Measuring blood pressure: the importance of understanding variation

RESUMO

Blood pressure is intrinsically variable. Because of this measured blood pressure shows a degree of random variation. In an individual patient, random variation in measured blood pressure causes chance variation in the diagnosis of hypertension. This means that decisions about whether to star treatment of high blood pressure are in part determined by chance. In particular it means that in population groups with a low prevalence of hypertension, the number who are incorrectly diagnosed may be greater than the number who are correctly diagnosed. In an individual patient who is started on treatment, random variation in measured blood pressure causes very significant chance variation when we try to determine whether a treatment is effectively reducing blood pressure. This means that decisions about whether to change treatments are in large part determined by chance. Random variation in measured blood pressure is much greater than the difference between a low dose and a high dose treatment or the difference between one drug treatment and another. Variation in blood pressure measurement therefore causes all subsequent decisions about to be subject to a great deal of arbitrary variation. Neither using the average of many blood pressure monitoring fully resolve this problem. The most satisfactory solution to he diagnostic problem is to follow the lad of New Zealand and European hypertension guidelines and base the decision to treat on the patient’s cardiovascular risk. Cardiovascular risk correlates better with potential benefit to he patient and because it is determined in large part by age and sex, it is a measurement that is less affected by chance variation in measured blood pressure. The solution to he problem of follow up is more radical. Many clinical trials have demonstrated the drugs are effective in lowering blood pressure. We do not need to confirm this fact in every one of our patients