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Selecting a Sphygmomanometer or Blood Pressure Monitor

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Time for a Better Sphygmomanometer
There's Lots of Information on the Web
Comparing aneroid sphygmomanometers and electronic blood pressure monitors

Time for a Better Sphygmomanometer

After a year or so of using my "economy" sphygmomanometer (and attending a birth where the mom's blood pressure became a real issue), I decided to spend a little money to get some better equipment.  I wanted to share what I learned during the process of selecting some upgraded equipment.

There's Lots of Information on the Web

First of all, I learned a little about the history of blood pressure.  (The first blood pressure reading was taken by inserting one end of a tube to a column of mercury and the other end into the artery of a horse, thus directly measuring the blood pressure.  Such invasive techniques are sometimes still used, but probably not by midwives and certainly not at a homebirth.  :-)   )

In any case, the "column of mercury" reading became the definition of blood pressure (as in "so many millimeters of mercury", also written mm Hg, since Hg is the symbol for the element mercury).  And it is still the "gold standard" in that it is the most accurate measurement and is standard across many different instruments, so it's typically used by health care providers who don't need their equipment to be portable, and who need "accurate" readings that will be meaningful when compared with readings taken on other machines.

However, most homebirth midwives prefer more portable equipment, so I wasn't even considering getting any kind of sphygmomanometer with mercury.  I was looking primarily at the aneroid sphygmomanometer and the electronic blood pressure monitors.  I learned some interesting things:

Comparing aneroid sphygmomanometers and electronic blood pressure monitors:

[NOTE - June, 2005 - this web page is one of the oldest here . . . if you want more up-to-date information, you might want to read

The text suggests that the information was updated May 2005 when in fact the current list of Hypertension Society Machines is reviewed each month.

You might also be interested in a site that is dedicated to providing information to help people correctly measure their blood pressure and within the site is a page about blood pressure during pregnancy:

Blood pressure monitors which type is recommended to use at home?

Home blood pressure monitors recommended by the British Hypertension Society

and the companion page - Automatic Digital Blood Pressure Monitors from Omron available in the USA]

HM International offers a good selection of Omron blood pressure monitors as well as Littmann stethoscopes.  The claims are that Omron blood pressure monitors fall within acceptable accuracy ranges, comparable to mercury devices.

So, I poked around on the Web to see what I could find from medical source about the relative accuracy of electronic or oscillometric blood pressure monitors:

The accurate measurement of blood pressure -  Report of the Canadian Hypertension Society Consensus Conference "Diagnosis of hypertension in adults"

Are Home Blood Pressure Monitoring Devices Accurate? - The investigators concluded that there is a significant  number of inaccurate readings obtained using home blood  pressure monitoring devices.  However, this was an uncontrolled comparison using random devices and is more a heads-up to physicians to get details about a patient's home monitoring device before trusting reported results.

DISCUSSION OF HOME AMBULATORY BLOOD PRESSURE MONITORING - "The device that was the most accurate of the three tested was the Omron HEM-705CP"

American Society of Hypertension Releases Guidelines on Home and Ambulatory Blood Pressure Monitoring - Concludes that aneroid devices are more accurate than electronic devices but may not be suitable for all users.

And here are some abstracts from Medline:

Accuracy of oscillometric blood pressure monitoring in pregnancy and pre-eclampsia.
Gupta M, Shennan AH, Halligan A, Taylor DJ, de Swiet M
Br J Obstet Gynaecol 1997 Mar;104(3):350-5

CONCLUSION: The Omron HEM 705 CP does not reach acceptable accuracy criteria for blood pressure measurement when compared with trained observers in women with pre-eclampsia, as judged by the British Hypertension Society Protocol. It also failed to meet the AAMI criteria, although the methodology stipulated by the AAMI may not be  applicable to a pregnancy population.
Blood pressure monitoring at the wrist: is it reliable in children and adolescents?
Bald M, Westhues R, Bonzel KE
Z Kardiol 1996;85 Suppl 3:106-8

The Blood pressure watch and Omron R1 were found to be inaccurate for children and adolescents.

Home self-monitoring of blood pressure: is fully automated oscillometric technique as good as conventional stethoscopic technique?
Stergiou GS, Voutsa AV, Achimastos AD, Mountokalakis TD
Am J Hypertens 1997 Apr;10(4 Pt 1):428-33

For hypertensive patients, oscillometric devices validated in the provider's office provided readings comparable to those taken by very carefully trained patients.

In clinical practice, HBP monitoring by using reliable automated devices is probably more feasible than to achieve a high standard of stethoscopic HBP measuring technique.

Blood pressure self-measurement in upper arm and in wrist for treatment control of arterial hypertension compared to ABPM.
Eckert S, Gleichmann S, Gleichmann U
Z Kardiol 1996;85 Suppl 3:109-11

The boso Oscillomat (upper arm) and Omron HEM-601 (wrist) were found to be comparable to automatic 24-h, ambulatory blood pressure measurement.

[The evaluation of a self-measurement arterial pressure monitor: the OMRON-HM 722C].
Cordoba R, Fuertes MI, Alvarez A, Molina I, Solans R, Melero I
Aten Primaria 1997 Sep 30;20(5):247-50

The OMRON-HM 722C self-measuring monitor could be useful for self-measurement of BP at home by primary care patients.
Comparison of the Omron HEM-713C automated blood pressure monitor with a standard ausculatory method using a mercury manometer.
Mufunda J, Sparks B, Chifamba J, Dakwa C, Matenga JA, Adams JM, Sparks HV
Cent Afr J Med 1996 Aug;42(8):230-2
The Omron HEM-713C compares well with the standard mercury manometer, we therefore recommend its use in both research and clinical applications which require blood pressure measurements.
An evaluation of the A&D UA-751 semi-automated cuff-oscillometric sphygmomanometer.
Jamieson MJ, Webster J, Witte K, Huggins MM, MacDonald TM, de Beaux A, Petrie JC
 J Hypertens 1990 Apr;8(4):377-81
"Thus the Conclusion Well, the research was a little mixed.  It seems that the electronic units are generally comparable to the aneroid devices for home monitoring, and a couple of the abstracts even implied that it was also suitable for clinical use.  And I was drawn to the features of the electronic unit, such as timed measurement and printout of readings along with the time.  This seemed a lot more convenient for routine monitoring of the mom in the immediate postpartum, allowing me to continue with my work and not even have to worry about changing gloves in order to check the mom's blood pressure and pulse.

However, I was nervous about the specific study showing inaccurate readings for pregnant women, especially those with high blood pressure readings.  As a homebirth midwife, I wouldn't expect to be managing care for someone with serious high blood pressure, but there are times when a mom can have a sudden change in blood pressure during labor or postpartum, and I'd hate to be doubting my equipment during a time of crisis.

So, I made the decision to purchase an aneroid sphygmomanometer for my baseline blood pressure equipment.  Perhaps sometime in the next few years, I'll be able to purchase an electronic monitor for normal postpartum, knowing that I always have my aneroid as a backup instrument in case I don't trust the electronic readings.


The best prices I found for the Tycos "Silver Ring" aneroid sphygmomanometers were at Family Practice Kit is the best deal if you need both the adult and large adult cuffs, and you get a pediatric cuff thrown into the bargain - the cost for this kit (item #5098-30) is $104, plus about $6 shipping.   I also ordered an upgraded stethoscope to go with my new sphygmomanometer and learned some useful things about using a stethoscope!


In the process of doing this research, I also came across a few pages that had some good information about taking blood pressure:
Taking BP Right - Reprinted from the American Heart Association, “Human Blood Pressure Determination by Sphygmomanometry” Copyright 1994, with links to Tips for Taking Blood Pressure and the Table of Most Common Mistakes.

More Blood Pressure Papers

And some related review material:
The Circulatory System - A basic review
Shock - including a discussion of hemorrhage, dehydration, heat stroke and anaphylactic shock.

And I also came across some information that's really fun, but not of much clinical value:
Hemodynamics II - Hemodynamics can be loosely defined as the physics of blood flow in the circulation
Fluid and Hemodynamic Derangements - an odd collection of interesting information.

This Web page is referenced from another page containing related information about Supplies


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