High Blood Pressure / Hypertension

Monitoring of Blood Pressure: Patient Counseling

By Cardiologist on May 3rd, 2011

Whether the patient is purchasing a home BP monitor on recommendation of a healthcare provider or on his or her own initiative, patient education should be provided. Counseling should focus on device selection, self-measurement procedure, monitoring schedule, blood pressure variability, interpretation of results, and the need for calibration.

Devices

Accuracy is the most important factor in selecting a device. A device that passes independent validation testing is preferred. The limitations of wrist and finger monitors should be explained to the patient. Ease of use, display readability, machine portability, and cost should be considered, as well as the need or desire for special features.

Cuffs

The patient should purchase an appropriately sized cuff. An inappropriately sized cuff can lead to incorrect blood pressure measurements. If the size of the bladder is too narrow or too short, overestimation of the blood pressure may occur. Conversely, if the bladder is too wide or too long, the blood pressure may be underestimated. Generally, standard-size cuffs are for arms 9 to 13 inches in circumference. Most large cuffs are designed for arms 13 to 17 inches. Because cuff-sizing varies slightly among manufacturers, product specifications should be consulted. Cuffs with a metal ring, known as a D-ring, are easiest to operate. The ring makes it possible to put the cuff on properly without assistance.

Self-Measurement Procedure

The monitoring procedure for home blood pressure monitoring is very similar to the procedure for office blood pressure measurement described in the SIDEBAR. Manufacturers’ instructions should be followed for specific models.

Measurement Procedure

A validated blood pressure monitoring device should be used. Arm monitors are preferred. Finger monitors should not be used. The appropriate cuff size must be used to ensure accurate measurement. The bladder within the cuff should encircle at least 80% of the arm. Many adults will require a large adult cuff. Measure blood pressure in the arm with the highest pressure. Patients should be seated in a chair with their backs supported. The cuffed arm should be supported at heart level. Patients should refrain from smoking or ingesting caffeine during the 30 minutes preceding the measurement. Measurement should begin after at least 5 minutes of rest. Measurement timing and frequency: patient specific. Typically, initiate with 2 readings twice a day. Systolic and diastolic blood pressure and heart rate should be recorded. Healthcare professionals should access values stored in memory function, if available, because patient diaries may be unreliable. Patients should be trained to perform self-measurement of blood pressure and reevaluated annually. Home blood pressure readings should be reported to and interpreted by medical personnel. Patients with physical or mental disabilities may be unsuited for home blood pressure monitoring.

Monitoring Schedule

There is no consensus on when and how often patients should measure blood pressure. Several schedules for home monitoring of blood pressure have been used in clinical research and practice. Many studies used single or duplicate measurements twice a day. The ad hoc panel of the American Society of Hypertension recommended that readings be taken in the morning and the evening, preferably including both work and non-work days. Others have suggested measuring blood pressure for seven consecutive days and only using data for the last five days, or measuring three workdays only and using average data from the second and third days. In patients whose condition is diagnosed and stable, readings may be taken less often.

If the home readings are being taken to determine the average blood pressure for diagnostic purposes, the readings should be made at different times, e.g., when the patient is either relaxed or stressed, anytime throughout the day or evening. If the readings are being taken to determine the adequacy of antihypertensive therapy, the readings should be taken at the same time of day, preferably in the early morning soon after arising from bed, to ensure 24-hour control with the regimen being prescribed. Readings should occasionally be taken repeatedly throughout the interval of a dose of therapy to determine both the peak effect and the duration of effect. The patient’s clinical situation should be considered in determining the frequency and timing of monitoring.

Variability of Blood Pressure

Patients should be educated about the variability of blood pressure and potential causes of variability. A multitude of factors may contribute to the variability of blood pressure seen on repeated measurements, both at a single reading and on separate occasions. Blood pressures may be higher with a distended urinary bladder, during defecation, during coitus, during ordinary conversation, on the day after sleep deprivation, with pain, when among strangers rather than family, or at work.Meals, alcohol, and caffeinated beverages may affect blood pressure for a short period of time. Readings may be lower after a meal, especially in the elderly. Acute ingestion of large amounts of alcohol can cause a definite rise in blood pressure. However, with chronic alcohol intake greater than two ounces per day, there may be considerable and persistent rises in blood pressures. In the case of coffee, blood pressure is increased within about 15 minutes of intake and this elevation can last as long as 3 hours. Thus it is best if patients take the self-measurements prior to meals and before drinking coffee, tea, or colas. Since smoking a cigarette can raise blood pressure and pulse rate for about 15­30 minutes, it is best to avoid smoking before measuring the blood pressure at home. Blood pressure elevations following the use of smokeless tobacco can be even more prolonged. Also, blood pressures may be lower than usual for a few hours after dynamic exercise. Diurnal variability, or variability over a 24-hour period, is substantial, with an average fall in pressure of about 15% during sleep. Although it is not always possible to modify many of these factors, their effect can be minimized by considering them in the interpretation of blood pressure measurements.

Interpretation of Results

Patients should be educated about the long-term benefits of home monitoring. Home blood pressure monitoring is not intended to be used as a tool to make daily adjustments the way patients with diabetes use home blood glucose monitoring to modify insulin doses or food intake. With hypertension, changing lifestyle generally does not immediately translate into blood pressure effect, and using antihypertensive drug therapy “as needed” should be discouraged. Patients should be advised to not be concerned by unusual fluctuations in blood pressure but to inform the healthcare provider’s office if sustained changes occur. Patients should be encouraged to record BP results and be reminded that home measurement is not a substitute for periodic evaluation by their primary care provider. Differences in the upper limit of normal of home and office BP measurements may be explained.

Maintenance

The accuracy of the patient’s device should be checked initially and then annually by comparing readings with simultaneously recorded auscultatory readings taken with a mercury device. If the error is more than 4 mmHg the device should be recalibrated, if possible. The blood pressure machines commonly found in pharmacies, such as the AvitaStat machine, are not suitable for verifying accuracy. These machines have been found to be less accurate than office sphygmomanometry.

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