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Are You Measuring Blood Pressure Correctly?
According to the National Institutes of Health website, www.nhlbi.nih.gov, the first item on the list of causes of resistant hypertension is “improper BP measurement” by the healthcare professional. That does not surprise me, as I have personally witnessed many incorrect methods being used. In such cases, the healthcare workers are probably in a hurry, or assume they know proper technique when they do not.
Why is this an important topic? One of the responsibilities we have to our patients and to our physician employers is to obtain accurate results when we perform tests. Blood pressure measurement is an important test. Otherwise, why would we bother to do it?
Take this little quiz to see if you are guilty of taking shortcuts when measuring blood pressure:
- Do you bare the upper arm entirely? If the sleeve is pushed up, do you check that it is not constricting the arm? Have you ever slipped the stethoscope under the cuff so you don’t have to hold it down? Do you position the cuff so it is at least 2 inches above the inner elbow? Have you ever tried to measure blood pressure through clothing?
- Are you sure you are using a properly sized cuff? Are the ear spuds on your stethoscope pointed slightly forward?
- Do you hold the patient’s arm or support it so that the arm is completely relaxed? Is the patient’s arm always held at heart level?
- Do you allow patients to rest for a bit if they have just arrived?
- Do you pump the cuff up to about 160 mm/hg to begin with? Do you release the pressure slowly, only about 2 increments per heartbeat?
- Are you familiar with all the increments on the manometers? Do you regularly check the manometers for accuracy?
Let’s discuss each of these issues:
1. Baring the arm entirely allows you adequate room to place the cuff the proper 2 inches above the elbow without placing the cuff over the sleeve. The only time you can place the cuff over fabric is with a very lightweight (sheer) fabric. If you push the sleeve up, make sure it is far enough up the arm to allow for proper placement of the cuff, and check to see if the sleeve is too tight. You should be able to slip your fingers easily under the sleeve. The best technique is to expose the entire arm and place the cuff properly. Never place the stethoscope under the cuff. The cuff needs to have equal pressure all around with nothing under it.
2. Using a cuff that is too small will give a higher than accurate reading, and using a cuff that is too big will have the opposite effect. Take the time to use the proper size. How can you tell what size to use? The general rule is that the bladder length should be at least 80% of the circumference of the arm and the width should be 40% of the circumference. The width is predetermined by the cuff size, but the length-to-arm ratio is a decision you need to make. Cuffs have a range of sizes marked on them. If you go beyond that marked range, go to a larger cuff.
|
Arm Circumference |
Cuff Length |
Cuff Width |
Regular adult cuff |
27–34 cm |
30 cm |
13 cm |
Large adult cuff |
35–44 cm |
38 cm |
16 cm |
Small adult cuff |
22–26 cm |
24 cm |
10 cm |
Pointing the ear spuds slightly inward ensures that they fit most ear canals snugly. If the spuds are pointed back, they can hit the back of the ear opening, deafening the slighter sounds.
3. The patient’s arm should always be held at heart level for an accurate reading. You can hold the arm or have it supported on a comfortable surface. Either way, the arm should be totally relaxed. I prefer holding the arm so I can tell if the arm is tensed or relaxed.
4. Let patients rest a bit if they have just arrived. Being at the doctor’s office is stressful enough, and sometimes patients have hurried to get there. These factors can cause artificially elevated vital signs.
5. The cuff should be pumped up quickly to about 160 mm/hg to begin with. Just the pain of a super inflated cuff can elevate the reading. If you know for a fact that the patient has hypertension, pump it to about 20 mm/hg above the suspected systolic pressure. Probably the most common mistake is to release the pressure too quickly. The pressure should be released about 2 mm per heartbeat. It is humanly impossible to catch an accurate BP if the pressure is released more quickly.
6. The most accurate equipment is undoubtedly the mercury sphygmomanometer, but with the dangers of using mercury, especially in homes, we have gone to aneroid manometers and automated devices. Regardless of the type of device used, the user must study the increments to be sure of accurately reading the scale. Does each line equal one mm or two? How many lines are between the 10 and the 20? The automated devices eliminate the errors caused by misreading, but most of us are using auscultory methods with aneroid manometers. Checking the accuracy of the manometer is as simple as making sure the needle is at 0 mm/hg when the cuff is completely deflated and under no pressure. This should be done for every patient.
Did any of this information surprise you? My intent in this article has been to raise your awareness of the actions we can take to ensure more accurate results with blood pressure readings. Share this newsletter with your colleagues, and maybe do an in-service workshop or focus group on measuring blood pressures accurately.
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