Perioperative Medicine: Clinical Science
Accuracy and Precision of Continuous Noninvasive Arterial Pressure Monitoring Compared with Invasive Arterial Pressure: A Systematic Review and Meta-analysis
Kim, Sang-Hyun M.D., Ph.D.; Lilot, Marc M.D.; Sidhu, Kulraj S. M.D.; Rinehart, Joseph M.D.; Yu, Zhaoxia Ph.D.; Canales, Cecilia M.P.H.; Cannesson, Maxime M.D., Ph.D.
Background: Continuous noninvasive arterial pressure monitoring devices are available for bedside use, but the accuracy and precision of these devices have not been evaluated in a systematic review and meta-analysis.
Methods: The authors performed a systematic review and meta-analysis of studies comparing continuous noninvasive arterial pressure monitoring with invasive arterial pressure monitoring. Random-effects pooled bias and SD of bias for systolic arterial pressure, diastolic arterial pressure, and mean arterial pressure were calculated. Continuous noninvasive arterial pressure monitoring was considered acceptable if pooled estimates of bias and SD were not greater than 5 and 8 mmHg, respectively, as recommended by the Association for the Advancement of Medical Instrumentation.
Results: Twenty-eight studies (919 patients) were included. The overall random-effect pooled bias and SD were −1.6 ± 12.2 mmHg (95% limits of agreement −25.5 to 22.2 mmHg) for systolic arterial pressure, 5.3 ± 8.3 mmHg (−11.0 to 21.6 mmHg) for diastolic arterial pressure, and 3.2 ± 8.4 mmHg (−13.4 to 19.7 mmHg) for mean arterial pressure. In 14 studies focusing on currently commercially available devices, bias and SD were −1.8 ± 12.4 mmHg (−26.2 to 22.5 mmHg) for systolic arterial pressure, 6.0 ± 8.6 mmHg (−10.9 to 22.9 mmHg) for diastolic arterial pressure, and 3.9 ± 8.7 mmHg (−13.1 to 21.0 mmHg) for mean arterial pressure.
Conclusions: The results from this meta-analysis found that inaccuracy and imprecision of continuous noninvasive arterial pressure monitoring devices are larger than what was defined as acceptable. This may have implications for clinical situations where continuous noninvasive arterial pressure is being used for patient care decisions.
What We Already Know about This Topic
* Recently, continuous noninvasive arterial pressure monitoring systems based on the volume clamp method and arterial tonometry have been developed. However, the accuracy and precision of continuous noninvasive pressure monitoring compared with invasive arterial pressure monitoring remain unclear.
* The current study is a systematic review and meta-analysis of previous studies comparing continuous noninvasive arterial pressure monitoring with invasive arterial pressure monitoring.
What This Article Tells Us That Is New
* This meta-analysis found that accuracy and precision of continuous noninvasive arterial pressure monitoring devices are larger than what was defined as acceptable by the Association for the Advancement of Medical Instrumentation.
INTERMITTENT arterial pressure monitoring is part of the American Society of Anesthesiologists’ standards for all patients undergoing anesthesia.*
In patients undergoing high-risk surgery and/or presenting with major comorbidities, invasive arterial pressure monitoring is often used as the standard of care. This technique allows continuous, beat-to-beat arterial pressure monitoring as well as access for blood draws and is used in approximately 10 to 12% of all patients undergoing anesthesia in the United States and in Europe.1
However, this invasive monitoring is associated with mechanical, infectious, and thrombotic complications.2
Recently, continuous noninvasive arterial pressure monitoring systems based on the volume clamp method and arterial tonometry have been developed and are now available at the bedside: Nexfin (BMEYE B.V., Amsterdam, The Netherlands); CNAP (CNSystems, Graz, Austria); and T-line (Tensys Medical, Inc., San Diego, CA).4
These devices display real-time, continuous arterial pressure waveforms and allow noninvasive beat-to-beat arterial pressure measurement. The main advantage of these technologies is that they can bridge the gap between noninvasive but intermittent oscillometric techniques and continuous but invasive arterial pressure monitoring. To date, these techniques have only been evaluated in small, single-center clinical studies, and no definitive validation studies have yet been performed.
We performed a systematic review and meta-analysis of studies that compared continuous noninvasive arterial pressure measurements with invasive arterial pressure measurements in adult patients in the perioperative and critical care settings. The principal outcomes were the accuracy and precision of continuous noninvasive systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and mean arterial pressure (MAP) compared with invasive arterial pressure measurements. Accuracy and precision were defined as acceptable if bias was not greater than 5 mmHg and precision not greater than 8 mmHg.
Materials and Methods
This systematic review and meta-analysis was conducted following the guidelines set forth in Preferred Reporting Items for Systematic Reviews and Meta-Analyses.5
The following characteristics were defined in advance as eligibility criteria for the studies to be included in our systematic review and meta-analysis:
1. Published studies comparing arterial pressure measured using commercially available continuous noninvasive arterial pressure monitoring systems with that measured by invasive arterial pressure monitoring.
2. Studies reporting extractable bias and SD of the differences (or 95% limits of agreement [LOA]) between continuous noninvasive arterial pressure monitoring systems and invasive arterial pressure monitoring.
3. Studies on adult patient populations (age ≥18 yr) that report identifiable demographic data (sex and age).
4. Studies performed in the perioperative and critical care settings.
Information Sources and Search
Three electronic databases (PubMed, Web of Science, and the Cochrane Library) were searched using the following key words: blood pressure, arterial pressure, monitor, measurement, noninvasive, Nexfin, CNAP, T-line, Finapres, Penaz, Vasotrac, volume clamp, pulse transit time, Wesseling, vascular unloading, preoperative, postoperative, perioperative, continuous, beat-to-beat, surgery, operative, anesthesia, intensive care unit, accuracy, precision, bias, limit of agreement, and Bland-Altman. The full electronic PubMed search strategy is presented in appendix 1. We restricted the search and subsequent bibliographic review to studies in the English language conducted on adult human subjects (≥18 yr old), and to published research articles (no case reports or correspondence). We also limited the search to studies expressing results as bias and either SD or 95% LOA. No restrictions were placed on the dates of the studies in our database search. In addition to the database search, we contacted the manufacturers of clinically available monitors—Nexfin, CNAP, and T-line—for other studies and hand-searched references in the studies included in the full-text retrieval for studies that had not been identified with the initial search.
Three investigators (S.-H.K., M.L., and K.S.S.) initially screened potentially eligible studies first by title and abstract. Remaining studies were then retrieved in full text. S.-H.K. and M.L. assessed eligibility according to inclusion criteria. If the eligibility of the study remained unclear, a third investigator (M.C.) made the final decision.
S.-H.K. and M.L. performed data extraction independently. A pilot data-extraction sheet was first used in five studies and then assessed for completeness and accuracy between S.-H.K. and M.L. Discrepancies between investigators were noted, the sheets updated, and then S.-H.K. and M.L. independently performed data extraction on the remaining studies. All data were then transferred separately to a standard Excel (Microsoft Corporation, Redmond, WA) spreadsheet. S.-H.K. and M.L. reviewed each other’s extractions for inconsistencies and, if needed, returned to the original work to validate the correct data.
Extracted study variables included patient age (mean, median, SD, range or interquartile range), sex, study setting (types of surgery, perioperative or critical care setting), number of patients enrolled in the study, and numbers of patients actually included in the analysis.
We extracted bias and SD of biases between invasive arterial pressure and the noninvasive arterial pressure measurement for SAP, DAP, and MAP from tables and Results sections of each article. If a study presented only bias and 95% LOA, SD was calculated as (upper LOA minus bias) divided by 1.96. As description of bias was not uniform among the studies (some articles described it as noninvasive minus invasive measurements, whereas others described it as invasive minus noninvasive measurements), we standardized bias in the current meta-analysis to mean noninvasive measurement minus invasive arterial pressure measurement and corrected source data as needed for reporting in this form. Authors of included studies were contacted to provide data if they were not published.
Risk of Bias in Individual Studies
Quality-assessment S...Image Tools
As there are no specific guidelines for the quality assessment of articles screened for inclusion in a meta-analysis focusing on method-comparison studies, we used modified Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) guidelines in order to meet our needs.6
Briefly, the original QUADAS-2 guidelines include four domains for the assessment of risk of bias (patient selection, index test, reference standard, and flow and timing) and three domains for the assessment of concerns related to applicability (patient selection, index test, and reference standard). Each domain consists of signaling questions that are marked yes, no, or unclear for the assessment of the quality of study; these are detailed in appendix 2
. Three investigators (S.-H.K., M.L., and K.S.S.) modified these guidelines in order to make them suitable for the current meta-analysis. Then, three investigators (S.-H.K., M.L., and K.S.S.) performed an independent pilot assessment on a set of five articles. Quality indicators were compared, updated, and the pilot assessment repeated until all three investigators’ assessments became consistent. Then, two investigators (S.-H.K. and M.L.) performed independent quality assessments on the full study set using the final modified QUADAS-2 form (appendix 2). Risk for each of the bias domains and each of the applicability domains is classified as low, high, or unclear according to the modified QUADAS-2 guidelines. Disagreement between investigators was resolved by discussion with a fourth investigator (M.C.).
Principal summary measures of the current meta-analysis were (1) accuracy of measurement (defined as noninvasive − invasive measurement, or bias); (2) precision of measurement (defined as SDs of accuracy); and (3) 95% LOA of SAP, DAP, and MAP. The accuracy and precision were evaluated for SAP, DAP, and MAP and were a priori (in advance of the meta-analysis) defined as acceptable if accuracy was no greater than 5 mmHg and precision not greater than 8 mmHg for SAP and DAP, based on the standards for the validation of automatic arterial pressure monitoring established by the Association for the Advancement of Medical Instrumentation (AAMI).7
Of note, this definition of acceptability was developed by the AAMI for the evaluation of automatic sphygmomanometers. To the best of our knowledge, no official guidelines presently exist for the evaluation of continuous noninvasive arterial pressure monitoring systems, but the AAMI guidelines have been cited as a reference for acceptability in several recently published studies evaluating commercially available devices for continuous noninvasive arterial pressure measurement.8–17
In addition, although most recently published studies define bias as the instantaneous absolute difference between noninvasive and invasive measurements, the AAMI guidelines define mean error as follows:
“If the value obtained from the sphygmomanometer-under-test determination lies within the range of the variation of blood pressure [the highest and lowest invasive blood pressure over a discreet time frame], assign an error of 0 mmHg to this determination. If the value obtained from the sphygmomanometer-under-test determination lies outside the range of the variation of blood pressure, subtract the value of the determination from the adjacent limit of the range of the variation of blood pressure. That difference represents the error for this determination.”
Consequently, bias as reported in method-comparison studies using Bland-Altman analysis18
would result in a greater mean error and SD than the way these standards recommend for comparison of a new sphygmomanometer with invasive arterial pressure measurements.
Synthesis of Results
For the synthesis of pooled estimates of bias and SD, we used random-effects models.20
We tested heterogeneity of biases and SDs across studies using a Q test21
and quantified them with an I2
statistic describes the percentage of variation across studies that is caused by heterogeneity rather than chance. If there were significant heterogeneity (I2
> 50%), we performed sensitivity analysis and meta-regression based on plausible clinical causes of the heterogeneity.23
Forest plots are presented with individual and random-effects pooled estimates of bias and 95% LOA to visualize the data.
Risk of Publication Bias across Studies
To assess for publication bias we created funnel plots for bias of SAP, DAP, and MAP against standard error for each study. These funnel plots were assessed visually for symmetry. In the absence of bias, these plots should resemble a symmetrical inverted funnel. To formally test for asymmetry, we applied Egger regression tests on secondary funnel plots using a significance level of 0.1 because of small sample size.24
We conducted sensitivity and subgroup analyses to explore the causes of heterogeneity. These were performed based on the funding source (department vs.
industry), identification of outliers (studies falling outside of mean ± 2SD for bias), setting (perioperative vs.
critical care), current commercial availability (commercially available vs.
unavailable devices), measurement site of invasive arterial pressure (radial vs.
femoral), statistical approach (modified Bland-Altman analysis for repeated measurement vs.
original Bland-Altman analysis), and risk of bias (low risk vs.
high/unclear risk in flow and timing domain according to the modified QUADAS 2). We also conducted a meta-regression analysis on demographic characteristics (age, sex, and body mass index) and year of publication in addition to the study characteristics assessed in subgroup analysis. All the calculations and tests were conducted using Microsoft Excel 2010 (Microsoft Corporation) and R.†
Data are presented as mean ± SD or bias ± SDs (95% LOA).
As of May 8, 2013, a total of 574 articles were retrieved from the database searches and manufacturers after removing duplicates. Three investigators excluded 533 studies by title and abstract screening. The remaining 41 studies were retrieved as full-text articles and were assessed for eligibility. Thirteen articles25–37
were excluded after full-text review for failure to meet the inclusion criteria or insufficient data for meta-analysis (appendix 3). The remaining 28 studies8–17
–55 were included in the systematic review (fig. 1
A total of 919 patients (65% male) were included in this meta-analysis. Most studies had small sample sizes (median, 25; range, 8 to 100). Among the 28 studies, 209–12
–17,40,41,43,44,46–49,52–55 were conducted in the operating room and 88
were conducted in the critical care setting. The CNAP device10–12
,15,41 was the most frequently evaluated, followed by T-line,16
Characteristics of individual studies are presented in table 1
Risk of Bias in Individual Studies
Results of Quality A...Image Tools
Results of quality assessment using the modified QUADAS-2 are presented in appendix 4
. In all included studies, the risk of bias was assessed as low with regard to patient selection, index test, and reference standard domain. In the flow and timing domains, 22 studies were at low risk. Five studies14
were at high risk and one study50
was at unclear risk. The concerns regarding three QUADAS-2 applicability domains were all low risk.
Synthesis of Results
Bias and 95% LOA for the 28 included articles are shown in figure 2
. Among these, bias and SD for SAP was extractable in 25, DAP in 24, and MAP in 26 studies. Overall, the average continuous noninvasive and invasive SAP were 112.9 ± 19.4 and 118.7 ± 19.4 mmHg, respectively, DAP were 64.3 ± 11.5 and 62.2 ± 10.6 mmHg, and MAP were 78.5 ± 13.1 and 76.9 ± 11.8 mmHg. The overall random-effects pooled bias and SDs of arterial pressure were −1.6 ± 12.2 mmHg (−25.5 to 22.2 mmHg) for SAP, 5.3 ± 8.3 mmHg (−11.0 to 21.6 mmHg) for DAP, and 3.2 ± 8.4 mmHg (−13.4 to 19.7 mmHg) for MAP. We found significant between-study heterogeneity for both biases (P
< 0.0001, I2
> 73%) and SDs (P
< 0.0001, I2
> 81%) for all arterial pressure variables.
Risk of Publication Bias across Studies
The funnel plots constructed for SAP, DAP, and MAP appeared symmetrical and Egger regression test for asymmetry was nonsignificant (P
> 0.1; fig. 3
Sensitivity Analysis...Image Tools
We did not find significant differences in biases and SDs in the sensitivity and subgroup analyses. There was, however, significant residual heterogeneity after performing subgroup and meta-regression analysis based on plausible causes (appendix 5
Sensitivity Analysis of Currently Available Technologies
A forest plot for the sensitivity analysis based only on currently commercially available technologies is depicted in figure 4
. Overall, for these studies, the average continuous noninvasive and invasive SAP were 111.1 ± 19.7 and 114.8 ± 19.1 mmHg, respectively, DAP were 64.1 ± 11.6 and 60.1 ± 10.7 mmHg, and MAP were 77.6 ± 13.2 and 75.0 ± 12.0 mmHg. The overall random-effects pooled bias and SDs of 14 studies8–17
–41 were −1.8 ± 12.4 mmHg (−26.2 to 22.5 mmHg) for SAP, 6.0 ± 8.6 mmHg (−10.9 to 22.9 mmHg) for DAP, and 3.9 ± 8.7 mmHg (−13.1 to 21.0 mmHg) for MAP. There was also significant residual heterogeneity with regard to bias and SDs for SAP (I2
= 79.8 and 90.9%), DAP (I2
= 87.3 and 85.3%), and MAP (I2
= 85.4 and 88.6%) within these currently available technologies.
Two of the commercially available devices are based on the volume clamp method (CNAP and Nexfin) and one is based on arterial tonometry (T-line) for the measurement of continuous noninvasive arterial pressure. We conducted sensitivity analysis by device to assess whether significant heterogeneity exited. CNAP and Nexfin showed residual heterogeneity in SAP, DAP, and MAP whereas T-line did not show residual heterogeneity in MAP and DAP (fig. 4
CNAP10–12,14,41 and Infinity CNAP SmartPod (Dräger Medical AG & Co. KG, Lübeck, Germany).15
The average CNAP and invasive SAP were 111.4 ± 20.2 and 118.0 ± 20.6 mmHg, respectively, DAP were 68.5 ± 13.8 and 64.8 ± 11.2 mmHg, and MAP were 74.0 ± 13.8 and 71.1 ± 11.0 mmHg. The overall random-effect pooled bias and SDs were −1.8 ± 12.8 mmHg (−26.8 to 23.2 mmHg) for SAP, 7.2 ± 8.5 mmHg (−9.5 to 24.0 mmHg) for DAP, and 5.5 ± 9.3 mmHg (−12.7 to 23.6 mmHg) for MAP.
The average T-line and invasive SAP were 112.3 ± 18.9 and 113.6 ± 18.6 mmHg, respectively, DAP were 61.8 ± 11.7 and 58.8 ± 10.9 mmHg, and MAP were 79.2 ± 13.2 and 77.9 ± 12.9 mmHg. The overall random-effects pooled bias and SDs were −0.1 ± 8.4 mmHg (−16.5 to 16.3 mmHg) for SAP, 2.9 ± 6.7 mmHg (−10.2 to 16.0 mmHg) for DAP, and 1.3 ± 5.7 mmHg (−9.8 to 12.4 mmHg) for MAP.
The average Nexfin and invasive SAP were 108.9 ± 20.5 and 113.5 ± 18.4 mmHg, respectively, DAP were 63.0 ± 8.0 and 56.5 ± 9.5 mmHg, and MAP were 78.7 ± 12.5 and 74.2 ± 11.6 mmHg. The overall random-effects pooled bias and SDs were −1.6 ± 8.4 mmHg (−18.1 to 15.0 mmHg) for SAP, 5.1 ± 6.6 mmHg (−7.8 to 18.0 mmHg) for DAP, and 3.5 ± 6.8 mmHg (−9.9 to 16.9 mmHg) for MAP.
Summary of Evidence
This meta-analysis of 28 studies assessing accuracy and precision of continuous noninvasive arterial pressure monitoring systems compared with invasive arterial pressure measurements in the operating room and critical care settings showed that the overall random-effects pooled bias of arterial pressure was −1.6 ± 12.2 mmHg for SAP, 5.3 ± 8.3 mmHg for DAP, and 3.2 ± 8.4 mmHg for MAP. When analysis was limited to commercially available technologies, the overall random-effects pooled bias of 14 studies was −1.8 ± 12.4 mmHg for SAP, 6.0 ± 8.6 mmHg for DAP, and 3.9 ± 8.7 mmHg for MAP. On the basis of these results, these devices would not satisfy the standards of the AAMI guidelines as they were interpreted.7
The goal of this meta-analysis was to assess the accuracy and precision of continuous noninvasive arterial pressure monitoring systems in order to inform clinicians about what should be expected from these devices in the clinical practice. We have identified 28 studies including a total of 919 patients for inclusion in this meta-analysis. These studies included between 8 and 100 patients, and only two of these studies (Ilies et al.10
and Hahn et al.11
) included 85 patients or more as recommended by the AAMI guidelines. However, even though Hahn et al.11
included 100 patients, their study evaluated two versions of the CNAP monitor—software v3.0 and v3.5—and only 50 patients only were studied for each version of the software. This meta-analysis allowed assessment of accuracy and precision on a much larger number of patients, increased the power of the study, and allowed subgroup analysis. Because some of these devices have recently been made commercially available and because arterial pressure management is crucial in the perioperative and critical care setting, it is important to have a clear understanding of the accuracy and precision of these systems before use in a clinical setting.
The goal of the continuous noninvasive arterial pressure monitoring devices is to bridge the gap between noninvasive but intermittent and continuous but invasive arterial pressure measurements. However, based on the results from the current study, healthcare providers should be cautious when using these new technologies. For example, if SAP measured using an invasive radial artery catheter was 100 mmHg, SAP measured using a currently available continuous noninvasive arterial pressure measurement system could range anywhere between 74 and 123 mmHg.
of 14 studies included in this meta-analysis and published since 2006 (all focusing on currently commercially available devices) cite the AAMI guidelines to calculate sample size or to define acceptability. Among the 14 remaining studies, 541
cited these guidelines to define acceptability, and 938–40
,43,46–48,50,52–55 did not use any standards or defined arbitrary allowable difference to define acceptability. Interestingly, although studies included in this meta-analysis defined bias as the instantaneous absolute difference between noninvasive and invasive measurements, the AAMI guidelines allow a wider range of values to represent “zero error” when a new sphygmomanometer is compared with invasive measurements. Consequently, the way bias was reported in the method-comparison studies using Bland-Altman analysis18
would result in a greater mean error and SD than the way these standards recommend. One possible reason may be that authors cited AAMI standards and replicated previously published methodologies without reading the original reference. It has been reported that approximately 80% of authors have not read all the articles they are citing.56
This leads to the publication of articles with errors or improper citations, which may eventually be responsible for the propagation of misleading knowledge.
It is of major importance for our community to clearly define what level of performance should be expected from these technologies and how method-comparison studies should be conducted and reported. During the past decade, the anesthesiology and critical care communities have been at the forefront of the evaluation of new noninvasive monitoring technologies such as noninvasive cardiac output and hemoglobin monitoring systems. Interestingly, these two device categories are similar to each other in the way they have been developed and tested. After being cleared by regulatory agencies, they were released in the market and extensively tested by clinical scientists who often published controversial results. The lack of consistency in the conduct and report of these studies raised awareness of the need for better standards for method-comparison studies conducted in the perioperative setting.57
The results from the current meta-analysis show a similar lack of consistency in the way continuous noninvasive arterial pressure monitoring systems are tested in clinical studies. Different methodologies have been used to evaluate these systems using different thresholds (some inappropriate) to define “acceptability.” This is concerning considering the importance of arterial pressure management in the perioperative and critical care setting. For this reason, the observed heterogeneity between studies and the lack of consistency in the way acceptability of these devices is defined are concerning and should lead our community to adopt more specific standards for conducting and reporting method-comparison studies.
Although we found significant heterogeneity between studies included in our meta-analysis, we did not identify a cause despite performing a series of sensitivity analyses and meta-regressions. It is possible that multiple factors are responsible for the heterogeneity, with each factor making a small contribution. This has been observed in previously published meta-analysis for method-comparison studies.58–60
Use of different devices in different populations as well as the quality of the studies included in the meta-analysis may also cause heterogeneity, but our results were not conclusive.
Our meta-analysis only assesses the relative accuracy of continuous noninvasive arterial pressure monitoring systems; it does not assess the potential clinical utility of these devices. Indeed, clinical decision-making, patient outcome, and/or patient safety encompass more than the assessment of accuracy and precision of a device. For instance, despite the relatively weak accuracies and precisions of mini- and noninvasive cardiac output monitoring systems,61
several studies have found a positive impact of these technologies on postoperative outcome (morbidity and length of stay in the hospital) when they are coupled with a protocol defining hemodynamic management strategies.62
However, we believe that arterial pressure is such an important variable for patient safety that strong recommendations about the way these systems should be evaluated and strong evidence related to their accuracies should be reported before any outcome study is conducted.
Another limitation is the mixture of different devices included in this meta-analysis. In particular, the newer systems (CNAP, T-line, and Nexfin) are based on different technologies.4
CNAP and Nexfin are based on the volume clamp method and measure arterial pressure at the finger; CNAP is calibrated on an oscillometric arterial pressure cuff whereas Nexfin is uncalibrated. The T-line, however, is based on arterial tonometry and measures arterial pressure from the radial artery. Despite these differences, however, the subgroup analyses showed very similar bias and precision for these three devices. Moreover, our goal was not to evaluate each device but rather to describe the overall accuracy of these technologies. Interestingly, the results from the sensitivity analysis suggest that there is no significant difference between new devices (studies published from 2006) and older technologies.
Finally, our research strategy was limited to studies in English, to PubMed, Web of Science, Cochrane Library, and to articles provided by manufacturers, and only included studies published in peer-reviewed journals and this may induce a bias. We purposely limited the search to peer-reviewed publications in order to avoid low-quality articles. Recent studies have suggested that the extent and effect of language bias has diminished in recent years because of the shift toward publication of studies in English even in national journals15
and the impact of the inclusion of “gray literature” in meta-analyses is still unclear, may itself introduce bias, and has not been evaluated for meta-analyses of method-comparison studies. Because we were not able to combine results coming from different statistical approaches, we only included studies that provided bias and SD or LOA. Different search strategies (especially using different languages) may have produced different results.
In conclusion, the results from this pooled, weighted meta-analysis demonstrate that the overall random-effects pooled bias of continuous noninvasive arterial pressure compared with invasive arterial pressure measurements was −1.6 ± 12.2 mmHg for SAP, 5.3 ± 8.3 mmHg for DAP, and 3.2 ± 8.4 mmHg for MAP. When analysis was limited to currently commercially available technologies evaluated since 2006, the overall random-effects pooled bias was −1.8 ± 12.4 mmHg for SAP, 6.0 ± 8.6 mmHg for DAP, and 3.9 ± 8.7 mmHg for MAP. On the basis of these results, these devices would not satisfy the standards of the AAMI guidelines. However, most studies evaluating these devices did not report bias and error the way the AAMI recommended, and following the recommendations in that standard would have led to significantly lower error values. Considering the importance of arterial pressure in the management of patients in the perioperative and critical care settings, this study suggests that there is a need to clearly define how these devices should be evaluated and what should be demonstrated to consider them acceptable for use in the clinical setting.
The authors thank Hao-min Cheng, M.D., Ph.D. (Department of Medical Education, Taipei Veterans General Hospital, Department of Medicine, Department of Public Health, National Yang-Ming University, Taipei, Taiwan; Division of Cardiology, Taipei Veterans General Hospital; Faculty of Medicine, National Yang-Ming University, Taiwan), for the kind supply of statistical software for the calculation of pooled data, and Linda Suk-Ling Murphy, M.L.I.S. (Ayala Science Library Reference Department, University of California, Irvine, Orange, California), for the development of search strategies.
Support was provided solely from institutional and/or departmental sources. Dr. Kim was supported from Soonchunhyang University Research Fund (Sinchang-myeon, Asan, South Korea).
Dr. Cannesson is a consultant for Edwards Lifesciences (Irvine, California), Covidien (Boulder, Colorado), Masimo Corp. (Irvine, California), ConMed (Irvine, California), Philips Medical System (Suresnes, France), and Fresenius Kabi (Sèvres, France). A Nexfin monitor (BMEYE B.V., Amsterdam, The Netherlands) and a CNAP monitor (CNSystems, Graz, Austria) were loaned to Dr. Cannesson and his research team in 2010. Dr. Cannesson publicly endorsed the Nexfin technology in a BMEYE newsletter. The other authors declare no competing interests.
* American Society of Anesthesiologists, Standards of the American Society of Anesthesiologists: Standards for Basic Anesthetic Monitoring. Available at: http://www.asahq.org/For-Members/~/media/For%20Members/documents/Standards%20Guidelines%20Stmts/Basic%20Anesthetic%20Monitoring%202011.ashx
. Accessed October 7, 2013. Cited Here...
† R Development Core Team: R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing. Available at: http://R-project.org
. Accessed October 7, 2013. Cited Here...
1. Cannesson M, Pestel G, Ricks C, Hoeft A, Perel A. Hemodynamic monitoring and management in patients undergoing high risk surgery: A survey among North American and European anesthesiologists. Crit Care. 2011;15:R197
2. Brzezinski M, Luisetti T, London MJ. Radial artery cannulation: A comprehensive review of recent anatomic and physiologic investigations. Anesth Analg. 2009;109:1763–81
3. Haddad F, Zeeni C, El Rassi I, Yazigi A, Madi-Jebara S, Hayeck G, Jebara V, Yazbeck P. Can femoral artery pressure monitoring be used routinely in cardiac surgery? J Cardiothorac Vasc Anesth. 2008;22:418–22
4. Chung E, Chen G, Alexander B, Cannesson M. Non-invasive continuous blood pressure monitoring: A review of current applications. Front Med. 2013;7:91–101
5. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JP, Clarke M, Devereaux PJ, Kleijnen J, Moher D. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: Explanation and elaboration. Ann Intern Med. 2009;151:W65–94
6. Whiting PF, Rutjes AW, Westwood ME, Mallett S, Deeks JJ, Reitsma JB, Leeflang MM, Sterne JA, Bossuyt PM. QUADAS-2: A revised tool for the quality assessment of diagnostic accuracy studies. Ann Intern Med. 2011;155:529–36
7. Non-invasive Sphygmomanometers—Part 2: Clinical Validation of Automated Measurement Type, ANSI/AAMI/ISO 81060–2:2009. 2009 Arlington Association for the Advancement of Medical Instrumentation:1–21
8. Hohn A, Defosse JM, Becker S, Steffen C, Wappler F, Sakka SG. Non-invasive continuous arterial pressure monitoring with Nexfin does not sufficiently replace invasive measurements in critically ill patients. Br J Anaesth. 2013;111:178–84
9. Martina JR, Westerhof BE, van Goudoever J, de Beaumont EM, Truijen J, Kim YS, Immink RV, Jöbsis DA, Hollmann MW, Lahpor JR, de Mol BA, van Lieshout JJ. Noninvasive continuous arterial blood pressure monitoring with Nexfin®
. ANESTHESIOLOGY. 2012;116:1092–103
10. Ilies C, Bauer M, Berg P, Rosenberg J, Hedderich J, Bein B, Hinz J, Hanss R. Investigation of the agreement of a continuous non-invasive arterial pressure device in comparison with invasive radial artery measurement. Br J Anaesth. 2012;108:202–10
11. Hahn R, Rinösl H, Neuner M, Kettner SC. Clinical validation of a continuous non-invasive haemodynamic monitor (CNAP™ 500) during general anaesthesia. Br J Anaesth. 2012;108:581–5
12. Gayat E, Mongardon N, Tuil O, Sievert K, Chazot T, Liu N, Fischler M. CNAP(®
) does not reliably detect minimal or maximal arterial blood pressures during induction of anaesthesia and tracheal intubation. Acta Anaesthesiol Scand. 2013;57:468–73
13. Fischer MO, Avram R, Cârjaliu I, Massetti M, Gérard JL, Hanouz JL, Fellahi JL. Non-invasive continuous arterial pressure and cardiac index monitoring with Nexfin after cardiac surgery. Br J Anaesth. 2012;109:514–21
14. Jeleazcov C, Krajinovic L, Münster T, Birkholz T, Fried R, Schüttler J, Fechner J. Precision and accuracy of a new device (CNAPTM) for continuous non-invasive arterial pressure monitoring: Assessment during general anaesthesia. Br J Anaesth. 2010;105:264–72
15. Biais M, Vidil L, Roullet S, Masson F, Quinart A, Revel P, Sztark F. Continuous non-invasive arterial pressure measurement: Evaluation of CNAP device during vascular surgery. Ann Fr Anesth Reanim. 2010;29:530–5
16. Szmuk P, Pivalizza E, Warters RD, Ezri T, Gebhard R. An evaluation of the T-Line Tensymeter continuous noninvasive blood pressure device during induced hypotension. Anaesthesia. 2008;63:307–12
17. Janelle GM, Gravenstein N. An accuracy evaluation of the T-Line Tensymeter (continuous noninvasive blood pressure management device) versus
conventional invasive radial artery monitoring in surgical patients. Anesth Analg. 2006;102:484–90
18. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307–10
19. Bland JM, Altman DG. Measuring agreement in method comparison studies. Stat Methods Med Res. 1999;8:135–60
20. Williamson PR, Lancaster GA, Craig JV, Smyth RL. Meta-analysis of method comparison studies. Stat Med. 2002;21:2013–25
21. DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials. 1986;7:177–88
22. Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. BMJ. 2003;327:557–60
23. Guolo A, Varin C. The R package metaLik for likelihood inference in meta-analysis. J Stat Softw. 2012;50:1–14
24. Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ. 1997;315:629–34
25. Colquhoun DA, Forkin KT, Dunn LK, Bogdonoff DL, Durieux ME, Thiele RH. Non-invasive, minute-to-minute estimates of systemic arterial pressure and pulse pressure variation using radial artery tonometry. J Med Eng Technol. 2013;37:197–202
26. Jagadeesh AM, Singh NG, Mahankali S. A comparison of a continuous noninvasive arterial pressure (CNAP™) monitor with an invasive arterial blood pressure monitor in the cardiac surgical ICU. Ann Card Anaesth. 2012;15:180–4
27. Stover JF, Stocker R, Lenherr R, Neff TA, Cottini SR, Zoller B, Béchir M. Noninvasive cardiac output and blood pressure monitoring cannot replace an invasive monitoring system in critically ill patients. BMC Anesthesiol. 2009;9:6
28. Steiner LA, Johnston AJ, Salvador R, Czosnyka M, Menon DK. Validation of a tonometric noninvasive arterial blood pressure monitor in the intensive care setting. Anaesthesia. 2003;58:448–54
29. Awad AA, Ghobashy MA, Stout RG, Silverman DG, Shelley KH. How does the plethysmogram derived from the pulse oximeter relate to arterial blood pressure in coronary artery bypass graft patients? Anesth Analg. 2001;93:1466–71
30. Belani KG, Buckley JJ, Poliac MO. Accuracy of radial artery blood pressure determination with the Vasotrac. Can J Anaesth. 1999;46(5 Pt 1):488–96
31. De Jong JR, Ros HH, De Lange JJ. Noninvasive continuous blood pressure measurement during anaesthesia: A clinical evaluation of a method commonly used in measuring devices. Int J Clin Monit Comput. 1995;12:1–10
32. Wilkes MP, Bennett A, Hall P, Lewis M, Clutton-Brock TH. Comparison of invasive and non-invasive measurement of continuous arterial pressure using the Finapres in patients undergoing spinal anaesthesia for lower segment caesarean section. Br J Anaesth. 1994;73:738–43
33. Jones RD, Brown AG, Roulson CJ, Smith ID, Chan SC. The upgraded Finapres 2300e. A clinical evaluation of a continuous noninvasive blood pressure monitor. Anaesthesia. 1992;47:701–5
34. Stokes DN, Clutton-Brock T, Patil C, Thompson JM, Hutton P. Comparison of invasive and non-invasive measurements of continuous arterial pressure using the Finapres. Br J Anaesth. 1991;67:26–35
35. Pace NL, East TD. Simultaneous comparison of intraarterial, oscillometric, and finapres monitoring during anesthesia. Anesth Analg. 1991;73:213–20
36. Kemmotsu O, Ueda M, Otsuka H, Yamamura T, Winter DC, Eckerle JS. Arterial tonometry for noninvasive, continuous blood pressure monitoring during anesthesia. ANESTHESIOLOGY. 1991;75:333–40
37. Epstein RH, Bartkowski RR, Huffnagle S. Continuous noninvasive finger blood pressure during controlled hypotension. A comparison with intraarterial pressure. ANESTHESIOLOGY. 1991;75:796–803
38. Saugel B, Meidert AS, Hapfelmeier A, Eyer F, Schmid RM, Huber W. Non-invasive continuous arterial pressure measurement based on radial artery tonometry in the intensive care unit: A method comparison study using the T-Line TL-200pro device. Br J Anaesth. 2013;111:185–90
39. Saugel B, Fassio F, Hapfelmeier A, Meidert AS, Schmid RM, Huber W. The T-Line TL-200 system for continuous non-invasive blood pressure measurement in medical intensive care unit patients. Intensive Care Med. 2012;38:1471–7
40. Dueck R, Goedje O, Clopton P. Noninvasive continuous beat-to-beat radial artery pressure via
TL-200 applanation tonometry. J Clin Monit Comput. 2012;26:75–83
41. Schramm C, Baat L, Plaschke K. Continuous noninvasive arterial pressure: Assessment in older and high-risk patients under analgesic sedation. Blood Press Monit. 2011;16:270–6
42. Jagomägi K, Talts J, Tähepõld P, Raamat R. A comparison of differential oscillometric device with invasive mean arterial blood pressure monitoring in intensive care patients. Clin Physiol Funct Imaging. 2011;31:188–92
43. Hager H, Mandadi G, Pulley D, Eagon JC, Mascha E, Nutter B, Kurz A. A comparison of noninvasive blood pressure measurement on the wrist with invasive arterial blood pressure monitoring in patients undergoing bariatric surgery. Obes Surg. 2009;19:717–24
44. Findlay JY, Gali B, Keegan MT, Burkle CM, Plevak DJ. Vasotrac arterial blood pressure and direct arterial blood pressure monitoring during liver transplantation. Anesth Analg. 2006;102:690–3
45. Heard SO, Lisbon A, Toth I, Ramasubramanian R. An evaluation of a new continuous blood pressure monitoring system in critically ill patients. J Clin Anesth. 2000;12:509–18
46. Weiss BM, Spahn DR, Rahmig H, Rohling R, Pasch T. Radial artery tonometry: Moderately accurate but unpredictable technique of continuous non-invasive arterial pressure measurement. Br J Anaesth. 1996;76:405–11
47. Young CC, Mark JB, White W, DeBree A, Vender JS, Fleming A. Clinical evaluation of continuous noninvasive blood pressure monitoring: Accuracy and tracking capabilities. J Clin Monit. 1995;11:245–52
48. Weiss BM, Spahn DR, Keller E, Seifert B, Pasch T. Continuous non-invasive blood pressure monitoring by brachial artery displacement method in high-risk surgical patients. Eur J Anaesthesiol. 1995;12:555–63
49. Siegel LC, Brock-Utne JG, Brodsky JB. Comparison of arterial tonometry with radial artery catheter measurements of blood pressure in anesthetized patients. ANESTHESIOLOGY. 1994;81:578–84
50. Novak V, Novak P, Schondorf R. Accuracy of beat-to-beat noninvasive measurement of finger arterial pressure using the Finapres: A spectral analysis approach. J Clin Monit. 1994;10:118–26
51. Searle NR, Perrault J, Ste-Marie H, Dupont C. Assessment of the arterial tonometer (N-CAT) for the continuous blood pressure measurement in rapid atrial fibrillation. Can J Anaesth. 1993;40:388–93
52. Bardoczky GI, Levarlet M, Engelman E, d’Hollander A, Schmartz D. Continuous noninvasive blood pressure monitoring during thoracic surgery. J Cardiothorac Vasc Anesth. 1992;6:51–4
53. Kurki TS, Smith NT, Sanford TJ Jr, Head N. Pulse oximetry and finger blood pressure measurement during open-heart surgery. J Clin Monit. 1989;5:221–8
54. Kurki T, Smith NT, Head N, Dec-Silver H, Quinn A. Noninvasive continuous blood pressure measurement from the finger: Optimal measurement conditions and factors affecting reliability. J Clin Monit. 1987;3:6–13
55. Smith NT, Wesseling KH, de Wit B. Evaluation of two prototype devices producing noninvasive, pulsatile, calibrated blood pressure measurement from a finger. J Clin Monit. 1985;1:17–29
56. Simkin MV, Roychowdhury VP. Read before you cite! Complex Systems. 2003;14:269–74
57. Riou B. Continuous measurement of hemoglobin: Methodological approach and lessons for the future. ANESTHESIOLOGY. 2013;118:497–9
58. Craig JV, Lancaster GA, Williamson PR, Smyth RL. Temperature measured at the axilla compared with rectum in children and young people: Systematic review. BMJ. 2000;320:1174–8
59. Craig JV, Lancaster GA, Taylor S, Williamson PR, Smyth RL. Infrared ear thermometry compared with rectal thermometry in children: A systematic review. Lancet. 2002;360:603–9
60. Cheng HM, Lang D, Tufanaru C, Pearson A. Measurement accuracy of non-invasively obtained central blood pressure by applanation tonometry: A systematic review and meta-analysis. Int J Cardiol. 2013;167:1867–76
61. Peyton PJ, Chong SW. Minimally invasive measurement of cardiac output during surgery and critical care: A meta-analysis of accuracy and precision. ANESTHESIOLOGY. 2010;113:1220–35
62. Hamilton MA, Cecconi M, Rhodes A. A systematic review and meta-analysis on the use of preemptive hemodynamic intervention to improve postoperative outcomes in moderate and high-risk surgical patients. Anesth Analg. 2011;112:1392–402
63. Myles PS, Cui J. Using the Bland-Altman method to measure agreement with repeated measures. Br J Anaesth. 2007;99:309–11
64. Bland JM, Altman DG. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat. 2007;17:571–82
PubMed Search Strategy
1. Blood pressure OR arterial pressure
2. Monitor OR monitors OR measure OR measuring OR measurement OR determinants OR determinant OR determined OR determination
3. 1 AND 2
4. Noninvasive OR non-invasive OR “non invasive”
5. 3 AND 4
6. Nexfin OR CNAP OR Finapres OR Tensys OR T-line OR TL-200 OR Penaz OR Vasotrac OR volume clamp OR applanation tonometry OR finger cuff OR “pulse transit time“ OR finger OR Wesseling OR vascular unloading
7. 5 OR 6
8. Continuous OR continued OR continual OR continually OR continuing
9. Beat-to-beat OR real time OR real-time OR simultaneous OR simultaneously
10. 8 OR 9
11. 7 AND 10
12. Preoperative OR pre-operative OR peri-operative OR perioperative OR intra-operative OR intraoperative OR post-operative OR postoperative OR anesthesia OR anaesthesia OR anesthesiology OR anaesthesiology
13. Surgery OR surgical OR operation OR operative OR operating
14. Critical care OR intensive care OR ICU
15. 12 OR 13 OR 14
16. 11 AND 15
17. Accuracy OR precision OR reliability OR validity OR validation OR standard deviation
18. Bias OR mean difference OR limit of agreement OR Bland Altman
19. 17 OR 18
20. 16 AND 19
List of 13 Excluded Studies
Colquhoun DA, Forkin KT, Dunn LK, Bogdonoff DL, Durieux ME, Thiele RH: Non-invasive, minute-to-minute estimates of systemic arterial pressure and pulse pressure variation using radial artery tonometry. J Med Eng Technol 2013; 37:197–202
Reason: Insufficient or lack of demographic data.
Jagadeesh AM, Singh NG, Mahankali S: A comparison of a continuous noninvasive arterial pressure (CNAP) monitor with an invasive arterial blood pressure monitor in the cardiac surgical ICU. Ann Card Anaesth 2012; 15:180–4
Reason: Patient under 18 yr of age (age >16 yr of age).
Stover JF, Stocker R, Lenherr R, Neff TA, Cottini SR, Zoller B, Béchir M: Noninvasive cardiac output and blood pressure monitoring cannot replace an invasive monitoring system in critically ill patients. BMC Anesthesiol 2009; 9:6
Reason: Insufficient or lack of demographic data (could not determine whether bias was calculated as noninvasive minus invasive or vice versa) and retrospective study.
Steiner LA, Johnston AJ, Salvador R, Czosnyka M, Menon DK: Validation of a tonometric noninvasive arterial blood pressure monitor in the intensive care setting. Anaesthesia 2003; 58:448–54
Reason: Insufficient or lack of demographic data (data were expressed as bias and 10th and 90th percentile. No SD could be calculated. Also, there was no extractable age and sex information).
Awad AA, Ghobashy MA, Stout RG, Silverman DG, Shelley KH: How does the plethysmogram derived from the pulse oximeter relate to arterial blood pressure in coronary artery bypass graft patients? Anesth Analg 2001; 93:1466–71
Reason: This study used an ordinary pulse oximeter rather than a device developed for blood pressure monitoring.
Belani KG, Buckley JJ, Poliac MO: Accuracy of radial artery blood pressure determination with the Vasotrac. Can J Anaesth 1999; 46:488–96
Reason: Not in perioperative or intensive care setting (volunteer study).
De Jong JR, Ros HH, De Lange JJ: Noninvasive continuous blood pressure measurement during anaesthesia: A clinical evaluation of a method commonly used in measuring devices. Int J Clin Monit Comput 1995; 12:1–10
Reason: Patient under 18 yr of age (one patient was 17 yr of age).
Wilkes MP, Bennett A, Hall P, Lewis M, Clutton-Brock TH: Comparison of invasive and noninvasive measurement of continuous arterial pressure using the Finapres in patients undergoing spinal anaesthesia for lower segment caesarean section. Br J Anaesth 1994; 73:738–43
Reason: Insufficient or lack of demographic data (the differences between Finapres and invasive systolic, diastolic and mean pressures were considered as a percentage of invasive arterial pressure ((Finapres pressure minus invasive pressure)/invasive pressure × 100)).
Jones RD, Brown AG, Roulson CJ, Smith ID, Chan SC: The upgraded Finapres 2300e. A clinical evaluation of a continuous noninvasive blood pressure monitor. Anaesthesia 1992; 47:701–5
Reason: Patient under 18 yr of age.
Stokes DN, Clutton-Brock T, Patil C, Thompson JM, Hutton P: Comparison of invasive and non-invasive measurements of continuous arterial pressure using the Finapres. Br J Anaesth 1991; 67:26–35
Reason: Insufficient or lack of demographic data (No bias and SD were presented).
Pace NL, East TD: Simultaneous comparison of intraarterial, oscillometric, and finapres monitoring during anesthesia. Anesth Analg 1991; 73:213–20
Reason: Insufficient or lack of demographic data.
Kemmotsu O, Ueda M, Otsuka H, Yamamura T, Winter DC, Eckerle JS: Arterial tonometry for noninvasive, continuous blood pressure monitoring during anesthesia. ANESTHESIOLOGY 1991; 75:333–40
Reason: Patient under 18 yr of age.
Epstein RH, Bartkowski RR, Huffnagle S: Continuous noninvasive finger blood pressure during controlled hypotension. A comparison with intraarterial pressure. ANESTHESIOLOGY 1991; 75:796–803
Reason: Patient under 18 yr of age (one 13 yr of aged and one 17 yr of aged males were included).
© 2014 American Society of Anesthesiologists, Inc.
Publication of an advertisement in Anesthesiology Online does not constitute endorsement by the American Society of Anesthesiologists, Inc. or Lippincott Williams & Wilkins, Inc. of the product or service being advertised.