Blood pressure measurement in atrial fibrillation: goodbye mercury?

Abstract

The mercury spygmomanometer – a masterpiece of engineering – pioneered by Riva-Rocci in 1896, has for the last century, dominated clinical medicine and the strive for improved healthcare. This, once ubiquitous piece of equipment, adorned the walls of clinics and graced the desk of (nearly) every general practitioner, and is now an increasingly rare sight. Doctors and nurses alike were trained in its accurate use. Sadly, the mercury sphygmomanometer is quickly becoming a relic of the past, to be found tucked away in a cupboard or in the collection of the more ‘traditional’ physician. The rapid pace of development of automated sphygmomanometers with improving accuracy and reliability combined with increasing affordability has meant that these devices have now replaced the mercury sphygmomanometer in many settings. Indeed, multifunction devices, which also serve to record (e.g.) pulse oximetry and temperature, are now commonplace and are used on the majority of hospital wards for routine observations. Concerns regarding the mercury sphygmomanometer have been aired for many years and are genuine and valid. The equipment is delicate – all too easily damaged from rough handling in the busy hospital setting, potentially resulting in hazardous mercury spillage. Moreover, it relies heavily on being used by a competent operator with a keen eye, who is willing to invest time and patience on taking an accurate reading. Yet, the demise of the sphygmomanometer has been surprisingly slow, and its fate been sealed only as automated machines have become so competitively priced with respect to their mercury counterparts. Nonetheless, much of the benefit of automated machines is immediately apparent, particularly when the whole process of blood pressure measurement is analysed. Traditionally, blood pressure has been measured based on the mercury sphygmomanometer reading to the nearest 2 mm Hg at the onset of first and fifth Korotkoff sounds audible over the antecubital fossa for systolic and diastolic blood pressure, respectively. It is true that blood pressure remains dynamic, varying from stroke to stroke. The accuracy of blood pressure recording using the mercury sphygmomanometer therefore relies heavily on taking multiple readings, having a relaxed patient (who has been sitting for at least several minutes before entering the clinic), and perhaps, most importantly, a competent operator. The latter needs to be able to select an appropriate-sized cuff (80% of the upper arm circumference), as well as being able to deflate the cuff at a relatively slow but continuous rate (2–3 mm Hg/s) and accurately auscultate and discriminate between the Korotkoff sounds to provide a reproducible reading. This time-consuming process serves to remove some, but not all confounding factors. For example, it is often difficult to correct for the ‘white-coat’ effect and often multiple readings may be required several minutes apart. Movement artefact or excessive pressure with the stethoscope over the antecubital fossa results in turbulent blood flow and distracts the operator from the task in hand, further proving that accurate use of the mercury sphygmomanometer requires some degree of skill and patience. Sadly, this potential user bias is often augmented by a general lack of equipment maintenance. The mercury sphygmomanometer is a delicate and valuable piece of equipment and should be treated as such. It is all too common for them to be handled carelessly, damaging not only the capillary tubing containing the mercury, but also the rubber tubes, the cuff and the inflator. Indeed, it has become commonplace to see competent operators struggle – a small leak having made accurate blood pressure measurement impossible. Is the automated sphygmomanometer the better alternative? It must be conceded that electronic blood pressure measurement devices have numerous advantages. They are small, compact and relatively inexpensive. It is recommended that automated devices should be subjected to independent validation for accuracy. To this end, various assessment protocols are available from the Association of Advanced Medical Instrumentation, the British Hypertension Society and the European Society for Correspondence: Professor GYH Lip, University Department of Medicine, City Hospital, Birmingham B18 7QH, England, UK. E-mail: G.Y.H.LIP@bham.ac.uk Published online 13 April 2006 Journal of Human Hypertension (2006) 20, 638–640 & 2006 Nature Publishing Group All rights reserved 0950-9240/06 $30.00