|Year : 2014 | Volume
| Issue : 2 | Page : 108-112
Inter-arm asymmetry in systolic and diastolic blood pressure measurements among normotensive primigravidae
Department of OBG, The Oxford Educational Institutions, The Oxford College of Nursing, Begur, Bengaluru, Karnataka, India
|Date of Web Publication||7-Jan-2015|
Dr. Ganapathy Thilagavathy
No. 305, Ganesh Nivas, VIth Cross, Arakarae, MICO Lay out, Bengaluru - 560 076, Karnataka
Source of Support: None, Conflict of Interest: None
Introduction: The detection of elevated BP during pregnancy is one of the major aspects of optimal antenatal care,and thus accurate measurement of BP is essential.
Methods: To evaluate whether there is a significant difference in inter-arm blood pressure (BP) measurements among normotensive low-risk primigravidae as an observational study was conducted at Yediur Municipal Maternity Corporation Hospital, Bangalore. A total of 100 low-risk women at 6-14 weeks of gestation attending antenatal clinic was selected by purposive sampling technique. Bilateral BP was measured by a calibrated Normal mercury Sphygmomanometer during the initial antenatal visit and the subsequent 2 months visits. Mean Inter-arm systolic blood pressure (SBP) and diastolic blood pressure (DBP) differences were computed for each visit and the three pairs of readings were averaged to obtain a mean SBP and DBP for each arm to derive the mean inter-arm difference.
Results: The results revealed a significant difference in the mean SBP in right (115.71 ± 0.827 standard deviation [SD]) versus left arm (105.23 ± 1.110 SD) and the mean DBP in right (73.10 ± 0.370 SD) versus left arm (69.43 ± 2.288) at P < 0.001. For SBP, the mean difference between the right and left arm was 11.87 mmHg, and the normal range was 2 mmHg to 16 mmHg. For DBP, the mean difference was 6.09 mmHg, and the normal range was 0 mmHg to 10 mmHg. Twenty-one (n = 21) primigravidae had clinically important differences >10 mmHg in SBP and DBP between their arms. None of the maternal characteristics were a significant predictor of inter-arm SBP and DBP differences at P > 0.001.
Conclusion: Assessment of bilateral BP should become a routine part of cardiovascular assessment of pregnant women in primary care to determine whether the risk to the pathological condition is present.
Keywords: Blood pressure, inter-arm differences, pregnancy
|How to cite this article:|
Thilagavathy G. Inter-arm asymmetry in systolic and diastolic blood pressure measurements among normotensive primigravidae. Indian J Health Sci Biomed Res 2014;7:108-12
|How to cite this URL:|
Thilagavathy G. Inter-arm asymmetry in systolic and diastolic blood pressure measurements among normotensive primigravidae. Indian J Health Sci Biomed Res [serial online] 2014 [cited 2019 May 19];7:108-12. Available from: http://www.ijournalhs.org/text.asp?2014/7/2/108/148811
| Introduction|| |
The measurement of maternal blood pressure (BP) is a key part of antenatal care, a modifiable risk factor and the accurate assessment of BP is vital for early detection, evaluation and treatment of hypertension  as hypertensive disorders in pregnancy has a major significance for the outcome of the pregnancy for both the mother and the fetus.  Unilateral measurement of BP may mask the diagnosis or delay the effective treatment of hypertension.  BP measurement guidelines by the World Health Organization - International Society of Hypertension Guidelines recommend that BP should be measured in both arms at the initial patient assessment and that, in the event a difference is observed, the arm with the higher pressure should be used for all future measurements.  This is because significant inter-arm differences (IADs) in BP may indicate the presence of congenital heart disease, peripheral vascular disease, unilateral neurological, musculoskeletal abnormalities, or aortic dissection.  However, even when the IAD has seemingly no pathological background, relevant IADs ≥10 mmHg are still important to know, as office measurements consequently performed at the arm with the lowest BP can lead to a wrong diagnosis and under treatment of hypertension.  In addition, to verify the effectiveness of antihypertensive therapy it is of clinical importance that BP is measured in the same arm with a higher pressure on all sequential occasions. 
Clinical studies have highlighted that failure to detect the presence of a difference in BP between arm measurements has been implicated in a delayed diagnosis of hypertension and is associated with a higher prevalence of poor control in hypertension and a failure to standardize measurement to the arm with the highest reading can mislead decisions about management.  Several studies , have established that BP measurements taken from either arm will give consistent results. However, some researchers have reported surprising variation in arm-to-arm BP differences. Fotherby et al.  noted an IAD of 10 mmHg or greater in 10% of his patients; Lane et al. found 20% with this degree of variation  Cassidy and Jones  discovered that 40% of their ambulatory patients demonstrated this 10 mmHg gradient. The new clinical guideline for hypertension from the National Institute for Health and Clinical Excellence considers an IAD of <10 mmHg to be normal and attributes a difference of >20 mmHg to underlying vascular disease. 
Failure to detect variation in inter-arm BP differences may lead to undesirable consequences, unnecessary referral to a specialist and cause an unnecessary burden for healthcare. The present study, therefore, aimed at investigating the difference in the systolic blood pressure (SBP) and diastolic blood pressure (DBP) in right versus left arm among normal low-risk healthy primigravidae at 6-14 weeks of gestation to provide evidence to influence governing attitudes among midwives and obstetricians to measure the BP in both arms at the first examination, and if there is a consistent IAD, the arm with the highest recording to be used for subsequent assessments to determine whether a pathologic condition in underlying.
| Methods|| |
The study was conducted from October to December 2012 at Yediur Municipal Maternity Corporation Hospital, Bangalore, Karnataka. Primigravidae subjects at 6-14 weeks of gestation attending the antenatal clinic for a routine antenatal visit and ultrasound examination were selected by a purposive sampling technique. All gave their written informed consent, after receiving oral and written information by the midwives responsible. Inclusion criteria were normal low-risk healthy primigravidae at 6-14 weeks of gestation with a singleton pregnancy. Exclusion criteria included uncertain gestational age, multiple pregnancy, antihypertensive medication, maternal hemoglobin <10 g%, hypertension, cardiovascular, renal diseases, diabetes and body mass index (BMI) over 25. Gestational age was determined from the known date of the last menstrual period. Clients age, medical and family history, body mass index, hemoglobin were retrieved from their charts.
Observer training and interrater reliability
The midwife was trained to inflate and deflate the bladder in the cuff gradually, see the manometer and the meniscus of the column of the mercury, palpate the brachial artery, place the cuff so that the midline of the bladder is over the arterial pulsation, wrap and secure the cuff snugly around the client's bare upper arm, hear the Korotkoff sounds, differentiating them from extraneous noises, make a note of the pressure on the manometer at the first appearance of sound (Phase I) and the muffling sound (Phase IV) and when they disappear (Phase V) to the nearest 2 mmHg. Interrater reliability of the BP measurements by the midwife and the principal researcher were computed by Pearson correlation coefficient and the "r" =0.97.
Participants were seated on a chair in a quiet room with their back supported, legs uncrossed and bared arm resting on a standard table, so the midpoint of the upper arm is at the level of the heart.
The bare arm circumference was measured with the non-stretchable measuring tape at the midpoint between the acromion and olecranon process (between the shoulder and elbow) and a standard cuff with a bladder width 13 cm length 30 cm for the arm circumference range at midpoint 27-34 cm was used to avoid errors due to incorrect cuff size to ensure complete or near-complete encirclement of each primigravidae's arm. For correct cuff placement, the midline of the cuff bladder was positioned over the arterial pulsation in the patient's upper arm in level with the right atrium, at the midpoint of the sternum following palpation of the brachial artery in the antecubital fossa, with 2-3 cm space for the stethoscope between the lower end of the cuff and the antecubital fossa. The Primigravidae and the midwife who was measuring the BP were instructed not to talk during the procedure to avoid errors in the measurements. BP was measured by a calibrated normal mercury Sphygmomanometer with the extended arm supported on a table at the level of the patient's heart.
The measurement was taken first in the right arm for consistency and comparison with the left arm, and the cuff was then swapped to the left arm and another measurement was taken. The arm was supported during each measurement. The first audible sound (Phase I) was recorded to define SBP and the disappearance of sound (last audible sound-Phase V) was recorded to define DBP and the both systolic and diastolic measurements were recorded to the nearest 2 mmHg. A single pair of measurements was obtained during the initial visit in the month of October and the mean inter-arm SBP, and DBP was calculated to find out the difference. Return visit was planned for the subsequent 2 months in the month of November and December 2012 and the participants were instructed that the same procedure of measurement of BP would be carried out by the midwife responsible. Mean inter-arm SBP and DBP differences were computed for each visit and the three pairs of readings were averaged to obtain a mean SBP and DBP for each arm to derive the mean IAD.
The study protocol was approved by the Ethics Committees of the Municipal Maternity Corporation Hospital, Bruhat Bangalore Mahanagare Palike and the study setting. A written informed consent was obtained from all the participants. The participants gave consent for the publication of the clinical details.
For each set of BP readings, those for each arm were averaged separately, and the IAD was defined as the difference in BP between the right arm and the left arm for SBP and DBP. The unpaired t-test was used to compare the mean differences in the right versus left arm SBP and DBP. The associations between inter-arm BP differences obtained and the maternal characteristics were analyzed by Chi-square/Fisher's exact probability test. For all analyzes, a significance level of P < 0.001 (two-tailed) was used. All statistical analyzes were performed using SPSS version 15.0.
| Results|| |
The total of n = 100 normal low-risk healthy Primigravidae at 6-14 weeks of gestation were selected for the study. The participants were homogenous with regards to their age, gestational weeks, maternal weight and hemoglobin as analyzed by Chi-square/Fisher's exact probability test which indicated that there is no sample selection bias [Table 1].
|Table 1: Distribution of the primigravidae by their maternal characteristics|
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The most important findings of the present study was that the SBP and DBP in the right versus left arm were significantly different in the initial visit, subsequent two visits with a month interval and the average of all three visits. The mean difference of SBP in the three pairs of visits in right (115.71 ± 0.827 standard deviation [SD]) versus left arm (105.23 ± 1.110 SD) t99 = 41.713; P < 0.001 and DBP in right were (73.10 ± 0.370 SD) versus left arm (69.43 ± 2.288) t99 = 22.533; P < 0.001, respectively. The mean difference in the SBP was 11.87 mmHg between the right versus left arms, and the range was from 2 mmHg to 16 mmHg. The mean difference in the DBP was 6.09 mmHg, and the range was 0-10 mmHg. Clinically, n = 21 (21%) Primigravidae had an IADs of SBP and DBP > 10 mmHg [Table 2]. The right arm BP measurements were higher than the left in the order of 2-16 mmHg.
Fisher' exact probability and Chi-square test showed that maternal age χ2 = 0.090, maternal weight; χ2 = 0.165; maternal hemoglobin; χ2 = 0.335 gestational weeks; χ2 = 0.335 did not influence the inter-arm SBP and DBP differences among the primigravidae at P > 0.001 level.
| Discussion|| |
The prevention and management of hypertension during pregnancy is a major public health challenge when we want to reduce maternal mortality rate in our country. If the rise in BP during pregnancy could be prevented or managed, much of hypertension, cardiovascular, renal diseases and stroke might be prevented. Primary preventive measures should be introduced to prevent BP level rising, which has the potential to substantially reduce the mortality and morbidity or at least a delay in onset of hypertension particularly in pregnancy. 
The most important findings of the present study were that there was a significant difference in the right versus left arm SBP and DBP in each of the three visits among healthy primigravidae ranging from 2 to 16 mmHg. The significant findings of presence of IADs in BP during pregnancy in this study is similar to that of non-pregnant normotensive population. 
In the present study, the mean SBP and DBP were higher by 11.87 mmHg and 6.09 mmHg in right vs left arm and these differences could reflect issues of population with risk factors complicating pregnancy. Similar findings were reported by Cassidy and Jones who conducted a pragmatic study among 237 normal adults attending general clinic at Suburban city in UK found that mean BPs were higher in right than left arms, with the right arm measuring greater than the left by 3.7 mmHg for diastolic and 4.8 mmHg for systolic. 
The study findings should be interpreted within the context of its limitations that the bilateral BP measurements were carried out by normal calibrated mercury Sphygmomanometer. Data from the present study revealed a proportionately minimal mean difference in SBP by 11.87 mmHg and DBP by 6.09 mmHg, which may be attributed to measurements of BP by manual device than the automated device. However, it is unlikely that this is the only cause of the minimal inter-arm BP difference obtained with a manual device because subsequent measurements in the next two visits could also lead to a smaller difference in IAD as the second measurement is taken with knowledge of the first which highlights the observer bias. Supportive findings from a systematic review and meta-analyses by Clark and Powell  who estimated the association between differences in simultaneous BP measurements by automated device between arms and each outcome among participants reported clinically a significant inter-arm mean difference of 36.9 mmHg (95% confidence interval 35.4-38.4) in SBP and DBP.
None of the demographic and clinical characteristics of the patients such as maternal age, gestational age, Hemoglobin, and maternal weight by Chi-squares/Fisher' exact probability test was a significant predictor of inter-arm SBP and DBP differences. Similar findings were reported by Orme et al.  who investigated the normal range for IADs in BP reported that there is no statistically a significant relationship between inter-arm BP difference and baseline characteristics such as age, gender, Hemoglobin, and weight. This association requires further evaluation in a larger study population.
Implications for practice
The IAD in BP has the potential to act as a simple noninvasive test, identifying those who could benefit from more intensive assessment. This study adds important information to the evidence base supporting the need to detect an inter-arm BP differences in the primary care assessment of pregnant women. Diagnosis for hypertension requires time, experience and training whereas bilateral brachial BP measurements can be easily taken and not at all a practical problem.
The magnitude of inter-arm BP difference should not be ignored clinically. Significant differences in mean inter-arm SBP and DBP emphasizes the importance of measuring BP in both arms initially to prevent the misdiagnosis of hypertension. In the right clinical situation, the differences in BP between the arms that are noted should be repeated and should be added to the total clinical picture of the patients to determine whether a risk to pathologic condition is present during pregnancy.
Limitation of the study
The study findings have a limited ability to generalize the findings to a population with any medical, surgical and obstetric risk factors complicating pregnancy.
| Conclusion|| |
This study data suggest that there are a significant inter-arm SBP and DBP differences between the two arms, being slightly higher on the right. Therefore, it is thus recommended that BP should be simultaneously measured in both arms at the initial consultation, and the higher of the two readings should be used to guide further management decisions.
| Acknowledgments|| |
I am grateful to all participants, midwives, obstetricians and medical officer of the study setting for their support and participation.
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[Table 1], [Table 2]