The Use and Misuse of Automatic Blood Pressure Monitors
Friday, March 30, 2007
Joshua Schwimmer, MD, FACP, FASN
I'm a fan of automatic blood pressure monitors like the Omron HEM series. These machines, which have become increasingly accurate and easy to use, allow you to check your own blood pressure automatically at the touch of a button. Most of the time, patients love the reassurance and sense of control these monitors provide.
And sometimes, blood pressure monitors will unmask a rare severe case of "white coat hypertension." In this situation, a person can have a nearly normal blood pressure at home but their blood pressure increases in the doctor's office -- sometimes to over 180/100 -- due to stress caused by seeing the "white coat." In this situation, if medications are given to aggressively treat the high blood pressures in the office, patients may even be at risk of passing out at home from low blood pressure. Automatic blood pressure monitors reveal the difference between the home and office pressures and are enormously helpful in these and other cases.
But rarely, the opposite happens -- the presence of the machine itself causes high blood pressure. The occasional person is so unnerved by their blood pressure monitor that it actually causes their blood pressure to increase. Seeing the high blood pressure reading, in turn, causes them to panic, and they press the button on the machine again and again to take more readings, becoming more and more panicked, which in turn causes their pressure to rise even more. This usually results in a frantic phone call and sometimes a visit to the emergency room.
To prevent this from happening, I tell people to take their blood pressure only once after sitting quietly for five minutes. Thankfully, this usually solves this rarely occurring problem, and the majority of people find automatic blood pressure monitors helpful and reassuring.
7 Comments:
At Wed Apr 04, 08:08:00 PM 2007,
Huck said…
In the VA population, they often come to clinic not having taken their morning meds. As a consequence, BP's run slightly high for that reason. I bottomed someone out because I didn't ask "did you take your meds THIS MORNING."
I have learned since then.
I usually tell my patients to take their BP TID for a week after they had a couple of weeks under their belt with a medication change.
I have occasionally adjusted schedules for medications based on morning or night time HTN, and smoothed out their BP control.
At Sat Apr 07, 06:16:00 PM 2007,
John said…
Huck's points are well-stated and here are a few of my own.
Automatic blood pressure monitors must be individually checked by the physician managing the patient's hypertension. This includes the automatic blood pressure monitors used in the hospital and in the doctor's office. Technique, fit, honesty in reporting the numbers and an assessment of the quality of the pulse all matter.
There is a tendency to ingore the complete assessment of pulse (e.g. bilateral checks, listening for a bruit, checking peripheral pulses and a willingness to reach for the doppler probe when neccessary are all important).
Unfortunately, delegating systolic and diastolic measurements to a machine feeds into the irresponsible trend of distancing the physician from the physical exam. The physical exam may be our last line of defense against errors perpetuated in the electronic medical record (e.g. if a patient has a loud murmur and a normal echo, suspect the echo has been accidently labelled with the wrong patient's name).
After a complete assessment of pulses is done by the physician, the machine is checked and results are documented, then I support the careful use of automatic blood pressure monitors.
We would never accept home blood glucose monitoring as a complete assessment of diabetes mellitus, and unfortunately, there is a growing tendency to accept blood pressure measurements as a sufficient assessment of vascular pathology.
At Sun Apr 08, 02:32:00 PM 2007,
Joshua Schwimmer, MD, FACP, FASN said…
Good point. Asking whether people have taken their meds that morning, I've also learned, is important. Many people, for unclear reasons, feel that they shouldn't take their meds before they see their doctors.
At Tue Apr 10, 09:15:00 PM 2007,
Nicole R said…
I've had a few really good Internists since I was first diagnosed with HTN back in my early 20s. Every one of "the good ones" re-checked my BP themselves -- slowly, methodically, patiently, waiting until I'd been sitting for a while. I have to say that say that most of the check-in staff do a REALLY crummy job on BP checks -- deflating the cuff way too fast, and taking your BP the instant you walk into the exam room.
The monitor I use at home is one that you listen to yourself, but you can take it yourself because the stethoscope is attached to the cuff -- sort of a modified manual cuff. Comparing this to various automatic machines I've tried at home over the years, the automatic machines are very sensitive to poor cuff fit, and never worked even close to properly when I was pregnant (???)
Anyhow, when having my most recent post-partum hypertensive crisis, the OB nurses absolutely insisted on using the automatic machines rather than using a regular manual cuff. In the week I was in the hospital, every single machine on the hospital floor visited my room at least once -- apparently the nurses kept hoping the numbers would be better with a different machine.
Two problems with this approach should be quite apparent. First, changing machines every time introduces an unnecessary potential source of variation beyond true physiologic variation. Second, WHY trade one machine for another when you are suspicious of (or don't like the results from) the first machine, given that you could just use the MANUAL cuff that is hanging right behind the bed and eliminate any questions about machine error???
Here's how those super-duper automatic hospital cuffs work when your BP is sky high. The cuff inflates to a preset initial level, starts deflating to "listen," and when the machine determines that it has not inflated high enough, the cuff immediately begins to inflate again, going higher without deflating first.
Once you reach the second inflation set point, this process is repeated. If the cuff senses that it's still not high enough, it then begins to inflate to a truly painful level, again without deflating first. It finally deflates those gazillion mmHg very, very, very, very, very slowly. By now, your arm has been in the death grip of this cuff for what seems like an hour.
Of course, when THAT measurement comes back astronomically high, the nurse will immediately start the cuff again to try to get a better reading for the chart. (She'd really prefer to discard the worst ones and only chart the better ones.)
Trust me, you don't have to be overly susceptible to "monitor induced" HTN to get a BP increase under circumstances like that...
At Wed Apr 11, 08:36:00 PM 2007,
Joshua Schwimmer, MD, FACP, FASN said…
Nicole,
Thank you for your comments. I probably should have stressed that I only use monitors that I trust (primarily Omrons), I test them mysef in the office to ensure that they're consistent with the manual cuff, and I try to make sure patients have the proper technique.
At Sun Apr 29, 04:01:00 AM 2007,
maclobell_lzrd@yahoo.com said…
Here in the Philippines, majority of our population is not properly educated with regards to hypertensions, likewise the use of modern methods and machines. Though health workers like myself tries to share and teach the public about the importance of knowing what hypertension is and how it can affect them or us. I also encourage them the use of modern tools in determining blood pressure and showing them what hypertension is. I just hope that I could be updated on what kinds of automatic bp monitors are really reliable and are clinically validated by experts.
At Thu Jul 31, 10:48:00 PM 2008,
zbaz said…
I have an early automatic inflate digital Omron HEM712C with a stethoscope and Aneroid meter attached.
After 6 years the digital display has been reading higher than the meter and the Stethoscope sound. My doctor compared it with his manual cuff and confirmed the error, and recommended re-calibration. It seems that the manual used by doctors are more reliable and accurate than the automatic digital used in hospitals.
I am now looking for a new digital automatic/manual machine similar to my old Omron and they are hard to find. Has anyone found similar errors between digital and manual BP machines?
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