In their guidelines, the diastolic BP recommendation changed to the start of phase V [2]. The second most common error in BP measurement is incorrect limb position. To accurately assess blood flow in an extremity, influences of gravity must be eliminated. The standard reference level for measurement of blood pressure by any technique — direct or indirect — is at the level of the heart. When using a cuff, the arm or leg where the cuff is applied must be at mid-heart level.
Measuring BP in an extremity positioned above heart level will provide a falsely low BP whereas falsely high readings will be obtained whenever a limb is positioned below heart level. Errors can be significant — typically 2 mmHg for each inch the extremity is above or below heart level. Patients lying on their side, or in other positions, can pose problems for accurate pressure measurement.
To correctly assess BP in a side lying patient, hold the BP cuff extremity at mid heart level while taking the pressure.
Arterial pressure transducers are subject to similar inaccuracies when the transducer is not positioned at mid-heart level.
This location, referred to as the phlebostatic axis, is located at the intersection of the fourth intercostal space and mid-chest level halfway between the anterior and posterior chest surfaces. Note that the mid-axillary line is often not at mid-chest level in patients with kyphosis or COPD, and therefore should not be used as a landmark. Incorrect leveling is the primary source of error in direct pressure measurement with each inch the transducer is misleveled causing a 1. When above the phlebostatic axis, reported values will be lower than actual; when below the phlebostatic axis, reported values will be higher than actual.
The standard for blood pressure cuff placement is the upper arm using a cuff on bare skin with a stethoscope placed at the elbow fold over the brachial artery. The patient should be sitting, with the arm supported at mid heart level, legs uncrossed, and not talking. Measurements can be made at other locations such as the wrist, fingers, feet, and calves but will produce varied readings depending on distance from the heart.
The mean pressure, interestingly, varies little between the aorta and peripheral arteries, while the systolic pressure increases and the diastolic decreases in the more distal vessels. Crossing the legs increases systolic blood pressure by 2 to 8 mm Hg. About 20 percent of the population has differences of more than 10 mmHg pressure between the right and left arms. In cases where significant differences are observed, treatment decisions should be based on the higher of the two pressures.
Prejudice for normal readings significantly contributes to inaccuracies in blood pressure measurement. Orthostatic hypotension is defined as a decrease in systolic blood pressure of 20 mm Hg or more, or diastolic blood pressure decrease of 10 mm Hg or more measured after three minutes of standing quietly.
There are circumstances when BP measurement is simply not possible. For many years, trauma resuscitation guidelines taught that rough estimates of systolic BP SBP could be made by assessing pulses.
In recent years, vascular surgery and trauma studies have shown this method to be poorly predictive of actual blood pressure [3]. Noise is a factor that can also interfere with BP measurement. Many ALS units carry doppler units that measure blood flow with ultrasound waves. Doppler units amplify sound and are useful in high noise environments.
BP by palpation or obtaining the systolic value by palpating a distal pulse while deflating the blood pressure cuff generally comes within 10 — 20 mmHg of an auscultated reading. How to use a home blood pressure monitor Be still. Don't smoke, drink caffeinated beverages or exercise within 30 minutes before measuring your blood pressure.
Empty your bladder and ensure at least 5 minutes of quiet rest before measurements. Sit correctly. Sit with your back straight and supported on a dining chair, rather than a sofa.
Your feet should be flat on the floor and your legs should not be crossed. Your arm should be supported on a flat surface such as a table with the upper arm at heart level.
Make sure the bottom of the cuff is placed directly above the bend of the elbow. Check your monitor's instructions for an illustration or have your healthcare provider show you how.
Measure at the same time every day. It is best to take the readings daily however ideally beginning 2 weeks after a change in treatment and during the week before your next appointment. Take multiple readings and record the results. Each time you measure, take two or three readings one minute apart and record the results using a printable PDF tracker.
If your monitor has built-in memory to store your readings, take it with you to your appointments. Some monitors may also allow you to upload your readings to a secure website after you register your profile. Don't take the measurement over clothes.
Know your numbers Learn what the numbers in your blood pressure reading mean. If your readings are still unusually high, contact your doctor immediately. You could be experiencing a hypertensive crisis. Instead, he or she will want to confirm the measurements on at least two occasions, usually within a few weeks of one another.
A result this high usually calls for prompt treatment. It's also a good idea to have your blood pressure measured in both arms at least once, since the reading in one arm usually the right may be higher than that in the left. A study in The American Journal of Medicine of nearly 3, people found average arm- to-arm differences in systolic blood pressure of about 5 points. The higher number should be used to make treatment decisions. However, your doctor may schedule a follow-up visit sooner if your previous blood pressure measurements were considerably lower; if signs of damage to the heart, brain, kidneys, and eyes are present; or if you have other cardiovascular risk factors.
Also, most doctors routinely check your blood pressure whenever you go in for an office visit. As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.
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