Blood Pressure Measurement: Worsening Chaos

DG Beevers and M Beevers University Department of Medicine, City Hospital, Birmingham B18 7QH, UK

Keywords: blood pressure; measurement

The measurement of blood pressure is one of the and there must be some concern about the amount most common and important tests performed on of mercury from broken sphygmomanometers, and patients. Both hypertension and hypotension have also thermometers, under the floorboards of some of major clinical implications in acute medicine and, our older and more ramshackle hospitals. It is on a longer-term basis, hypertension itself is after because of these worries that a new European Union age and gender, the most accurate predictor of life directive will prohibit the use of mercury in sphyg- expectancy. The history of blood pressure measure- momanometer and thermometers.8 ment can be regarded as one of steady progress, cul- Advances in technology now mean it is possible minating in the invention of the sphygmoman- to measure blood pressure using automatic or semi- ometer that we now know by Scipione Riva-Rocci in automatic devices without the need for a mercury 1896 and the discovery of the systolic and diastolic manometer. It has become clear, however, that many sounds by Nicholai Korotkoff in 1905. Since then of these machines are inaccurate and the British the gold standard of blood pressure measurement Hypertension Society (BHS) as well as the American has been the mercury manometer which has served Association for Medical Instrumentation (AAMI) us well for over 100 years.1 have both issued guidelines on how the blood press- The distinguished American neurosurgeon, Har- ure machines should be assessed.9 By any criteria a vey Cushing, should take the credit for being the first very large proportion of the currently available auto- person to suggest that the measurement of blood matic and semi-automatic machines were found to pressure be carried out routinely in all patients, be unacceptable. It is interesting to note that some although, sadly, this is an ideal that has still not manufacturers have marketed these machines with- been achieved.2 out any apparent effort to ensure that they are accur- There is an extensive literature on the sources of ate. Presumably it was argued that because the error encountered with blood pressure measurement machine should be accurate therefore it will be and these can be neatly divided into those that are accurate. Thus field trials were not conducted. Sev- associated with the observer, with his or her bias eral Health Authorities in the UK have proudly or inaccuracy, the manometer itself which may be opted to go ‘mercury free’ and have bulk purchased inaccurate or damaged and the cuff which may be automatic machines that are frankly inaccurate. the wrong size.3 Tests of blood pressure measurers Others have opted to bulk purchase cheaper aneroid have shown depressing results and there are also manometers despite their well-recognised tendency many studies examining blood pressure machines to become inaccurate with the passage of time. 4,5 and cuffs which are equally woeful. This One of the few automatic blood pressure measur- prompted the St George’s Hospital group to suggest ing systems which has passed both BHS and AAMI that as conventional mercury sphygmomanometers criteria is the OMRON HEM 705 CP.10 This desk- are so bad they should be abolished in favour of top model together with printer has therefore been 6 electronic equipment as soon as possible. purchased by a great many blood pressure units and Meanwhile, there are increasing anxieties about research workers. It is the machine currently being the possible hazards of mercury to the environ- used in the Anglo-Scandinavian Cardiac Outcome 7 ment. Metallic mercury and inorganic mercury salts Trial (ASCOT) and the sales must be enormous. are probably not particularly toxic but there is a con- General practitioners in Britain have been mailed a cern about organic mercury which might, in theory, leaflet advertising the OMRON 705 CP and the enter the food chain. Very little mercury is recycled World Hypertension League (WHL) has circulated a leaflet on blood pressure measurement which Correspondence: Prof DG, Beevers, University Department of specifically mentions the HEM 705 CP. Medicine, City Hospital, Birmingham B18 7QH, UK Most blood pressure machines do not really need Received 8 March 2000; accepted 15 March 2000 a printer and for that reason the OMRON M4 appar- Blood pressure measurement DG Beevers and M Beevers 416 atus has become available and can be used by doc- blood pressure is more important than the diastolic tors, nurses and patients to monitor blood pressure. pressure. Indeed the diastolic blood pressure may Many clinicians hoped that one could extrapolate provide little information after the systolic blood from the 705 CP to the M4, both machines being pressure has been taken into account. Central to this made by the same company. argument of course is the truth or otherwise of the An alarming paper is published in this month’s observation that isolated diastolic hypertension, a issue of the Journal of Human Hypertension.11 Nas- rare syndrome, does not carry a poor prognosis. If chitz and co-workers from Israel have developed a this is the case and we do decide that diastolic press- simplified method of testing the accuracy of auto- ure does not need to be measured, then the systolic matic blood pressure devices and when they had blood pressure alone would become the gold stan- turned their attention to the OMRON M4 they have dard. The technology of automatic and semi-auto- come up with some surprising findings.12 They con- matic blood pressure monitors could be greatly sim- cluded that the M4 device did not meet the criteria plified simply to detect the pressure within the arm of the British Hypertension Society and could not cuff when the first jet of blood passes under it. With be recommended for clinical use. mercury manometers one could therefore measure Meanwhile how confident are we of the OMRON the systolic blood pressure simply by palpation of HEM 705 CP? It is the experience of many clinicians the brachial artery. Things would indeed be a great that this machine sometimes turns up isolated rogue deal simpler and doctors and nurses could spend readings which are totally improbable and not con- less time with stethoscopes in their ears. firmed 30 seconds later. Sometimes the 705 CP More than a century after the invention of the first seems to go on strike and flashes up a somewhat dis- usable mercury manometer, blood pressure concerting ‘E’. The choice of cuffs is limited to two, measurement seems to be in more chaos than ever the larger one being designed with the assumption before. If the experts are behaving like headless that obese people also have longer arms. One of our chickens what are general practitioners, general cuffs spontaneously tore apart whilst in use. physicians and nurses meant to do? One of the senior research nurses in our department was so exasperated with the OMRON appar- References atus that she has abandoned it and now maintains 1 O’Brien ET, Fitzgerald D. The history of blood pressure that she would much rather measure blood pressure measurement. J Hum Hypertens 1994; 8: 73–84. with a well-maintained mercury manometer, using 2 Fulton JF. Harvey Cushing, a biography. The Classics the strict criteria laid down in the BHS. The advan- of Medicine Library: New York, 1991. tages of an automatic system are however that one 3 Perry IJ, Beevers DG. Measurement of blood pressure can, effortlessly, take several bias-free blood press- in epidemiological surveys. In: O’Brien ET, O’Malley ure readings and obtain results that are more basal K (eds), Handbook of Hypertension Vol 14, Blood than a one-off reading in patients who have just Pressure Measurement. Elsevier: Amsterdam, 1991, walked into the clinic room. It is not uncommon for pp 174–183. 4 Feher M, Harris-St John K. Blood Pressure measure- patients systolic blood pressures to fall by 25 mm Hg ment by junior hospital doctors—a gap in medical edu- or more over 5 or 6 min during a consultation. The cation. Health Trends 1992; 24: 59–61. clinician meanwhile can check the case notes, make 5 Beevers M, Morgan HEG. An audit of blood pressure sure that the ECG has been done, the blood test equipment in two teaching hospitals. J Hum Hypertens results are filed and may be have the time to think 1993; 7: 98. out a more rational blood pressure lowering regime. 6 Markandu ND, Whitcher F, Arnold A, Carney C. The The convenience is undeniable but possibly with mercury manometer should be abandoned before it is the OMRON M4 the clinician is being misled by proscribed. J Hum Hypertens 2000; 14: 31–36. blood pressure readings which are inaccurate. Can 7 Langford NJ, Ferner RE. Toxicity of Mercury. J Hum Hypertens 1999; 13: 651–656. we recommend this apparatus to our patients? What 8 European Council Directive 93/42/EEC. should blood pressure experts say when contacted 9 O’Brien E et al. The British Hypertension Society pro- by clinicians and administrators enquiring about the tocol for the evaluation of blood pressure measuring best machines to purchase, often on a large scale. It devices. J Hypertens 1993; 11 (Suppl 2); S43–S62. would be interesting to know what the readership 10 O’Brien ET, Mee F, Alkins N. An accurate automated of this journal think. device for home blood pressure measurement at last! Meanwhile on a longer term basis there may be The OMRON HEM 705 CP. J Hypertens 1994; 12: light at the end of the tunnel. There is an increasing 1317–1318. body of opinion that the diastolic blood pressure is 11 Naschitz JE et al. Accuracy of the OMRON M4 blood 13 pressure measuring device. J Hum Hypertens 2000; 14: no longer worth measuring. Epidemiological stud- 423–427. ies, echocardiographic studies, randomised con- 12 Naschitz JE et al. In-field validation of automatic blood trolled trials and investigations into the vascular pressure measuring devices. J Hum Hypertens 2000; biology of isolated systolic hypertension and systo- 14: 37–42. diastolic hypertension strongly suggest that systolic 13 Sever PS. Abandoning diastole. BMJ 1999; 318: 1773.

Journal of Human Hypertension