Given the limited data on rAAA, it seems reasonable to consider evidence from cardiac surgery, a field where TEG has been widely adopted and validated. In coronary artery bypass grafting (CABG), TEG and platelet mapping (TEG-PM) reduced blood product use (red blood cells - RBC and fresh frozen plasma - FFP), minimised bleeding and led to cost savings up to 45% (12). Similar outcomes were reported by Ak et al., where a kaolin-activated TEG (kTEG) strategy was used in CABG patients. They reported that the kTEG group received 33% less FFP and platelet transfusions and required less tranexamic acid than the clinician-directed group (13). Comparable findings have also emerged from large institutional studies and meta-analyses, including fewer transfusions, fewer reoperations, lower rates of acute kidney injury (AKI), and shorter ICU stays (14–17). Using TEG significantly reduced the transfusion rate of blood products (RBC, FFP, cryoprecipitate) and reduced the number of reoperations due to haemorrhage (14). When comparing ROTEM with standard coagulation laboratory tests (APPT, INR, PLT, fibrinogen, etc.) as a tool to guide transfusion in patients with significant bleeding after cardiac surgery, similar overall transfusion rates, but the ROTEM group had significantly lower 24-hour blood loss (ROTEM: 1538.2 ± 806.4 ml vs. control: 2,056.8 ± 974.5 ml; p = 0.032) and lower long-term mortality (ROTEM: 0% vs. control: 15%; p = 0.03) in patients with prolonged cardiopulmonary bypass times (15). The meta-analysis conducted by Meco et al. found that TEG or ROTEM protocols significantly reduced RBC and FFP transfusions. It also led to a significant reduction in bleeding 12 and 24 h after surgery, fewer reoperations and a shorter ICU stay (16). In another systematic review and meta-analysis it has been shown that the use of TEG/ROTEM resulted in a 12% reduction in TBC transfusions and a 22% reduction in platelet concentrate transfusions, which was statistically significant. Moreover, a lower incidence rate of AKI was observed in the TEG/ROTEM group (17).

It appears that the findings of the following studies can be applied to the treatment of rAAA, including the need for cardiopulmonary support, fluid volume changes and complex coagulopathy, as cardiac surgery shares several features with vascular surgery. Viscoelastic-guided strategies successfully minimised 24 h blood loss and improved clinical outcomes in patients undergoing prolonged bypass surgery. These conditions closely mimic the physiological derangements observed in rAAA, which are typically associated with persistent hypotension, haemorrhagic shock, and complex coagulopathy.

Much more direct are the parallels with trauma surgery. TEG-guided resuscitation in trauma patients has been shown to improve early and 28-day survival, reduce transfusion needs, and allow earlier recognition of coagulopathy. Rapid TEG and ROTEM protocols outperform traditional coagulation lab tests in terms of speed and specificity, which are crucial factors in time-sensitive emergencies such as rAAA (18). Hartmann et al. further advocated for threshold-based, goal-directed transfusion protocols using r-TEG and ROTEM — an approach that could also be used effectively in vascular emergencies. For example, if the clotting time is prolonged, defined as ACT > 140 s (r-TEG) or EXTEM CT > 80 s (ROTEM), then the administration of FFP/PCC is recommended. In case of slow clot formation kinetics characterised by an α-angle <45° (r-TEG) or <63° (EXTEM), cryoprecipitate/fibrinogen should be considered. If the clot strength is also reduced - MA < 48 mm (r-TEG) or MCF < 45 mm (ROTEM)—platelets/fibrinogen should be administered (19).

More insight comes from the study by Reed et al. in which they investigated the utility of viscoelastic tests in 40 emergency department patients with significant bleeding, including gastrointestinal (GI), trauma and rAAA. They documented that the ROTEM A10 test recognized coagulopathy on admission in 25% of trauma patients and 13% of patients with GI haemorrhage on admission, but not in rAAA cases—possibly due to early arrival at hospital or too small sample size. In addition, the ROTEM A10 test provides faster results than standard coagulation tests, enabling earlier intervention (2). Similar results were documented by Cotton et al. They showed that in trauma patients, rapid TEG can predict faster and more precisely the need for transfusion within an hour of admission—early r-TEG and late r-TEG results (within a median time of 5.2 and 14.9 min) were available significantly earlier than conventional coagulation tests (median time of 27 min). These differences emphasise the time-sensitive advantage of TEG in emergency situations (20).

Another study emphasised that viscoelastic tests can predict massive transfusion requirements as early as during triage. It was reported that low MA and α-angle were associated with higher transfusion needs later in the course of treatment (21). The European guideline on the management of major bleeding and coagulopathy following trauma reported that point-of-care strategies such as viscoelastic tests reduce transfusion, transfusion complications (such as TRALI, TACO) and mortality with an average cost reduction per patient of £688 for ROTEM and £721 for TEG compared to conventional coagulation tests (22). Comparable outcomes were described by Whitning et al. The authors observed savings of more than £700 per patient due to fewer ICU days, reduced blood product use, and improved outcomes associated with TEG-guided treatment (23).

Beyond trauma, other specialities also offer additional insightful findings. In neurosurgical patients undergoing resection of large primary brain tumors (>4 cm), preoperative, intraoperative and postoperative TEG tests revealed perioperative coagulopathies, typically hypercoagulability, that standard tests failed to detect, guiding tailored transfusion decisions to be made (24). Further evidence of utility of TEG is provided by Neyens et al. They reported the case of an elderly patient taking dabigatran who suffered a subdural haematoma that required urgent surgical treatment. Despite the use of a specific reversal drug, standard coagulation tests indicated severe coagulopathy, while TEG parameters showed adequate clot formation and strength. This illustrates the potential of TEG to support surgical decision-making in anticoagulated patients (25).

In obstetrics, the utility of viscoelastic testing is well supported by clinical evidence. It has been shown that a TEG-guided algorithm for postpartum haemorrhage (PPH) significantly reduced the need for hysterectomy and lowered the volume of FFP transfused compared to standard management (26). In addition, TEG can detect hypercoagulability more sensitively than standard coagulation tests in pregnant women with pre-eclampsia, particularly on the day of delivery. This suggests its potential utility in both acute and postnatal haemostatic assessment (27). Also coagulation index calculated from TEG parameters can serve as a predictive marker for severe pre-eclampsia when measured in early pregnancy (13–20 weeks) (28). Further support comes from McNamara et al. who applied a ROTEM-based transfusion algorithm for postpartum haemorrhage. This approach significantly reduced both the volume and frequency of blood product use and the incidence of transfusion-related complications (29). These and other findings were summarised in a systematic review,in which TEG/ROTEM were used to detect hypercoagulability during pregnancy to guide transfusion strategies for postpartum haemorrhage, which reduced blood product use compared to standard tests (30).

TEG has been successfully used in elective vascular surgery. In systematic review Kim et al. investigated implementation of TEG in cerebrovascular disease, peripheral arterial disease (PAD), deep vein thrombosis (DVT) and arteriovenous malformation (AVM). TEG was successfully implemented to check the stability of carotid plaque and stent outcomes. It assessed bleeding and thrombotic tendencies in patients undergoing surgery for PAD and AVMs. In critically ill and surgical patients, MA levels were used to predict the possibility of DVT and pulmonary embolism (PE), providing physicians with an early indicator of these conditions (31). Further evidence was provided by Cvirn et al. They checked the application of viscoelastic tests in patients undergoing superficial femoral artery (SFA) stenting and documented that a shortened thromboelastometry-derived clotting time (CT) and a higher α-angle on ROTEM were associated with a higher risk of in-stent restenosis (ISR). More interestingly, traditional coagulation tests showed no difference between the high and low ISR risk groups. These results are valuable because they show that viscoelastic tests can be used not only to assess intra-operative bleeding and thrombosis management, but also for long-term follow-up of patients with PAD who have undergone stenting procedures (32).

TEG is also used in elective AAA repairs. For example Stoneham et al. used TEG in elective AAA repairs with a combination of cell salvage and swab-wash. They showed that in the group of 53 patients, only four required perioperative transfusions. TEG revealed no evidence of coagulopathy or fibrinolysis in these patients at high risk of bleeding, suggesting its value in confirming haemostatic stability and supporting more conservative transfusion strategies. TEG has the potential to be a powerful tool to guide safe transfusion in situations with massive bleeding (3). During thoracoabdominal aortic aneurysm repair, the FIBTEM A10 parameter on the ROTEM has shown utility as both a predictor of severe postoperative bleeding and a guide for fibrinogen supplementation, with a value ≤3 mm serving as a transfusion trigger. These results emphasise the diagnostic power of viscoelastic testing and its potential to tailor interventions to real-time coagulation profiles. Authors emphasise that guidelines based on cardiac surgery are not fully applicable to vascular surgery interventions such as thoracoabdominal aortic aneurysm (TAAA) repair (29). TEG has also been integrated into intraoperative protocols. An example was conducted by Dang et al. in their standardised protocol for ruptured AAAs at Houston Methodist Hospital. TEG was used alongside conventional parameters for haemorrhage monitoring and intraoperative fluid management. Moreover, TEG was proposed as a non-invasive replacement for Swan-Ganz catheters in mechanically ventilated patients to guide fluid and blood-product transfusions (5).

Overall, these findings show that TEG play an important role in individualised transfusion and coagulation management in vascular surgery and thanks to that, cost-effectiveness through fewer transfusions, reoperations and better outcomes. While these results are promising, they are mostly limited to elective procedures. rAAA presents a fundamentally different scenario characterised by haemodynamic instability, active bleeding and time-critical decisions.

Unfortunately, there are few studies specifically investigating TEG in rAAA. In one emergency department study, ROTEM examination of five rAAA patients did not reveal coagulopathy on admission, though this may reflect early presentation rather than absence of dysfunction. Nevertheless, the speed of ROTEM (A10 available in a few minutes compared to 57 min for traditional coagulation tests) supports its potential for early triage and management (2). Summary of included studies evaluating TEG/ROTEM in Vascular, Cardiac andTrauma Surgery is presented in Table 2.