists certain monitors and the protocol used to validate them.17
Instructions for HBPM
There are no universally accepted guidelines for how often a patient should perform HBPM, nor is there agreement on an optimal schedule. However, one regimen suggests beginning with measurements taken twice daily (morning and evening) for seven consecutive days.6 The patient should ignore readings taken in the first 24 hours. The average of 12 or more readings is acceptable.
Measurement Location: The upper arm is the standard location to measure blood pressure, using an occluding cuff placed at the crease of the elbow over the brachial artery. 4,16,18 However, some devices claim accuracy when using measurements derived from the wrist or finger.11 This may appeal to patients because of the reduced weight and size of these devices, which increase portability and comfort level.3,18 The accuracy of wrist/finger devices has been questioned, as they are generally considered to be less reliable than those using the upper arm as the measurement site.3 The major reason is that blood pressure varies depending on which part of the anatomy is being measured. As measurements move from the upper arm downward to the finger, vascular resistance changes.16 The net effect is an overestimation of blood pressure. Thus, the use of finger monitors is generally discouraged.4 Wrist measurement devices are subject to variations caused by such factors as wrist anatomy, degree of dorsal or ulnar flexion, and incorrect limb position. If the pharmacist offers them for sale, it would be wise to restrict the models to those with full approval via external validation.3
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17. Omron Healthcare, Inc. Validation standards & testing for home blood pressure monitors. Available at: www.omronhealthcare.com/enTouchCMS/app/viewPromotion?promotionId=884. Accessed December 18, 2007.
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