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Coagulation

Comparison between the new fully automated viscoelastic coagulation analysers TEG 6s and ROTEM Sigma in trauma patients

A prospective observational study

Ziegler, Bernhard; Voelckel, Wolfgang; Zipperle, Johannes; Grottke, Oliver; Schöchl, Herbert

Author Information
European Journal of Anaesthesiology: November 2019 - Volume 36 - Issue 11 - p 834-842
doi: 10.1097/EJA.0000000000001032

Abstract

Introduction

In major trauma, severe bleeding remains a significant cause of mortality.1 Viscoelastic tests (VETs) are increasingly used to characterise a patient's coagulation status, helping to determine appropriate haemostatic therapy.2–6 TEG 5000 (Haemonetics Corporation, Braintree, Massachusetts, USA) and ROTEM (Instrumentation Laboratory, Barcelona, Spain) are the most commonly used viscoelastic devices. For both of these devices, a blood sample is added to a test cup, into which a pin is immersed vertically. TEG uses a rotating cup and ROTEM uses a rotating pin. Generation of fibrin filaments between the cup wall and the pin restricts the range of rotation, and this information is represented on a graphical display.5–7 Manual pipetting is required to perform coagulation assays with the TEG 5000 and ROTEM devices, and this is an important limitation in clinical practice.

To avoid the need for pipetting and increase ease of use, both Haemonetics and Instrumentation Laboratory have developed ‘fully automatic’ analysers, namely the TEG 6s and ROTEM Sigma devices. Mechanically, ROTEM Sigma is comparable with the previous ROTEM device. Schenk et al.8 analysed blood samples simultaneously on a ROTEM delta and the full automated ROTEM Sigma and reported a strong correlation between both devices (all P < 0.0001 and R > 0.8).

In contrast to the ROTEM technology, TEG 6s works by exposing coagulating blood to vibration frequencies and the resonant frequency is ascertained. The resonant frequency changes with clot strength, enabling the coagulation process to be depicted in the same way as with the TEG 5000 device.9 Despite the fundamental technological difference between the TEG 5000 and TEG 6s devices, assessments of blood samples from healthy volunteers and cardiac surgery patients have shown that they provide similar results.10 Former studies comparing TEG 5000 and the ROTEM reported only a poor correlation between test results of comparable assays.11 This finding was in part related to handling problems, in particular if non-laboratory staff, for example physicians, run the analyses.11 The hypothesis of the current study was that due to automatic processing of the blood samples correlation coefficients between test results of TEG 6s and ROTEM Sigma might be higher than previously reported.

Materials and methods

The prospective, observational, descriptive cohort study was performed on blood samples gathered from trauma patients admitted to the AUVA Trauma Centre Salzburg, Austria between August 2017 and September 2018. Patients were included regardless of platelet count or fibrinogen concentration. Exclusion criteria were age less than 17 years, pregnancy, coagulation disorders and anticoagulant therapy (although treatment with aspirin or low molecular weight heparin was permissible).

The local Ethical Committee of Salzburg, Sebastian-Stief-Gasse 2, 5020 Salzburg, Austria provided ethical approval for this study on 5 February 2017 (Chairperson: Dr Bernhard Graf, Reference number 415-E/2161/2-2017). Informed consent was obtained from the patients or next of kin. Since 2005, ROTEM measurements have been part of our standard diagnostic protocol for all severe trauma patients upon emergency room admission and during their ICU stay.12 For TEG 6s analyses an additional citrated blood sample of 1.4 ml was taken.

Blood samples were obtained upon emergency room admission, during the initial phase of surgical care, and subsequently during patients’ ICU and hospital stays. For VETs, blood was collected in tubes containing 0.3 ml of buffered 3.2% trisodium citrate (S-Monovette; Sarstedt AG, Nürmbrecht, Germany), resulting in a citrate:blood volume ratio of 1 : 9. VETs were performed simultaneously on a TEG 6s and ROTEM Sigma device within 15 min after blood sampling.

TEG 6s methodology

The principles of TEG 6s are described in detail elsewhere.9 Briefly, coagulation analyses are performed with a four-channel microfluidics cartridge. After the cartridge is inserted into the device aperture, approximately 400 μl of citrated blood must be injected via a pipette or syringe into an entry port. The required amount of blood to run all four tests simultaneously is drawn automatically, recalcified and mixed with different activators of the coagulation process.

The following four assays were run simultaneously: kaolin-activated (CK) test; tissue factor (TF) and kaolin activated (RapidTEG or CRT) test; kaolin-activated and heparinase (CKH) test; TF activated and abciximab (functional fibrinogen) test.

TEG 6s provides the following parameters for the CK test, CRT test and CKH test: time from coagulation initiation until a clot amplitude of 2 mm is reached (reaction time or r-time, min); time elapsing before a clot amplitude of 20 mm is reached (kinetic time or k-time, min); angle formed by the tangent line at the midway point of the r-time and the k-time, α-angle, degrees; maximum clot strength (maximum amplitude, mm); and reduction of the clot amplitude 30 min after the maximum amplitude is reached (lysis 30 or LY30, %). The functional fibrinogen test provides only maximum amplitude and the functional fibrinogen concentration (FLEV, g l−1), which is calculated from the maximum amplitude.

ROTEM Sigma methodology

ROTEM Sigma uses the same measurement principles as previous ROTEM devices, ROTEM Delta and ROTEM Gamma.13 After calibration of the device, a cartridge and a tube containing citrated blood are inserted into the device. The required amount of blood to run all four channels is drawn automatically. After recalcification, dried activators are added and the blood sample is transferred automatically to a cup where a vertical plastic pin is immersed.

The following four assays were run simultaneously: ellagic acid activated (INTEM) test; TF activated (EXTEM) test; ellagic acid activated and heparinase (HEPTEM) test; and TF activated and cytochalasin D (FIBTEM) test.

ROTEM Sigma provides the following parameters for the EXTEM, HEPTEM and FIBTEM assays: time from start of test until a clot firmness of 2 mm is detected (clotting time or CT, s); time elapsing before a clot amplitude of 20 mm is reached (clot formation time or CFT, s); angle formed by the tangent line when the clot amplitude reaches 2 mm (α-angle, degrees); maximum clot strength [maximum clot firmness (MCF), mm]; and clot strength as a percentage of the MCF, 60 min after the CT is reached (lysis index at 60 min or LI60, %).

Additional tests

Methods for blood cell count measurements, arterial blood gas analyses and standard coagulation tests are described in the Supplementary data, https://links.lww.com/EJA/A211.

Statistical analysis

A power calculation (G Power Version 3.1.9.1, Heinrich Heine Universität, Düsseldorf, Germany) before data acquisition revealed that a sample size of 79 is required to have 95% power to detect a significant correlation with a two-tailed significance level (alpha) of 5%. Data distribution was tested using the Shapiro–Wilk normality test. Continuous variables are expressed as median [IQR].

The following assays were compared: CK and INTEM; CRT and EXTEM; CKH and HEPTEM; and functional fibrinogen and FIBTEM. For the first three of these pairs of assays r-time vs. CT, k-time vs. CFT, α-angle vs. α-angle and maximum amplitude vs. MCF were compared. In addition, FLEV values were compared with Clauss fibrinogen concentration measurements.

Differences between the two devices in categorical variables were analysed using Fisher exact test (χ2). For continuous variables, differences were tested using the paired t test or the Wilcoxon matched-pairs signed rank test. Correlations between TEG 6s and ROTEM Sigma measurements were calculated using the Spearman nonparametric test. Correlations were classified as weak (0.20 to 0.39), moderate (0.40 to 0.59), strong (0.60 to 0.79) or very strong (≥0.80).

All statistical calculations were performed using GraphPad Prism 5.03 (GraphPad Software, La Jolla, California, USA). The level of significance was set at P less than 0.05.

Results

A total of 125 samples were assessed, of which 20 analyses were excluded due to the exclusion criteria. The remaining 105 samples were taken from 67 patients. The population was predominantly male (71.6%), with a median [IQR] age of 43 [31 to 61] years and the median injury severity score was 25 [14 to 38] (Supplementary Table 1, https://links.lww.com/EJA/A211). Forty-seven samples (44.8%) were taken upon emergency room admission, 12 (11.4%) were taken intra-operatively and 46 (43.8%) were taken during the patients’ ICU stay (Fig. 1).

F1-6
Fig. 1:
Flow chart of the study. DOAC, direct oral anticoagulant; ER, emergency room.

Spearman correlation coefficients for corresponding TEG 6s and ROTEM parameters from six different assays are shown in Fig. 2. Strong correlations were observed between r-time in the TEG 6s CK and CKH assays, and CT in the INTEM and HEPTEM assays (ROTEM Sigma). However, only moderate correlation was observed between CRT r-time and EXTEM CT. Strong correlations were evident between k-time in the CK and CKH assays, CFT in the INTEM and HEPTEM assays, and between α-angle in the CRT and CKH assays and the EXTEM and HEPTEM assays. The correlation between α-angle in the CK and INTEM assays was moderate. Very strong correlation was observed between TEG 6s values for CRT k-time and EXTEM CFT, and TEG 6s maximum amplitude in the CK, CRT and CKH assays, and the corresponding ROTEM Sigma MCF values (INTEM, EXTEM and HEPTEM). Correlation between LY30 and LI60 for CK and INTEM as well as CRT and EXTEM was strong (0.6412 and 0.7490, respectively, both P < 0.0001). Functional fibrinogen maximum amplitude correlated very strongly with FIBTEM MCF, and FLEV correlated very strongly with Clauss fibrinogen concentration. FIBTEM MCF revealed stronger correlation with Clauss fibrinogen than functional fibrinogen maximum amplitude (0.8515 vs. 0.7865; both P < 0.0001) (Fig. 3).

F2-6
Fig. 2:
Relationships between comparable parameters of TEG 6s and ROTEM Sigma tests; values shown are Spearman correlation coefficients and associated P values. (a) CK vs. INTEM, (b) CRT vs. EXTEM, (c) CKH vs. HEPTEM. CFT, clot formation time; CK, kaolin-activated test; CKH, kaolin-activated and heparinase test; CRT, tissue factor and kaolin activated test; CT, clotting time; EXTEM, tissue factor activated test; HEPTEM, ellagic acid activated and heparinase test; INTEM, ellagic acid activated test; k-time, kinetic time; MA, maximum amplitude; MCF, maximum clot firmness; r-time, reaction time.
F3-6
Fig. 3:
TEG 6 s and ROTEM Sigma fibrinogen-related parameters; values shown are Spearman correlation coefficients and associated P values. (a) Functional fibrinogen vs. FIBTEM, (b) functional fibrinogen level vs. Clauss fibrinogen, (c) FIBTEM vs. Clauss fibrinogen, (d) Functional fibrinogen vs. Claus fibrinogen. Functional fibrinogen, tissue factor activated and abciximab (functional fibrinogen) test; FIBTEM, tissue factor activated and cytochalasin D test; FLEV, functional fibrinogen level; MA, maximum amplitude; MCF, maximum clot firmness.

Correlations between TEG 6s and ROTEM Sigma parameters and standard coagulation tests are outlined in Supplementary Fig. 1, https://links.lww.com/EJA/A211.

Absolute values for most comparable parameters showed statistically significant differences between TEG 6s and ROTEM Sigma (Supplementary Table 1, https://links.lww.com/EJA/A211). The r-times in the CK and CKH assays were significantly longer than CT in the INTEM and HEPTEM assays and, accordingly, the α-angle was significantly lower in CK and CKH than in INTEM and HEPTEM. In addition, k-time in the CK assay was significantly longer than INTEM CFT. In contrast, r-time and k-time in the CRT assay were significantly shorter than CT and CFT in the EXTEM assay. Maximum clot strength as indicated by maximum amplitude in the CK, CRT and CKH assays and MCF in the INTEM, EXTEM and HEPTEM assays, was similar between the different devices and clotting activators. The CRT and EXTEM maximum clot strength values were examined in patients with platelet counts less than 150 × 109 l−1, within (150 to 450 × 109 l−1) or above the normal range (<450 × 109 l−1) (Fig. 4). Similarity of the two tests was maintained for all of these subgroups. In contrast, values for functional fibrinogen maximum amplitude were significantly higher than those for FIBTEM MCF in patients with normal and low platelet counts. No difference was observed between fibrin polymerisation in patients with platelet counts above normal limits (Fig. 4). The absolute values of the lyses parameters LY30 and LI60 revealed significantly higher numbers using ROTEM tests compared with corresponding TEG assays.

F4-6
Fig. 4:
Comparisons of absolute values for CRT maximum amplitude vs. EXTEM maximum clot firmness and functional fibrinogen maximum amplitude vs. FIBTEM maximum clot firmness, with stratification by platelet count (above, below or within the normal range). Data are presented as box and whisker plots depicting values for median, interquartile range and range. TEG 6s, light grey; ROTEM Sigma, white. P values derived from paired t test or Wilcoxon matched-pairs signed rank test. CRT, tissue factor and kaolin activated test; EXTEM, tissue factor activated test; functional fibrinogen, tissue factor activated and abciximab (functional fibrinogen) test; FIBTEM, tissue factor activated and cytochalasin D test; MA, maximum amplitude; MCF, maximum clot firmness.

Values for FLEV were consistently higher than the Clauss fibrinogen concentration, with median values of 3.63 [IQR 3.15 to 4.45] and 2.62 [2.16 to 3.62] g l−1, respectively (P < 0.0001).

Values outside predefined normal ranges

Significant differences between the two devices were observed in the numbers of patients with test results outside the normal ranges (Table 1). In the EXTEM assay, ROTEM Sigma indicated larger numbers of patients below normal limits than was observed with TEG 6s in the CRT assay. In contrast, measurements above normal ranges were more frequently evident with TEG 6s CK assay compared with INTEM.

T1-6
Table 1:
Numbers of measurements outside the normal ranges defined for TEG 6s and ROTEM Sigma parameters

Compared with FIBTEM MCF, functional fibrinogen maximum amplitude values indicated that more patients were below normal limits. Hypercoagulability was apparent in more patients according to the INTEM assay vs. the CK assay.

Discussion

This is the first study comparing the fully automated viscoelastic point-of-care analysers TEG 6s and ROTEM Sigma in a cohort of trauma patients. Strong correlations were observed between many comparable parameters from the two devices, although absolute values differed significantly. Numbers of patients with measurements outside the normal range, indicating either hypo-coagulability or hyper-coagulability, differed significantly between coagulation analysers.

Few previous studies have compared TEG and ROTEM in patients and only one study compared TEG 6s and ROTEM Sigma measurements in blood samples from healthy volunteers.11,14–18 Hagemo et al.11 reported the results from simultaneous analyses performed on a TEG 5000 and ROTEM Delta in a cohort of 182 trauma patients upon emergency room admission. Correlation coefficients between parameters representing different stages of the clotting process were poor to moderate, and particularly low (0.15 to 0.67) at the centre where measurements were performed by the attending physicians.11 In a previous study, Meyer et al.15 simultaneously performed the functional fibrinogen (TEG 5000) and FIBTEM (ROTEM Delta) assays in trauma patients upon emergency room admission. The linear regression coefficient between functional fibrinogen maximum amplitude and FIBTEM MCF was only 0.50 (P < 0.0001). In contrast, the current study found strong to very strong correlations for most comparable parameters, which is probably related to the reduced probability of handling errors with the fully automated devices.

Prüller et al.16 compared maximum clot strength with functional fibrinogen (TEG 5000) and FIBTEM (ROTEM Delta) in 261 surgical patients. Values for functional fibrinogen maximum amplitude were significantly higher than those for FIBTEM MCF. This finding is consistent with the results of the current study and is related to different efficacy of platelet inhibition in the two assays. Accordingly, the correlation coefficient between FIBTEM MCF and fibrinogen concentration was higher compared with functional fibrinogen maximum amplitude. The functional fibrinogen test uses the glycoprotein IIb/IIIa antibody abciximab, and this does not fully eliminate the contribution of platelets to the strength of the fibrin clot.19 Cytochalasin D, which is used in the FIBTEM assay, is a more effective inhibitor of platelet activity.20 Our group reported recently that a combination of abciximab and cytochalasin D completely eliminates any platelet contribution to clot amplitude in fibrin polymerisation assays.21,22

The current study showed major differences between the two devices in the number of results outside the normal ranges as provided by the manufactures. However, results outside the predefined limits do not necessarily trigger haemostatic therapy. Established treatment algorithms are based primarily on expert opinion, with treatment triggers that often differ from the boundaries of the normal range.23

TEG 6s transforms functional fibrinogen maximum amplitude to the ‘functional fibrinogen level’ (FLEV).24 Despite very strong correlation between FLEV and Clauss fibrinogen, the absolute values were consistently higher with FLEV. Similar differences in absolute values have been reported in previous studies25,26 and therefore the validity of FLEV as a measure of fibrinogen concentration is questionable and, based on our findings, we do not recommend using FLEV to guide fibrinogen replacement therapy.

In the current study, both analysers were located in the emergency room and none of the measurements suggested disturbance due to unintended movement of the devices. The use of resonance in the TEG 6s device results in low sensitivity to vibrations or shock. Meledeo et al.14 placed the TEG 6s on a platelet shaker and performed analyses during perpendicular or horizontal movements; no differences in the measurements between stationary and moving conditions were observed. In contrast, the previous TEG 5000 device was highly sensitive to vibrations due to the free suspension of the pin and therefore had limited capacity for use within the emergency room. Thus, many trauma centres perform TEG 5000 tests in the laboratory rather than at the point of care.3

Another difference between the fully automated devices and their predecessors is the reduced amount of blood needed to perform the measurements. This advantage, which is most likely to be significant in small children with low blood volumes, is greater with TEG 6s (∼400 μl needed to run all four channels) than with ROTEM Sigma (1360 μl required for four channels).

TEG 6S analyser delivers first test results (CRT r-time) approximately 3 min earlier than ROTEM Sigma (FIBTEM CT). In contrast to ROTEM Sigma, the software of the TEG 6s used for the current study does not provide numbers of the clot amplitude after 5 or 10-min running time (A5 or A10). This might be of interest for rapid decision-making regarding fibrinogen substitution or platelet transfusion. However, a recent software update is now able to deliver these numbers.

Strengths and limitations

Strengths of the study are the real-world clinical setting, the inclusion of a range of VETs and parameters, and the application of only a small number of exclusion criteria. Furthermore, the results may be applicable to settings other than trauma, although there are caveats to this. For example, with the exception of low molecular weight heparin, the patients were not receiving therapeutic heparin. Therefore, the study results may not be applicable to patients receiving high-dose unfractionated heparin, which is commonly used in cardiac surgery.

Several limitations of this study must be considered, firstly regarding the extent to which the TEG 6s and ROTEM Sigma assays are comparable. The coagulation activators used in the two devices are not identical with regard to the pathways of the coagulation process that are activated, raising uncertainty as to whether equivalent results should be expected for parameters usually considered as comparable. Low platelet count and low fibrinogen concentration can affect most coagulation measurements, and only a limited number of patients (those with severe bleeding) met these criteria.

Moreover, measurements were performed on blood samples from trauma patients only. Therefore, we cannot rule out the possibility that, in other cohorts such as cardiac surgery or liver transplant patients, similar results would be obtained.

Conclusion

Most of the parameters compared in this study showed strong to very strong correlations between the TEG 6s and ROTEM Sigma devices. Absolute values for maximum clot strength showed similarity, but absolute values for most other parameters showed significant differences between the two devices, indicating that device-specific interpretation of results is needed. In comparison with the previous generation of devices, the analytical process is greatly simplified with TEG 6s and ROTEM Sigma. The results of our study suggest that this increases the consistency and accuracy of VET results in clinical practice.

Acknowledgements relating to this article

Assistance with the study: we would like to thank Lisa Santner and her team from the Central Laboratory of the AUVA Trauma Centre Salzburg for their generous assistance in running some of the analyses.

Financial support and sponsorship: only hospital resources funded this study.

Conflict of interests: HS has received honoraria for participation in advisory board meetings for Bayer Healthcare, Böhringer Ingelheim and Tem International, and has received study grants from CSL Behring. OG has received study grants from CSL Behring, Portola, TEM International. BZ has received speaker fees from CSL Behring.

Presentation: none.

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