Methodological Considerations for Studies Evaluating Bleeding Prediction Using Hemostatic Point-of-Care Tests in Cardiac Surgery

A certain proportion of patients undergoing cardiac surgery may experience bleeding complications that worsen outcomes. Numerous studies have investigated bleeding in cardiac surgery and some evaluate the role of hemostatic point-of-care tests in cardiac surgery patients. The prevalence of excessive bleeding varies in the literature, and such variability stems from the lack of a standardized definition of excessive bleeding. Herein, we report numerous definitions of excessive bleeding and methodological considerations for studies evaluating bleeding using hemostatic point-of-care tests in cardiac surgery patients. We evaluated the role of hemostatic point-of-care devices in contemporary research on bleeding complications and hemostatic management in cardiac surgery. The type of studies (prospective vs. retrospective, interventional vs. observational), patient selection (less complex vs. complex cases), as well as data analysis with comprehensive statistical considerations have also been provided. This article provides a comprehensive insight into the research field of bleeding complications in cardiac surgery and may help readers to better understand methodological flaws and how they influence current evidence.

Acetylsalicylic acid alone or in combination with either enoxaparin or unfractionated heparin for postoperative thromboprophylaxis in coronary artery bypass surgery patients. A randomised clinical trial assessing surrogate outcomes

INTRODUCTION

Coronary artery bypass graft surgery has considerable effects on patient haemostasis. Heparins as thromboprophylaxis may be beneficial but may also increase the risk of bleeding complications.

OBJECTIVES

To assess the effects of heparins on haemostasis in post-coronary artery bypass graft patients.

METHODS

Across one year, we randomised 60 participants scheduled for an elective coronary artery bypass graft-procedure with or without aortic valve replacement. The trial was a prospective, open-label (though blinded for the laboratory), randomised, single-centre trial with three intervention groups (n = 20 in each): group 1 received acetylsalicylic acid, group 2 received subcutaneous low molecular weight heparin and acetylsalicylic acid, and group 3 received intravenous unfractionated heparin and acetylsalicylic acid. Primary outcomes were platelet activation (Multiplate® ASPI-test) and time to clot initiation (TEG® R-time). We secondly assessed several additional Multiplate® and TEG® parameters.

RESULTS

Group 3 (intravenous unfractionated heparin) compared with group 1 (acetylsalicylic acid alone) showed evidence of 1) increased clot initiation time (R-time + 0.9 min; 95 % CI: +0.4 to +1.4 min; P = 0.009), and 2) decreased 30-min lysis (-1.3 %; 95 % CI: -2.1 to -0.5 %; P = 0.02). The remaining analyses of primary and secondary outcomes showed no evidence of a difference between the three groups.

DISCUSSION

Intravenous unfractionated heparins may increase the clot initiation time post-operatively after coronary artery bypass graft surgery and reduce lysis. Otherwise, there seems to be no effect of low molecular weight or unfractionated heparin on haemostatic parameters after coronary artery bypass surgery patients.

Factors associated with reoperation due to bleeding and outcomes after cardiac surgery: a prospective cohort study

OBJECTIVE

Identify the incidence and factors associated with reoperation due to bleeding in the postoperative of a cardiac surgery, in addition to the clinical outcomes of patients.

METHOD

Prospective cohort study, conducted in an Intensive Care Unit (ICU), with adult patients undergoing cardiac surgery. Patients diagnosed with coagulopathies were excluded. The patients were followed up from hospitalization to hospital discharge.

RESULTS

A total of 682 patients were included, and the incidence of reoperation was 3.4%. The factors associated with reoperation were history of renal failure (p = 0.005), previous use of anticoagulant (p = 0.036), higher intraoperative heart rate (p = 0.015), need for transfusion of blood component during intraoperative (p = 0.040), and higher SAPS 3 score (p < 0.001). The outcomes associated with reoperation were stroke and cardiac arrest.

CONCLUSÃO

Reoperation was an event associated with greater severity, organic dysfunction, and worse clinical outcomes, but there was no difference in mortality between the groups.

Fatores associados à reoperação por sangramento e desfechos após cirurgia cardíaca: estudo de coorte prospectivo

RESUMO Objetivo: Identificar a incidência e os fatores associados à reoperação devido sangramento no pós-operatório de cirurgia cardíaca, além dos desfechos clínicos dos pacientes. Método: Estudo de coorte prospectivo, realizado em Unidade de Terapia Intensiva (UTI), com pacientes adultos submetidos à cirurgia cardíaca. Foram excluídos pacientes com diagnóstico de coagulopatias. Os pacientes foram acompanhados desde a internação até a saída hospitalar. Resultados: Foram incluídos 682 pacientes e a incidência de reoperação foi 3,4 %. Os fatores associados à reoperação foram: histórico de insuficiência renal (p = 0,005), uso prévio de anticoagulante (p = 0,036), maior frequência cardíaca intraoperatória (p = 0,015), necessidade de transfusão de hemocomponentes no intraoperatório (p = 0,040) e maior pontuação no SAPS 3 (p < 0,001). Os desfechos associados a reoperação foram: acidente vascular encefálico e parada cardiorrespiratória. Conclusão: A reoperação foi um evento associado a maior gravidade, disfunção orgânica, e piores desfechos clínicos, porém não houve diferença de mortalidade entre os grupos.

Assessment of Rotational Thromboelastometry and Thrombin Generation Assay to Identify Risk of High Blood Loss and Re-Operation After Cardiac Surgery

Introduction: We aimed to investigate parameters for prediction of post-operative blood loss and re-operation in patients who underwent cardiopulmonary bypass. Methods: Thrombin generation assay, activated partial thromboplastin time, activated clotting time and rotational thromboelastometry (ROTEM) tests were performed at 4 time points in 65 patients: before skin incision (T1), after heparin injection (T2), after protamine reversal (T3) and before skin closure (T4). Results: Pre-operative endogenous thrombin potential (ETP) and peak thrombin levels were significantly lower in patients with high post-operative blood loss (≥ 800 mL) within 24 h than in those with low blood loss (< 800 mL). Clotting time (CT), maximal clotting firmness, clotting firmness time and alpha angle values of ROTEM measured at T2, T3 or T4 were significant predictors for high post-operative blood loss. An increase in CT-EXTEM over 4 time points was significant in patients who had a re-operation within 48 h compared to their counterparts. Conclusions: This study indicates that pre-operative ETP could predict high post-operative blood loss and that intra-operative ROTEM also helps to stratify risks of high post-operative blood loss and re-operation.

The Prognostic Performance of Rotational Thromboelastometry for Excessive Bleeding and Increased Transfusion Requirements in Hip Fracture Surgeries

BACKGROUND

 Hip fracture surgeries are associated with considerable blood loss, while the perioperative coagulopathy is associated with the bleeding risk of these patients. We aimed to evaluate the ability of rotational thromboelastometry (ROTEM) to detect patients at high risk for excessive bleeding and increased transfusion requirements.

METHODS

 We conducted a prospective observational study of 221 patients who underwent hip fracture surgeries. ROTEM analysis was performed preoperatively and immediately postoperatively. Blood loss parameters including blood loss volume, number of transfused red blood cell (RBC) units, and drop in hemoglobin levels were recorded. ROTEM parameters were compared between patients with and without excessive bleeding, and between patients with and without increased transfusion requirements (i.e., ≥2 RBC units).

RESULTS

 The postoperative FIBTEM MCF value ≤15 mm had 66.6% (95% confidence interval [CI]: 59.7-74.1%) sensitivity and 92.0% (95% CI: 80.7-97.7%) specificity to prognose excessive bleeding, and preoperative FIBTEM MCF value ≤15 mm had 80.4% (95% CI: 73.5-86.2%) sensitivity and 91.2% (95% CI: 80.7-97.0%) specificity to prognose increased transfusion requirements. Preoperative FIBTEM MCF ≤11 mm and postoperative FIBTEM MCF ≤15 mm were associated with considerably increased risks of excessive bleeding (odds ratio [OR]: 44.8, 95% CI: 16.5-121.3, p < 0.001; and OR: 23.0, 95% CI: 7.8-67.0, p < 0.001, respectively).

CONCLUSION

 ROTEM parameters demonstrated high prognostic accuracy for excessive bleeding and increased transfusion requirements. This can enable implementation of blood sparing strategies in high-risk patients, while blood banks could be better prepared to ensure adequate blood supply.

Thromboelastography and rotational thromboelastometry for the surgical intensivist: A narrative review

BACKGROUND

Viscoelastic tests (VETs), specifically thromboelastography (TEG) and rotational thromboelastometry (ROTEM), are gaining popularity in the management of critically ill surgical patients with hemorrhage or thrombosis due to their comprehensive characterization of the coagulation process and point-of-care availability in comparison to conventional coagulation tests (CCTs). We review current evidence for VET use in patients in the surgical intensive care unit (SICU).

METHODS

We searched PUBMED, EMBASE and the Cochrane Library through May 30, 2018 for articles that evaluated the use of VETs in patient populations and clinical scenarios germane to the surgical intensivist. Individual articles were critically evaluated for relevance and appropriate methodology using a structured technique. Information on patient characteristics, timing and methods of CCTs/VETs, and outcomes was collected and summarized in narrative form.

RESULTS

Of 2,589 identified articles, 36 were included. Five (14%) were interventional studies and 31 (86%) were observational. Twenty-five (69%) evaluated TEG, 11 (31%) ROTEM and 18 (50%) CCTs. Investigated outcomes included quantitative blood loss (13 (36%)), blood product transfusion (9 (25%)), thromboembolic events (9 (25%)) and mortality (6 (17%)). We identified 12 clinical scenarios with sufficient available evidence, much of which was of limited quantity and poor methodological quality. Nonetheless, research supports the use of VETs for guiding early blood product administration in severe traumatic hemorrhage and for the prediction of abstract excess bleeding following routine cardiac surgery. In contrast, evidence suggests VET-based heparin dosing strategies for venous thromboembolism prophylaxis are not superior to standard dosing in SICU patients.

CONCLUSION

While VETs have the potential to impact the care of critically ill surgical patients in many ways, current evidence for their use is limited, mainly because of poor methodological quality of most available studies. Further high-quality research, including several ongoing randomized controlled trials, is needed to elucidate the role of TEG/ROTEM in the SICU population.

LEVEL OF EVIDENCE

Systematic review, level IV.

An Audit of the Diagnostic Accuracy of Rotational Thromboelastometry for the Identification of Hypofibrinogenaemia and Thrombocytopenia during Cardiopulmonary Bypass

We audited the diagnostic accuracy of ROTEM® (TEM Innovations, GmbH, Munich, Germany) measurements of hypofibrinogenaemia (fibrinogen <1.5 g/l) and thrombocytopenia (platelet count <100 × 109/l) in 200 adult non-transplant patients during cardiopulmonary bypass (CPB). Blood samples were obtained for FIBTEM (assay for the fibrin part of the clot), PLTEM (calculated platelet-specific component), and laboratory measurements simultaneously. Our thresholds for FIBTEM and PLTEM were A10 (clot firmness 10 minutes after clotting time) ≤8 mm, and <35 mm respectively. We also calculated the accuracy of smaller thresholds and earlier indices. We found that FIBTEM A10 ≤8 mm had low sensitivity (0.62) for hypofibrinogenaemia. With the 13% hypofibrinogenaemia prevalence in our sample, the positive predictive value (PPV) was 0.47. In contrast, FIBTEM A10 ≤8 mm had higher specificity (0.90) (negative predictive value [NPV] 0.94). Of the other FIBTEM values analysed, only A5 ≤6 mm had similar or superior accuracy. The PLTEM results were less encouraging (sensitivity 0.81, specificity 0.62). With our prevalence of thrombocytopenia (also 13%), the PPV was only 0.24. However, the NPV was high (0.96). Of the other PLTEM values analysed, only A5 <25 mm had similar or superior accuracy. These findings indicate that during CPB FIBTEM A10 ≤8 mm and PLTEM A10 <35 mm have greater accuracy in identifying the absence of hypofibrinogenaemia and thrombocytopenia respectively than their presence. On the basis of these results we would be reassured by FIBTEM A10 values >8 mm and PLTEM A10 values ≥35 mm, but would continue to use laboratory measurements for confirmation. We would not use FIBTEM A10 ≤8 mm or PLTEM A10 <35 mm values alone to guide replacement therapy unless clinical conditions warranted an immediate decision before laboratory measurements were available.

Factors associated with the increased bleeding in the postoperative period of cardiac surgery: A cohort study

AIMS AND OBJECTIVES

To identify factors associated with the increased bleeding in patients during the postoperative period after cardiac surgery.

BACKGROUND

Bleeding is among the most frequent complications that occur in the postoperative period after cardiac surgery, representing one of the major factors in morbidity and mortality. Understanding the factors associated with the increased bleeding may allow nurses to anticipate and prioritise care, thus reducing the mortality associated with this complication.

DESIGN

Prospective cohort study.

METHODS

Adult patients in a cardiac hospital who were in the postoperative period following cardiac surgery were included. Factors associated with the increased bleeding were investigated by means of linear regression, considering time intervals of 6 and 12 hr.

RESULTS

The sample comprised 391 participants. The factors associated with the increased bleeding in the first 6 hr were male sex, body mass index, cardiopulmonary bypass duration, anoxia duration, metabolic acidosis, higher heart rate, platelets and the activated partial thromboplastin time in the postoperative period. Predictors in the first 12 hr were body mass index, cardiopulmonary bypass duration, metabolic acidosis, higher heart rate, platelets and the activated partial thromboplastin time in the postoperative.

CONCLUSIONS

This study identified factors associated with the increased postoperative bleeding from cardiac surgery that have not been reported in previous studies. The nurse is important in the vigilance, evaluation and registry of chest tube drainage and modifiable factors associated with the increased bleeding, such as metabolic acidosis and postoperative heart rate, and in discussions with the multiprofessional team.

RELEVANCE TO CLINICAL PRACTICE

Knowledge of the factors associated with the increased bleeding is critical for nurses so they can provide prophylactic interventions and early postoperative treatment when needed.

Meta-analysis of the Sources of Bleeding after Adult Cardiac Surgery

OBJECTIVE

The aim of this study was to pool data on the proportion and prognostic impact of sources of bleeding in patients requiring re-exploration after adult cardiac surgery.

DESIGN

Systematic review of the literature and meta-analysis.

SETTING

Multistitutional study.

MEASUREMENTS AND MAIN RESULTS

A literature review was performed to identify studies published since 1990 evaluating the outcome after reoperation for bleeding or tamponade after adult cardiac surgery. Eighteen studies including 5,1497 patients fulfilled the selection criteria. Reoperation for bleeding/tamponade was performed in 2,455 patients (4.6%; 95% confidence interval [CI] 3.9%-5.2%, I² 92%). These had a significantly higher risk of in-hospital/30-day mortality compared with patients not reoperated for bleeding (pooled rates: 9.3% v 2.3%; risk ratio 3.30; 95% CI 2.52-4.32; I² 47%; 8 studies; 25,463 patients). Surgical sites of bleeding were identified in 65.7% of cases (95% CI 58.3%-73.2%; I² 94%), cardiac site bleeding in 40.9% of cases (95% CI 29.7%-52.0%; I² 94%), and mediastinal/sternum site bleeding in 27.0% of cases (95% CI 16.8%-37.3%; I² 94%). The main sites of bleeding were the body of the graft (20.2%), the sternum (17.0%), vascular sutures (12.5%), the internal mammary artery harvest site (13.0%), and anastomoses (9.9%). In metaregression, surgical site bleeding was associated with a lower risk of in-hospital/30-day mortality compared with diffuse bleeding (p = 0.003).

CONCLUSIONS

Surgical site bleeding is identified in two-thirds of patients undergoing re-exploration after adult cardiac surgery. Meticulous surgical technique and systematic intraoperative checking of potential surgical sites of bleeding at the time of the original cardiac surgery may reduce the risk of such a severe complication.

Perioperative changes in platelet count and function in patients undergoing cardiac surgery

Background: Patients undergoing cardiac surgery are at increased risk of bleeding due to multifactorial coagulopathies. In the present study, we aimed at investigating the changes in platelet count and function during and after surgery as well as determining the association of the platelet dysfunction with bleeding and transfusion requirements in these patients.

Methods: A total of 40 adult patients scheduled for elective valve coronary cardiac surgery were included in this prospective observational study. Changes in platelet count and function with ADP, acid arachidonic, and collagen (light transmission aggregometry) were analyzed at three time points: before CPB, after CPB, and 24 hours after end of surgery. Postoperative bleeding and intraoperative transfusion requirements were recorded.

Results: There were a significant reverse correlation between CPB time and ADP-induced aggregation, particularly after CPB and postoperative AA-induced aggregation. There was not any significant correlation between platelet count and function at all-time points. Both platelet count and platelet aggregation significantly reduced during CPB. While platelet aggregation increased on postoperative Day 1, platelet count reduced by about 40% after CPB, and remained at this level postoperatively. Patients with abnormal ADP-induced aggregation had significant increased postoperative bleeding and transfusion requirements.

Conclusion: The results of this study demonstrate that platelet count and platelet aggregation are reduced during CPB. Our results emphasized the effect of platelet dysfunction on increased postoperative bleeding and transfusion requirements. Perioperative monitoring of platelet function can be considered as a bleeding management strategy for implantation of PBM programs.

Rotational thromboelastometry can detect factor XIII deficiency and bleeding diathesis in patients with cirrhosis

BACKGROUND & AIMS

Patients with progressive liver disease exhibit complex coagulation disorders. Factor XIII plays a crucial role in the last steps of haemostasis, and its deficiency is associated with an increased incidence of bleeding diathesis. However, current conventional coagulation tests cannot detect factor XIII deficiency. In this study, we examined factor XIII activity and the ability of rotational thromboelastometry to detect factor XIII deficiency and bleeding diathesis in patients with cirrhosis.

METHODS

We retrospectively studied 74 patients with cirrhosis, comparing the results of conventional coagulation tests (international normalized ratio, activated partial thromboplastin time, platelet count, fibrinogen level), rotational thromboelastometry, factor XIII activity and clinical scores.

RESULTS

Patients with cirrhosis exhibited reduced factor XIII activity. Factor XIII activity was positively correlated with conventional coagulation parameters and rotational thromboelastometry values, such as maximum clot formation (MCF)_extem (r=.48, P<.0001) and MCF_fibtem (r=.60, P<.0001). However, maximum lysis (ML)_extem and ML_aptem were not correlated with factor XIII activity. Three-month mortality rates (P=.0469) and bleeding complications (P<.0001) were significantly associated with lower factor XIII activity. Patients with haemorrhage exhibited significantly altered rotational thromboelastometry values.

CONCLUSIONS

Reduced levels of MCF_extem and MCF_fibtem but not high levels of ML_extem and ML_aptem are associated with factor XIII deficiency in patients with liver disease. Therefore, substituting factor XIII should be considered for such patients to strengthen clot formation in patients experiencing haemorrhage or those who have undergone interventions.

Is viscoelastic coagulation monitoring with ROTEM or TEG validated?

Recent years have seen increasing worldwide interest in the use of viscoelastic coagulation monitoring tests, performed using devices such as ROTEM and TEG. The use of such tests to guide haemostatic therapy may help reduce transfusion of allogeneic blood products in bleeding patients and is supported in European guidelines for managing trauma and severe perioperative bleeding. In addition, viscoelastic tests form the basis of numerous published treatment algorithms. However, some publications have stated that viscoelastic tests are not validated. A specific definition of the term validation is lacking and regulatory requirements of the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) have been fulfilled by ROTEM and TEG assays. Viscoelastic tests have been used in pivotal clinical trials, and they are approved for use in most of the world's countries. Provided that locally approved indications are adhered to, the regulatory framework for clinicians to use viscoelastic tests in routine clinical practice is in place.

Thromboelastogram reduces blood use by inspecting coagulation in heart surgery

OBJECTIVE

Blood transfusion after coronary artery bypass surgery is carried out according to general coagulation tests and blood counts. Our aim was to determine the effects of rotational thromboelastography results on the amount of blood products used in the intraoperative and postoperative periods in coronary artery bypass patients.

METHODS

Our study included 164 patients who underwent coronary artery bypass. A control group was formed from 82 patients picked from hospital records, who had elective coronary artery bypass before the introduction of rotational thromboelastography in our clinic. Blood transfusion was performed in this group according to conventional laboratory data. The study group comprised 82 patients who had elective coronary artery bypass after the introduction of rotational thromboelastography. Blood transfusion was performed in the study group according to rotational thromboelastogram results. The amounts of blood products used in the 2 groups were compared.

RESULTS

There were statistically significant decreases in the intraoperative and postoperative amounts of packed red blood cells (p = 0.012 and p = 0.006) and postoperative whole blood (p = 0.013) used in the study group compared to the control group. Postoperative bleeding was also significantly reduced (p = 0.001) in the study group.

CONCLUSION

Blood transfusion is an important issue after coronary artery bypass, and because of the decreased amount of blood products used, a rotational thromboelastography-based blood transfusion algorithm should be applied in patients undergoing coronary artery bypass.

Simultaneous measurement of thrombin generation and fibrin formation in whole blood under flow conditions

Assays based on the formation of thrombin and fibrin are frequently used, and results are considered exchangeable in research/clinical settings. However, thrombin generation and fibrin formation do not always go hand in hand and flow profoundly influences thrombus formation. We describe the technical/clinical evaluation of an assay to simultaneously measure thrombin generation and fibrin formation under conditions of flow. Introduction of a fluorometer into a 'cone and base principle'-based rheometer allowed the measurement of thrombin generation (using a thrombin-sensitive substrate) and fibrin formation (changes in viscosity), while applying a linear shear flow. Increasing shear rates inversely related with thrombin generation and fibrin formation. Increasing fibrinogen concentrations in defibrinated plasma resulted in increased thrombin generation and fibrin formation. In pre-operative samples of 70 patients undergoing cardiothoracic surgery, fibrin formation and thrombin generation parameters correlated with fibrinogen content, rotational thromboelastometry (ROTEM) and whole blood Calibrated Automated Thrombinography (CAT) parameters, respectively. Upon dividing patients into two groups based on the median clot strength, a significant difference in perioperative/total blood loss was established. In conclusion, we clinically evaluated a method capable of simultaneously measuring thrombin generation and fibrin formation in plasma/whole blood under continuous flow, rendering our method one step closer to physiology. Importantly, our test proved to be indicative for the amount of blood loss during/after cardiothoracic surgery.