Abstract
It is recommended that the cuff should be wrapped around the upper arm with the midline of the bladder placed over the brachial artery during blood pressure (BP) measurement. However, in practice, the cuff of sphygmomanometers is often incorrectly placed. The authors aimed to assess the effect on the accuracy of BP measurement as to the placement of the cuff bladder by using oscillometric devices. Participants aged 18 years or older were enrolled. The center of the cuff bladder was placed directly over the brachial artery as the standard position (correct position), which was rotated by 90°medially (medial position), 90°laterally (lateral position), and rotated by 180°(contralateral position), respectively. The main outcomes were non‐invasive brachial BP in the four cuff positions, brachial artery pulse wave velocity, ankle‐brachial index, and invasive radial BP. Of 799 participants, 56.4% were men (60.37 ± 12.73 years), and of the 104 intensive care unit participants, 60.57% were men (57.78 ± 15.89 years). There were no significant differences in non‐invasive brachial BP among the four cuff positions (P > .1), and the mean BP differences between incorrect and standard cuff positions were within 1.0 mm Hg. BP of the incorrect positions was positively correlated with standard position (P < .001, r > .88) and showed good consistency. There was no effect on the accuracy of BP measurement as to the location of the midline of the cuff bladder by using oscillometric devices with a conventional cuff.
Keywords: blood pressure measurement, invasive, non‐invasive, oscillometric devices, position
1. INTRODUCTION
Hypertension is one of the important risk factors for cardiovascular diseases. 1 , 2 It is well‐known that effective blood pressure (BP) management is important to reduce hypertension‐related cardiovascular disease and death. 3 Consequently, as the basis of hypertension management, the accurate BP measurement plays a vital role. 4 , 5 , 6 , 7
The guidelines recommend standardized BP measurements, which are described in detail of the process of BP measurements, mainly including properly preparing the patient, using proper technique for BP measurements and taking the proper measurements. 5 , 7 , 8 Notwithstanding the protocol is concrete and detailed, the application of which in clinical practice is unsatisfactory. 9 , 10 , 11 In general, the placement of cuff and stethoscope is the critical point of the BP measurement technique. The traditional method using mercury sphygmomanometer involves auscultation of the brachial artery with a stethoscope to detect the change of the Korotkoff sounds, which is used to estimate systolic blood pressure (SBP) and diastolic blood pressure (DBP). 12 Moreover, standardized measurements of BP are based on auscultation method and highly dependent on pressure changes of the cuff bladder to the brachial artery so that the placement of the cuff and stethoscope is critical. 5 , 6 , 7 , 8 , 13
It is recommended that the observer must palpate the brachial artery in the antecubital fossa, wrap the cuff over the bare upper arm, and place the center of the cuff bladder over the brachial artery. 5 , 8 , 14 However, oscillometry uses a pressure sensor to record the pressure oscillations within the cuff, instead of listening to Korotkoff sounds with a stethoscope. Then, the extracted oscillometric pulses form the oscillometric waveform envelope and the algorithms are based on analyzing the oscillometric waveform envelope to estimate SBP and DBP. 15 In view of no transducer needs to be placed over the brachial artery, the location of the cuff bladder might not be critical. Additionally, oscillometric devices avoid mercury contamination and reading errors have been widely used in ambulatory, home, and hospital. 8 , 16 , 17 Consequently, whether the oscillometric devices need to fully follow standardized measurements is worth reconsidering.
In this study, we aimed to evaluate the error introduced by incorrect cuff positioning in BP measurement by using oscillometric devices with a conventional cuff. What's interesting that we have not found a formal study on this issue, but it was clearly specified in the guidelines and manufacturers' instructions that the center of the cuff bladder should be placed positively over the brachial artery. 5 , 8 , 14
2. PARTICIPANTS AND METHODS
2.1. Participants
Participants who underwent non‐invasive brachial BP measurement were patients who were admitted to the Department of Cardiology, Second Hospital of Hebei Medical University from May 2018 to June 2019. Participants who underwent non‐invasive brachial BP and radial intra‐arterial BP measurement were patients who were admitted to the intensive care unit (ICU) from May 2018 to July 2018. We included patients who were 18 years or older, and their upper arm circumference ranged from 22 to 34 cm. We excluded patients with atrial fibrillation and bradyarrhythmia, and who was not able to provide informed consent. Before BP measurement, we recorded factors, such as age, sex, smoking, height, weight, and the history of hypertension in the participants. This study follows the principles of the Declaration of Helsinki and was approved by the Ethics Committee of the Second Hospital of Hebei Medical University.
2.2. Blood pressure measurement
Before BP measurements, the participants were in the supine position and rested for 5 minutes, and the cuffed arm was supported with a pillow. 8 The BP measurements followed the recommendations of the Scientific Statements from the American Heart Association, 7 , 8 except for the placement of cuff bladder in relation to the brachial artery.
The center of the bladder length of the cuff was placed directly over the brachial artery as the standard position (correct position), which was rotated by 90°medially (medial position), 90°laterally (lateral position), and rotated by 180°(contralateral position), respectively. The four positions were numbered, and the order of measurements was randomly determined by a lottery. Two validated oscillometric devices (Omron upper arm type HEM‐8102A and Omron upper arm type HEM‐7112, OMRON HEALTH CARE, Kyoto, Japan) were used to measure non‐invasive brachial BP. They were both equipped with the same size adult cuffs, which were both suitable for the upper arm circumferences ranged from 22 to 34 cm. One oscillometric device (HEM‐8102A) was used in the participants recruited from ICU, and the other device (HEM‐7112) was used in the participants recruited from the Department of Cardiology. The two oscillometric devices have the same accuracy and were calibrated with the same mercury sphygmomanometer at the same time, which can ensure consistent measurement readings. Two trained examiners took BP measurements three times at each position, with a 1‐minute interval between each measurement. The average value of the second and third measurements was recorded as the BP value of the particular position.
The radial artery was punctured with a disposable needle, and a pressure transducer‐sensing device was placed in the radial artery. The outer end of the pressure transducer‐sensing device was connected with a pressure sensor. Intra‐arterial pressure was transmitted to the pressure sensor through pressure transmission, thereby obtaining a dynamic waveform of pressure changes and invasive BP monitoring values were recorded. Meanwhile, the non‐invasive brachial BP measurements were taken in the same arm at the four previously described cuff positions. The average value of the second and third measurements was recorded as the non‐invasive BP value of the particular position. The radial intra‐arterial BP was recorded before and after each non‐invasive brachial BP measurement, and the average value of the six recorded values was used as the invasive BP value at the particular position.
An arteriosclerosis diagnostic device (Omron BP‐203RPEIII, OMRON HEALTH CARE, Kyoto, Japan) was used for measuring brachial artery pulse wave velocity (baPWV) and the ankle‐brachial index (ABI). The participants were placed in the supine position in a quiet state. The BP sensing cuff was wrapped over the patient's upper arm and the ankle joint. An electrocardiogram sensor clip was installed on the double forearm and a heart sound probe was placed on the fourth intercostal space on the left sternal border. Measurements were then started. The higher value of the two sides for baPWV and the lower value of the ABI were analyzed. Three trained examiners were involved in the process.
2.3. Statistical analysis
IBM SPSS statistical software (version 22; SPSS Inc) was used for most of the analyses. The mean and standard deviation (SD) of BP values at each cuff bladder position was calculated. Analysis of variance (ANOVA) was used to determine whether there were significant differences among the four previously described positions of non‐invasive BP. The differences in BP between incorrect and the standard cuff positions were expressed as mean and 95% confidence intervals (95% CI). The Kruskal‐Wallis H test was used to analyze the difference between non‐invasive and invasive BP values at the four positions. The difference in BP at each position was expressed as median and quartile range (QD). A value of P < .05 was regarded as statistically significant. The correlations between non‐invasive BP in incorrect positions and that in the standard positions were analyzed. Pearson correlation analysis was performed, and P < .05 was considered as a significant correlation coefficient. MedCalc statistical software (version 18.1.1) was used for scatter mapping. The consistency of BP between the incorrect and standard cuff positions was analyzed. Bland‐Altman mapping analysis was performed using MedCalc statistical software.
3. RESULTS
Of the 799 participants who were recruited from the Department of Cardiology, 451 (56.4%) were men. The mean age was 60.37 years (SD: 12.73), and 380 (47.6%) had hypertension. The mean (SD) height, weight, and BMI were 166.24 (7.84) cm, 69.44 (10.64) kg, and 25.10 (3.27) kg/m2, respectively. Of the 104 participants recruited from ICU who underwent radial artery catheterization to monitor radial intra‐arterial BP, 63 (60.6%) were men. The mean age was 57.78 years (SD: 15.89). Stable patients were defined as those had no active or passive activities, no postural changes, no obvious emotional changes, and no medication adjustment during BP measurements. Otherwise, patients were defined as unstable. There were 57 stable patients and 47 unstable patients. None were current smokers. There were no significant differences of non‐invasive brachial BP among the four cuff positions in the 799 participants (P > .1), and the mean BP differences between incorrect and standard positions were within 1.0 mm Hg. Corresponding difference values between the incorrect and the standard positions were 0.04, 0.51, and 0.26 mm Hg for SBP, while 0.04, 0.14, and 0.30 mm Hg for DBP, respectively. Neither difference was significant (Table 1). BP of the incorrect positions was positively correlated with that of the standard position (SBP: P < .001, r > .93; DBP: P < .001, r > .88) and showed good consistency (Figures 1, 2, 3).
TABLE 1.
Mean blood pressure for 799 participants among different cuff positions and mean differences between the incorrect cuff positions and the standard positions
| Cuff positions | BP, mean (SD) | Δ BP, mean (95% CI) | P |
|---|---|---|---|
| SBP | |||
| S | 130.80 (17.42) | ||
| M | 130.76 (17.75) | −0.04 (−1.77, 1.70) | .97 |
| L | 131.30 (18.03) | 0.51 (−1.23,2.24) | .57 |
| C | 130.54 (17.64) | −0.26 (−2.00, 1.48) | .77 |
| DBP | |||
| S | 74.98 (9.60) | ||
| M | 74.94 (9.73) | −0.04 (−1.01,0.92) | .93 |
| L | 74.84 (10.10) | −0.14 (−1.11, 0.82) | .77 |
| C | 74.68 (9.84) | 0.30 (−1.27, 0.66) | .54 |
Abbreviations: C, contralateral position; CI, confidence intervals; DBP, diastolic blood pressure, mean (SD), mm Hg; L, lateral position; M, medial position; S, standard position; SBP, systolic blood pressure, mean (SD), mm Hg; SD, standard deviation; ΔBP, mean blood pressure differences between the incorrect cuff positions and the standard position measurements.
FIGURE 1.
Bland‐Altman plots of the medial position—the standard position differences for (A) non‐invasive systolic blood pressure and (B) non‐invasive diastolic blood pressure. (n = 799). The x‐axis represents the mean of the medial position and the standard position measurements, and the y‐axis shows the discrepancy between the medial position and standard position measurements
FIGURE 2.
Bland‐Altman plots of the lateral position—the standard position differences for (A) non‐invasive systolic blood pressure and (B) non‐invasive diastolic blood pressure. (n = 799). The x‐axis represents the mean of the lateral position and the standard position measurements, and the y‐axis shows the discrepancy between the lateral position and standard position measurements
FIGURE 3.
Bland‐Altman plots of the contralateral position—the standard position differences for (A) non‐invasive systolic blood pressure and (B) non‐invasive diastolic blood pressure. (n = 799). The x‐axis represents the mean of the contralateral position and the standard position measurements, and the y‐axis shows the discrepancy between the contralateral position and standard position measurements
As shown in Table 2, based on age (<65, ≥65 years old), SBP (<120, 120‐139.5, 140‐159.5, and ≥160 mm Hg), pulse pressure (20‐39.5, 40‐59.5, 60‐79.5, and ≥80 mm Hg), baPWV (≤1400, >1400 cm/s), ABI (≤0.9, >0.9), and the history of hypertension for subgroup analysis, there were no significant differences in BP among the four locations (P > .1). BP of the incorrect positions was positively correlated with that of the standard position (P < .001, r > .78) and showed good consistency in each subgroup. There were also no significant differences of non‐invasive brachial BP among the four previously described cuff positions in ICU patients (P > .1), and the mean BP differences between incorrect and standard cuff positions were within 5.0 mm Hg. Corresponding difference values between the incorrect and the standard cuff positions were 0.24, 4.99, and 1.79 mm Hg for SBP, and 0.25, 1.82, and 0.75 mm Hg for DBP, respectively. Neither difference was significant. For all of the participants who were recruited from ICU, the mean difference values between non‐invasive brachial and radial intra‐arterial SBP were 5.83, 4.75, 0.50, and 4.17 mm Hg in the standard position, medial position, lateral position, and the contralateral position, respectively. The values for DBP were 6.92, 7.50, 9.00, and 8.08 mm Hg, respectively. The difference values of SBP in incorrect cuff positions were not higher than that of the standard position, while the difference values of DBP between the incorrect and the standard cuff position were within 2.1 mm Hg. For stable participants, the difference values of SBP in the incorrect cuff positions were not higher than that of the standard positions, while the difference values of DBP were within 1.0 mm Hg. Neither difference was significant (Table 3).
TABLE 2.
Mean blood pressure in four different cuff positions for each subgroup. (n = 799)
| Subgroups | S (mm Hg) | M (mm Hg) | L (mm Hg) | C (mm Hg) | P |
|---|---|---|---|---|---|
| SBP (mm Hg) | |||||
| <120 (n = 207) | |||||
| SBP | 110.61 ± 6.70 | 110.85 ± 7.43 | 111.89 ± 8.83 | 111.22 ± 8.43 | .38 |
| DBP | 67.50 ± 7.26 | 67.76 ± 7.23 | 67.52 ± 7.86 | 67.46 ± 7.65 | .98 |
| 120‐139.5 (n = 383) | |||||
| SBP | 129.31 ± 5.49 | 129.57 ± 6.93 | 129.86 ± 7.77 | 129.41 ± 7.19 | .71 |
| DBP | 75.21 ± 7.04 | 75.13 ± 7.40 | 75.13 ± 7.73 | 75.09 ± 7.61 | .99 |
| 140‐159.5 (n = 148) | |||||
| SBP | 147.21 ± 5.21 | 146.09 ± 7.91 | 146.54 ± 9.29 | 145.26 ± 9.67 | .22 |
| DBP | 79.89 ± 8.96 | 79.51 ± 9.47 | 79.11 ± 9.50 | 78.76 ± 9.49 | .75 |
| ≥160 (n = 61) | |||||
| SBP | 168.79 ± 8.43 | 168.57 ± 11.52 | 169.25 ± 10.46 | 167.42 ± 11.10 | .80 |
| DBP | 87.06 ± 11.44 | 87.01 ± 11.53 | 87.48 ± 12.30 | 86.71 ± 11.32 | .99 |
| Age (y) | |||||
| <65 (n = 326) | |||||
| SBP | 126.66 ± 15.71 | 126.67 ± 16.03 | 127.17 ± 16.68 | 126.40 ± 16.05 | .94 |
| DBP | 76.19 ± 10.21 | 76.24 ± 10.40 | 76.33 ± 10.85 | 76.10 ± 10.49 | .99 |
| ≥65 (n = 473) | |||||
| SBP | 133.64 ± 17.98 | 133.58 ± 18.34 | 134.15 ± 18.38 | 133.39 ± 18.13 | .93 |
| DBP | 74.15 ± 9.07 | 73.80 ± 9.36 | 73.81 ± 9.43 | 73.70 ± 9.25 | .87 |
| PP (mm Hg) | |||||
| 20‐39.5 (n = 72) | |||||
| SBP | 107.76 ± 8.61 | 108.09 ± 7.59 | 109.06 ± 9.87 | 108.90 ± 10.05 | .79 |
| DBP | 72.81 ± 8.08 | 71.79 ± 7.41 | 71.39 ± 9.36 | 72.03 ± 8.65 | .78 |
| 40‐59.5 (n = 461) | |||||
| SBP | 125.07 ± 10.89 | 125.38 ± 11.79 | 125.74 ± 11.91 | 125.07 ± 11.57 | .79 |
| DBP | 74.78 ± 9.13 | 74.66 ± 9.23 | 74.61 ± 9.34 | 74.39 ± 9.32 | .94 |
| 60‐79.5 (n = 216) | |||||
| SBP | 142.89 ± 11.92 | 142.41 ± 13.29 | 143.06 ± 13.71 | 142.00 ± 13.60 | .97 |
| DBP | 76.00 ± 10.60 | 76.43 ± 10.86 | 76.24 ± 11.29 | 75.95 ± 10.91 | .84 |
| ≥80 (n = 50) | |||||
| SBP | 164.47 ± 14.35 | 162.65 ± 17.48 | 163.85 ± 16.96 | 162.54 ± 16.08 | .92 |
| DBP | 75.63 ± 10.87 | 75.65 ± 10.90 | 75.89 ± 11.38 | 75.68 ± 10.54 | .99 |
| ABI | |||||
| ≤0.9 (n = 53) | |||||
| SBP | 129.68 ± 14.24 | 128.64 ± 13.76 | 128.38 ± 14.71 | 128.08 ± 13.63 | .94 |
| DBP | 73.23 ± 8.72 | 72.89 ± 8.38 | 72.26 ± 8.83 | 71.76 ± 8.26 | .82 |
| >0.9 (n = 499) | |||||
| SBP | 128.03 ± 13.96 | 127.87 ± 14.63 | 127.80 ± 14.62 | 127.41 ± 14.33 | .92 |
| DBP | 74.94 ± 8.33 | 74.82 ± 8.81 | 74.70 ± 9.13 | 74.58 ± 8.90 | .93 |
| baPWV (cm/s) | |||||
| ≤1400 (n = 192) | |||||
| SBP | 121.03 ± 11.89 | 120.83 ± 11.99 | 120.10 ± 12.29 | 120.12 ± 12.00 | .82 |
| DBP | 71.95 ± 7.22 | 71.69 ± 7.58 | 71.16 ± 7.94 | 71.31 ± 7.71 | .73 |
| >1400 (n = 360) | |||||
| SBP | 132.01 ± 13.53 | 131.74 ± 14.36 | 131.99 ± 14.09 | 131.42 ± 13.79 | .94 |
| DBP | 76.28 ± 8.57 | 76.20 ± 8.97 | 76.22 ± 9.23 | 75.94 ± 9.04 | .96 |
| Hypertension | |||||
| Yes (n = 380) | |||||
| SBP | 135.22 ± 17.87 | 135.12 ± 18.42 | 135.84 ± 18.75 | 134.49 ± 18.15 | .79 |
| DBP | 75.57 ± 9.70 | 75.72 ± 10.05 | 75.73 ± 10.33 | 75.33 ± 9.95 | .94 |
| No (n = 419) | |||||
| SBP | 126.78 ± 15.99 | 126.80 ± 16.16 | 127.19 ± 16.31 | 126.95 ± 16.37 | .98 |
| DBP | 74.45 ± 9.49 | 74.23 ± 9.38 | 74.02 ± 9.83 | 74.09 ± 9.71 | .92 |
Abbreviations: ABI, the ankle‐brachial index; baPWV, brachial artery pulse wave velocity; C, contralateral position; DBP, diastolic blood pressure, mean (SD), mm Hg; L, lateral position; M, medial position; PP, pulse pressure, mm Hg; S, standard position; SBP, systolic blood pressure, mean (SD), mm Hg.
TABLE 3.
Comparison of non‐invasive and invasive blood pressure measurements at four cuff positions
| Groups | Position | NSBP (mm Hg) | NDBP (mm Hg) | ISBP (mm Hg) | IDBP (mm Hg) | NID‐SBP (mm Hg) | NID‐DBP (mm Hg) |
|---|---|---|---|---|---|---|---|
| Stable patients (n = 57) | S | 119.34 ± 16.44 | 70.98 ± 11.72 | 125.76 ± 17.72 | 64.26 ± 11.26 | −4.83 (−9.50, 1.17) | 7.00 (2.33,10.75) |
| M | 120.51 ± 16.07 | 70.97 ± 11.45 | 126.27 ± 17.20 | 64.51 ± 11.14 | −4.67 (−10.17, −0.83) | 7.00 (2.58,10.33) | |
| L | 123.86 ± 18.38 | 72.24 ± 12.12 | 126.62 ± 17.96 | 64.45 ± 11.39 | −1.67 (−8.67, 4.17) | 7.83 (2.67,12.83) | |
| C | 121.22 ± 16.84 | 71.61 ± 11.59 | 126.38 ± 17.57 | 64.66 ± 11.74 | −4.17 (−9.25, 2.00) | 7.67 (3.92,11.08) | |
| Unstable patients (n = 47) | S | 119.67 ± 14.82 | 72.01 ± 9.63 | 128.82 ± 20.91 | 66.24 ± 12.28 | −9.00 (−14.83,5.73) | 6.67 (2.17,10.17) |
| M | 118.79 ± 16.99 | 71.48 ± 9.80 | 126.21 ± 20.74 | 64.84 ± 11.62 | −5.50 (−12.83,6.47) | 7.83 (3.00,11.33) | |
| L | 125.23 ± 15.73 | 74.51 ± 12.49 | 126.17 ± 18.63 | 64.67 ± 12.50 | 0.33 (−6.00, 6.33) | 10.33 (5.67,15.67) | |
| C | 121.36 ± 14.86 | 72.89 ± 10.64 | 125.53 ± 18.56 | 65.60 ± 12.03 | −4.17 (−9.83, 2.50) | 8.17 (4.33,12.33) | |
| Total (n = 104) | S | 119.49 ± 15.65 | 71.45 ± 10.79 | 127.14 ± 19.19 | 65.16 ± 11.71 | −5.83 (−13.79,0.75) | 6.92 (2.21,10.17) |
| M | 119.73 ± 16.43 | 71.20 ± 10.69 | 126.24 ± 18.79 | 64.66 ± 11.31 | −4.75 (−11.58,6.17) | 7.50 (3.00,10.79) | |
| L | 124.48 ± 17.16 | 73.26 ± 12.29 | 126.42 ± 18.18 | 64.55 ± 11.85 | −0.50 (−6.79, 5.29) | 9.00 (4.38,14.33) | |
| C | 121.28 ± 15.90 | 72.19 ± 11.14 | 126.00 ± 17.94 | 65.08 ± 12.29 | −4.17 (−9.54, 2.13) | 8.08 (4.00,11.50) |
Abbreviations: C, contralateral position; IDBP, invasive diastolic blood pressure; ISBP, invasive systolic blood pressure; L, lateral position; M, medial position; NDBP, non‐invasive diastolic blood pressure; NID‐DBP, differences of non‐invasive and invasive diastolic blood pressure; NID‐SBP, differences of non‐invasive and invasive systolic blood pressure; NSBP, non‐invasive systolic blood pressure; S, standard position.
With regard to intra‐arterial BP variability, fluctuation in mean SBP was 22.36 ± 15.82 mm Hg, the maximum value was 71 mm Hg, and the minimum value was 4 mm Hg. These values for DBP were 12.76 ± 8.82, 40, and 2 mm Hg, respectively. Fluctuation in mean SBP in stable patients was 12.32 ± 5.55 mm Hg, the maximum value was 26 mm Hg, and the minimum value was 4 mm Hg. These values for DBP were 8.37 ± 5.19, 34, and 2 mm Hg, respectively.
4. DISCUSSION
In this study, we assessed the BP measurement error introduced by incorrect bladder positioning when using oscillometric devices with a conventional cuff. We found that there were no significant differences in BP when the midline of the cuff bladder was placed in the medial position, the lateral position, and the contralateral position compared with the standard position. For the participants who were recruited from the Department of Cardiology, the mean BP differences between measurements made in the incorrect and standard cuff positions were within 1.0 mm Hg, while for the participants who were recruited from ICU, the values were within 5.0 mm Hg. It is worth emphasizing that the mean difference values of the medial position were lower than that of the lateral and contralateral positions, which were within 0.25 mm Hg. Besides, BP of the incorrect positions was positively correlated with that of the standard positions and showed good consistency for all the participants. Thereby, no matter for the participants from the general ward or participants from ICU, the errors introduced by incorrect cuff positions were both acceptable in clinical settings. A previous study had shown that there was no effect on the accuracy of BP measurement as to the placement of the center of cuff bladder using an oscillometric device with a wide, semi‐rigid cuff. 18 Herein, we used oscillometric devices with a conventional cuff and obtained a consistent conclusion. Accordingly, we can conclude that this practice is not only applied to a special cuff, but also a conventional cuff.
The amplitude of the oscillation of oscillometric devices is affected by the stiffness of the artery. 7 Age and hypertension are the influencing factors of arterial stiffness. ABI and baPWV are indicators of arterial stiffness. Pulse pressure (SBP − DBP) is also a measure of pulsatile hemodynamic stress and a marker of arterial stiffness. 8 Therefore, we did subgroup analysis based on age, SBP, pulse pressure, baPWV, the ABI, and a history of hypertension and found no significant differences in BP measurements when the midline of the cuff bladder was placed in the four previously mentioned positions. Besides, the mean BP differences between measurements made in the incorrect cuff positions and that made in the standard positions were within 2.0 mm Hg for all the subgroups, and the errors were acceptable in clinical settings. Furthermore, BP of the incorrect positions was positively correlated with that of the standard positions and showed good consistency in each subgroup.
As peripheral arterial BP, radial intra‐arterial BP can reflect the change of central arterial pressure and is most commonly used for continuous invasive BP monitoring. 19 Therefore, we performed radial intra‐arterial BP monitoring, meanwhile measuring non‐invasive brachial BP in the four previously described cuff positions for the participants from ICU. We found that the mean values of non‐invasive brachial SBP in the four cuff positions were lower than radial intra‐arterial SBP, and the difference was not higher than 6.0 mm Hg. A previous study had shown that the mean brachial intra‐arterial SBP was 5.5 mm Hg lower than radial intra‐arterial SBP. 20 According to their result, we could infer that the difference between non‐invasive brachial SBP in the four cuff positions and brachial intra‐arterial SBP maybe even smaller in our study. For all the participants who were recruited from ICU, the mean difference of DBP between the non‐invasive brachial artery in the four cuff positions and radial intra‐artery was within 2.1 mm Hg, which was even lower in the stable patients (within 1.0 mm Hg). This may be related to the effect of patients’ unstable state on the oscillating signal during BP measurement. 21 Consequently, these findings further confirmed the reliability of our results of the main study. In addition, we found that the mean SBP in the radial artery was higher than that in the brachial artery, while DBP is lower. This phenomenon can be explained as distal pulse amplification and is in relation to the characteristics of the vascular tree.
BP is a variable hemodynamic phenomenon affected by many factors. 14 , 22 When we performed continuous BP monitoring, BP values were not completely consistent and have some fluctuation, which is called BP variability. There is natural variation in the BP measurement process, which is due to the influence of the patient's own state. 14 , 22 When the patient is in an unstable state, BP variability increases, which increases the natural variation. In our study, the natural variation of SBP fluctuated from 4 to 61 mm Hg, and the natural variation of DBP fluctuated from 2 to 39 mm Hg, which indicated that the effect caused by the change of the cuff position is less than that of natural variation during BP measurement.
Mercury sphygmomanometers are based on auscultation, which depends on the change in pressure of the cuff over the brachial artery during filling and deflation of the cuff bladder. Cuff pressure and the longitudinal and circumferential position of the stethoscope are important factors in the generation of Korotkoff sounds. 13 Oscillometric devices are based on the principle of oscillation and use algorithms to estimate BP. During the deflation period, pressure oscillation in the cuff is evaluated by the software within a device. The maximum oscillating point corresponds to the average intra‐arterial pressure. 21 Because of the oscillometric devices does not rely on auscultation, and no transducer needs to be placed over the brachial artery, so the cuff placement is not so critical. 7 The above theories provide a theoretical basis to support the conclusion of this study.
In the present study, we firstly identified the size of the error introduced by incorrect placement of cuff bladder and demonstrated that the cuff placement did not affect the accuracy of BP measurement by using oscillometric devices with a conventional cuff. Furthermore, we monitored intra‐arterial BP to verify the reliability of the above‐mentioned conclusion and compared it with the effect of natural variability on BP. The significance of this study is that our findings will help simplify the BP measurement process.
There are a few limitations in this study. Firstly, we have only monitored non‐invasive brachial BP and radial intra‐arterial BP, rather than brachial intra‐arterial BP, because of radial intra‐arterial BP is most commonly used for continuous invasive BP monitoring. Moreover, a previous study has quantified the magnitude of difference between brachial and radial intra‐arterial BP. 20 Secondly, we only measured blood pressure in the supine position, but not in the sitting position. Because of the participants are easier to maintain a stable and relaxed state in the supine position, and reduce the participants’ muscle contraction and isometric exercise‐dependent increases in blood pressure, which may be a potential confounding factor that affect the results. Thirdly, we did not use the large adult cuff, and the conclusion cannot be simply applied to obese patients, which need further study. Furthermore, we did not conduct subgroup analysis on the participants whose SBP was lower than 100 mm Hg or higher than 180 mm Hg, because there are fewer participants with SBP lower than 100 mm Hg in this study, while patients with SBP higher than 180 mm Hg often have been given drug intervention timely in clinical. This is another limitation of this study, which needs further study. Finally, we only used the oscillometric devices, so the conclusion of the present study is not applied to air pump sphygmomanometers and mercury sphygmomanometers. However, mercury sphygmomanometers are gradually being phased out, and oscillometric devices are commonly used. 23 Therefore, the conclusion of this study still has a broad application.
5. CONCLUSION
In our study, we conclude that there is no effect on the accuracy of BP measurement as to the location of the midline of the cuff bladder by using oscillometric devices with a conventional cuff. The factors of age, a history of hypertension, SBP, pulse pressure, baPWV, and ABI have no effect on the above conclusion. There is a natural variation in BP. The effect caused by the change of the cuff position is less than that of natural variation during BP measurement.
CONFLICT OF INTEREST
There are no conflicts of interest.
AUTHOR CONTRIBUTIONS
Wei Cui and Ya Li involved in study design. Ya Li, Fang Li, Yi Li, Xiaoran Cui, and Jing Li involved in data collection. Ya Li, Hua Zhi, Yanyan Sun, and Weidong Wang analyzed the data. Wei Cui and Ya Li wrote manuscript and revised for important intellectual content.
Li Y, Li F, Li Y, et al. Effect of cuff positioning on the accuracy of blood pressure measurement with automated electronic blood pressure monitors. J Clin Hypertens. 2020;22:1163–1172. 10.1111/jch.13902
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