11 Manual Blood Pressure
Key Points
• Hypertension detection, referral, and treatment guidelines are based on blood pressures (BPs) by trained observers using the standardized BP technique recommended by the American Heart Association (AHA) (1).
• All clinical studies of BP use a mercury manometer, because it is the most accurate and reliable instrument available and should always be the primary standard for indirect BP mea- surement.
• Inaccuracies are the result of equipment error or human observer error. Observer errors include errors in technique and errors related to the subject or patient(2).
• Because of inadequate training and lack of knowledge, BP readings taken in practice today are rarely accurate, precise, or reliable.
• A few simple techniques allow you to detect error and increase accuracy of readings taken in your clinical setting.
Indirect BP measurement is one of the most frequently performed health care procedures. Because BP measurement is a simple procedure, it is taken for granted that all graduates from medical training programs have the ability to record accurate, precise, and reliable BP readings.
However, research since the 1960s has shown this assumption to be false. Most health professionals do not measure BP in a manner known to be accurate and reliable. If you doubt this statement, watch as BPs are taken in your own clinical setting to determine whether the guidelines discussed herein are followed, and then examine recorded readings for signs of observer bias. We have published a teaching curriculum that ensures that those who take BP have mastered the knowledge, skills, and behaviors needed to obtain an accurate and reliable BP (see ref.
3 for more details on the training and testing of observers).
BP errors may be equipment related, observer related, or patient related. The two factors that contribute most to poor BP measurement by modern-day observers are lack of depth when teaching the basic skills needed to master BP measurement during professional education;
and the growing tendency to rely on, and failure to question, BPs measured by non-mercury devices. Such devices have been repeatedly proven less accurate and reliable than a well-trained observer utilizing a standard mercury manometer, the low-frequency detector of the stethoscope (bell), and the “old fashioned,” auscultatory method.
Fig. 11-1.Proper BP technique using American Heart Association Guidelines.
Although one’s work might require few manual readings, it is necessary to know and understand the principles and steps needed to obtain accurate indirect auscultatory BPs to verify any automated device.
This chapter provides tools to assess the quality of BP measurement in your setting and suggestions for implementing a system of quality assurance. It is likely that patients you care for will be healthier once you adopt these methods (Fig. 11.1).
OBSERVER ERRORS: CORRECT INTERPRETATION OF KOROTKOFF SOUNDS
When asked what they were taught about how to measure BP, most professionals state that they were told only to record the first and last sounds heard. Accurate measurement is a simple procedure that most people can learn in a few hours with repeated practice. However, accurate measurement requires knowledge of the Korotkoff sounds as
well as knowledge and performance of the steps required to control factors that can alter BP readings. Accurate measurement also depends on one’s ability to see, hear, coordinate hand and eye movements, interpret sounds, and remember the readings.
Errors are common and may be owing to lack of knowledge, inability to perform the skills necessary to obtain accurate readings, observer bias, poor judgment, and poor interaction with the subject being mea- sured. Eyesight and hearing must be good enough to allow the observer to see the small marks on the manometer and hear the Korotkoff sounds needed to interpret the reading. In addition, he or she must know the current recommendations about which Korotkoff phases determine systolic and diastolic readings.
Hand-eye coordination must be sufficient to release the pressure at the rate of 2 mmHg per beat while counting backward down the scale. The observer must learn to listen for the onset and disappearance of regular sounds, to concentrate in order to remember the systolic until arriving at the diastolic, and to record the reading immediately and accurately.
RECOMMENDATIONS/ALERTS
How Well Do You Measure Up?
Assess your own and others’ ability to listen for and interpret Korot- koff sounds using standardized videotapes of recorded BP readings and using a dual or teaching stethoscope to listen and compare readings with a colleague.
When hearing loss is suspected, test acuity and document the results.
Persons with documented hearing loss in a range that affects ability to read BPs should not take readings. So-called enhanced stethoscopes do not guarantee readings comparable to those by persons with average hearing, using a standard stethoscope. We have found that it is not possible to set these devices so that those with impaired hearing can reliably obtain accurate readings.
Quality Assurance
Warning signs that readers are not precise and accurate:
• More than 30% of recorded systolics and diastolics end in 0 (terminal digit bias).
continued
• Readings ending in odd numbers. The AHA guidelines recom- mend reading to the nearest 2 mmHg.
• Readings consistently slightly above or below treatment cutoffs (cutoff bias or knowledge of treatment bias).
• Readings very similar or identical to last recorded reading (pre- vious reading bias).
Assessment Tip
• Common errors occur because people are taught to listen for the first loud, distinct, or strong sound. As a result, they may record single sounds (artifacts or noise) and ignore most soft regular sounds when they occur at the systolic or diastolic level.
Before deciding that an observer is unable to hear, make sure he or she knows how to rule out extraneous sounds and is listening for the soft sounds that sometimes occur at the systolic or diastolic levels.
• The usual error is in the range of 8, 10, or 12 mmHg.
Observer Errors: Selecting and Using Equipment
Equipment selection errors include failure to choose the primary standard mercury manometer and lack of a selection of cuffs with bladder sizes to accommodate your patient population in your equip- ment inventory. Common equipment use errors include failure to choose the correct cuff for a given individual, failure to center the cuff bladder over the brachial artery in the upper inner arm so that pressure is maximally transmitted over the brachial artery during measurement, inflating too slowly, and deflating too quickly. Common reading errors include failure to record systolic and diastolics to the nearest 2 mmHg and a tendency to read only the left or only the right side of the mercury column.
Quality Assurance: BP Equipment
• Sphygmomanometers:
—Set up a maintenance schedule.
—Clean and check mercury manometers yearly.
continued
Fig. 11-2.How to check and mark the cuffs used in your setting to ensure that you use the most accurate cuff. Most cuffs made today are not marked correctly according to the AHA guidelines. The width of the cuff should encircle at least 40% of the arm circumference. The markings for the correct length range for any cuff are shown in the figure.
—Check aneroid manometers at purchase and at least every 6 mo.
—Check automated devices for ambulatory and home use at purchase and prior to placing on a given patient.
—Educate staff about how to avoid and what to do in the case of a mercury spill.
• Stethoscopes:
—Tubing should be thick and no longer than 15 inches.
—Earpieces should be adjustable and eartips cleaned fre- quently.
—Chestpiece should have a low-frequency detector—most commonly the bell.
• Cuffs: mark your cuffs (Fig. 11.2):
—Make certain large cuffs are available in each work area.
—Mark cuffs with bladder center and appropriate arm circum- ference.
—Inflation system: replace when tubing/bladder is weak or cracked.
—Large cuffs need large bulbs for proper inflation. (Some prefer large bulbs for all devices.)
—Replace valves and bulbs as needed.
continued
—Wash or clean cuff fabric frequently. We know of no stan- dards or practice for this cleaning interval.
Assessment Tip
• Look for errors in the range of 8, 10, or 12 mmHg. This occurs when the observer releases the pressure too fast, tends to read only one side of the mercury gage, or fails to concentrate enough to remember the reading. When pressure is released at 10 mm/
beat, readings can only be to the closest 10.
• What to do when observers have difficulty hearing blood pressure:
—Make sure they palpate to locate the best place to listen over the brachial artery.
—Check to see that eartips fit and are pointing in the direction of the ear canal.
—Use a dual stethoscope to check an observer’s hearing.
• Recheck elevated readings on patients with large or muscu- lar arms:
—Measure the arm circumference at the midpoint between the olecranon and acromial process and verify cuff size referring to Table 11.1.
—When in doubt, use the larger cuff.
—Check to see that the arm and cuff size are recorded in the patient’s record.
• Questionable readings owing to arm size >41 cm and shape:
choose the cuff that fits the forearm:
—Center the bladder and place the stethoscope over the radial artery.
—Support the forearm at heart level.
—If unable to hear, palpate the systolic.
—In some patients with large and short arms, it is not possible to obtain an accurate BP with a large cuff. In these cases, compare the palpated pressure taken with the large cuff on the upper arm to that taken with an appropriately sized cuff on the forearm. If the palpated systolic pressures are within 10 mm Hg of each other, then the upper arm pressure is reliable. If the forearm is over 10 mm Hg less, then prefer to use the forearm palpated pressures.
Table 11-1
Label Your Cuffs: Acceptable Bladder Dimensions (in cm) for Arms of Different Sizes
Best Available Cuff from Practice Setting
AHA AHA Arm (Bladder width
Bladder Bladder Circumference should Fit
Width Length Midpoint 40% of arm
Cuff (cm) (cm) (cm) circumference)
Newborn 3 6 )6
Infant 5 15 6–15
Child 8 21 16–21
Small adult 10 24 22–26
Adult 13 30 27–34
Large Adult 16 38 35–44
Adult thigh 20 42 45–52
The shaded portion of this table is taken directly from Appendix D of the American Heart Association’s “Human Blood Pressure Determination by Sphygmomanometry”
and shows ideal cuff bladder sizes for a given arm circumference. Complete the 4th column by measuring the bladders in your cuffs. Make sure you have at least one cuff with a bladder width at least 40% of the arm circumference for each range.
OBSERVER ERRORS: FAILURE TO OBTAIN READINGS THAT ESTIMATE BP OUTSIDE THE OFFICE OR
CLINICAL SETTING
The goal of BP measurement in the clinical setting is to get the best estimate of usual BP, a measurement that has been used in the research setting to diagnose and treat increased BP. To accomplish this, one must attempt to control the biological and environmental factors that cause temporary changes in BP and obtain an average reading in the arm with the highest reading.
Positioning
Failure to properly position the patient for seated, standing, and supine readings is a frequent occurrence in the clinical setting. Regard- less of the position, the limb wearing the cuff should be resting and
supported on a flat surface allowing the center of the cuff to be at the subject’s heart level. Inaccurately low readings occur when the cuff is above heart level, and inaccurately high readings occur when the cuff is below heart level. Seated readings require back support. Seat the patient in a straight-back chair, next to a table or desk, with legs uncrossed and feet flat on the floor. Standing readings require that the arm be supported on an inanimate object adjusted, prior to standing, to place the cuff at heart level. Supine readings may require a small support such as a firm pillow to raise the center of the cuff to midchest level. Position yourself and the manometer so that you can easily view the instrument at eye level.
Environment
Whether BPs are taken in an office or an examination room, the environment must be controlled in order to obtain accurate readings.
It should be private, quiet, and have good lighting and a comfortable temperature. After measuring and placing the correct cuff on the patient’s arm, provide a simple explanation of the procedure and let the patient rest for 5 min prior to taking the first reading.
Patient Instruction Prior to Measurement
• Ask about the following:
—Exercise within the past hour
—Intake: prescription and over-the-counter medications, food, and alcohol
—Need to empty bladder prior to measurement
• Determine cuff size and arm required to obtain an accurate reading. Make sure each person knows the proper cuff size.
• Explain the following:
—The need to rest quietly for at least 5 min
—The need to sit straight with legs uncrossed, feet flat on the floor
—The need for silence during the reading
—That you will take more than one reading to get an average
—That you will first feel the pulse to estimate the systolic in order to know how much pressure is needed for an accu- rate reading
These steps are necessary for good technique. Following these steps will help you hear BP sounds more clearly, decrease patient discomfort, and obtain accurate readings when there is an auscultatory gap.
• Determining how high to inflate the cuff:
—Prior to listening, estimate the systolic pressure by palpating the brachial or radial artery for pulse obliteration as the cuff is inflated.
—Wait 15 s and reinflate to 30 mm Hg above the estimated systolic. Then begin to listen. This is the only way to avoid missing an auscultatory gap.
• Allowing the arm to rest between readings:
—Listen as you allow the mercury to fall at 2 mm Hg/s.
—Remember the first of at least two regular beats (systolic reading).
—Control the valve so that the mercury falls at 2 mm Hg/beat until the last regular sound is heard.
—Listen for an additional 10–20 mm Hg to confirm disap- pearance.
—Record systolic and diastolic readings.
—Wait 1 to 2 min before repeating the reading. This is a good time to take the pulse.
• Placing the stethoscope:
—Hyperextend and support the patient’s elbow while palpating to locate the best listening point over the brachial artery.
This is usually just under and to the inside of the biceps tendon. If doing multiple sitting and standing readings, mark the spot for subsequent readings.
—Gently rest the bell of the stethoscope over this artery listen- ing point. Make sure the bell is fully in contact with the skin surface on all sides. This can be determined by lightly touching the skin next to the bell. If no sound is heard, the bell needs to be repositioned.
• Avoiding diastolic errors in the presence of an ausculta- tory gap:
—When the diastolic is high, listen for an additional 40 mmHg to make certain the Korotkoff sounds do not reappear after a period of silence.
continued
• Obtaining accurate estimates when the pulse is irregular:
—Take more readings to get the best average.
—Start listening earlier and listen longer.
—Deflate very slowly.
—Note on the chart that the pulse is irregular.
When sounds are difficult to hear and you have used accurate technique, try one of these methods to make the sounds louder.a
• Method 1:
—Explain what you are going to do and why.
—Get ready by wearing the stethoscopes’ earpieces forward.
—Support the patient’s arm in a raised position above the head for 15 s.
—Quickly inflate the cuff while the arm is raised and supported to 60 mmHg above the palpated systolic pressure.
—Quickly and gently lower the arm to the table.
—Place the stethoscope over the artery.
—Deflate and listen.
—Record the reading and that enhancement was used.
• Method 2:
—Explain what you are going to do and why.
—Ask the patient to pump his or her hand, making a fist 8–10 times after the cuff is inflated.
—Quickly inflate the cuff while the arm is still resting on the table.
—Remind the patient to start squeezing.
—Stop the patient after 8–10 squeezes.
—Deflate and listen after the patient relaxes his or her arm.
—Record the reading and that enhancement was used.
aUse of enhancement techniques can change the true BP. Use them only when you are sure you have followed good technique and are listening in the best place.
ENSURING THAT THE EQUIPMENT USED BY YOU AND YOUR PATIENTS IS ACCURATE
Accurate equipment is key to good clinical practice. Every clinic should have at least one mercury manometer to use as the primary
standard. If the tube is clean, the top of the meniscus is at zero, and the pressure rises and falls quickly and evenly as pressure is changed in the cuff, the manometer is accurate. It is the primary standard for pressure measurement and the same device used for the primary stan- dard at the National Bureau of Standards.
Campaigns to minimize the use of mercury in medical practice in order to minimize the loss of mercury into the environment are taking place throughout the world. You should know that compared to other sources, mercury manometers are not a significant source of mercury released into the environment and that every office should have at least one manometer.
If you use aneroid instruments, someone in your setting must be responsible for regular inspection and repair. Indeed, most research has shown that at least 30% of aneroid devices go out of calibration with age (4). The only way to be certain your aneroid devices are accurate is to check them against a mercury device at regular intervals.
This process takes less than 10 min and can also be used to test the accuracy of a patient’s home device. If using a Y tube, simply connect the two devices and a bulb and inflate to compare readings. The follow- ing method explains how to compare aneroid calibration to an accurate mercury manometer without a Y tube:
1. Remove the aneroid device from the tubing connecting it to the cuff on the mercury device.
2. Take the mercury system cuff and pump enough air into it so that you can squeeze the rolled up cuff, and the pressure in the manometer will rise and fall (approx 10–20 mmHg).
3. Fold over the tubing leading to the bulb and pinch it off to hold the air while you remove the bulb.
4. While continuing to pinch the tubing, replace the bulb with the aneroid device gage.
5. Release the pinched tubing. Now you should be able to squeeze the rolled up cuff to vary the pressure in the mercury and the aneroid gage. You can now “set” the pressure in the mercury manometer to the level of pressure you want to compare on the aneroid. We recom- mend you start at 200 mmHg and pause to check each device at the levels of pressure used to make medical decisions: 180, 150, 140, 130, 120, 110, 100, 90, and 80. If the aneroid reads greater than±3 mmHg it should be discarded or returned to the manufacturer for recalibration.
6. Place a sticker with the day’s date on the device. Record the results on your equipment inventory or quality control document. Implement a quality assurance system in your office that ensures that all devices are inspected and calibrated every 3 mo.