Andersons pediatric cardiology 1600

instrument.9 Following concerns regarding the safety of mercury for users in the clinical environment, for technicians who have to service the instrument, and for the environment itself, these instruments have now been phased out of clinical practice.10,11 An issue with any method using auscultation is the introduction of the phenomenon of terminal digit preference, and bias of the observer because of knowledge of previous measurements Any instrument that eliminates or reduces these two is to be welcomed This initially led to the development of the random-zero sphygmomanometer, which was developed and shown to minimize or eliminate both these items.12,13 Unfortunately, these devices were shown subsequently significantly to underestimate blood pressure, and were therefore abandoned.14,15 Automated oscillometric devices have similarly been developed These improve on the shortcomings of the auscultatory method by eliminating both terminal digit preference and the bias of the observer They work by the detection of pressure pulses in the cuff These are generated as a result of the volume pulses of the artery When blood starts flowing through the artery at the point of systolic pressure, a pressure pulse is generated As pressure within the deflating cuff is reduced in a stepwise manner, a series of pressure pulses generate the pulse oscillogram The pulse amplitudes of this oscillogram provide an envelope curve, with the maximal value on this curve equating to the mean arterial pressure Systolic and diastolic pressures are calculated from preset algorithms in the instrument microchip, and are a function of the mean The algorithms are specific to the instrument, and are not declared by the manufacturers, although one would presume these algorithms have been improved over the years by the manufacturers.16,17 Although these automated devices are increasingly being used in primary care and pediatric departments, there are some particular concerns that need to be highlighted The Dinamap devices are the most commonly studied automated oscillometric devices reported in pediatric series An earlier version of this device, model 1846 SX, had been shown to have superior correlation with intra-arterial measurements.18 Other studies, however, reported higher mean systolic measurements using models 1846, 8100, and 845 when compared with the random-zero sphygmomanometer and mercury sphygmomanometer.19,20 Diastolic measurements had been reported to have better agreement.19 A more recent report using the Dinamap 8100 monitor highlighted the discrepancy between the two methods, with measurements using the device higher by a mean of 10 mm Hg for systolic and 5 mm Hg for diastolic blood pressure.21 Therefore, although normative limits have been proposed using the Dinamap 8100 instrument from the United Kingdom, caution needs to be proposed before applying these limits in clinical practice.22 Another particular practical observation with oscillometric devices is the phenomenon of measurements being higher by about 3 to 5 mm Hg on first measurement, despite control of factors involving the patient, the observer, and the environment.20,23 The second reading has been reported to be more accurate Automatically inflated cuffs have recently been introduced These instruments measure both systolic and diastolic pressures, recording the results at preset intervals by detecting oscillations in the pressure from the cuff They are especially useful in the care of the critically ill child, saving nursing time and reducing disturbance to the patient The calibration needs to be checked frequently if the result is to be regarded as accurate, but they are useful in detecting changes Indeed, they will alarm automatically if preset parameters are exceeded Aneroid sphygmomanometers have also gained popularity in clinical practice because of their portability and their reliance on techniques similar to the standard mercury sphygmomanometer Because of this, however, they have no influence on the biases existing with the mercury sphygmomanometer The devices have proven their accuracy when regular 6-month maintenance is in place to service the instruments.24 The majority of devices in clinical use, nonetheless, have not been evaluated independently for accuracy using the two most widely accepted protocols for validation.25,26 These protocols have been proposed by the British Hypertension Society and the Association for the Advancement of Medical Instrumentation Several updates of validation have been published, but the best method of finding up-to-date information is on the nonprofit website http://www.dableducational.com.27 Technique of Measurement The child should be relaxed and quiet when blood pressure is recorded Should this not be possible, but readings are made, then the conditions should be recorded A simple description of the process of measurement of a child at a level appropriate for age will usually lead to a cooperative patient, thus allowing accurate recordings Measuring pressures in infants who are crying is not useful The standard position is the sitting position when children are older than 3 years, with the fully exposed arm supported or resting on a table at the level of the heart.23 An arm higher than the heart will underestimate the pressure, while a lower position will produce overestimations.28 In younger children and infants, pressure should be routinely measured when the patient is in the supine position The sphygmomanometer should be placed at the level of the eye of the observer to eliminate error from parallax The cuff should be inflated about 30 mm Hg above the point at which the radial pulse disappears In some patients, there will be a silent gap between the systolic and diastolic pressures Simply inflating the cuff until the sound disappears in such individuals may produce a serious underestimation of systolic pressure Once inflated, the cuff should be deflated at a rate of 2 to 3 mm Hg/s while auscultating with the stethoscope The sudden distension of the collapsed artery at the systolic pressure is associated with a clear tapping sound, defined as phase 1 of the Korotkoff sounds The murmur of turbulent blood flowing through the partially occluded artery is phase 2 Phase 3 is a high-pitched sound produced when the artery, closed during diastole, opens in systole When the artery no longer closes during diastole, the tapping sounds are low pitched and muffled and quieter This is phase 4 Phase 5 is when the sounds disappear This is variable and may not occur in some children The fourth phase, however, tends to overestimate the diastolic pressure, while the fifth phase underestimates it Although the fifth sound is widely accepted as the optimal measurement of diastolic pressure among adolescents and adults, there has been considerable debate in the literature concerning its value in children younger than 13 years For these younger children, the fourth sound had generally been preferred, and was recommended by the Task Force Reports on Blood Pressure Control in Children.29,30 An international committee, nonetheless, recommended the fifth sound,31,32 and the update of the Task Force Recommendations also advocates using this sound It is preferred because of its easier identification by observers and the comparability it provides for measuring diastolic pressures across age groups The two sounds are not equal in most children, and may vary considerably, by up to 10 mm Hg.33 The measurement of blood pressure in infants, and in some older children, is sometimes difficult because the sounds are inaudible The old flush technique is unreliable It has now been superseded by the use of Doppler ultrasound, using an ultrasonic beam to detect motion of the arterial wall when the cuff is deflated This technique is remarkably reliable for measurement of the systolic pressure,