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Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients
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NS-2375; No. of Pages 10 International Journal of Nursing Studies xxx (2014) xxx–xxx
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Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients Karen Schimanski a,*, Andrew Jull b, Nancy Mitchell c, Jessica McLay d a
Emergency Department, Auckland City Hospital, Private Bag 92024, Auckland, New Zealand School of Nursing, University of Auckland, New Zealand c Emergency Department, Auckland City Hospital, New Zealand d Department of Statistics, University of Auckland, New Zealand b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 July 2013 Received in revised form 21 March 2014 Accepted 27 March 2014
Background: Forearm blood pressures have been suggested as an alternative site to measure blood pressures when the upper arm is unavailable. However there is little evidence utilising clinical populations to support this substitution. Objectives: To determine agreement between blood pressures measured in the left upper arm and forearm using a singular oscillometric non-invasive device in adult Emergency Department patients. The secondary objective was to explore the relationship of blood pressure differences with age, sex, ethnicity, smoking history and obesity. Design: Single centre comparison study. Setting: Adult Emergency Department, Tertiary Trauma Centre. Participants: Forty-four participants who met inclusion/exclusion criteria selected sequentially from the Emergency Department arrival board. Methods: A random assignment of order of measurement for left upper arm and forearm blood pressures was utilised. Participants were eligible if they were aged 18 years or older, had been assigned an Australasian Triage Scale code of 2, 3, 4, or 5, were able to consent, and able to have blood pressures measured on their left arm whilst lying at a 458 angle. The Bland–Altman method of statistical analysis was used, with the level of agreement for clinical acceptability for the systolic, diastolic and mean arterial pressure defined as 10 mmHg. Results: The forearm measure overestimated systolic (mean difference 2.2 mmHg, 95% limits of agreement 19 mmHg), diastolic (mean difference 3.4 mmHg, 95% limits of agreement 14.4 mmHg), and mean arterial pressures (mean difference 4.1 mmHg, 95% limits of agreement 13.7 mmHg). The systolic measure was not significantly different from zero. Evidence of better agreement was found with upper arm/forearm systolic measures below 140 mmHg compared to systolic measures above 140 mmHg using the Levene’s test (p = 0.002, F-statistic = 11.09). Blood pressure disparity was not associated with participant characteristics. Conclusions: Forearm measures cannot routinely replace upper arm measures for blood pressure measurement. If the clinical picture requires use of forearm blood pressure, the potential variance from an upper arm measure is 19 mmHg for systolic pressure, although the variability may be close to 10 mmHg if the systolic blood pressure is below 140 mmHg. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Blood pressure determination Blood pressure accuracy Upper arm blood pressure Forearm blood pressure Emergency nursing
* Corresponding author. E-mail addresses: [email protected], [email protected], [email protected] (K. Schimanski). http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008 0020-7489/ß 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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What is already known about the topic? The gold standard for a non-invasive blood pressure measurement is auscultation of the upper arm at heart level. Previous studies recommend substituting forearm blood pressure measures for upper arm measures when clinically necessary. Agreement between the two measures has not been established. Previous studies have not always used appropriate analytical methods or used clinical populations that can be generalised to the acute adult patient in Emergency Department. What this paper adds Forearm measures cannot be routinely substituted for upper arm measures of blood pressure in Emergency Department patients due to clinical unacceptable variability. This is the first study to report evidence of better agreement between upper arm and forearm systolic measures below 140 mmHg. 1. Introduction Blood pressure measurements provide essential baseline cardiovascular information and reflect a patient’s response to medications, intravenous fluids, and other acute treatments. In an Emergency Department, treatment decisions are contingent upon the clinical scenario, systolic blood pressure trends and other related information. Accuracy and speed in obtaining a blood pressure can be imperative, but obtaining blood pressure measurements presents a challenge when the upper arm is inaccessible due to injury, disease process or when the upper arm is too large for the standard range of blood pressure cuffs. Guidelines have suggested the forearm be used when the upper arm is unavailable. These guidelines also identify the need for studies to validate this practice (O’Brien et al., 2003; Pickering et al., 2005). The evidence supporting the practice of using the forearm alternate is somewhat equivocal. Most studies suggest that there are statistically significant differences between upper and forearm blood pressure measurements and that the measures cannot be used interchangeably (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010; Singer et al., 1999; Tachovsky, 1985). However, measurement of blood pressure and analysis of results have varied across studies. Earlier studies used auscultatory sphygmomanometer (Palatini et al., 2004; Tachovsky, 1985), utilised non-invasive wrist devices (Emerick, 2002; Palatini et al., 2004), measured with different devices between sites (Palatini et al., 2004), did not state validation of their device (Fortune et al., 2008) or did not measure inter-rater reliability when more than one researcher was utilised (Domiano et al., 2008; Palatini et al., 2004). Others did not measure the site circumference
and used variable or unspecified cuff size and or site positions. (Domiano et al., 2008; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Tachovsky, 1985). Some studies used different anatomical patient positions ranging in degrees between lying to sitting (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010; Singer et al., 1999; Tachovsky, 1985). A number of studies also did not use the Bland–Altman method (Domiano et al., 2008; Fortune et al., 2008; Pierin et al., 2004; Singer et al., 1999; Tachovsky, 1985), the accepted statistical analysis for determining agreement between two measures (Preiss and Fisher, 2008). The majority of studies used healthy volunteers with a high proportion of non-obese white American females being recruited rather than clinical populations so may not be generalisable to unwell Emergency Department patients with multi-ethnic backgrounds (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Schell and Waterhouse, 2007; Schell et al., 2007; Tachovsky, 1985). In addition, the majority of quality studies conducted on blood pressure measurement comparison between the upper arm and forearm have been completed by the same lead investigator K.A. Schell (Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010). The objective of this study was to assess agreement between the systolic blood pressures as measured on the left upper arm and forearm using the same non-invasive blood pressure oscillometric device designed for upper arm measures in a clinical adult population presenting to an Emergency Department. This study used a computer generated random sequence with a block sequence size of two blinded to the investigator, a single validated electronic oscillometric non-invasive blood pressure device, appropriate cuff sizes based on forearm and upper arm measurements, accurate measured placement for position of cuff and adhered to guidelines for blood pressure measurement by Pickering et al. (2005). The Bland–Altman-method was used for statistical analysis (Bland and Altman, 1986). This study also sampled a more varied clinical Emergency Department population than previously researched. 2. Methods The Adult Emergency Department Blood Pressure (AEDBP) study was a single centre, prospective comparison study. The aim of this study was to determine the agreement between a single left upper arm and forearm blood pressure obtained in Adult Emergency Department (AED) presentations using the same oscillometric noninvasive electronic device dedicated to obtaining standard upper arm measures to reflect current clinical practice at the study site. Singular blood pressure measures were undertaken and a randomised cross-over order of measurement was used to mitigate normal physiological variation for singular blood pressure measures. The level of agreement for clinical acceptability for this study was defined as 10 mmHg by the Adult Emergency Research Group (AERG). The variability of 10 mmHg was considered as unlikely to change acute clinical management in adult
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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Emergency Department patients. The Bland–Altman method of statistical analysis was used to determine variability. Secondary objectives were to explore the relationship of blood pressure differences with the participant characteristics of age, sex, ethnicity, smoking history and obesity using hypothesis testing, linear regression and a multivariate analysis. Ethical approval was obtained from Northern Regional Health and Disability Ethics Committee (NTY/11/ 01/003) and the study was registered with the Australian New Zealand Clinical Trials Registry (ANZCTRN 12610000977077). 2.1. Recruitment Recruitment of adults began in May 2011 and was completed in June 2011 from patients presenting to an Emergency Department (ED) at a major urban hospital and trauma centre. Potential eligible participants were obtained from the ED patient list each weekday and were selected consecutively by time of presentation (i.e. those that arrived in ED first were approached first). Patients were eligible for inclusion if they were adults aged 18 years or older, had been assigned an Australasian Triage Scale (ATS) code of 2, 3, 4, or 5, were able to consent, and were able to have blood pressures taken on their left arm whilst lying at a 458 angle. The ATS codes patients on a scale of one to five, with patients categorised as requiring resuscitation (ATS 1), emergency (ATS 2), urgent (ATS 3), semi-urgent (ATS 4) and non-urgent (ATS 5) (Australasian College of Emergency Medicine, 2013). Patients requiring immediate resuscitative care with an ATS code of 1 were excluded with all other ATS categories included in the study. 2.2. Sample size calculation An estimate of the standard deviation (SD) of the paired differences and the desired mean difference to detect were both needed to be specified to calculate the sample size. To do this a feasibility study was conducted by the primary author in October 2010 prior to the commencement of the NIBP study where ten paired left upper arm and forearm blood pressure measurements were obtained from healthy volunteers. The SD of the paired differences in the feasibility study was 9.41 mmHg. This value was compared with the reported SD of paired differences in three published studies (Schell et al., 2005, 2006, 2010) and it was found that the SD was also around 10 mmHg for all three (see Table 1). Hence a SD of 10 mmHg of the paired differences was used for the sample size calculation. Table 1 Standard deviations of the paired differences in systolic blood pressures measured on bicep and forearm found in three published studies and our pilot data on 10 volunteers. Study Schell 2005 Schell 2006 Schell 2007 Our pilot data
Mean difference UA FA (mmHg) 1.3 8.3 1.2 1.9
Standard deviation of the paired differences (mmHg) 9.39 10.15 10.26 9.41
UA = upper arm, FA = forearm, mmHg = millimetres of mercury.
3
After considering the mean of the paired differences in the feasibility study and the three published studies used for the SD (also shown in Table 1), it was decided that powering the study to detect a mean paired difference of 5 mmHg would be clinically meaningful. The sample size was calculated using a standard formula (using normal distribution theory) for testing a single mean (Chow et al., 2008). A sample size of 44 patients was determined to have 90% power to detect a difference in systolic blood pressures measured at the bicep and at the forearm (paired differences) of 5 mmHg. This assumed a type 1 error rate (a) of 0.05, a standard deviation of the paired differences of 10 mmHg and that a paired t-test was to be performed to test for a difference. 2.3. Randomisation The order of blood pressure measurement on the left arm was determined by a computer generated random sequence with a block size of two (Altman and Bland, 1999). The allocation sequence was protected using sealed, sequentially numbered opaque envelopes with matching numbered slips (folded over three times) assigning the sequence of measurement. Blinding of participants and the primary investigator was not feasible once allocation was revealed. 2.4. Measurement A Carescape V100 non-invasive blood pressure device with a current certificate of calibration was used. The accuracy of this device complied with the standard of 5 mmHg (standard deviation of 8 mmHg) recommended by the Association for the Advancement of Medical Instrumentation (AAMI) standards (AAMI, 2013). Arm circumference measurements were taken at both the left upper arm and left forearm of the patient using a standard measuring tape. The upper arm was measured mid-way between the acromion and olecranon. The forearm was measured mid-way between the olecranon and styloid process. Selection of the correct blood pressure cuff was based on the arm measurements recommended by the manufacturer (G.E. Healthcare, 2011). The base of the blood pressure cuffs were positioned 2.5 cm above the ante-cubital fossa for the upper arm measure and 2.5 cm above the styloid process for the forearm measure. The cuff cursor was placed at the level of the radial artery for upper arm measures and at the level of the ulnar artery for forearm measures. No clothing was allowed underneath the cuff. All participants had their measures taken by a single trained researcher whilst lying on a stretcher with the head of bed elevated at a 458 angle (as measured with a goniometer). The standard left upper arm blood pressure measurement was taken with the participant on a stretcher with their arm lying beside them. The forearm blood pressure was taken by lifting the participants left arm to the level of the right atrium and supporting it on an adjustable hospital bedside table as per recommended guidelines (O’Brien et al., 2003; Pickering et al., 2005). Utilising a stopwatch, the second measure was commenced one minute after change of arm position and completed within three minutes.
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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Height was measured using a stadiometer or tape measure when the participant was unable to stand. Weight was obtained on the AED weigh scales and body mass index was categorised according to current guidelines, irrespective of ethnicity (Jull et al., 2011). Data on triage code, mode of arrival, discharge destination and discharge code were collected from clinical notes. Participants provided information on self-identified ethnicity and smoking status. 2.5. Data analysis Excel 2010 (version 14) was used to collate study data with 40% of the data entry being checked for accuracy by a co-investigator (NM). Data was analysed using R (version 2.14.1). The Bland–Altman method was used to determine agreement between the forearm and upper arm measures (Bland and Altman, 1986, 1999). Assessment of agreement was contingent on the normal distribution of the data and normality of data was investigated by the Shapiro–Wilk test method and Q–Q plots. Student’s t-test investigated whether the mean differences could be null, with the threshold for significance set at 5%. The Levene test examined group variances within the data. Linear regression was used to assess the relationship between the mean pressure and the difference in the pressure for systolic, diastolic and mean arterial pressure. To ascertain the relationship of blood pressure disparities with participant characteristics a multivariable analysis was conducted.
3. Results Forty-seven participants met inclusion criteria (Fig. 1). Forty-six provided written consent and were randomised. Two participants were unable to complete both blood pressure measures due to the unavailability of a correctly sized cuff and therefore were excluded after randomisation. Participant ages ranged from 18 to 96 years and nearly half of the participants were New Zealand European (Table 2). Triage acuity ranged from emergency, urgent to semi-urgent with just over half requiring admission to either the Short Stay Unit or hospital ward for ongoing medical care (Table 3). Presenting conditions included chest pain, non-ST elevation myocardial infarction, asthma, renal colic, allergic reaction, dizziness, diabetic ketoacidosis and various minor traumas varying from rib fractures and pneumothorax to lower limb fractures and sprains. Discharge categories are presented in Table 4. Systolic blood pressure measures ranged from 99 to 186 mmHg at the upper arm and 100 to 186 mmHg at the forearm. Diastolic blood pressures ranged from 53 to 104 mmHg at the upper arm and 56 to 102 mmHg at the forearm. Mean blood pressures ranged from 71 to 138 mmHg at the upper arm and 74 to 158 mmHg at the forearm. Normality was acceptable for the systolic, diastolic blood pressure and mean arterial pressure measures as determined by the Shapiro–Wilk test (p = 0.93, 0.54, 0.19, respectively) and the Q–Q plots (not shown). The forearm
Fig. 1. Flow diagram.
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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NS-2375; No. of Pages 10 K. Schimanski et al. / International Journal of Nursing Studies xxx (2014) xxx–xxx Table 2 Participant demography and blood pressure statistics. Mean (SD)
Characteristic
N (%)
53.0 (21.1) Age Sex (female) Ethnicity NZ European Maori Pasifika Asian Other Systolic blood pressure (mmHg) Upper arm 131 (21.9) 133 (23.5) Forearm Mean arterial pressure (mmHg) Upper arm 94 (13.8) Forearm 98 (16.3) Diastolic blood pressure (mmHg) Upper arm 72 (10.9) Forearm 75 (10.4)
(47.7) (15.9) (18.2) (9) (9)
mmHg = millimetres of mercury, N = number, SD = standard deviation; means and standard deviations have been rounded to one decimal place.
Table 3 Participant clinical characteristics. Mean (SD)
Characteristic 2
BMI (kg/m ) <20 20–25 25–30 >30 Mode of arrival Ambulance Triage code ATS 2 ATS 3 ATS 4 Smoking status Current Never Ex-smoker ED discharge destination Home Hospital
N (%)
27.5 (5.9) 2 16 12 14
(4.5) (29.5) (27.3) (31.8)
20 (46%) 7 (15.9) 25 (56.8) 12 (27.3) 13 (29.5) 19 (43.2) 12 (27.3) 20 (45.5) 24 (54.5)
kg/m2 = kilogram per square metre, N = number, SD = standard deviation; means and SD have been rounded to one decimal place.
systolic measure overestimated the upper arm systolic blood pressure by an average of 2.2 mmHg (95% CI 0.7 to 5.2 mmHg, Fig. 2). The difference was not statistically significant from zero (p = 0.14). The 95% limits of agreement for systolic blood pressure were calculated at Table 4 ED discharge categories. Discharge category
N
Musculoskeletal Neurological Gastrointestinal Ear/nose/throat Cardiovascular Respiratory Renal Miscellaneous
20 4 4 4 3 3 3 3
N = number.
Table 5 Univariable regression results from regressions of the difference in upper arm and forearm measurements and the mean of the upper arm and forearm measurements. Slope estimate Standard t-Value p-Value error
22 (50.0) 21 16 8 4 4
5
Diastolic Mean arterial pressure Systolic
0.058 0.174 0.070
0.112 0.068 0.067
0.51 2.55 1.05
0.61 0.0144 0.30
21.2 mmHg and 16.8 mmHg (range 19 mmHg). The Levene’s test found that the variances in the participants with systolic blood pressure less than 140 and above 140 mmHg were significantly different (p = 0.002, F-statistic = 11.09). Linear regression showed no significant relationship between mean systolic pressure and the difference in systolic pressure (Table 5). This indicates that the limits of agreement may be able to be applied across the board to patients regardless of their underlying systolic blood pressure. Forearm diastolic measures overestimated the upper arm diastolic measure by an average of 3.4 mmHg (95% C.I. 1.2–5.7 – Fig. 3) and this difference was statistically different from zero (p = 0.0034, t = 3.10, df = 43). The 95% limits of agreement were 17.8 mmHg and 11 mmHg (range of 14.4 mmHg). No significant relationship between the mean diastolic pressures the difference in the diastolic measures was detected (Table 5). The forearm mean arterial pressure overestimated the upper arm mean arterial pressure by an average of 4.1 mmHg (95% C.I. 2.0 to 6.2 – Fig. 4) and the difference was significantly different from zero (p = 0.0003, t = 3.91, df = 43). Limits of agreement were 17.8 mmHg and 9.6 mmHg (range of 13.7 mmHg). A significant negative relationship was found between the difference in mean arterial pressures and the mean pressure (Table 5). Hypothesis testing and a multivariable analysis showed the mean differences of the non-invasive blood pressure measures were not explained by patient characteristics. Systolic, diastolic and mean arterial pressure results for secondary outcomes of age, sex, ethnicity, smoking history and BMI are shown in Tables 6–8. No statistically significant differences were found. 4. Discussion Forearm measures all overestimated the upper arm measures with greatest variability in systolic blood pressures. The limits of agreement exceeded the 10 mmHg difference that was set as clinically significant a priori. Interestingly, there was evidence of better agreement below 140 mmHg for systolic blood pressures. This study is the first to report this pattern of variance. It was not within the remit of the study to explore this new finding. However, it suggests direction for future investigators. Linear regression was utilised to detect a relationship within the results. No significant relationship between mean systolic or diastolic pressure and the difference in systolic or diastolic pressure was found indicating the
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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20 10
Upper LOA 21.2
-10
0
Mean 2.2
Lower LOA -16.8
-20
Difference in systolic pressures (forearm - upper arm)
Systolic BP
100
120
140
160
180
200
Mean of systolic pressures in the upper arm and forearm Fig. 2. Bland–Altman plot for systolic blood pressure (mmHg) as measured using an automated oscillometric non-invasive blood pressure machine (Carescape V100).
Table 6 Multivariable model for systolic blood pressure. Estimate Intercept Sex: Male (reference = Female) Age BMI Ethnicity: New Zealand European (reference = Maori/Pacific) Ethnicity: Other Smoking: Ex-smoker (reference = Current smoker) Smoking: Never smoked
Standard error
t-Value
p-Value
1.04 0.37
9.02 3.24
0.12 0.11
0.909 0.911
0.01 0.02 3.02
0.09 0.29 3.82
0.12 0.06 0.79
0.905 0.952 0.434
4.44 0.59
4.78 4.70
0.93 0.13
0.359 0.901
1.76
4.12
0.43
0.671
Table 7 Multivariable model for diastolic blood pressure. Estimate Intercept Sex: Male (reference = Female) Age BMI Ethnicity: New Zealand European (reference = Maori/Pacific) Ethnicity: Other Smoking: Ex-smoker (reference = Current smoker) Smoking: Never smoked
Standard error
t-Value
p-Value
4.63 0.73
7.02 2.52
0.66 0.29
0.513 0.772
0.01 0.04 2.53
0.07 0.23 2.97
0.10 0.16 0.85
0.919 0.877 0.399
2.13 0.79
3.72 3.66
0.57 0.22
0.569 0.830
1.99
3.20
0.62
0.539
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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7
20 10
Upper LOA 17.8
-10
0
Mean 3.4
Lower LOA -11.0
-20
Difference in diastolic pressures (forearm - upper arm)
Diastolic BP
60
70
80
90
100
Mean of diastolic pressures in the upper arm and forearm Fig. 3. Bland–Altman plot for diastolic blood pressure (mmHg) as measured using an automated oscillometric non-invasive blood pressure machine (Carescape V100).
Table 8 Multivariable model for mean arterial pressure. Estimate Intercept Sex: Male (reference = Female) Age BMI Ethnicity: New Zealand European (reference = Maori/Pacific) Ethnicity: Other Smoking: Ex-smoker (reference = Current smoker) Smoking: Never smoked
Standard error
t-Value
p-Value
0.09 2.28
6.00 2.15
0.02 1.06
0.988 0.298
0.02 0.12 2.87
0.06 0.20 2.54
0.26 0.59 1.13
0.795 0.577 0.265
2.58 3.43
3.17 3.12
0.81 1.10
0.422 0.279
2.13
2.74
0.78
0.442
limits of agreement may be able to be applied across the board to patients regardless of their underlying systolic or diastolic blood pressure. However, a significant negative relationship was found between the difference in mean arterial pressures and the mean pressure. This suggests that, on average, the difference between the pressure measurements in the upper arm and the forearm is closer to zero for people with lower underlying mean arterial pressures than for people with greater underlying mean arterial pressures. This result affects the way in which the limits of agreement can be interpreted, indicating that it may not be appropriate to apply the limits of agreement across the board and that future work on calculating
separate limits of agreement for people with low and high blood pressures could be undertaken. Interest in the utility of the forearm as a blood pressure site in place of the upper arm has increased over the last 10 years. The numbers of citations have increased from two for the period prior to 2000 (Singer et al., 1999; Tachovsky, 1985) to ten in the years since (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2010; Schell et al., 2007). Only two previous studies have used Emergency Department patients and both used participants less heterogeneous than would be expected in clinical practice (Schell et al.,
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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Upper LOA 17.8
-10
0
Mean 4.1
Lower LOA -9.6
-20
Difference in mean arterial pressures (forearm - upper arm)
Mean Arterial Pressure
80
100
120
140
Mean of mean arterial pressures in the upper arm and forearm Fig. 4. Bland–Altman plot for mean arterial pressures (mmHg) as measured using an automated oscillometric non-invasive blood pressure machine (Carescape V100).
2005; Singer et al., 1999). More acute patients were excluded as the study samples were restricted to stable ambulatory patients not arriving via ambulance (Schell et al., 2005; Singer et al., 1999). Further, the mean age of the study samples was around 36 years with some including paediatric populations, suggesting that older patients were under-represented (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010; Singer et al., 1999; Tachovsky, 1985). The older adult population comprises a significant component of local Emergency Department attendances at our AED, accounting for approximately 44% of annual presentations in 2010 (Reeves, 2010). In contrast, this study set out to use a clinical sample of independently triaged patients, which included all patients arriving by ambulance except those that required resuscitation. Literature supports the Bland–Altman technique as the accepted statistical analysis for determining agreement between two measures (Preiss and Fisher, 2008). The Bland–Altman method compares the actual agreement between two measures, even when the ‘‘true’’ value of the measure is unknown and enables clinicians to determine whether the two measurement techniques can be used interchangeably or the new method can substitute the old method (Altman and Bland, 1983; Bland and Altman, 1986, 1999). It is important in a study investigating agreement between measures to specify a clinically acceptable limit of
variability so results can be interpreted with transparency (Hanneman, 2008). Whilst current literature provides little guidance in defining a clinically acceptable level of difference between blood pressure measurement sites, it has been acknowledged that attempts to determine a level of agreement should be made (Mantha et al., 2000). Only one investigating team stated an a priori level of agreement, for their analysis, but provided no clinical rationale for their level of 5 mmHg (Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010). Two other authors have used the limits set by the AAMI for device validation (<5 mmHg 8 SD) but have not identified the rationale for selecting this cut off point (Emerick, 2002; Palatini et al., 2004). This study was the first to use a level of agreement (10 mmHg) endorsed by Emergency clinicians as clinically acceptable. This study found site variability of 19 mmHg exceeding the 10 mmHg set a priori. However in the context of the Emergency Department alternative site blood pressure measures may still provide useful information. Blood pressure measures are not used in isolation, but interpreted as part of the entire clinical picture of the patient. Inaccuracies in measurements may be mitigated by other pertinent diagnostics including level of consciousness, other vital signs and their subsequent trends. With consideration of these other patient variables, if the forearm site was used consistently to obtain blood pressure trends, patient management may remain similar to that if the upper arm site was
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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used consistently. Therefore 19 mmHg for sufficient agreement could be acceptable for working purposes. Further exploration to quantify the definition of a clinically acceptable level of agreement within the acute context would be beneficial. This study was subject to four main limitations and one lesson learned. First, the sampling method used for this study was reliant on participants meeting the inclusion criteria during the hours the primary investigator was working (week days/evenings) and it is possible that different types of patients might present after hours. However, the range of Australasian Triage codes suggests the participants broadly reflected those that present to the Emergency Department. Secondly, the sub-group analysis of participant characteristics in this study lacked external validity. Larger studies specifically powered to analyse each sub-category would be helpful to address these areas so more conclusive associations between blood pressure disparity and participant characteristics can be made. Thirdly, only a small number of patients with blood pressures above 160 mmHg were recruited to this study as patients were recruited by inclusion criteria not by blood pressure category. Therefore, findings may not be generalisable to hypertensive patients. Fourth, it is important to note the results of the present study may not be immediately generalisable to wrist devices or to other upper-arm oscillometric devices secondary to the variability of different manufacturing specifications. The lesson learned was with respect to the sample size calculation. Such calculations are based on assumptions and guided by evidence wherever possible. For this study the estimate of 10 mmHg SD was accurate and provided the correct sample size to estimate the power to detect whether the mean was significantly different from zero. However, it may have been better to do a sample size calculation to ensure a prescribed width for the limits of agreement rather than basing the sample size calculation on testing a mean. 5. Conclusion Taken in isolation, the findings of this study do not support the routine replacement of the upper arm blood pressure by the forearm blood pressure. The clear clinical implication is that the upper arm should continue to be used as the standard site for blood pressure measurements. However, recent literature still suggests that using the forearm can be a clinical solution to measuring a blood pressure when the upper arm is unavailable. If using a forearm blood pressure, it is recommended the same site is used consistently, measured at the level of the right atrium and documented clearly. Clinicians should also be aware the potential variance is up to 19 mmHg for systolic pressure when compared to the upper arm, but may be less variable in patients with a systolic blood pressure between 100 and 140 mmHg. Conflict of interest: None declared. Funding: Educational grant from the New Zealand Nursing Organisation Nursing Education and Research Trust.
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Ethical approval: Northern Regional Health and Disability Ethics Committee (NTY/11/01/003).
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Schell, K.A., Richards, J.G., Farquhar, W.B., 2007. The effects of anatomical structures on adult forearm and upper arm non-invasive blood pressures. Blood Press. Monit. 12 (1), 17–22. Singer, A.J., Kahn, S.R., Thode Jr., H.C., Hollander, J.E., 1999. Comparison of forearm and upper arm blood pressures. Prehosp. Emerg. Care 3 (2), 123–126. Tachovsky, B.J., 1985. Indirect auscultatory blood pressure measurement at two sites in the arm. Res. Nurs. Health 8 (2), 125–129.
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Contents lists available at ScienceDirect
International Journal of Nursing Studies journal homepage: www.elsevier.com/ijns
Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients Karen Schimanski a,*, Andrew Jull b, Nancy Mitchell c, Jessica McLay d a
Emergency Department, Auckland City Hospital, Private Bag 92024, Auckland, New Zealand School of Nursing, University of Auckland, New Zealand c Emergency Department, Auckland City Hospital, New Zealand d Department of Statistics, University of Auckland, New Zealand b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 July 2013 Received in revised form 21 March 2014 Accepted 27 March 2014
Background: Forearm blood pressures have been suggested as an alternative site to measure blood pressures when the upper arm is unavailable. However there is little evidence utilising clinical populations to support this substitution. Objectives: To determine agreement between blood pressures measured in the left upper arm and forearm using a singular oscillometric non-invasive device in adult Emergency Department patients. The secondary objective was to explore the relationship of blood pressure differences with age, sex, ethnicity, smoking history and obesity. Design: Single centre comparison study. Setting: Adult Emergency Department, Tertiary Trauma Centre. Participants: Forty-four participants who met inclusion/exclusion criteria selected sequentially from the Emergency Department arrival board. Methods: A random assignment of order of measurement for left upper arm and forearm blood pressures was utilised. Participants were eligible if they were aged 18 years or older, had been assigned an Australasian Triage Scale code of 2, 3, 4, or 5, were able to consent, and able to have blood pressures measured on their left arm whilst lying at a 458 angle. The Bland–Altman method of statistical analysis was used, with the level of agreement for clinical acceptability for the systolic, diastolic and mean arterial pressure defined as 10 mmHg. Results: The forearm measure overestimated systolic (mean difference 2.2 mmHg, 95% limits of agreement 19 mmHg), diastolic (mean difference 3.4 mmHg, 95% limits of agreement 14.4 mmHg), and mean arterial pressures (mean difference 4.1 mmHg, 95% limits of agreement 13.7 mmHg). The systolic measure was not significantly different from zero. Evidence of better agreement was found with upper arm/forearm systolic measures below 140 mmHg compared to systolic measures above 140 mmHg using the Levene’s test (p = 0.002, F-statistic = 11.09). Blood pressure disparity was not associated with participant characteristics. Conclusions: Forearm measures cannot routinely replace upper arm measures for blood pressure measurement. If the clinical picture requires use of forearm blood pressure, the potential variance from an upper arm measure is 19 mmHg for systolic pressure, although the variability may be close to 10 mmHg if the systolic blood pressure is below 140 mmHg. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Blood pressure determination Blood pressure accuracy Upper arm blood pressure Forearm blood pressure Emergency nursing
* Corresponding author. E-mail addresses: [email protected], [email protected], [email protected] (K. Schimanski). http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008 0020-7489/ß 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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What is already known about the topic? The gold standard for a non-invasive blood pressure measurement is auscultation of the upper arm at heart level. Previous studies recommend substituting forearm blood pressure measures for upper arm measures when clinically necessary. Agreement between the two measures has not been established. Previous studies have not always used appropriate analytical methods or used clinical populations that can be generalised to the acute adult patient in Emergency Department. What this paper adds Forearm measures cannot be routinely substituted for upper arm measures of blood pressure in Emergency Department patients due to clinical unacceptable variability. This is the first study to report evidence of better agreement between upper arm and forearm systolic measures below 140 mmHg. 1. Introduction Blood pressure measurements provide essential baseline cardiovascular information and reflect a patient’s response to medications, intravenous fluids, and other acute treatments. In an Emergency Department, treatment decisions are contingent upon the clinical scenario, systolic blood pressure trends and other related information. Accuracy and speed in obtaining a blood pressure can be imperative, but obtaining blood pressure measurements presents a challenge when the upper arm is inaccessible due to injury, disease process or when the upper arm is too large for the standard range of blood pressure cuffs. Guidelines have suggested the forearm be used when the upper arm is unavailable. These guidelines also identify the need for studies to validate this practice (O’Brien et al., 2003; Pickering et al., 2005). The evidence supporting the practice of using the forearm alternate is somewhat equivocal. Most studies suggest that there are statistically significant differences between upper and forearm blood pressure measurements and that the measures cannot be used interchangeably (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010; Singer et al., 1999; Tachovsky, 1985). However, measurement of blood pressure and analysis of results have varied across studies. Earlier studies used auscultatory sphygmomanometer (Palatini et al., 2004; Tachovsky, 1985), utilised non-invasive wrist devices (Emerick, 2002; Palatini et al., 2004), measured with different devices between sites (Palatini et al., 2004), did not state validation of their device (Fortune et al., 2008) or did not measure inter-rater reliability when more than one researcher was utilised (Domiano et al., 2008; Palatini et al., 2004). Others did not measure the site circumference
and used variable or unspecified cuff size and or site positions. (Domiano et al., 2008; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Tachovsky, 1985). Some studies used different anatomical patient positions ranging in degrees between lying to sitting (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010; Singer et al., 1999; Tachovsky, 1985). A number of studies also did not use the Bland–Altman method (Domiano et al., 2008; Fortune et al., 2008; Pierin et al., 2004; Singer et al., 1999; Tachovsky, 1985), the accepted statistical analysis for determining agreement between two measures (Preiss and Fisher, 2008). The majority of studies used healthy volunteers with a high proportion of non-obese white American females being recruited rather than clinical populations so may not be generalisable to unwell Emergency Department patients with multi-ethnic backgrounds (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Schell and Waterhouse, 2007; Schell et al., 2007; Tachovsky, 1985). In addition, the majority of quality studies conducted on blood pressure measurement comparison between the upper arm and forearm have been completed by the same lead investigator K.A. Schell (Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010). The objective of this study was to assess agreement between the systolic blood pressures as measured on the left upper arm and forearm using the same non-invasive blood pressure oscillometric device designed for upper arm measures in a clinical adult population presenting to an Emergency Department. This study used a computer generated random sequence with a block sequence size of two blinded to the investigator, a single validated electronic oscillometric non-invasive blood pressure device, appropriate cuff sizes based on forearm and upper arm measurements, accurate measured placement for position of cuff and adhered to guidelines for blood pressure measurement by Pickering et al. (2005). The Bland–Altman-method was used for statistical analysis (Bland and Altman, 1986). This study also sampled a more varied clinical Emergency Department population than previously researched. 2. Methods The Adult Emergency Department Blood Pressure (AEDBP) study was a single centre, prospective comparison study. The aim of this study was to determine the agreement between a single left upper arm and forearm blood pressure obtained in Adult Emergency Department (AED) presentations using the same oscillometric noninvasive electronic device dedicated to obtaining standard upper arm measures to reflect current clinical practice at the study site. Singular blood pressure measures were undertaken and a randomised cross-over order of measurement was used to mitigate normal physiological variation for singular blood pressure measures. The level of agreement for clinical acceptability for this study was defined as 10 mmHg by the Adult Emergency Research Group (AERG). The variability of 10 mmHg was considered as unlikely to change acute clinical management in adult
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Emergency Department patients. The Bland–Altman method of statistical analysis was used to determine variability. Secondary objectives were to explore the relationship of blood pressure differences with the participant characteristics of age, sex, ethnicity, smoking history and obesity using hypothesis testing, linear regression and a multivariate analysis. Ethical approval was obtained from Northern Regional Health and Disability Ethics Committee (NTY/11/ 01/003) and the study was registered with the Australian New Zealand Clinical Trials Registry (ANZCTRN 12610000977077). 2.1. Recruitment Recruitment of adults began in May 2011 and was completed in June 2011 from patients presenting to an Emergency Department (ED) at a major urban hospital and trauma centre. Potential eligible participants were obtained from the ED patient list each weekday and were selected consecutively by time of presentation (i.e. those that arrived in ED first were approached first). Patients were eligible for inclusion if they were adults aged 18 years or older, had been assigned an Australasian Triage Scale (ATS) code of 2, 3, 4, or 5, were able to consent, and were able to have blood pressures taken on their left arm whilst lying at a 458 angle. The ATS codes patients on a scale of one to five, with patients categorised as requiring resuscitation (ATS 1), emergency (ATS 2), urgent (ATS 3), semi-urgent (ATS 4) and non-urgent (ATS 5) (Australasian College of Emergency Medicine, 2013). Patients requiring immediate resuscitative care with an ATS code of 1 were excluded with all other ATS categories included in the study. 2.2. Sample size calculation An estimate of the standard deviation (SD) of the paired differences and the desired mean difference to detect were both needed to be specified to calculate the sample size. To do this a feasibility study was conducted by the primary author in October 2010 prior to the commencement of the NIBP study where ten paired left upper arm and forearm blood pressure measurements were obtained from healthy volunteers. The SD of the paired differences in the feasibility study was 9.41 mmHg. This value was compared with the reported SD of paired differences in three published studies (Schell et al., 2005, 2006, 2010) and it was found that the SD was also around 10 mmHg for all three (see Table 1). Hence a SD of 10 mmHg of the paired differences was used for the sample size calculation. Table 1 Standard deviations of the paired differences in systolic blood pressures measured on bicep and forearm found in three published studies and our pilot data on 10 volunteers. Study Schell 2005 Schell 2006 Schell 2007 Our pilot data
Mean difference UA FA (mmHg) 1.3 8.3 1.2 1.9
Standard deviation of the paired differences (mmHg) 9.39 10.15 10.26 9.41
UA = upper arm, FA = forearm, mmHg = millimetres of mercury.
3
After considering the mean of the paired differences in the feasibility study and the three published studies used for the SD (also shown in Table 1), it was decided that powering the study to detect a mean paired difference of 5 mmHg would be clinically meaningful. The sample size was calculated using a standard formula (using normal distribution theory) for testing a single mean (Chow et al., 2008). A sample size of 44 patients was determined to have 90% power to detect a difference in systolic blood pressures measured at the bicep and at the forearm (paired differences) of 5 mmHg. This assumed a type 1 error rate (a) of 0.05, a standard deviation of the paired differences of 10 mmHg and that a paired t-test was to be performed to test for a difference. 2.3. Randomisation The order of blood pressure measurement on the left arm was determined by a computer generated random sequence with a block size of two (Altman and Bland, 1999). The allocation sequence was protected using sealed, sequentially numbered opaque envelopes with matching numbered slips (folded over three times) assigning the sequence of measurement. Blinding of participants and the primary investigator was not feasible once allocation was revealed. 2.4. Measurement A Carescape V100 non-invasive blood pressure device with a current certificate of calibration was used. The accuracy of this device complied with the standard of 5 mmHg (standard deviation of 8 mmHg) recommended by the Association for the Advancement of Medical Instrumentation (AAMI) standards (AAMI, 2013). Arm circumference measurements were taken at both the left upper arm and left forearm of the patient using a standard measuring tape. The upper arm was measured mid-way between the acromion and olecranon. The forearm was measured mid-way between the olecranon and styloid process. Selection of the correct blood pressure cuff was based on the arm measurements recommended by the manufacturer (G.E. Healthcare, 2011). The base of the blood pressure cuffs were positioned 2.5 cm above the ante-cubital fossa for the upper arm measure and 2.5 cm above the styloid process for the forearm measure. The cuff cursor was placed at the level of the radial artery for upper arm measures and at the level of the ulnar artery for forearm measures. No clothing was allowed underneath the cuff. All participants had their measures taken by a single trained researcher whilst lying on a stretcher with the head of bed elevated at a 458 angle (as measured with a goniometer). The standard left upper arm blood pressure measurement was taken with the participant on a stretcher with their arm lying beside them. The forearm blood pressure was taken by lifting the participants left arm to the level of the right atrium and supporting it on an adjustable hospital bedside table as per recommended guidelines (O’Brien et al., 2003; Pickering et al., 2005). Utilising a stopwatch, the second measure was commenced one minute after change of arm position and completed within three minutes.
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Height was measured using a stadiometer or tape measure when the participant was unable to stand. Weight was obtained on the AED weigh scales and body mass index was categorised according to current guidelines, irrespective of ethnicity (Jull et al., 2011). Data on triage code, mode of arrival, discharge destination and discharge code were collected from clinical notes. Participants provided information on self-identified ethnicity and smoking status. 2.5. Data analysis Excel 2010 (version 14) was used to collate study data with 40% of the data entry being checked for accuracy by a co-investigator (NM). Data was analysed using R (version 2.14.1). The Bland–Altman method was used to determine agreement between the forearm and upper arm measures (Bland and Altman, 1986, 1999). Assessment of agreement was contingent on the normal distribution of the data and normality of data was investigated by the Shapiro–Wilk test method and Q–Q plots. Student’s t-test investigated whether the mean differences could be null, with the threshold for significance set at 5%. The Levene test examined group variances within the data. Linear regression was used to assess the relationship between the mean pressure and the difference in the pressure for systolic, diastolic and mean arterial pressure. To ascertain the relationship of blood pressure disparities with participant characteristics a multivariable analysis was conducted.
3. Results Forty-seven participants met inclusion criteria (Fig. 1). Forty-six provided written consent and were randomised. Two participants were unable to complete both blood pressure measures due to the unavailability of a correctly sized cuff and therefore were excluded after randomisation. Participant ages ranged from 18 to 96 years and nearly half of the participants were New Zealand European (Table 2). Triage acuity ranged from emergency, urgent to semi-urgent with just over half requiring admission to either the Short Stay Unit or hospital ward for ongoing medical care (Table 3). Presenting conditions included chest pain, non-ST elevation myocardial infarction, asthma, renal colic, allergic reaction, dizziness, diabetic ketoacidosis and various minor traumas varying from rib fractures and pneumothorax to lower limb fractures and sprains. Discharge categories are presented in Table 4. Systolic blood pressure measures ranged from 99 to 186 mmHg at the upper arm and 100 to 186 mmHg at the forearm. Diastolic blood pressures ranged from 53 to 104 mmHg at the upper arm and 56 to 102 mmHg at the forearm. Mean blood pressures ranged from 71 to 138 mmHg at the upper arm and 74 to 158 mmHg at the forearm. Normality was acceptable for the systolic, diastolic blood pressure and mean arterial pressure measures as determined by the Shapiro–Wilk test (p = 0.93, 0.54, 0.19, respectively) and the Q–Q plots (not shown). The forearm
Fig. 1. Flow diagram.
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Characteristic
N (%)
53.0 (21.1) Age Sex (female) Ethnicity NZ European Maori Pasifika Asian Other Systolic blood pressure (mmHg) Upper arm 131 (21.9) 133 (23.5) Forearm Mean arterial pressure (mmHg) Upper arm 94 (13.8) Forearm 98 (16.3) Diastolic blood pressure (mmHg) Upper arm 72 (10.9) Forearm 75 (10.4)
(47.7) (15.9) (18.2) (9) (9)
mmHg = millimetres of mercury, N = number, SD = standard deviation; means and standard deviations have been rounded to one decimal place.
Table 3 Participant clinical characteristics. Mean (SD)
Characteristic 2
BMI (kg/m ) <20 20–25 25–30 >30 Mode of arrival Ambulance Triage code ATS 2 ATS 3 ATS 4 Smoking status Current Never Ex-smoker ED discharge destination Home Hospital
N (%)
27.5 (5.9) 2 16 12 14
(4.5) (29.5) (27.3) (31.8)
20 (46%) 7 (15.9) 25 (56.8) 12 (27.3) 13 (29.5) 19 (43.2) 12 (27.3) 20 (45.5) 24 (54.5)
kg/m2 = kilogram per square metre, N = number, SD = standard deviation; means and SD have been rounded to one decimal place.
systolic measure overestimated the upper arm systolic blood pressure by an average of 2.2 mmHg (95% CI 0.7 to 5.2 mmHg, Fig. 2). The difference was not statistically significant from zero (p = 0.14). The 95% limits of agreement for systolic blood pressure were calculated at Table 4 ED discharge categories. Discharge category
N
Musculoskeletal Neurological Gastrointestinal Ear/nose/throat Cardiovascular Respiratory Renal Miscellaneous
20 4 4 4 3 3 3 3
N = number.
Table 5 Univariable regression results from regressions of the difference in upper arm and forearm measurements and the mean of the upper arm and forearm measurements. Slope estimate Standard t-Value p-Value error
22 (50.0) 21 16 8 4 4
5
Diastolic Mean arterial pressure Systolic
0.058 0.174 0.070
0.112 0.068 0.067
0.51 2.55 1.05
0.61 0.0144 0.30
21.2 mmHg and 16.8 mmHg (range 19 mmHg). The Levene’s test found that the variances in the participants with systolic blood pressure less than 140 and above 140 mmHg were significantly different (p = 0.002, F-statistic = 11.09). Linear regression showed no significant relationship between mean systolic pressure and the difference in systolic pressure (Table 5). This indicates that the limits of agreement may be able to be applied across the board to patients regardless of their underlying systolic blood pressure. Forearm diastolic measures overestimated the upper arm diastolic measure by an average of 3.4 mmHg (95% C.I. 1.2–5.7 – Fig. 3) and this difference was statistically different from zero (p = 0.0034, t = 3.10, df = 43). The 95% limits of agreement were 17.8 mmHg and 11 mmHg (range of 14.4 mmHg). No significant relationship between the mean diastolic pressures the difference in the diastolic measures was detected (Table 5). The forearm mean arterial pressure overestimated the upper arm mean arterial pressure by an average of 4.1 mmHg (95% C.I. 2.0 to 6.2 – Fig. 4) and the difference was significantly different from zero (p = 0.0003, t = 3.91, df = 43). Limits of agreement were 17.8 mmHg and 9.6 mmHg (range of 13.7 mmHg). A significant negative relationship was found between the difference in mean arterial pressures and the mean pressure (Table 5). Hypothesis testing and a multivariable analysis showed the mean differences of the non-invasive blood pressure measures were not explained by patient characteristics. Systolic, diastolic and mean arterial pressure results for secondary outcomes of age, sex, ethnicity, smoking history and BMI are shown in Tables 6–8. No statistically significant differences were found. 4. Discussion Forearm measures all overestimated the upper arm measures with greatest variability in systolic blood pressures. The limits of agreement exceeded the 10 mmHg difference that was set as clinically significant a priori. Interestingly, there was evidence of better agreement below 140 mmHg for systolic blood pressures. This study is the first to report this pattern of variance. It was not within the remit of the study to explore this new finding. However, it suggests direction for future investigators. Linear regression was utilised to detect a relationship within the results. No significant relationship between mean systolic or diastolic pressure and the difference in systolic or diastolic pressure was found indicating the
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20 10
Upper LOA 21.2
-10
0
Mean 2.2
Lower LOA -16.8
-20
Difference in systolic pressures (forearm - upper arm)
Systolic BP
100
120
140
160
180
200
Mean of systolic pressures in the upper arm and forearm Fig. 2. Bland–Altman plot for systolic blood pressure (mmHg) as measured using an automated oscillometric non-invasive blood pressure machine (Carescape V100).
Table 6 Multivariable model for systolic blood pressure. Estimate Intercept Sex: Male (reference = Female) Age BMI Ethnicity: New Zealand European (reference = Maori/Pacific) Ethnicity: Other Smoking: Ex-smoker (reference = Current smoker) Smoking: Never smoked
Standard error
t-Value
p-Value
1.04 0.37
9.02 3.24
0.12 0.11
0.909 0.911
0.01 0.02 3.02
0.09 0.29 3.82
0.12 0.06 0.79
0.905 0.952 0.434
4.44 0.59
4.78 4.70
0.93 0.13
0.359 0.901
1.76
4.12
0.43
0.671
Table 7 Multivariable model for diastolic blood pressure. Estimate Intercept Sex: Male (reference = Female) Age BMI Ethnicity: New Zealand European (reference = Maori/Pacific) Ethnicity: Other Smoking: Ex-smoker (reference = Current smoker) Smoking: Never smoked
Standard error
t-Value
p-Value
4.63 0.73
7.02 2.52
0.66 0.29
0.513 0.772
0.01 0.04 2.53
0.07 0.23 2.97
0.10 0.16 0.85
0.919 0.877 0.399
2.13 0.79
3.72 3.66
0.57 0.22
0.569 0.830
1.99
3.20
0.62
0.539
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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7
20 10
Upper LOA 17.8
-10
0
Mean 3.4
Lower LOA -11.0
-20
Difference in diastolic pressures (forearm - upper arm)
Diastolic BP
60
70
80
90
100
Mean of diastolic pressures in the upper arm and forearm Fig. 3. Bland–Altman plot for diastolic blood pressure (mmHg) as measured using an automated oscillometric non-invasive blood pressure machine (Carescape V100).
Table 8 Multivariable model for mean arterial pressure. Estimate Intercept Sex: Male (reference = Female) Age BMI Ethnicity: New Zealand European (reference = Maori/Pacific) Ethnicity: Other Smoking: Ex-smoker (reference = Current smoker) Smoking: Never smoked
Standard error
t-Value
p-Value
0.09 2.28
6.00 2.15
0.02 1.06
0.988 0.298
0.02 0.12 2.87
0.06 0.20 2.54
0.26 0.59 1.13
0.795 0.577 0.265
2.58 3.43
3.17 3.12
0.81 1.10
0.422 0.279
2.13
2.74
0.78
0.442
limits of agreement may be able to be applied across the board to patients regardless of their underlying systolic or diastolic blood pressure. However, a significant negative relationship was found between the difference in mean arterial pressures and the mean pressure. This suggests that, on average, the difference between the pressure measurements in the upper arm and the forearm is closer to zero for people with lower underlying mean arterial pressures than for people with greater underlying mean arterial pressures. This result affects the way in which the limits of agreement can be interpreted, indicating that it may not be appropriate to apply the limits of agreement across the board and that future work on calculating
separate limits of agreement for people with low and high blood pressures could be undertaken. Interest in the utility of the forearm as a blood pressure site in place of the upper arm has increased over the last 10 years. The numbers of citations have increased from two for the period prior to 2000 (Singer et al., 1999; Tachovsky, 1985) to ten in the years since (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2010; Schell et al., 2007). Only two previous studies have used Emergency Department patients and both used participants less heterogeneous than would be expected in clinical practice (Schell et al.,
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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20 10
Upper LOA 17.8
-10
0
Mean 4.1
Lower LOA -9.6
-20
Difference in mean arterial pressures (forearm - upper arm)
Mean Arterial Pressure
80
100
120
140
Mean of mean arterial pressures in the upper arm and forearm Fig. 4. Bland–Altman plot for mean arterial pressures (mmHg) as measured using an automated oscillometric non-invasive blood pressure machine (Carescape V100).
2005; Singer et al., 1999). More acute patients were excluded as the study samples were restricted to stable ambulatory patients not arriving via ambulance (Schell et al., 2005; Singer et al., 1999). Further, the mean age of the study samples was around 36 years with some including paediatric populations, suggesting that older patients were under-represented (Domiano et al., 2008; Emerick, 2002; Fortune et al., 2008; Palatini et al., 2004; Pierin et al., 2004; Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010; Singer et al., 1999; Tachovsky, 1985). The older adult population comprises a significant component of local Emergency Department attendances at our AED, accounting for approximately 44% of annual presentations in 2010 (Reeves, 2010). In contrast, this study set out to use a clinical sample of independently triaged patients, which included all patients arriving by ambulance except those that required resuscitation. Literature supports the Bland–Altman technique as the accepted statistical analysis for determining agreement between two measures (Preiss and Fisher, 2008). The Bland–Altman method compares the actual agreement between two measures, even when the ‘‘true’’ value of the measure is unknown and enables clinicians to determine whether the two measurement techniques can be used interchangeably or the new method can substitute the old method (Altman and Bland, 1983; Bland and Altman, 1986, 1999). It is important in a study investigating agreement between measures to specify a clinically acceptable limit of
variability so results can be interpreted with transparency (Hanneman, 2008). Whilst current literature provides little guidance in defining a clinically acceptable level of difference between blood pressure measurement sites, it has been acknowledged that attempts to determine a level of agreement should be made (Mantha et al., 2000). Only one investigating team stated an a priori level of agreement, for their analysis, but provided no clinical rationale for their level of 5 mmHg (Schell and Waterhouse, 2007; Schell et al., 2005, 2006, 2007, 2010). Two other authors have used the limits set by the AAMI for device validation (<5 mmHg 8 SD) but have not identified the rationale for selecting this cut off point (Emerick, 2002; Palatini et al., 2004). This study was the first to use a level of agreement (10 mmHg) endorsed by Emergency clinicians as clinically acceptable. This study found site variability of 19 mmHg exceeding the 10 mmHg set a priori. However in the context of the Emergency Department alternative site blood pressure measures may still provide useful information. Blood pressure measures are not used in isolation, but interpreted as part of the entire clinical picture of the patient. Inaccuracies in measurements may be mitigated by other pertinent diagnostics including level of consciousness, other vital signs and their subsequent trends. With consideration of these other patient variables, if the forearm site was used consistently to obtain blood pressure trends, patient management may remain similar to that if the upper arm site was
Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008
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used consistently. Therefore 19 mmHg for sufficient agreement could be acceptable for working purposes. Further exploration to quantify the definition of a clinically acceptable level of agreement within the acute context would be beneficial. This study was subject to four main limitations and one lesson learned. First, the sampling method used for this study was reliant on participants meeting the inclusion criteria during the hours the primary investigator was working (week days/evenings) and it is possible that different types of patients might present after hours. However, the range of Australasian Triage codes suggests the participants broadly reflected those that present to the Emergency Department. Secondly, the sub-group analysis of participant characteristics in this study lacked external validity. Larger studies specifically powered to analyse each sub-category would be helpful to address these areas so more conclusive associations between blood pressure disparity and participant characteristics can be made. Thirdly, only a small number of patients with blood pressures above 160 mmHg were recruited to this study as patients were recruited by inclusion criteria not by blood pressure category. Therefore, findings may not be generalisable to hypertensive patients. Fourth, it is important to note the results of the present study may not be immediately generalisable to wrist devices or to other upper-arm oscillometric devices secondary to the variability of different manufacturing specifications. The lesson learned was with respect to the sample size calculation. Such calculations are based on assumptions and guided by evidence wherever possible. For this study the estimate of 10 mmHg SD was accurate and provided the correct sample size to estimate the power to detect whether the mean was significantly different from zero. However, it may have been better to do a sample size calculation to ensure a prescribed width for the limits of agreement rather than basing the sample size calculation on testing a mean. 5. Conclusion Taken in isolation, the findings of this study do not support the routine replacement of the upper arm blood pressure by the forearm blood pressure. The clear clinical implication is that the upper arm should continue to be used as the standard site for blood pressure measurements. However, recent literature still suggests that using the forearm can be a clinical solution to measuring a blood pressure when the upper arm is unavailable. If using a forearm blood pressure, it is recommended the same site is used consistently, measured at the level of the right atrium and documented clearly. Clinicians should also be aware the potential variance is up to 19 mmHg for systolic pressure when compared to the upper arm, but may be less variable in patients with a systolic blood pressure between 100 and 140 mmHg. Conflict of interest: None declared. Funding: Educational grant from the New Zealand Nursing Organisation Nursing Education and Research Trust.
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Ethical approval: Northern Regional Health and Disability Ethics Committee (NTY/11/01/003).
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Please cite this article in press as: Schimanski, K., et al., Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients. Int. J. Nurs. Stud. (2014), http://dx.doi.org/10.1016/j.ijnurstu.2014.03.008