The trouble with blood pressure cuffs
BMJ 2008; 337 doi: https://doi.org/10.1136/bmj.39577.688229.47 (Published 31 July 2008) Cite this as: BMJ 2008;337:a431
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Ed,
Enjoyed the article[1], and could see it all happening, as
indifference to cuff selection, and indeed technique, is a persistent
hospital problem - based, I believe, in the fundamentals of minor
sphygmomanometer maintenance not being taught properly to nurses. I've
given talks to nurses on the very subject recently, and it's remarkable
how many say they were never taught, at any stage.
Cuff type and cuff selection become irrelevant, if you do not use
proper non-Luer plastic connectors to mate cuff to gauge, because metal
Luers will freeze together making disconnection impracticable without
forceps to assist - they also will leak with repeated use. Plastic
connectors should be mandatory therefore, and metal Luers banned. A list
of the desirable characteristics of a cuff to gauge connector looks
something like this:-
1. Plastic, not metal(non-corrosive easily cleaned)
2. Low in bulk
with no sharp edges(no pressure areas)
3. Cannot be overtightened (easy to
change, regardless of strength, promotes changing)
4. Free
flowing(internal diameter of = >3mm, and no valves preventing or
restricting deflation)
5. Non-Luer(can't connect to IV line)
6. Leak
proof(plastic connectors with "O" ring seals offer pressure ratings five
times maximum gauge pressure)
7. Inexpensive(plastic connectors are five
times cheaper than metal Luers)
8. Colour coded - eg. white female half-
connector for cuff, black male half-connector for gauge, - allows
complete assembly of inflation bulb, cuff, and cuff to gauge half-
connector as single unit, for any given size cuff. Allows quick change
without assembling parts - essential in emergencies.
The basics of taking readings which I teach:-
1. Cuff too big - reading too small, cuff too small - reading too
big.
2. Arm too high - reading too low, arm too low - reading too high
3. Rate of fall of gauge = 2 mm Hg(one division) per pulse beat.
Most blood pressure readings in general hospital wards are
colloquially termed "radar obs". That is, you would be just as accurate in
satisfying yourself your patient is well on the basis of temperature,
respiration and pulse, together with general demeanor, and then
documenting a "line of best fit" from the existing blood pressure
"readings". I see this radar behaviour every day in the wards, and though
it looks "busy", with cuffs being applied, it is total nonsense.
It is not outside the realm of possibility that the very noble status
being afforded the mercury manometer[1], is itself, at fault. The badly
educated practitioner simply reassures himself with "I've got a mercury
manometer, so I must be going well". Do we drive well because we drive the
Rolls?
[1]J E Bellamy, H Pugh, and D J Sanders.The trouble with blood
pressure cuffs. BMJ 2008; 337: a431 [Full text]
Competing interests:
None declared
Competing interests: No competing interests
Don't always believe the diastolic
Bellamy et al give highlight the pitfalls of using an incorrectly
sized bladder when measuring blood pressure. Within their case reports
they mention the use of automated oscillometry (DINAMAP). 1
Within such devices the diastolic pressure is measured as the onset
of rapidly decreasing oscillations, but is also calculated as the mean
arterial pressure minus 1/3 pulse pressure. Therefore, the displayed
measurement is either derrived or measured from a relatively 'soft' end
point. The mean and systolic pressures are however measured as the oset
of oscillation and maximum oscillation respectively.
This should be bourne in mind when interpreting the results of non-
invasive oscillometry i.e. the mean and systolic presures are those which
should be most trusted.
1 - Bellamy JE, Pugh H, Danders DJ. The trouble with blood pressure
cuffs. BMJ 2008;337:515-516
Competing interests:
None declared
Competing interests: No competing interests