HOW CONSISTENT ARE THE BLOOD PRESSURE AND PULSE RATE MEASUREMENTS OF THE ELECTRONIC BP APPARATUS AND THE MANUAL SPHYGMOMANOMETER Naser KA. Teaching Hospital Peradeniya, Peradeniya, Sri Lanka Zawahir S School of Pharmacy, Management and Science University Redhwan Ahmed Al-Naggar Faculty of Medicine, Universiti Teknologi MARA ABSTRACT Electronic blood pressure devices commonly used in home monitory and clinical setup. Our objective was to determine the accuracy of different types of digital (electronic) blood pressure and pulse measuring devices. Methods: Two hundred patients were studied at a Diabetes clinic in Sri Lanka. Five digital devices were tested comparing with that of mercury sphygmomanometer (40 patients for each digital device). Blood pressure and pulse rate were recorded in each patient with mercury sphygmomanometer and one of the study digital sphygmomanometers. Precision of measurement for mercury sphygmomanometer was 2mm Hg and for digital device was 1mm Hg. Data were descriptively analyzed by using Kappa measurement of agreement method and paired t-test. Results: Compared to sphygmomanometer readings, Systolic Blood Pressure (SBP) readings were higher in all digital devices and the median pulse rate readings were also showing the same results. Kappa measure of agreement between digital devices and mercury device readings were calculated. In device A both SBP and (Diastolic Blood Pressure)DBP showed Kappa<0.3 but findings are not significant. The pulse rate showed Kappa >0.3 with a significant fair agreement with manual counting. In device B pulse rate showed very good agreement (Kappa-0.8, P<0.01), while Blood Pressure showed poor agreement between devices (p=0.09). Device C and E showed considerable agreement between the devices (P<0.001). The device D showed moderate to good agreement between the devices (P<0.001) except for SBP. A paired-samples t-test was conducted to evaluate the mean differences between each of digital measure of blood pressure and pulse rates with a mercury sphygmomanometer. Significant mean differences were found in BP and pulse between electronic devices and manual readings in all five groups (device A to device E) except pulse rate on device B (p=0.05), SBP on device D (p=0.45) and DBP in device E (p=0.89). The mean BP and pulse rates were higher in digital devices except diastolic BP in device D. Discussion: Blood pressure is an important determinant of cardiovascular outcome in diabetes. In order to ensure that these new devices provide accurate data, they should be calibrated and validated periodically. Calibration ensures that measurements start from zero on all occasions. Clinicians should consider device accuracy when selecting the method for BP measurement in situations where readings are likely to influence medical management, such as when BP readings will be used to adjust cardiac medications for inpatients or in the out patients clinics. Routine use of electronic BP devices in hospitalized patients, when accuracy of the BP measurement is often critical for appropriate disease management, should be reconsidered and any abnormal values have to be reconfirmed with a mercury sphygmomanometer.
1. INTRODUCTION There is no visible way one can understand changes in human blood pressure, and naturally, checking regularly is the only means to keep track of it. The blood pressure results can predict the risks for body and health, thereby enabling physician to suggest appropriate medications, food and work schedules for the patients. Hypertension is an important worldwide public health problem and is a major risk factor for cardiovascular disease, the leading cause of death and disability worldwide [1, 2]. Screening for hypertension is the most commonly performed screening test in medical practice and is important not least because individuals with a normal blood pressure (BP) at the age of 50 still run a 90% life-time risk of developing hypertension [3]. Twentytwo percent of persons who have hypertension are unaware that they have it [3]. In addition, one-fourth of the population 20 years and older is estimated to be pre-hypertensive, which is defined as a systolic blood pressure of 120-139 mm Hg, and/or a diastolic blood pressure of 80-89 mm Hg. Pre-hypertension contributes to about 15% of blood pressure related deaths from coronary artery disease [4]. Hypertension and prehypertension in children and adolescents 8 to 17 years old have increased since 1999, and both are frequently undiagnosed in children 3 to 18 years of age [5, 6]. Childhood blood pressure is a strong predictor of High blood pressure levels in adulthood, and hypertension and prehypertension are a significant health issue in the young, especially with the prevalence of childhood obesity [7, 8]. Therefore it is very important for both young and older individuals with hypertension and prehypertension to be identified and treated [8-10]. Furthermore, trial evidence indicates that even small differences in systolic BP of 2 4mmHg are clinically important, thus accurate measurement is vital [11, 12]. Different blood pressure monitors provide different readings, errors in measurement occur through three main sources: device errors, user errors and patient errors [13]. Device errors are potentially the most fundamental of these three sources, and, in particular, accurate measurement is underpinned by the requirement for an instrument that measures pressure accurately in patients across the range of pressures. To date, the gold standard instrument for BP measurement is a mercury to gauge the blood pressure with a hand pump attached to the arm of the patient (mercury sphygmomanometer) [4, 14-16], but in recent years this has been superseded in many clinical settings by automated electronic devices. Medical engineers, on the hunt for more convenience, took the principles of digital monitors and adapted them to make a device for the arm and wrist. But, increased usage of these digital devices by ordinary patients will fulfill the requirement of BP measures accurately? Therefore, it is important to understand the accuracy of different digital BP devices used by the public. 1.1 Objective Our objective was to determine the accuracy of different types of digital (electronic) BP and pulse measuring devices. 2. METHODOLOGY Data were prospectively collected for three consecutive months by four trained nurses from five different groups of consented patients (group A to group E ); they were presented to private general clinic at Royal Care Hospital Akurana, Sri Lanka. For each group, 40 subjects were selected by simple random sampling method. The age range was 15-40 years. Every patient was asked to randomly select one rolled paper from randomization box to allocate the digital device to be used (the randomization box was filled with 200 rolled papers and each of five devices (A to E) name was written in forty rolled paper) In addition to demographical data from each group of participants; resting position BP and pulse rate were measured three times (to strengthen the accuracy of the blood pressure measurements) using one of digital wrist or upper arm digital BP apparatus, the average was calculated [4, 17, 18]. And the same procedure was repeated with mercury sphygmomanometer for BP (as a standard one) and pulse rates were measured manually from every respondent. Body weight, height, hip circumferences and chronic co-morbid illnesses also were recorded from each of the patients.
Data were descriptively analyzed and the comparisons between each digital apparatus and mercury sphygmomanometer were done by Kappa measurement of agreement method and paired t-test, using SPSS 18. The level of significant was set as p <0.05. 3. RESULTS There were total of 200 patients studied in five groups and each group consisted of 40 patients. The median age in each group was laid between 37 and 48 year old and the most of the participants were females. Group D and E participants were obese compare to other groups and the highest median Body Mass Index (BMI) (27; IQR 24-29) was reported in group D. The median hip circumference was also greater than the normal on group D patients (96.5 cm; IQR 84.5-102). As compare to sphygmomanometer readings, the median systolic and diastolic blood pressure readings were higher in all digital devices except group D. The median pulse rate readings were also showing higher in digital devices than manual readings (table 1). As shown in table 2, in group A and B, both systolic BP and diastolic BP, and group D systolic BP shown Kappa (KA) <0.14 with poor agreements between digital device and sphygmomanometer readings. However, these agreements were not statistically significant (p>0.05). The diastolic BP of devices C, D and E were showing significant fair, good and very good agreement with sphygmomanometer readings (KA=0.3, p=0.007; KA=0.64, p<0.001, and KA=1, p<0.001) respectively. The systolic BP of devices C and E were showing significant moderate agreement with sphygmomanometer. The pulse readings from digital devices of group B, C, D and E were showing significant moderate to good agreement with manual pulse readings (KA between 0.42 and 0.8 and P<0.05), whereas group A digital pulse reading showed significant fair agreement with manual reading (KA=0.31 and P=0.022). A paired-samples t-test was conducted to determine the mean differences between each of digital measure of blood pressure and pulse rates with manual methods, there were significant mean differences on BP and pulse rates between electronic devices and manual readings in almost all five groups (group A to group E ) except pulse rate on group B (p=0.053), group D (p=0.45) and diastolic BP in group E (p=0.89). The mean BP and pulse rates were higher in all digital devices except diastolic BP in group D (table 3). 4. DISCUSSION This study revealed that there were statistically significant difference on mean BP and pulse readings between each of the electronic devices and manual readings.the findings of this study are similar to prior studies of earlier models of the automated BP device in which statistically significant systolic differences were noted between the electronic and manual readings for BP determination [19-23]. All these studies findings indicate that despite technologic improvements in the automated device over the years, significant differences still exist in BP readings obtained with the two different methods. Different from the majority of method-comparison studies of electronic and manual devices which used one or two individuals for data collection. This study had BP and pulse rate data collected by three different clinical research assistants. This situation more closely approximates usual practice on inpatient nursing care units, where BP readings are obtained commonly by multiple providers during a 24-hour shift. The manufacturer s operating instructions highlight the concern that cardiac rhythm irregularity may influence the accuracy of the device, few clinical users of the device restrict its use to patients with regular cardiac rhythms. Given that if the electronic BP measurement is done commonly in patients with irregular rhythms, it is especially important to determine if this practice is leading to even greater differences in BP between the two methods. Further studies are needed to confirm these results in a variety of clinical situations, including patients with irregular cardiac rhythms, and patients with systolic BP less than 90 mmhg and greater than 170 mmhg. The widespread use of and reliance on automated devices should be brought into question for inpatient clinical use. Many nursing and medical interventions for hospitalized patients and outpatients clinics are influenced by BP values obtained by nursing staff (for example, administration of antihypertensive and vasoactive
medications; monitoring for changes in BP after surgery or procedures). Using a less accurate BP method may lead to inappropriate alterations in medication or medical care which could negatively impact patient outcomes. 5. CONCLUSION Different types of devices for BP and pulse measurement are used commonly in the out patients clinics and hospitals. We found a statistically significant differences in BP (systolic and diastolic) measurements taken with the electronic devices and manual methods. Similarly, significant differences in pulse rates were also seen with electronic devices and manual methods. Clinicians should consider device accuracy when selecting the method for BP measurement in situations where readings are likely to influence medical management, such as when BP readings will be used to adjust cardiac medications for inpatients or in the out patients clinics. Routine use of electronic BP devices in hospitalized patients, when accuracy of the BP measurement is often critical for appropriate disease management, should be reconsidered and any abnormal values have to be reconfirmed with a mercury sphygmomanometer. Acknowledgment Special thanks to Dr. Mahindaratne KMNK, Farzana MMF, Nursing staff of the Royal Care Hospital for their voluble contribution in data collection and the authors acknowledge all the respondents for their voluntary participation on this study. Corresponding Author: Mohamed Shukry Zawahir, School of Pharmacy, Management and Science University (MSU), Section 13, 40100, Shah Alam, Selangor, Malaysia. Telephone: +60174032614 Fax: +60355216487 E-Mail: shukry2010@gmail.com
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Table 1: Demographic characteristics and baseline median BP and Pulse rate from five different types of electronic BP apparatus and Sphygmomanometer Group-A Group-B Group-C Group-D Group-E Age; median (IQR) 46 (25.5-53) 37 (27-52) 40 (28-53) 39 (30-49) 48 (38-59) Sex (Female); (N) % (25) 72% (23) 65% (26) 65% (26) 57% (29) 62% BMI (KgM -2 ); median (IQR) 23 (20-27) 23.5 (21-26.5) 23.5 (21-26) 27 (24-29) 25 (22-28) Hip circumference (cm) median (IQR) 87 (71-94) 87 (77-97) 83 (71-93) 96.5 (84.5-102) 94 (80-97.5) Average systolic BP (mmhg) (electronic); median(iqr) 162 (138-186) 149 (125-169) 124 (114-124) 119 (107-137) 124 (116-135) Average systolic BP (mmhg); median(iqr)(sphygmomanometer) 120 (98-130) 113 (107-130) 120 (100-133) 120 (110-130) 113 (100-130) Average diastolic BP (mmhg); median (IQR) (electronic) 99.5 (80-105) 87.5 (76-99.5) 81 (74-93.8) 72 (64.3-81) 72.5 (68.3-83) Average diastolic BP (mmhg); median (IQR) (manual) 77.0 (60-82.3) 73 (70-80) 78 (64-80) 80 (70-82.3) 71 (69.3-80) Average pulse rate (beats/minute); median (IQR) (electronic) 80 (74-90) 82 (74-92) 84 (76-90) 85 (76-96) 85 (78-95) Average pulse rate (beats/minute); median (IQR) (manual) 77 (71-83) 80 (74-84) 80 (73-85) 81 (72-88) 79 (71-85)
Table 2: Measure of agreement Kappa of BP and Pulse rate between digital devices and mercury sphygmomanometer (N=40 in each group) Group A Pulse rate Kappa Agreement 0.01 0.06 0.31 p- value Strength of agreement 0.58 0.24 0.022 Fair Group B Pulse Rate 0.14 0.05 0.80 0.085 0.58 <0.001 Good Group C Pulse Rate 0.45 0.30 0.61 0.001 0.007 <0.001 Moderate Fair Good Group D Pulse Rate 0.20 0.64 0.48 0.16 <0.001 0.001 Good Moderate Group E Pulse Rate 0.47 1.00 0.42 0.003 <0.001 0.004 Moderate Very good Moderate Kappa; <0.2 poor, 0.21-4.00 - fair agree, 0.41-0.6- moderate, 0.61-8.0 good, 0.81 1.00 Very good agree
Table 3: Mean differences of BP and Pulse rate between digital devices and mercury Mean (SD) Electronic Manual t-value (df) P value Group- A 166.18 (35) 116.73 (21.04) 10.66 (39) <0.001 group-a 94.70 (16.45) 74.30 (13.97) 7.3 (39) <0.001 Pulse rate Group-A 82.60 (14.52) 77.72 (12.10) 2.97 (39) 0.005 Group-B 151 (32.55) 117.50 (18.60) 7,68 (39) <0.001 Group-B 90.68 (19.76) 75.78 (11.50) 5.14 (39) <0.001 Pulse rate Group-B 83.43 (13.37) 80.08 (9.74) 1.94 (39) 0.053 Group-C 131.28 (23.70) 119.30 (20.71) 3.58 (39) 0.001 Group-C 84.45 (14.87) 75.28 (12.64) 4.86 (39) <0.001 Pulse rate group-c 84.10 (12.58) 80.33 (10.97) 2.90 (39) 0.006 Group-D 125.98 (24.87) 123.88 (19.31) 0.76 (39) 0.451 Group-D 76.03 (15.58) 79.45 (12.67) -2.68 (39) 0.011 Pulse Electronic-D 86.25 (12.15) 80.18 (11.38) 3.58 (39) 0.001 Group-E 126.38 (16.60) 116.43 (18.33) 5.58 (39) <0.001 Electronic-E 74.43 (10.66) 74.58 (9.55) -0.14 (39) 0.890 Pulse Electronic-E 86.38 (14.35) 80.03 (11.97) 3.68 (39) 0.001 Mean differences from paired t-test, significant level 0.05 (N=40 in each group)