Inter-arm blood pressure differences in pregnant women

Transcription

1 DOI: /j x Maternal medicine Inter-arm blood pressure differences in pregnant women LCY Poon, N Kametas, I Strobl, C Pachoumi, KH Nicolaides Harris Birthright Research Centre for Fetal Medicine, King s College Hospital, London, UK Correspondence: Dr N Kametas, Harris Birthright Research Centre for Fetal Medicine, King s College Hospital, Denmark Hill, London SE5 9RS, UK. n.kametas@btinternet.com Accepted 23 January Objective To determine the prevalence of blood pressure interarm difference (IAD) in early pregnancy and to investigate its possible association with maternal characteristics. Design A cross-sectional observational study. Setting Routine antenatal visit in a university hospital. Population A total of 5435 pregnant women at weeks of gestation. Methods Blood pressure was taken from both arms simultaneously with a validated automated device. Main outcome measures The presence of inter-arm blood pressure difference of 10 mmhg or more. Results The IAD in systolic and diastolic blood pressure was 10 mmhg or more in 8.3 and 2.3% of the women, respectively. Systolic IAD was found to be significantly related to systolic blood pressure and pulse pressure, and diastolic IAD was found to be significantly related to maternal age, diastolic blood pressure and pulse pressure. The systolic and diastolic IAD were higher in the hypertensive group compared with the normotensive group and absolute IAD increased with increasing blood pressure. About 31.0 and 23.9% of cases of hypertension would have been underreported if the left arm and the right arm were used, respectively, in measuring the blood pressure. Conclusions There is a blood pressure IAD in a significant proportion of the pregnant population, and its prevalence increases with increasing blood pressure. By measuring blood pressure only on one arm, there is a one in three chance of underreporting hypertension. Therefore, it would be prudent that during the booking visit blood pressure should be taken in both arms and thus provide guidance for subsequent blood pressure measurements during the course of pregnancy. Keywords Automated blood pressure measurement, inter-arm difference, pregnancy. Please cite this paper as: Poon L, Kametas N, Strobl I, Pachoumi C, Nicolaides K. Inter-arm blood pressure differences in pregnant women. BJOG 2008;115: Introduction A difference between the two arms in the systolic and/or diastolic blood pressure of 10 mmhg or more was first reported in This is a common finding in certain pathological conditions, such as dissection or coarctation of the aorta, peripheral vascular disease and unilateral neurological and musculoskeletal abnormalities, but it is also found in normal healthy individuals. 2,3 However, its prevalence and relevance to accurate blood pressure monitoring remains uncertain. In the nonpregnant population, it is recommended that the blood pressure should be measured in both arms at the first examination, and if there is a consistent inter-arm difference (IAD), the arm with the highest recording should be used for subsequent assessments. 4,5 Currently, this practice is not widely recommended in pregnancy. 6 8 The aim of this study was to determine the prevalence of blood pressure IAD in early pregnancy and to investigate its possible association with maternal characteristics. Methods Study population Blood pressure measurements were obtained from 5435 women with singleton pregnancies attending the hospital for a routine ultrasound examination at weeks of gestation between 28 April and 30 November Only pregnancies with live fetuses demonstrated by ultrasound were included, and all women gave written informed consent to participate in the study. Gestational age was determined from the known date of the last menstrual period and confirmed by the sonographic measurement of the fetal crown rump length. When 1122 ª 2008 Fetal Medicine Foundation Journal compilation ª RCOG 2008 BJOG An International Journal of Obstetrics and Gynaecology

2 Inter-arm blood pressure differences there was a discrepancy of more than 7 days between the gestational age calculated by the maternal last menstrual period and the fetal measurement, the gestational age was based on the measurement of the fetal crown rump length. Blood pressure measurements The blood pressure was taken by automated devices (3BTO- A2; Microlife, Taipei, Taiwan) 9 that were calibrated before and at regular intervals during the study. The recordings were made by doctors who had received appropriate training ontheuseofthesemachines.womenwereallowedtorest for minutes in a calm environment prior to their examination. Blood pressure taken in a quite room with its temperature standardised between 20 and 24 C. The women were in the sitting position, their arms were supported at the level of the heart and either a small (<22 cm), normal (22 32 cm) or large (33 42 cm) adult cuff was used depending on the mid-arm circumference. 4 The blood pressure was measured in both arms simultaneously and a series of recordings were made at 1-minute intervals until variations between consecutive readings fell within 10 mmhg in systolic pressure and 6 mmhg in diastolic pressure in both arms. 5 A small number of women whose blood pressure did not achieve the prespecified stability levels after six consecutive measurements were allowed a 30-minute rest period prior to their blood pressure being retaken. The systolic and diastolic blood pressure measurements from the arm with the highest mean arterial pressure were chosen for the analyses. Definitions Hypertension was considered to be present if the systolic and/or diastolic blood pressures were greater than or equal to 140 mmhg and 90 mmhg, respectively. Significant blood pressure IAD was considered to be present if the difference between the two arms in the average of the last two measurements was 10 mmhg or more in either the systolic and/or diastolic blood pressure. 10 Statistical analysis The Bland Altman analysis was carried out to compare the systolic and/or diastolic blood pressure in the left or right arm in the overall population and in the subgroups of righthanded and left-handed subjects. Regression analysis was used to determine the significance of the association between blood pressure IAD and the continuous variables of maternal age in years, body mass index (BMI) in kg/m 2, gestational age in days, systolic blood pressure in mmhg, diastolic blood pressure in mmhg and pulse pressure (systolic diastolic blood pressure) in mmhg; the categorical variables of ethnicity (Caucasian, Afro-Caribbean, Indian or Pakistani, Chinese or Japanese and mixed), parity (nulliparous or parous), right handedness (yes or no), cigarette smoker (yes or no), alcohol drinker (yes or no), drug abuser (yes or no), medical history (none, hypertension, diabetes mellitus, asthma, thyroid disease, epilepsy, haemoglobinopathy and miscellaneous), medication during pregnancy (none, antihypertensives, insulin, steroids, b-mimetics, thyroxine, antiepileptics, heparin/aspirin and miscellaneous). Women were divided into four groups according to their blood pressure IAD ( 5, 6 10, and >15 mmhg). Chisquare test for trend was used to assess the differences between the normotensive and hypertensive subjects according to the blood pressure IAD groups. Additionally, women were divided into four groups according to their systolic blood pressure (<110, , and 130 mmhg) and diastolic blood pressure (<60, 60 69, and 80 mmhg). Cuzick trend test was used to examine the trend in the absolute IADs between the different blood pressure groups. The statistical analyses were performed using SPSS software version 12.0 (SPSS Inc., Chicago, IL, USA). Results The maternal and pregnancy characteristics are summarised in Table 1. In the Bland Altman plots (Figure 1), the mean difference between the left and right arms in systolic blood pressure was 0.8 mmhg (95% CI 11.9 to 10.3 mmhg) and in diastolic blood pressure was 0.6 mmhg (95% CI 7.0 to 8.3 mmhg). The mean difference between the left and right arms in systolic blood pressure in right-handed subjects was 0.9 mmhg (95% CI 12 to 10.3 mmhg) and in lefthanded subjects was 0.2 mmhg (95% CI 11 to 10.7 mmhg) (Figure 2). The respective values for diastolic blood pressure were 0.6 mmhg (95% CI 0.7 to 8.3 mmhg) and 0.9 mmhg (95% CI 6.4 to 8.2 mmhg) (Figure 3). The IAD in systolic and diastolic blood pressure was 10 mmhg or more in 450 (8.3%) and 124 (2.3%) women, respectively. Univariate regression analyses demonstrated that the systolic IAD was significantly associated with BMI, systolic blood pressure, diastolic blood pressure, pulse pressure, Caucasian racial group and the use of steroids (Table 1). Multivariate regression was used to assess the independent predictors of blood pressure IAD among the aforementioned statistically significant variables of the univariate models. As there was a high collinearity between systolic and diastolic blood pressure and pulse pressure, we used only two of these variables in the multivariate analysis: systolic blood pressure and pulse pressure were chosen as giving the highest R 2. Systolic IAD was found to be significantly related to systolic blood pressure and pulse pressure (R 2 = 0.069, P < ; Table 2). In the univariate analyses, the diastolic IAD was significantly associated with maternal age, BMI, systolic blood pressure, diastolic blood pressure and pulse pressure ª 2008 Fetal Medicine Foundation Journal compilation ª RCOG 2008 BJOG An International Journal of Obstetrics and Gynaecology 1123

3 Poon et al. Table 1. Univariate regression analysis on the association between the IAD in blood pressure and maternal characteristics Maternal characteristics Systolic IAD Diastolic IAD r P r P Maternal age in years, mean (range) 31.9 (16 49) BMI in kg/m 2, mean (range) 25.1 ( ) 0.062, , Gestational age in days, mean (range) 88 (77 101) Systolic blood pressure in mmhg, mean (range) (81 176) 0.246, , Diastolic blood pressure in mmhg, mean (range) 70.8 (48 105) 0.056, , Pulse pressure in mmhg, mean (range) 47.7 ( ) 0.235, , Ethnicity Caucasian, n (%) 3917 (72.0) Afro-Caribbean, n (%) 976 (18.0) Indian or Pakistani, n (%) 271 (5.0) Chinese or Japanese, n (%) 85 (1.6) Mixed, n (%) 186 (3.4) Nulliparous, n (%) 2613 (48.1) Right handedness, n (%) 4993 (91.9) Cigarette smoker, n (%) 481 (8.9) Alcohol drinker, n (%) 54 (1.0) Drug abuser, n (%) 21 (0.4) Medical history None, n (%) 4685 (86.2) Hypertension, n (%) 47 (0.9) Diabetes mellitus, n (%) 44 (0.8) Asthma, n (%) 235 (4.3) Thyroid disease, n (%) 80 (1.5) Epilepsy, n (%) 35 (0.6) Haemoglobinopathy, n (%) 25 (0.5) Miscellaneous, n (%) 284 (5.2) Medication during pregnancy None, n (%) 4933 (90.8) Antihypertensives, n (%) 33 (0.6) Insulin, n (%) 43 (0.8) Steroids, n (%) 88 (1.6) b-mimetics, n (%) 76 (1.4) Thyroxine, n (%) 76 (1.4) Antiepileptics, n (%) 28 (0.5) Heparin/aspirin, n (%) 51 (0.9) Miscellaneous, n (%) 107 (2.0) (Table 1). For the multivariate analysis, we omitted systolic blood pressure and included diastolic blood pressure and pulse pressure. Diastolic IAD was found to be significantly related to maternal age, diastolic blood pressure and pulse pressure (R 2 = 0.072, P < ; Table 2). The systolic and diastolic IAD were generally higher in the hypertensive group compared with the normotensive group (Figure 4A, B). The chi-square test for trend test showed a highly significant difference between the two groups for both systolic and diastolic IAD (systolic IAD: chi-square test = , d.f. = 1, P < ; diastolic IAD: chi-square test = , d.f. = 1, P < ). Additionally, the absolute IADs increased with increasing systolic and diastolic blood pressures (Figure 5A, B; Cuzick trend test: P < for both systolic and diastolic blood pressures). There were 155 cases of hypertension when the highest measurements between the two arms were chosen for the diagnosis. About 31.0 and 23.9% of women would have been underreported if the left arm and the right arm were used, respectively, in measuring the blood pressure (Table 3). Discussion The present study, performed in an unselected pregnant population, has shown that there is a difference between the blood 1124 ª 2008 Fetal Medicine Foundation Journal compilation ª RCOG 2008 BJOG An International Journal of Obstetrics and Gynaecology

4 Inter-arm blood pressure differences Figure 1. Bland Altman plots of the differences between the left and right arm (left right) blood pressure against the mean blood pressure: (A) systolic and (B) diastolic. The solid line represents the mean difference and the two dotted lines represent ±2 SD for individual differences between the two arms. pressure measured in the left and right arms of 10 mmhg or more in systolic and diastolic blood pressure in 8.3 and 2.3% of the women, respectively. Additionally, we have shown that independent predictors of blood pressure IAD are the level of blood pressure and pulse pressure. Our study is the largest to date reporting on blood pressure IAD and is the first one to show these findings in a pregnant population. The data showed that the reported blood pressure IAD and its 95% CI in women in early pregnancy is similar to that of nonpregnant populations. 2,10 Furthermore, the results Figure 2. Bland Altman plots of the differences between the left and right arm (left right) systolic blood pressure against the mean systolic blood pressure: (A) right-handed women and (B) left-handed women. ª 2008 Fetal Medicine Foundation Journal compilation ª RCOG 2008 BJOG An International Journal of Obstetrics and Gynaecology 1125

5 Poon et al. Figure 3. Bland Altman plots of the differences between the left and right arm (left right) diastolic blood pressure against the mean diastolic blood pressure: (A) right-handed women and (B) left-handed women. confirm the findings of the study by Kimura et al. 2 that in nonpregnant populations, there was a significant independent association between blood pressure IAD with systolic and diastolic blood pressure and pulse pressure. However, the prevalence of a significant blood pressure IAD reported in our study was lower than that in the studies on nonpregnant women with similar methodology. 3,10 12 This finding could be attributed to the study population as our sample consisted of only pregnant women who are generally younger with fewer medical problems. In previous reports in nonpregnant populations, the prevalence of blood pressure IAD of 10 mmhg or more ranged between 3 and 83%. 13 The differences in prevalence between these studies could be due to differences in methodology because in the majority of them, mercury sphygmomanometers were used, with a concomitant bias due to inter-observer variability. In addition, sequential rather than simultaneous blood pressure measurements were made. A recent literature review by Clark et al. 13 had identified 31 studies that reported a prevalence figure for IAD for systolic and diastolic blood pressures. Only four studies measured blood pressure simultaneously in both arms and showed a mean prevalence of 19.6% for a systolic IAD of 10 mmhg or more. 3,10 12 On the contrary, the remaining 27 studies, which measured blood pressure sequentially, tended to overestimate the prevalence of blood pressure IAD to about 34.5% for a systolic IAD of 10 mmhg or more. Of the aforementioned four studies, the two earlier ones that have used nonautomated devices for simultaneous blood pressure recordings yielded higher prevalences of blood pressure IAD of 10 mmhg or more when compared with the two more recent studies that used automated devices. It appears therefore that nonsimultaneous measurements and the use of nonautomated devices inflate both the degree and the prevalence of significant blood pressure IAD. More recently, Kimura et al. examined 1090 subjects and measured blood pressure simultaneously in both arms with an automated device. Similar to our data, they demonstrated a prevalence of 9.1% for a systolic IAD of 10 mmhg or more. The pathophysiology of the blood pressure IAD remains unclear. Anatomical explanations, such as the angulation and the branching of the aorta, 14 aortic aneurysms and the compression of the aorta by thoracic tumour or cervical ribs 15 have been proposed. However, the difference in blood pressure between the left and right arms is observed in a relatively large proportion of the general population and therefore cannot be totally explained by the above-mentioned pathology. There is emerging evidence that in nonpregnant populations, a higher prevalence of blood pressure IAD is found in patients with coronary heart disease 16,17 or peripheral vascular disease. 18 In a general medical practice setting, Kay and Gardner 17 observed the blood pressure IAD in 125 patients and showed that greater differences were found in the arteriosclerotic and hypertensive patients, especially those with angina and aortitis. A prospective study of 610 patients who attended the hospital emergency department showed a 40% greater systolic IAD with known coronary artery disease than without. 16 In addition, data from hospital general surgical wards showed a three times higher prevalence of IAD greater than 10 mmhg in patients with peripheral vascular disease compared with controls. 18 It is therefore possible that in 1126 ª 2008 Fetal Medicine Foundation Journal compilation ª RCOG 2008 BJOG An International Journal of Obstetrics and Gynaecology

6 Inter-arm blood pressure differences Table 2. Multivariate regression analysis on the association between the IADs in blood pressure and maternal characteristics Systolic IAD Diastolic IAD Coefficient of regression (95% CI) P Coefficient of regression (95% CI) P Maternal age (years) ( to ), BMI (kg/m 2 ) ( to 0.012) ( to 0.019) Systolic blood pressure (mmhg) (0.046 to 0.072), ( to ), Diastolic blood pressure (mmhg) ( to ), (0.074 to 0.092), Pulse pressure (mmhg) (0.047 to 0.083), (0.031 to 0.049), Caucasian ( to 0.262) Use of steroids ( to 1.314) a large proportion of patients, the blood pressure IAD may be reflecting pathophysiological changes related to cardiovascular disease rather than anatomical variations. A clinically important observation in the literature, confirmed by our data in pregnant women, is that the prevalence of blood pressure IAD of 10 mmhg or more is lower in normotensive subjects and higher in hypertensive subjects. 2,11,12 Additionally, an intriguing finding of this study was the strong positive correlation of blood pressure IAD with pulse pressure, which is related to the compliance (stiffness) of the aorta. A meta-analysis of three studies with a total sample size of nearly 8000 patients reviewed the independent roles of pulse pressure and mean pressure in determining the cardiovascular prognosis in older hypertensive patients, and it was found that a 10 mmhg wider pulse pressure was correlated with an increased risk of cardiovascular complications and by 10 20%. 19 Similar findings were demonstrated by Panagiotakos et al. 20 who assessed the relationship between the pulse pressure and the cardiovascular mortality in men from seven countries. They demonstrated a highly significant independent contribution of pulse pressure measurements in the prediction Figure 4. The percentage distribution of (A) systolic and (B) diastolic blood pressure IADs in the normotensive (white) and hypertensive (black) subjects. ª 2008 Fetal Medicine Foundation Journal compilation ª RCOG 2008 BJOG An International Journal of Obstetrics and Gynaecology 1127

7 Poon et al. Figure 5. Box-whiskers plots of the absolute IADs with increasing (A) systolic and (B) diastolic blood pressures. of cardiovascular death compared with systolic and diastolic blood pressures. The age-adjusted hazard ratio per 10 mmhg increase in pulse pressure varied among cohorts from 1.19 in the USA to 1.29 in southern Europe. The correlation of blood pressure IAD with pulse pressure provides further indirect evidence that IAD could present in asymptomatic arterial disease and may have an additional role in the risk assessment for cardiovascular disease and its complications. The present study also examined the effect of handedness on blood pressure IAD and found that there was no significant difference in blood pressure between the two arms in right- or left-handed subjects. Our results are in agreement with the report from Lane et al. 3 where 400 subjects were Table 3. Diagnosis of hypertension depending on whether blood pressure is recorded in both arms and the highest blood pressure is used or measurements are taken only from the left arm or the right arm only Definition of hypertension Blood pressure measurements Highest, n Left arm, n (%) Right arm, n (%) Systolic 130 mmhg and/or diastolic 85 mmhg (73.2) 516 (76.1) Systolic 140 mmhg and/or diastolic 90 mmhg (69.0) 118 (76.1) Systolic mmhg and/or diastolic mmhg (69.2) 110 (76.9) Systolic 160 mmhg and/or diastolic 100 mmhg 12 8 (66.7) 8 (66.7) Systolic blood pressure (mmhg) (69.5) 466 (77.7) (60.3) 98 (81.0) (71.4) 17 (81.0) (55.6) 6 (66.7) Diastolic blood pressure (mmhg) (82.2) 159 (64.4) (79.7) 53 (67.1) (75.0) 15 (75.0) (83.3) 5 (83.3) 1128 ª 2008 Fetal Medicine Foundation Journal compilation ª RCOG 2008 BJOG An International Journal of Obstetrics and Gynaecology

8 Inter-arm blood pressure differences examined and the blood pressure was not significantly higher in the dominant hand. Similarly, Singer and Hollander 16 examined 610 acutel unwell patients in the hospital emergency department and found that IAD was not associated with handedness. Currently, there is no evidence to suggest that IAD in blood pressure is related to handedness. Hence, handedness cannot guide us as to which arm we should take blood pressure from for diagnosing hypertension. With the current evidence of significant blood pressure IAD in patients with manifestations of peripheral vascular disease, one could postulate that there is potentially a similar underlying aetiology of asymptomatic preclinical arterial disease causing the inter-arm blood pressure differences. Therefore, the assessment for IAD in any new medical consultation should become a routine practice. With pregnancy being a window of opportunity for a healthcare system to screen most women of reproductive age for risk factors of cardiovascular disease, one should attempt to maximise the amount of information (i.e. the actual blood pressure levels as well as the IAD and pulse pressure) to be obtained at any given antenatal visit. Currently, although for nonpregnant individuals, it is recommended that at the initial visit blood pressure should be examined on both arms, 4,5 this practice has not been widely recommended in routine antenatal care. 6 8 Failure to appreciate the blood pressure IAD in the pregnant population and to standardise recordings to the arm with high measurement could lead to the risks of inadequate antihypertensive treatment and delay in the diagnosis of hypertension, especially for the diagnosis of pre-eclampsia in pregnancy. Changing our clinical practice would have serious implications to our antenatal healthcare system where we could potentially increase the sensitivity or the false-positive rate in the diagnosis of hypertension by choosing the highest measurements. However, at present, as there are limited published data on the correlation of IAD in blood pressure with adverse cardiovascular outcomes, larger studies using standardised simultaneous bilateral assessments of blood pressure are needed to examine the additional contribution of IAD as part of the risk assessment for hypertensive-related complication in pregnancy and for cardiovascular disease in the long term. Conclusions In conclusion, we have demonstrated that there is a blood pressure IAD in a significant proportion of the pregnant population and its prevalence increases with increasing blood pressure. By measuring blood pressure only on one arm, there is as high as a one in three chance of underreporting hypertension. Until more evidence is available on the impact of assessing the blood pressure IAD in screening and treatment of hypertensive disorders in the general population and in pregnancy, it would be prudent that at least during the booking visit in early pregnancy blood pressure measurements should be taken in both arms in a standardised manner and thus provide guidance for subsequent blood pressure measurements during the course of pregnancy. Ethics approval This study was approved by King s College Hospital Ethics Committee (06/Q0703/88). Acknowledgement This study was funded by the Fetal Medicine Foundation (registered charity ). j References 1 Cyriax EF. Unilateral alterations in blood-pressure caused by unilateral pathological conditions: the differential blood pressure sign. QJMed 1920;13: Kimura A, Hashimoto J, Watabe D, Takahashi H, Ohkubo T, Kikuya M, et al. 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