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Rapid Responses: Rapid Responses published:
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THIS IS NOT RELEVANT
- Graeme M Mackenzie (3 August 2002)
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Problems with BP measurement in clinical practice
- Tom Marshall (4 August 2002)
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Dont throw out the sphygmo just yet
- Ben d Ewald (5 August 2002)
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Conformation of observed effect.
- Neil J.P. Fagan (5 August 2002)
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2 charts
- Mark C Aley (5 August 2002)
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Mercury sphygmomanometers cause occupational mercury exposure.
- Phillip J. Colquitt (6 August 2002)
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statistical response
- Alvine Bissery (9 August 2002)
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Use the sphygmomanometers more, not less.
- William T Hamilton, Deborah Sharp (14 August 2002)
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Measuring BP should remain a priority in general practice
- Adrian G Stanley, Bryan Williams (15 August 2002)
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Better tools needed to assess individual cardiovascular risk
- Risto A Laitila (15 August 2002)
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Ambulatory blood pressure monitoring: really a gold standard?
- Paolo Palatini (2 September 2002)
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Site fo BP measurement
- Em Ebbs, 75237 (24 July 2004)
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Graeme M Mackenzie, GP
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We treat blood pressure because studies done ON CLINIC BLOOD PRESSURES showed a risk. Home blood pressure measurements are not the same. You would need to repeat all the MRC type trials to make this meaningful. As well as being the wrong thing to measure, home BP recordings just increase neurosis about health. |
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Tom Marshall, Lecturer in Public Health Medicine Birmingham University B15 2TT
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Basic psychology indicates that our attitudes are shaped by our actions. After a lifetime of clinical BP measurement and making decisions based on these measurements it is likely that Little et al's article will be greeted with incredulity. However, this is short sighted. They have clearly demonstrated important problems with blood pressure measurement which merit some consideration. Blood pressure measurement is subject to both systematic error and random error. Research evidence on the relationship between blood pressure and risk of CHD is based on clinic measurements, taken after an appropriate (5 minutes) seated rest period [1], using calibrated equipment. In day to day clinical practice decisions based on blood pressures taken under varying conditions: sometimes opportunistically (when pain, anxiety or malaise affect blood pressure); sometimes in a hurry (when inadequate rest periods); sometimes when expectation of a blood test increases blood pressure;[2] usually with uncalibrated equipment.[3] These can be expected to lead to systematic overestimation of blood pressure. Little et al have empirically confirmed this systematic error. It remains difficult to know which kind of measurement is closest to the measurements taken in clinical trials; whether we should add a factor (e.g. 5 mm Hg) to the most stable measurement; or what that factor should be. Blood pressure also shows biological (within individual) variation. A single measurement of blood pressure should more correctly be quoted with a 95% confidence interval equivalent to 18% of its value e.g. 140 mm Hg +/ - 25 mm Hg. [4] In epidemiologic studies the effects of random error (regression dilution bias due to within individual blood pressure variability) are corrected for during analysis; in clinical trials the effects of random error are eliminated by comparing blood pressures with a control group. However in clinical practice changes in blood pressure due to treatment are assessed on the basis of a few measurements. In practice this means that deciding whether or not a patient has achieved a "target" blood pressure of (for example) 140 mm Hg systolic is subject to a great deal of error. A patient whose true mean systolic blood pressure is 130 mm Hg will on one in six occasions give a readings of over 140 mm Hg. With regular follow up, it is only a matter of time before his a second treatment is added or the dose increased. Perhaps it is time to rethink the concept of "target" blood pressures in the light of an understanding of biological variation. Perhaps it is also time to rethink the follow up of patients on treatment. We know that antihypertensives work from the experience of many clinical trials in which thousands of patients had repeated blood pressure measurements. A few measurements taken in one individual are more likely to be misleading than informative. If we really need to know the effect of treatment in an individual patient we need many (>10) measurements before and many (>10) measurements after treatment. References 1. Bakx JC, Netea RT, van den Hoogen HJM, Oerlemans G, van Dijk R., van den Bosch WJHM, Thien T. De invloed van een rustperiode op de bloeddruk. {The influence of a rest period on blood pressure measurement.} Huisarts en Wetenschap 1999;42:53-6. 2. Marshall T., Anantharachagan A., Choudhary K., Chue C., Kaur I. A randomised controlled trial of the effect of anticipation of a blood test on blood pressure. Journal of Human Hypertension Sept 2002 [Accepted for publication 5th June 2002 - in press] 3. Rouse A., Marshall T. The extent and implications of sphygmomanometer calibration error in primary care. Journal of Human Hypertension 2001;15(9):587-592. 4. Wright JM, Musini VJ. Blood pressure variability: lessons learned from a systematic review. Poster presentation D20, 8th International Cochrane Colloquium. October 2000, Cape Town. |
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Ben d Ewald, lecturer in epidemiology and GP Newcastle NSW 2300
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The study by Little et al threatens the role of the most honoured gadget on a GP's desk, the sphygmomanometer, however I feel it has not out lived its usefulness yet. In my study of ambulatory blood pressure monitoring in Australian general practice I found that 26% of newly diagnosed patients did not warrant treatment on 24 hour criteria and that the monitoring was cost saving overall. I feel that the place of ambulatory monitoring is to confirm that clinic readings are correct. In patients shown to have good agreement between clinic and 24 hour readings the diagnosis and treatment can proceed as usual, while in those with sizable discrepancies at diagnosis it must be assumed that follow up while on treatment will be similary affected. A rational approach would be to "calibrate" each patient's clinic readings against their 24 hour reading at diagnosis, and set their treatment target accordingly. reference Ewald and Pekarsky Cost analysis of ambulatory blood pressure monitoring in initiating antihypertensive drug treaatment in Australian general practice. Med J Aust 2002:176;580-83 (17 June) |
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Neil J.P. Fagan, Tech. Sup't. Uni of Southampton, SO17 1BJ
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This has confirmed my experience as a front-line ambulance worker in the past, and the husband of a post-operative long term monitored heart surgery patient. At each annual hospital unit check the doctor takes her blood pressure and refers her to her G.P. for high blood pressure monitoring. Her G.P. usually finds a slightly lower pressure and the follow-up visits to the practice nurses lower still. Her G.P. also asks that we take a trending chart at home as I have the experience to do so, this results in the lowest readings of all as the stressors of the practice environment and hospital unit are missing. White coat, and other stress causation factors do make a difference. |
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Mark C Aley, GP so53 1sh
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Unfortunately our targets and 'levels for intervention' are based upon trial results that use a mixture of readings, notably from doctors and nurses. one would guess that the effect is 'evened out' over large numbers, but if we were to use purely nurse-based readings, or indeed patient based readings, then our threshold for intervention, and indeed our targets, would need to reflect this (ie, would need to be lower). Until such time as the trial work is done showing what the risk level is for an average BP done by the patient/nurse/ambulatory etc ALONE, then all we can do is best-guess from the trial results which we have (and they have included the 'higher' doctor based readings). most importantly, it would be wrong to base a decision NOT TO TREAT a BP reading that was just below the threshold when measured by a nurse or patient, as this would not give a true representation of the risk (as calculated from the Doctor included trials). Likewise one should not accept a target if this has been purely patient or nurse measured (? set a lower target). |
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Phillip J. Colquitt, Independent Technical Advisor
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Sir, Reproduced below, with kind permission from the editors of your related journal - "Occupational and Environmental Medicine", is a 1994 article reporting my experience with mercury sphygmomanometers, whilst working as a health and safety representative in a large Australian hospital (Colquitt PJ. The effect of occupational exposure to mercury vapour on the fertility of female dental assistants. Occup Environ Med. 1995 Mar;52(3):214). I suggest the article should be required reading for nurses and doctors in 2002, as debate about methods of blood pressure measurement and the mercury sphygmomanometer, do both continue with the article by Little P. et al.[BMJ 2002; 325: 254] and related responses. I have not seen any evidence in the six years since my report, that Australian GP surgeries are complying with the need for hazard warning labels on mercury sphygmomanometers. "THE EFFECT OF OCCUPATIONAL EXPOSURE TO MERCURY VAPOUR ON THE FERTITLITY OF FEMALE DENTAL ASSISTANTS" Editor – Rowland et al found lower fertility among women who did not work with amalgam compared with women exposed to low levels of mercury[1]. Other exposures to mercury incurred by dental assistants who do not work with amalgam was offered as a possible explanation. In 1994 as health and safety representative for a surgical ward at a metropolitan hospital, I found that 60% of trays at the base of sphygmomanometers, wall mounted, at the head of each patient’s bed, contained leaked mercury[2]. Nurses unprotected hands are often in this cuff tray. The inspecting authorities, with a Jerome analyser, found mercury vapour concentrations of 85 µg/m3 in the breathing zone of a patient at one bed. This is of course the work zone of the nurse. The rate of replacement of thermometers for the complex was 750/month, which becomes 72 kg mercury/10 y at 0.8 g/thermometer. Cases of acrodynia caused by one broken thermometer in the domestic environment are documented[3]. No mercury hygiene protocol was in place. With the same poor hygiene factors that Rowland et al used to assess risk of exposure to vapour – for example, hand contact with mercury – general nurses seem to be at risk. With factors such as lack of knowledge of general nurses about mercury toxicity and the appropriate hygiene protocol[4], a reported rate of leakage from hospital sphygmomanometers of 48%[5], the absence of hazard warning labels on sphygmomanometers(mercury is a classified hazardous substance), the hazard to sphygmomanometer repairers having been unreported until 1986[6], the understandable focus of medical professional on accuracy rather than safety in blood pressure measurement[7], and reported poorer reproductive outcomes for nurses[8,9], it becomes difficult not to conclude that general nurses are chronically exposed to mercury. If the unexposed group in the paper of Rowland et al were taking blood pressures and temperatures, exposure to mercury is suggested. Dentists have shown interest in the suggestion that general nurses are exposed to mercury from sphygmomanometers and thermometers because a percentage of clients who chose non-amalgam restorations will be general nurses[10]. PHILLIP J COLQUITT PO Box 175, Fortitude Valley, Queensland 4006, Australia 1.Rowland AS, Baird DD, Weinberg CR, Shore DL, Shy CM, Wilcox AJ. The effect of occupational exposure to mercury vapour on the fertility of female dental assistants. Occup Environ Med. 1994;51(1):28-34. 2.Colquitt PJ. Unpublished report, to Division of Workplace Health and Safety, North Brisbane Region. 1994. 3.von Muhlendahl KE. Intoxication from mercury spilled on carpets. Lancet. 1990 Dec;336:1578. 4.National Health and Medical Research Council. Approved occupational health guide-Inorganic mercuy. Canberra: Commonwealth Department of Health. 1982. 5.Burke MJ, Towers HM, O'Malley K, Fitzgerald DJ, O'Brien ET. Sphygmomanometers in hospital and family practice: problems and recommendations. BMJ 1982;285;469-71. 6.Ide CW. Mercury hazards arising from the repair of sphygmomanometers. BMJ 1986;293:1409-10. 7.Bailey RH, Bauer JH. A review of common errors in the indirect measurement of blood pressure. Sphygmomanometry. Arch Intern Med. 1993 Dec 27;153(24):2741-8. Review. 8.Matte TD, Mulinare J, Erickson JD. Case-control study of congenital defects and parental employment in health care. Am J Ind Med. 1993;24:11-23. 9.Roeleveld N, Zielhuis GA, Gabreels F. Mental retardation and parental occupation: a study on the applicability of job exposure matrices. Br J Ind Med. 1993;50:945-54. 10.Akers H. Response to letter “mercury exposure in general nurses”. Australian Dental Association Newsletter-QLD, 1994;386:20. Phillip J. Colquitt, Independent Technical Advisor, New Farm, Queensland, Australia. |
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Alvine Bissery Paris (75013)
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I would like to mention one misleading use of statistics in your article, which is very frequent : you can not study agreement between different methods with correlation. Correlation coefficients measure association, not agreement. It measures the degree of "straight line" between the values of two variables. When you study agreement, you want to know if the values of the differents methods are the same, that means, if they are on the line y=x. You could have a perfect correlation between variables (X,Y)with the relation Y=2X, and the agreement will be very bad. |
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William T Hamilton, Research Fellow Division of Primary Care, University of Bristol, BS6 6JL., Deborah Sharp
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Dear Editor, Little et al’s neat study has shown that doctor’s measurements of blood pressure are much higher than those taken by nurses, by the patient at home or by ambulatory monitoring1. From this the authors conclude that conventional general practitioner measurements may be misleading in guiding treatment decisions. However, we believe that this conclusion runs ahead of the evidence. The chain of research evidence that is required to make this conclusion has three links. The first link is finding a reliable method of measuring blood pressure; the second link is demonstrating that raised blood pressure diagnosed by the chosen method increases the patient’s risk of a cardiovascular event; the last link is showing that treatment reduces the risk. As past of the last link, it is valuable to know the absolute benefits of treatment, and what target blood pressure to aim for. Our concern is that the research evidence for treatment decisions based on newer methods is not available for the last link. We know from well-conducted trials that treatment based on clinic readings reduces risk2 3. Additionally, these trials have given us evidence to support a target for treatment2 3. This evidence is much weaker for newer methods of diagnosing and monitoring hypertension. In essence we have two different diagnoses: hypertension diagnosed conventionally and hypertension diagnosed otherwise. The epidemiology of the latter is currently much less understood. Why are doctors’ measurements higher than the other methods? The study did not address this but it is also important in extrapolating from their results. One possibility is that the stakes are higher for the patient in a consultation with a doctor. This is presumably because the doctor has the power to label the patient with a diagnosis, and to suggest and prescribe treatment. If we assume that this psychological stress underlies the raised doctor measurements4, then transferring the responsibility for measurement (and by inference diagnosis) to practice nurses may be self-defeating as the concern may be transferred too. Doctors should not discard their sphygmomanometers – or give them to their nurses – rather, they should use them more so that clinical decisions are based on multiple readings. In this aspect we are wholly in agreement with the authors. Yours sincerely, William Hamilton, research fellow Deborah Sharp, professor Division of Primary Health Care, University of Bristol, Cotham House, Bristol BS6 6JL. References. 1. Little P, Barnett J, Barnsley L, Marjoram J, Fitzgerald-Barron A, Mant D. Comparison of agreement between different measures of blood pressure in primary care and daytime ambulatory blood pressure. BMJ 2002;325:258-259. 2. Hansson L, Zanchetti A, SG C, Dahlof B, Elmfeldt D, Julius S, et al. Effects of intensive blood-pressure lowering and low-dose aspirin in patients with hypertension: principal results of the Hypertension Optimal Treatment (HOT) randomised trial. Lancet 1998;351:175562. 3. UK Prospective Diabetes Study Group. Tight blood pressure control and risk of macrovascular and microvascular complications in type 2 diabetes: UKPDS 38. BMJ 1998;317:703-713. 4. Carroll D, Davey Smith G, Sheffield D, Shipley MJ, Marmot MG. Pressor reactions to psychological stress and prediction of future blood pressure: data from the Whitehall II study. BMJ 1995;310:771-775. |
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Adrian G Stanley, Clinical Lecturer in Medicine Cardiovascular Research Institute, University of Leicester, Leicester. LE2 7LX, Bryan Williams
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Editor - The white-coat phenomenon among treated and untreated hypertensive patients is difficult to define in everyday clinical practice and therefore the article highlighting the difference between blood pressure measured by general practitioners and values recorded in the home environment is welcomed [1]. Importantly, this could also apply to hospital physicians. However, we must caution against the dogmatic conclusion that ‘It is time to stop using high blood pressure readings documented by general practitioners to make treatment decisions’ that resulted in The Times to report “GPs ‘cause’ high blood pressure” [2]. This white-coat effect is more common in the elderly hypertensive subjects [3]. Although the authors report an average difference of 18.9/11.4mmHg between clinic and mean daytime ambulatory recordings, they did not specify whether there is an age-related factor. We, therefore, question whether the conclusion can be applied equally to young and elderly hypertensive patients? Furthermore, current advice regarding the treatment targets and thresholds of high blood pressure, published by the British Hypertension Society [4], are based on clinical studies using clinic readings. Crucially, it has never been established how home readings relate to these treatment targets. A consensus has suggested that the upper limit of normal for mean daytime ambulatory blood pressure and home monitoring is 135/85mmHg and therefore equivalent to a clinic blood pressure of 140/90mmHg [5]. However, equivalent values have not been determined for treatment targets in hypertensive subjects with diabetes or chronic renal failure. Significantly, morbidity or mortality outcome data to support ambulatory or home readings is lacking. An ambulatory blood pressure sub-study of the Syst-Eur trial presented by Staessen at the American Society of Hypertension Scientific Meeting in May 2002 demonstrated that the best predicator of cardiovascular outcome is mean nighttime ambulatory blood pressure. However, this has not been translated into guidelines and the study population was restricted to subjects with systolic hypertension aged over 65 years. Therefore, while acknowledging the superiority of blood pressure reading in a home environment, we would caution against using these readings at face value to determine treatment for hypertension across all age-groups. For example, reducing blood pressure control by at least 5/5 mmHg in patients at high cardiovascular risk would be inappropriate. Essentially, clinic blood pressure readings can be unreliable; but we await newer guidelines incorporating ambulatory and home blood pressure readings based on clinical outcome studies before relieving doctors of their duty to measure blood pressure.’ References: 1. Little P, Barnett J, Barnsley L, Marjoram J, Fitzgerald-Barron A, Mant D. Comparison of agreement between different measures of blood pressure in primary care and daytime ambulatory blood pressure, BMJ 2002;325:254-7 2. Hawkes N. GPs ‘cause’ high blood pressure. The Times 2002 Aug 2 3. Mansoor GA, McCabe EJ, White WB. Determinants of the white-coat effect in hypertensive subjects. Journal of Human Hypertension 1996:10(2):87-9. 4. Ramsay L, Williams B, Johnston G, MacGregor G, Poston L, Potter J et al. Guidelines for management of hypertension: report of the third working party of the British Hypertension Society. J of Human Hyper 1999; 13:569- 592. 5. Staessen JA, Thijs L. Development of diagnostic thresholds for automated self-measurement of blood pressure in adults. First International Consensus Conference on Blood pressure Self-Measurement. Blood Press Monit 2000; 5(2): 101-9. Adrian G. Stanley,
Bryan Williams,
There are no competing interests to declare. |
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Risto A Laitila, GP Finland 44800 Pihtipudas
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Appreciating the outcome of Little and al´s study and the correspondence it has yet generated it comes clear that assessing individual cardiovascular risk of a patient perhaps needs more accurate tools than blood pressure monitoring, at least when other known risk factors are non existent or weak. Blood pressure monitoring can cause anxiety and high measurement readings may induce neurotic awareness of blood pressure resulting again in hypertensive readings, a circulus vitiosus that may be hard to tackle. Hopes are targeted at genetics or traces of distorted metabolism ? |
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Paolo Palatini, Professor of Medicine University of Padova 35128
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Sir--I read with interest the article on different measures of blood pressure (BP) by Little P et al. (1). Although the authors implemented and accomplished an interesting study by comparing so many measures of BP, I am afraid that they should have limited their inferences and comments to the comparison between the levels of the various pressures. The interpretation of their results is fully based on the assumption that ambulatory BP is the gold standard in the assessment of a subject’s BP. To support this statement the authors quote several papers which claimed that ambulatory BP is superior to clinic BP for predicting outcome. What those studies actually showed is that ambulatory BP has a greater predictive value than a few clinic readings taken in one or two visits. However, if clinic BP is measured several times over an adequate period of observation, as suggested by current Guidelines of Scientific Societies for patients with newly diagnosed mild hypertension, its predictive power may be superior to that for the ambulatory measurement (2,3). More to the point, is there any published evidence that ambulatory BP has a greater predictive value for outcome than BP measured by the nurse, or by the patient at home or in the surgery? The authors claim that ambulatory BP can give a reliable estimate of the patient’s white-coat effect. However, the few studies which dealt with this matter showed that the difference between clinic and daytime BP does not reflect the true white-coat effect measured with beat-by-beat recording during doctor’s visit (4,5). Moreover, recent results indicate that home BP measurement can predict white-coat hypertension more precisely than does ambulatory BP (2). In conclusion, although ambulatory BP monitoring can provide unique information on BP variability within the 24 hours in well selected patients, there is no proof that mean daytime BP is superior to self- measured BP, to BP measured by the nurse, or even to clinic BP measured repeatedly for prediction of outcome. Thus, the concept that ambulatory BP should be taken as the reference standard when comparing different measures of BP is not founded on published evidence. More research is needed to really know whether ambulatory BP monitoring can expand the repertoire of tools available to support medical decision making in primary care. Competing interests: None declared. Professor Paolo Palatini, MD
References: 1. Little P, Barnett J, Barnsley L, Marjoram J, Fitzgerald-Barron A, Mant D. Comparison of agreement between different measures of blood pressure in primary care and daytime ambulatory blood pressure. BMJ. 2002;325:254- 9. 2. Palatini P. Too much of a good thing: a critique of overemphasis on the use of ambulatory blood pressure monitoring in clinical practice. J Hypertens 2002;20: (in press). 3. Fagard R, Staessen J, Thijs L. Prediction of cardiac structure and function by repeated clinic and ambulatory blood pressure. Hypertension 1997; 29:22–29. 4. Parati G, Ulian L, Santucciu C, Omboni S, Mancia G. Difference between clinic and daytime blood pressure is not a measure of the white coat effect. Hypertension. 1998;31:1185-9. 5. Lantelme P, Milon H, Vernet M, Gayet C. Difference between office and ambulatory blood pressure or real white coat effect: does it matter in terms of prognosis? J Hypertens. 2000;18:383-9. |
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Em Ebbs, RN MHS PO Box 655999 Dallas, TX, 75237
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Upper arm has been preferred site for BP. I did not see your site of measurement listed. Some hospital staff have started placing the cuff on the arm below the elbow, and maybe around the ankle at times. Do you have any references or know of research or guidelinge for BP on lower arms, wrists, and ankles? Has that been studied? Thanks! Em Competing interests: None declared |
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