EBME Forums Forums Management Training Manual Blood Pressure Equipment

Our Trust is looking at replacing our mercury sphygs and rationalising our manual blood pressure equipment to one make and model. We have looked at both the UM101 and the Green Light systems and wondered if there was feedback from other hospitals which use these? We are also looking at going away from using electronic devices to measure BP (except in critical care areas)and converting to all manual BP recordings and would be interested in hearing if any other hospitals have gone down this route. Please get in touch!

At Portsmouth we have just started a training programme on taking BP correctly. The Greenlight will be used for one off measurements, where an accurate BP is needed. The main problem is getting the staff to take a BP correctly but this is where the clinical tutors come in.
Automatic machines are to be used for repetative BP measurements where you are looking for a trend rather than an absolute reading i.e. post op recovery.
This is not a programme to replace mercury but to use manual BP machines again, rather than relying on automated machines for one off measurements. But this involved te purchase of more equipment, the Greenlight. As the older anaeroid and mercury sphygs come to the end of therir life they will be replaced.
Get in contact if you need to know more.
Robert

For those of us who were wondering!

Nice to see that good old Accuson have made a come-back! I had imagined they might have fallen upon hard times following the move away from traditional mercury sphygs.

MHRA recommendations state that each clinical area should have at least one manual blood pressure measurement device that uses the auscultatory method of blood pressure measurement, i.e. a sphygmomanometer, available.

The manual hybrid sphymomanometer (one that uses non-mechanical indication of blood pressure but works on the same principles as the aneroid and mercury sphygmomanometer) is preferred since there's apparently less effects on electronic calibration and BP scale due to cycling or abuse thus the servicing/calibration verification interval can be extended. Irrespective of this the recommended interval for checking of these devices is 12 months, I believe.

The reason why the auscultatory method is preferred is that automated methods, e.g. oscillometric methods, may fail, under certain circumstances, to determine blood pressure repeatably and give large discrepancies when compared to the auscultatory method if there is beat to beat variation in the patient's pulse due to arrythmias or any anomaly that the automated algorithm is not compatible with.

As an example we've had reports of operators in cardiac rehabilitation being dissatisfied with automated and semi-automated devices, in that they fail to make a spot-determination at all, stay inflated and cause discomfort, give consecutive readings with poor repeatability or readings that cannot be believed. I've suggested that operators' rely on manual methods under these circumstances and the standard manual device that's recommended in our Trust is the Accoson Greenlight 300.

The auscultatory method, based on the audible korotkoff sounds produced by blood flowing in the brachial artery under the cuff (heard using a stethoscope placed in the ante-cubital fossa), during the blood pressure determination, is still considered the "gold Standard" method of determining blood pressure. The clinician can judge, subjectively, where the appropriate phase 1 (systolic) and phase 5 (diastolic) sounds occur at.

This means that when the automated method gives a blood pressure indication that is considered unsatisfactory, by the clinician or nurse and that may be due to irregularities in the heart rhythm, then there is a manual method available that allows the clinician to use subjective judgement and experience to estimate the patient's blood pressure in the clinical context in which it's measured.

The oscillometric method typically used in automated and semi-automated devices usually correlates to invasive blood pressure readings (e.g. AAMI validation) and will tend to over-estimate systolic BP and underestimate diastolic BP due to the sensitivity of the pressure transducer and amplifier utilsed. However the MAP is usually the most representative measurement since it is determined most accurately by the oscillometric method (as used by the DINAMAP, for example).

The auscultatory (manual) method can give a more representative measurement of systolic and diastolic BP under a range of conditions that may affect the pulsatile arterial waveform but MAP can only be estimated very roughly by the clinician who does not have the benefit of statistical processing of pressure readings "on the fly".

The validity of a particular manual device, using the auscultatory method, is assessed via clinical validation. A clinical trial is conducted using a number of "volunteers" and simultaneous BP measurements are made on individuals by trained and experiencced researchers to statistically derive figures for the accuracy of a particular manual device.

This validation or trial is undertaken according to a particular validation protocol, e.g. international or BHS protocols. Devices that meet the BHS, European and international protocols are usually preferred to those that are not. This demonstrates that a clinical trial or validation has been performed on the device.

My personal recommendation as an Engineer working in medical engineering and based on the recommendations, technical & clinical evidence that's available, would be to have a manual hybrid device such as the Accoson Greenlight 300 available to all clinical areas as a backup for automated and semi-automated devices using the oscillometric method in particular. Hybrid devices such as the Greenlight 300 have a reasonable service interval, and have been clinically validated.

Of course the implication is that there must be operators available that can perform BP measurement using the auscultatory method. Irrespective of NBP measurement method the readings are affected significantly by miscuffing - choosing the size of cuff for use on a patient inappropriately so a range of cuff sizes must also be provided for each device and used appropriately.

The reason we are "going back" to a manual method of BP measurement is accuracy. Automated BP machines are good for identifying trends but not good for an absolute measurement. Have a look at the specifications of these machines, not just the stated static accuracy but the dynamic reading accuracy, especially on real, ill patients.
A difference of only 10mmHg (less than 10% of the systolic reading) can mean the difference between treating hypertension and not.
Robert

It'd be interesting if you could expand on what you mean by "accuracy" Rojo - relative to what? The actual systolic and diastolic IBP of the patient at any particular time the NBP is taken for example or an automated device under the same circumstances? I'm not sure the accuracy figures are directly comparable is what I'm trying to say.

The validation of manual devices is normally a comparison between clinicians estimates of NBP using a manual device on a trial of patients rather than an assessment of the absolute accuracy of a device in comparison to an automated device or patients' IBP. They're not necessarily comparable figures.

I don't think you can directly compare accuracy of the automated and manual methods without some statistical jiggery-pokery. I think what you're possibly saying is that "subjective accuracy" of the manual device is likely to correllate more closely with what clinicians think the patients actual blood pressure should be than automated methods do - when considering a spot reading.

It's a "trick" that works because the clinician has the luxury of estimating NBP rather than applying a fixed algorithm that "can "fall over" if there's beat to beat variation in the patients blood pressure or an abnormal rhythm.

I think manual is considered most "accurate" because clinicians can obtain readings that they, subjectively speaking, are happy with (since they measured it, of course). The clinical validation is not strictly an assessment of the "accuracy" of the manual device but the method as well.

Considering clinical validation of manual methods a figure for accuracy is usually derived from correlation between determinations made by two clinicians over a trial of patients, statistically speaking effectively giving the likelihood that a device will perform within certain tolerances.

Anyone can take an "inaccurate" blood pressure at any time but using the manual method they're likely to repeat until what they think is a "meaningful" reading, in their judgement, is obtained.

Users I have spoken to seem inclined to use automated electronic BP measuring devices which utilise the oscillometric method where the perceived advantage is that it is less time consuming for the nurse or doctor to set up and take the measurement. However they are not convinced about the “accuracy” of some of the cheap automated units. One GP surgery I visited recently wanted to go a step further and purchase an automated BP machine which would allow the patients to take their own blood pressure in the waiting area which would give a print out and this would then be presented to the doctor when the patient arrived in the doctors room. Again, this was to free up the doctors/ nurses time… a step too far in my opinion.

However, I do also think you get what you pay for and I have been informed quite often from practitioners that there are “accuracy” issues with some of the cheaper automated NBP units in relation to manual measurements they have taken and also with the repeatability of the measurements from these units. Sometimes I find practitioner no longer wants to hear me harp on about taking manual measurements and just want “good and accurate” NBP machines.

I think sometimes these practitioners perceive their time is better utilised doing other things than taking manual BP reading and in this respect this important skill is fading out among a lot of them. There does need to be training available for the practitioners to instil the importance of good diagnostic and observational BP measurements. These measurements must be performed by skilled practitioners irrespective of whether a machine is used or not as they are the ones who are supposed to be skilled in observing deflation rates, cardiac arrhythmias cuff size ect. Also the staff should be inspecting this equipment regularly to ensure it is undamaged, calibrated and the cuffs are in good condition.

I have heard good reports about the greenlight unit, and I think it is good that the practitioner is using their valuable skill to take the reading, this in my opinion would be the way forward for diagnostic BP recording even if it costing the practitioner extra time to take the reading. Either that or has anyone any brilliant ideas of how to take a non invasive blood pressure “accurately” without using a cuff?

What I don’t understand is why these clever medical people can’t themselves understand the different modalities (ie, NIBP versus "manual" measurement). Clearly a case of "horses for courses", I would have thought. If they can’t be bothered to sit down and take a traditional BP measurement (which also affords the great benefit of presenting an opportunity to actually interact with – as in "talk to" – the patient), then they’ll have to accept the "inaccurate" (?) readings given by their cheap Chinese NIBP toys. They can’t have it both ways. Seems to me that the docs are being dumbed down like everyone else! NIBP – what’s that, blood pressure measurement for the Nintendo generation? BP is just what is says on the can – millimeters of mercury!

Dare I mention the words "laziness" and "reduced skills"?
It is easier to wrap a cuff around a patients are and push the Go button than to take a manual BP.
But as the clinical lead on this project has pointed out, the machine cannot feel the quality of the pulse, is it weak and thready or strong and bounding? Both have a clinical significance.

As Geoff mentioned, it is hourses for course.
To take manual BP properly takes time but is more accurate, so it is appropriate to a one off measurement where you want to know whether to treat or not, or what the "normal" baseline for that patient is.
You would not want to do this every 10 minutes post op when you are looking for a change in BP to indicate the onset of complications. This is when an automated machine is appropiate.

People have said about "cheap" automated BP machines but even the high cost, hospital grade ones have a stated accuracy that would mean a reading could be in accurate enough to make the difference between treatment for hypertension and not.

mmHg surely kPa is the correct SI unit of pressure - I know some monitors have that as an option as it is used in some countries!!! Anyone know which coutries?

Robert