For DBP pairs, TL-300 showed lower coefficient of determination in comparison with the invasive DBP (y=1.018x+1.561, r2=0.803; Fig. 3B); however, there was no apparent change in the regression relationship between either low or high BP. The noninvasive DBP values were higher than invasive values with a bias of 2.8±6.40 mm Hg (P<0.001). The 95% limits of agreement of bias for SBP were from −9.8 to 15.3 mm Hg (Fig. 3E). The percentage of bias of DBP pairs between 2 methods within 5, 10, and 15 mm Hg was 59.3%, 87.6%, and 96.6%, respectively (Table 3). Compared with other nonlinear regression of DBP pairs, a linear model also presented a higher coefficient of determination (Supplementary Table 3, Supplemental Digital Content 2, http://links.lww.com/JNA/A29).
For MBP pairs, TL-300 also showed a high coefficient of determination with the invasive MBP (y=1.033x−0.875, r2=0.922; Fig. 3C). Similarly, there was no apparent change in the regression relationship between either low or high BP. The noninvasive MBP values were higher than invasive values with a bias of 1.8±4.20 mm Hg (P<0.001). The 95% limits of agreement of bias for MBP were from −6.4 to 10.1 mm Hg (Fig. 3F). The percentage of bias of MBP pairs between 2 methods within 5, 10, and 15 mm Hg was 76.0%, 97.6%, and 99.7%, respectively (Table 3). Similarly, compared with other nonlinear regression of MBP pairs, a linear model presented a higher coefficient of determination (Supplementary Table 4, Supplemental Digital Content 2, http://links.lww.com/JNA/A29).
In the current retrospective study, we compared TL-300 noninvasive BP measurements with invasive radial artery beat-to-beat BP monitoring. The TL-300 determined SBP, DBP, and MBP accurately and precisely with association bias and precision for SBP, DBP, and MBP being 1.3±5.87, 2.8±6.40, and 1.8±4.20 mm Hg, respectively. Between 2 methods, the percentage of bias of BP pairs within 5, 10, and 15 mm Hg was acceptable (SBP: 64.2%, 92.9%, and 99.0%; DBP: 59.3%, 87.6%, and 96.6%; MBP: 76.0%, 97.6%, and 99.7%).
Noninvasive BP measured by oscillometric upper arm cuff is one of the classic methods for monitoring of hemodynamics. However, the inability to track rapid fluctuations in BP or short episodes of hemodynamic instability in real time is a limitation.14 According to the advanced perioperative management consensus statement, the criteria for an ideal hemodynamic monitoring device includes accuracy, reproducibility, ease of use, ready available, patient safety, besides the ability to capture as much information as possible to guide hemodynamic therapy. It also recommends that a continuous beat-to-beat hemodynamic parameter is more reliable than intermittent BP values.15 As invasive BP by arterial catheter provides accurate continuous BP values, it is considered the gold standard for BP monitoring and widely used intraoperatively,3 especially in critical patients, those with high ASA status or for high-risk surgeries, that may require fine tuning of the depth of anesthesia and timely management of hemodynamic instability. However, due to its invasive nature the arterial catheter may be difficult to place and lead to arterial complications.4,5 Thus, a reliable and continuous beat-to-beat noninvasive BP monitor would benefit elective high ASA and high-risk surgery patients. T-Line Tensymeter (Tensys Medical Inc.) is an alternative method with good accuracy and precision, especially for those patients in whom monitoring for rapidly changing individual BP readings are important intraoperatively without the need for arterial cannulation and where intermittent automatic oscillometric monitors may not be able to deliver a high-degree precision and accuracy.16,17 Ron Dueck et al18 revealed that the bias in MBP, SBP, and DBP for TL-200 was 2.3±5.9 Hg, 2.3±7.8, and 1.7±6.2 mm Hg, respectively, whereas for the TL-200pro the values were 0.72±5.15, −1.39±8.85, and 4.36±6.64 mm Hg, respectively.19 TL-300 is a new generation completely noninvasive device with a new, modified disposable locator in sensor to track patient’s radial artery7; however, the evidence base backing its accuracy and precision in clinical settings is yet to be established.
The Association for the Advancement of Medical Instrumentation ANSI/AAMI SP10 recommends that the test device would be clinically acceptable if the mean difference is <5 mm Hg with its SD <8 mm Hg compared with the reference method.20 On the basis of our results, the TL-300 met this recommendation. Moreover, it also met the standard of British Hypertension Society grade “A” accuracy which requires the percentage of bias within 5, 10, 15 mm Hg >60%, 85%, 95%, respectively.21 Besides, TL-300 had a relatively high precision with the narrow BP bias 95% limits of agreements (SBP: −10.2 to 12.8, DBP −9.8 to 15.3, and MBP: −6.4 to 10.2 mm Hg). Compared with previous T-Line devices series, TL-300 also showed good precision with more narrow SD.18,19,22–24 Besides, the current study also confirmed the ability of TL-300 to track BP changes reliably. Its coefficient of determination (r2) with invasive BP for SBP, DBP, and MBP was 0.908, 0.803, and 0.922, respectively. The r2 of TL-300 and invasive BP values were all high, although the DBP correlation was characteristically lower. No apparent change in the regression relationship was found at either low or high BP values. These findings suggest a good correlation of TL-300 measurements with the invasive method.
Although every effort was made to minimize bias during data collection and analyses, several limitations exist in the present study. First, as the current study was a retrospective analysis, a prospective study protocol is needed. Second, the sample size of 23 patients for this analysis was relatively small. Third, no very high or low body mass index as well as critically ill patients were included, although previous study demonstrated that TL-200 was competent for the obese18 and critically ill patients.7 The question on how to evaluate and validate new technologies for hemodynamic monitoring is of crucial importance and complex. Thus, what we need are methodologically sound and correct method comparison studies including a variety of different patients without selecting/excluding patients. Fourth, the evidence of kurtosis, that is presence of very high values in the distribution of BP values, was noted, which might be due to limited number of subjects included in the study. In addition, the invasive DBP values also showed a significantly higher skew and kurtosis than the invasive SBP values. Technically, the T-Line device measures MBP, then computes a derived SBP and DBP value. It is typical for the DBP values to be less reliable than the MBP and SBP values. This is noteworthy insofar as it affects the precision of the invasive DBP values. Some invasive BP values may have been affected by “damping,” due to inadequate flushing of the invasive BP line. This concern seems valid given that the data collection and analysis occurred in a retrospective manner. It is also noteworthy that kurtosis was lower for the TL-300 values than the invasive BP values for all 3 measurements. This information could imply an advantage for the TL-300 BP values. A prospective study should make it feasible to specifically look at details that affect invasive versus noninvasive beat-to-beat BP precision. Finally, the slope changes were noticed in the Bland-Altman plot for the lower or higher range of all BP values. These slope changes may indicate an element of subpopulation differences, for example, study subjects with undiagnosed hypertension, or alternatively, differences in anesthetic agent dose(s) and/or perhaps use of vasodilator medication to limit intraoperative hypertension.
To summarize, TL-300 is a promising new noninvasive beat-to-beat device with acceptable accuracy and precision in measurement of BP values in patients undergoing routine surgeries. It can, to a large extent, bridge the gap between noninvasive but intermittent and continuous but invasive BP monitoring. However, further prospective method comparison studies are needed.
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noninvasive blood pressure; invasive blood pressure; correlation; Bland-Altman analysis; retrospective study
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