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manufacture manufacturer maker producer stops
the air going back into the bulb. After the cuff has been inflated and the blood
pressure taken, the cufy may be deflated by opening valve C. The reservoir contains
the supply of mercury which rises up the measurement tube. Normally the apparatus
is contained within a box. When opened the graduated tube becomes vertical,
and the mercury reservoir is at the bottom. As the pressure within the cuff
increases the mercury is displaced from the reservoir into the graduated tube.
The two leather discs (D and E) allow air to pass in and out of the column,
but prevent mercury escaping from the sphygmomanometer. The following points
are important for accurate blood pressures:
The inflatable part of the cuff must be the correct size for the arm. It should
cover two thirds of the length of the upper arm. A blood pressure cuff which
is too small will cause an abnormally high blood pressure reading and a low
reading may result from too large a cuff. The cuff should be firmly applied
with the centre of the inflatable part over the brachial artery. The cuff must
be free of leaks. The mercury should be clean and at the zero mark before use.
During cuff inflation the mercury should rise smoothly, and stop immediately
inflation stops. Problems with the mercury sphygmomanometer Remember mercury
vapour is poisonous. Any maintenance should be performed in an area of good
ventilation. Store mercury in a plastic bottle with a little water placed on
top of the ercury. Be careful not to inhale black mercuric oxide powder during
cleaning procedures.
Black discoloration of the mercury. The mercury should be a clean silver colour.
With time, a black powder (mercuric oxide), forms on the surface. A little black
powder in the column does not matter. If there is a large amount, the mercury
should be removed from the sphygmomanometer and the column and reservoir cleaned.
Do this by laying the machine on its side with the reservoir downwards. Remove
the column, ensure that you do not lose the leather disc at the top. Undo the
reservoir top and pour the mercury out into a plastic bottle. Blow the reservoir
and the leather disc in the reservoir top clean with compressed air and wipe
with a cloth. (If you don't have compressed air, take an old blood pressure
inflation bulb, find a large bore needle, file off the tip and fit it to the
inflation bulb. By squeezing the inflation bulb you will have a source of compressed
air). Clean the inside of the column and replace it. Remember to replace the
leather disc at the top and the washer at the bottom. Replace the mercury in
the reservoir to the zero mark. Use a syringe and needle to draw up the mercury
from the plastic bottle. Keep the needle under the surface of the mercury to
avoid returning any black powder. Replace the reservoir top with its sealing
ring, connect the cuff and check the system is airtight by inflating the cuff
until the mercury is at the top of the column. Check that it does not spill
out-if this happens, the top leather disc is faulty or missing. (This disc should
allow the air to pass in and out as the mercury rises and falls, but not allow
mercury to escape.) Mercury continues to rise slowly after stopping inflation.
This is caused by the air at the top of the column failing to escape through
the top leather disc quickly enough as the mercury rises up the column. When
the sphygmomanometer is used, this fault may result in abnormally high readings
as the mercury falls more slowly than the cuff pressure, due to the faulty leather
disc restricting the air entering the top of the column. The cause of these
faults is in the top leather disc. It is either too thick or dirty. It should
be removed as described before and cleaned. Replace it and test the sphygmomanometer.
If the fault persists, remove the disc. Holding it between your finger and thumb
on a flat surface, gently scrape it with a scalpel blade. Turn it continually
to ensure it keeps its round shape and take care not to put a hole in it. Refit.
The mercury does not rise but the cuff inflates. This indicates blockage at
D in the figure or a kinked or obstructed tube. The cuff will not inflate or
mercury rise. This indicates that there is a leak. Check valves A, B and C,
the rubber bladder, tubing and connections. Rubber bladders may be repaired
with an ordinary bicycle tyre puncture kit. Valve B can usually be removed and
cleaned. Valve A may be a small ball bearing which can be removed from its cage
and, with care, cleaned and replaced. Valve C cannot normally be removed. After
full assessment reassemble the sphygmomanometer and test. Many hospitals are
replacing mercury sphygmomanometers with cost-competitive aneroid sphygmomanometers.
An aneroid sphygmomanometer is a mechanical gage with a round dial and needle
that rotates to indicate pressure from 0-300 mm Hg. On the inside, a bellows
and spring mechanism senses and transmits the blood pressure measurement to
the dial. Aneroid units have several features that are appealing to healthcare
professionals: The dial of an aneroid gage is much easier to read and requires
considerably less effort than the meniscus of a mercury column, which requires
awkward head movement to do a good job. It is easy to see if the aneroid needle
is off zero when not in use. This provides a good indication of whether the
gage has been damaged or needs maintenance, and is an easy check each time a
reading is taken. It is easy to check the needle for smooth rotation, another
way of verifying that the aneroid device is in good working order. When procuring
new sphygmomanometers, a few considerations up front can make your life easier
in the long run: Verify that all components are latex free. Some manufacturers
routinely offer free lifetime calibration, or this can be negotiated in the
contract. Consider the implications of calibration done at your site (more convenient)
or at the manufacturer (which requires addition units on hand). One hospital's
contract called for the manufacturer to randomly evaluate accuracy of 25% of
the units quarterly, so that each year a unit is inspected once by the manufacturer.
When you buy the aneroid devices, ask the manufacturer to accept intact mercury
sphygmomanometers for recycling. If this is negotiated in the contract, it saves
the expense of disposing of mercury devices. Consider the need for spare units.
For offsite calibration, extra units allow a swap with instruments in current
use. These spares keep the hospital running while allowing the use of more cost
efficient ground shipment to and from calibration. When you receive new units,
consider bar coding them. This allows you to track reliability and performance,
calibration status, and inventory status. If you check sphygmomanometer accuracy
at your site, make sure your reference gage is mercury free. An example of a
viable digital reference is the NETECH DigiMano 2000
Welch Allyn, Inc., one of the world's leading manufacturers of medical diagnostic
instruments, today announced the introduction of the Welch Allyn® DuraShock™
Integrated Aneroid Sphygmomanometer. The device incorporates patented, gear-free,
helix-spring technology that represents the first major innovation in aneroid
sphygmomanometers in over 100 years. This new technology meets the current AMI
SP9 Standard for shock-resistant aneroid sphygmomanometers and makes the gauge
ideal for use in active medical environments where it may be handled roughly
or dropped.
"Welch Allyn DuraShock™ gear-free aneroid technology is the next step
in the evolution of manual non-invasive blood pressure measurement technology
that began with mercury manometers in 1834, evolved to mercury-free aneroid
manometers in 1897, and now progressed to shock-resistant, gear-free aneroid
technology," according to Thomas Grant, Welch Allyn marketing manager.
"Our first Tycos® brand aneroid sphygmomanometer was made in 1907,
and through aggressive innovation, today's Welch Allyn blood pressure machine
