January 28, 2021

To Your Good Health: Proper technique is key to accurate BP reading

I have always read that when you are having your blood pressure taken, your arm should be elevated above your heart. When mine is taken this way, it is normal, around 120/70. When I go to the doctor, my blood pressure is taken with my arm hanging at my side. I often get a much higher reading taken this way, say, 140/90. Is there a correct way to take it, and does it affect the reading? My doctor said the position doesn’t matter and wants to prescribe medication.

When taking the blood pressure, the goal is to approximate the blood pressure in the heart. That means that the blood pressure cuff should be at the level of the heart.

If the blood pressure cuff is above the heart, then the blood pressure reading will be artificially low. If the blood pressure cuff is dangling below the level of the heart, the reading will be high.

For every 10 cm, about 4 inches, above the heart, the blood pressure will be about 7 mm of mercury too low. If I stretch out my arm as high as I can above my heart, I can get it about 30 cm higher than my heart, which would be enough to explain the difference between the 140/90 and 120/70 you have observed.

However, for most people when sitting up straight, a properly placed cuff on the arm will approximate the same level as the heart. Although you are right the position matters, it sounds like the doctor’s office is taking the reading correctly.

I should also note that the feet should be resting on the floor, not dangling, which can artificially raise the blood pressure. The arm should be supported while taking the blood pressure. I recommend taking the blood pressure three times and using the average.

Given how important blood pressure is, correct technique is essential in order to properly recommend who should get blood pressure treatment.

Evidence is increasing that a 24-hour home blood pressure device is more accurate at determining who might need medication, especially in suspected white coat hypertension, where the readings are artificially high just because a person is in the office, even if they don’t feel nervous.

I recently had a cancer growth removed from my upper arm by a dermatologist. I was instructed to use Vaseline on the wound. I told them I use an antibiotic with pain reliever. I was told that because this is an antibiotic, I will become immune to the usage. Does the topical antibiotic have the same effect as a pill or shot? Because it is on the outside of my body, will I become immune as described, or is it safe to use as I have done for 40 years?

I agree with your dermatologist. Petrolatum, such as Vaseline, is effective at keeping a wound moist, which promotes healing, and acts as a barrier to keep out dirt and bacteria.

Topical antibiotics may have additional usefulness in areas of skin infection or to reduce carriage of a dangerous bacteria like MRSA, but is no better than petrolatum for a clean surgical wound. Potential downsides to topical antibiotics include not only resistance, but also skin reactions. Accordingly, they should be used sparingly and only for clear indications.

Dr. Keith Roach

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu. © 2021 North America Synd., Inc.