Original Article
Thromboelastography in off-pump coronary artery bypass grafting
Asian Cardiovascular & Thoracic Annals 2015, Vol. 23(4) 430–434 ß The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0218492314558636 aan.sagepub.com
Sushil Kumar Singh1, Vijayant Devenraj1, Vivek Tewarson1, Sarvesh Kumar1, Dinesh Kaushal2 and Tulika Chandra3
Abstract Background: Thromboelastography enables complete evaluation of the process of clot initiation, the structural characteristics of the formed clot and its stability. Many previous studies have assessed the predictive role of thromboelastography in on-pump cardiac surgery, but there are no clear guidelines on its use in off-pump coronary artery bypass. The aim of this study was to evaluate the use of thromboelastography and its relevance during the postoperative period following off-pump coronary artery bypass. Methods: This was a one-year prospective study on 55 patients undergoing off-pump coronary artery bypass for coronary artery disease. Thromboelastography was performed as a bedside investigation in the cardiothoracic and vascular surgery intensive care unit. Results: The association between maximum amplitude and total blood loss 500 mL was statistically significant (p < 0.001). Using receiver operator characteristic curve analysis, it was seen that with increasing maximum amplitude values, a decrease in blood loss was observed. A cutoff value of maximum amplitude 500 mL. Conclusions: Thromboelastographic parameters show a reliable correlation with increased blood loss in off-pump coronary artery bypass grafting, and predict patients with an increased chance of blood requirement as well as those at risk of a hypercoagulable state.
Keywords Blood coagulation tests, blood transfusion, coronary artery bypass, point-of-care systems, postoperative hemorrhage, thromboelastography
Introduction Thromboelastography (TEG) enables global assessment of hemostatic function from a single blood sample, documenting the interaction of platelets with the protein coagulation cascade from the time of the initial platelet-fibrin interaction through platelet aggregation, clot strengthening and fibrin cross linkage, to eventual clot lysis. The signature of the generated tracings can give information on clotting factor activity, platelet function, and any clinically significant fibrinolytic process, within 20–30 min. The thromboelastograph is a small instrument that can be set up easily in the operating or anesthetic room and allows coagulation to be monitored directly at regular intervals. Unlike conventional coagulation tests, TEG enables
complete evaluation of the process of clot initiation, the structural characteristics of the formed clot and its stability.1 Many of the conventional coagulation 1 Department of Cardiothoracic and Vascular Surgery, King George’s Medical University, Lucknow, Uttar Pradesh, India 2 Department of Anesthesiology, King George’s Medical University, Lucknow, Uttar Pradesh, India 3 Department of Transfusion Medicine, King George’s Medical University, Lucknow, Uttar Pradesh, India
Corresponding author: Sushil Kumar Singh, MCh, Department of Cardiothoracic and Vascular Surgery, King George’s Medical University, Lucknow, Uttar Pradesh 226003, India. Email: [email protected]
Downloaded from aan.sagepub.com at TEXAS SOUTHERN UNIVERSITY on May 27, 2016
Singh et al.
431
tests end with the formation of the first fibrin strands, whereas TEG begins at this point and continues to generate data as clotting continues through to eventual clot lysis or retraction. While there have been many studies seeking a correlation between abnormal TEG parameters and bleeding and/or blood requirement, they have been carried out mainly in on-pump cardiac surgery such as coronary artery bypass grafting (CABG). The aim of this study was to evaluate the use of TEG and its relevance during the postoperative period, endeavoring to define TEG parameters in patients who undergo offpump coronary artery bypass (OPCAB), which is necessary for developing a protocol for TEG-based bleeding predictors and transfusion requirements in such surgeries.
Patients and methods This study was conducted in the Department of Cardiothoracic and Vascular Surgery, King George’s Medical University, Lucknow, India. This prospective study included all consecutive patients undergoing OPCAB for coronary artery disease, admitted and operated on from November 2012 to October 2013. The study was performed using a Hemologix thromboelastometer (Framar Biomedica, Rome, Italy) as a bedside investigation in the cardiothoracic surgery intensive care unit. The same surgeon and team operated on all patients. All patients were first-time cardiac surgery patients undergoing isolated OPCAB. Aspirin or clopidogrel was discontinued at least 4 days preoperatively. All patients had baseline investigations and were operated on only when these were within the normal range (except in cases of known renal disease and diabetes). Their mean age was 56.75 9.72 years, and 80% were male. The mean body mass index was 25.15 4.12 kgm2. The majority of patients had ejection fractions of 40%–54%; 7 had a low ejection fraction of less than 40%. The most common risk factor was hypertension followed by diabetes. The mean values of all hematological and biochemical parameters were within the normal ranges. All operations were performed under general anesthesia via a median sternotomy. Postoperative management in the intensive care unit consisted of maintaining good perfusion of organs and tissues. Mean arterial pressure was kept between 60 and 70 mm Hg, and ionotropic support was provided as required. Demographic data, pre- and postoperative laboratory investigations, ventilator requirement, ionotropic requirement, intensive care unit and hospital stay, fever, wound infection, and transfusion requirement were recorded. Sampling was carried out after the patient reached the intensive care unit. A 360-mL sample of arterial blood was taken, and the test was performed at 37 C immediately after
taking the sample and before transfusion of any blood products. Postoperative blood loss was recorded at 1 h, 6 h, and at chest drain removal (total blood loss). Statistical analysis was performed using SPSS version 15.0 software (SPSS, Inc., Chicago, IL, USA). Values are represented as number (percentage) and mean standard deviation. The following statistical formulas were used: mean, standard deviation, Student’s t test, the paired t test, receiver operator characteristic curve analysis, and bivariate correlation. A value of p < 0.05 was considered significant.
Results The lowest recorded hemoglobin level was 9.4 gdL1. The mean hematocrit was 37.6% 4.7%. Platelet counts in all patients were above 100,000/mL with a mean of 1.78 0.41 105/mL. The mean prothrombin time and international normalized ratio were 14.3 0.7 s and 1.0 0.1 s, respectively. Bleeding times ranged from 2:30 to 3:45 min, and the clotting time ranged from 4:30 to 6:30 min. The mean serum creatinine was 1.1 0.2 gdL1; the highest recorded value was 1.7 gdL1. No jaundice was seen in any patient and the liver enzymes showed no evidence of hepatic dysfunction. The total mediastinal drainage ranged from 170 to 1200 mL with a mean of 525.64 197.39 mL. The majority of patients (n ¼ 35) did not require a transfusion. The duration of postoperative ventilatory support in the intensive care unit was 11.13 3.79 h (range from 6–18 h). Reintubation was required in 2 (3.6%) cases. No patient had a fever. Intensive care unit stay >3 days was required in only 9 (16.4%) cases. Most patients were discharged from the hospital before the 8th postoperative day. The TEG findings are shown in Table 1. The mean values of reaction time (RT) and kinetic time (KT) were higher, while those of a-angle, maximum amplitude (MA), and clot lysis at 30 and 60 min were lower in patients with blood loss >500 mL compared to those with blood loss 500 mL. Of the TEG variables, MA had the highest sensitivity as well as specificity, while RT had the lowest sensitivity and KT had the lowest specificity (Table 4).
Discussion The value of TEG in the management of patients undergoing orthotopic liver transplantation has been
established.2–4 On the other hand, although studies have reported that viscoelastic point-of-care coagulation devices may predict excessive bleeding after cardiopulmonary bypass (CPB), the findings are not consistent, and evidence supporting its usefulness as a predictor of bleeding is minimal.5–7 An increasing number of patients have impaired baseline platelet function due to administration of antiplatelet drugs. Because of the complex process of anticoagulation with heparin and antagonism with protamine (routine in CABG), there is a potential to predict postoperative hemostatic disturbances and guide transfusion,8 and while the use of TEG has been investigated in various general surgeries and orthopaedics, evaluation in a broad range of patients is clearly needed before recommending its routine use in cardiac surgery.9,10
Table 4. Regressed cut-off and predicted sensitivity and specificity of thromboelastography variables. Variable
Regressed cut-off
Predicted sensitivity
Predicted specificity
Reaction time (mm) Kinetic time (mm) Alpha angle Maximum amplitude (mm)
>9.50 >6.50
Thromboelastography in off-pump coronary artery bypass grafting
Asian Cardiovascular & Thoracic Annals 2015, Vol. 23(4) 430–434 ß The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0218492314558636 aan.sagepub.com
Sushil Kumar Singh1, Vijayant Devenraj1, Vivek Tewarson1, Sarvesh Kumar1, Dinesh Kaushal2 and Tulika Chandra3
Abstract Background: Thromboelastography enables complete evaluation of the process of clot initiation, the structural characteristics of the formed clot and its stability. Many previous studies have assessed the predictive role of thromboelastography in on-pump cardiac surgery, but there are no clear guidelines on its use in off-pump coronary artery bypass. The aim of this study was to evaluate the use of thromboelastography and its relevance during the postoperative period following off-pump coronary artery bypass. Methods: This was a one-year prospective study on 55 patients undergoing off-pump coronary artery bypass for coronary artery disease. Thromboelastography was performed as a bedside investigation in the cardiothoracic and vascular surgery intensive care unit. Results: The association between maximum amplitude and total blood loss 500 mL was statistically significant (p < 0.001). Using receiver operator characteristic curve analysis, it was seen that with increasing maximum amplitude values, a decrease in blood loss was observed. A cutoff value of maximum amplitude 500 mL. Conclusions: Thromboelastographic parameters show a reliable correlation with increased blood loss in off-pump coronary artery bypass grafting, and predict patients with an increased chance of blood requirement as well as those at risk of a hypercoagulable state.
Keywords Blood coagulation tests, blood transfusion, coronary artery bypass, point-of-care systems, postoperative hemorrhage, thromboelastography
Introduction Thromboelastography (TEG) enables global assessment of hemostatic function from a single blood sample, documenting the interaction of platelets with the protein coagulation cascade from the time of the initial platelet-fibrin interaction through platelet aggregation, clot strengthening and fibrin cross linkage, to eventual clot lysis. The signature of the generated tracings can give information on clotting factor activity, platelet function, and any clinically significant fibrinolytic process, within 20–30 min. The thromboelastograph is a small instrument that can be set up easily in the operating or anesthetic room and allows coagulation to be monitored directly at regular intervals. Unlike conventional coagulation tests, TEG enables
complete evaluation of the process of clot initiation, the structural characteristics of the formed clot and its stability.1 Many of the conventional coagulation 1 Department of Cardiothoracic and Vascular Surgery, King George’s Medical University, Lucknow, Uttar Pradesh, India 2 Department of Anesthesiology, King George’s Medical University, Lucknow, Uttar Pradesh, India 3 Department of Transfusion Medicine, King George’s Medical University, Lucknow, Uttar Pradesh, India
Corresponding author: Sushil Kumar Singh, MCh, Department of Cardiothoracic and Vascular Surgery, King George’s Medical University, Lucknow, Uttar Pradesh 226003, India. Email: [email protected]
Downloaded from aan.sagepub.com at TEXAS SOUTHERN UNIVERSITY on May 27, 2016
Singh et al.
431
tests end with the formation of the first fibrin strands, whereas TEG begins at this point and continues to generate data as clotting continues through to eventual clot lysis or retraction. While there have been many studies seeking a correlation between abnormal TEG parameters and bleeding and/or blood requirement, they have been carried out mainly in on-pump cardiac surgery such as coronary artery bypass grafting (CABG). The aim of this study was to evaluate the use of TEG and its relevance during the postoperative period, endeavoring to define TEG parameters in patients who undergo offpump coronary artery bypass (OPCAB), which is necessary for developing a protocol for TEG-based bleeding predictors and transfusion requirements in such surgeries.
Patients and methods This study was conducted in the Department of Cardiothoracic and Vascular Surgery, King George’s Medical University, Lucknow, India. This prospective study included all consecutive patients undergoing OPCAB for coronary artery disease, admitted and operated on from November 2012 to October 2013. The study was performed using a Hemologix thromboelastometer (Framar Biomedica, Rome, Italy) as a bedside investigation in the cardiothoracic surgery intensive care unit. The same surgeon and team operated on all patients. All patients were first-time cardiac surgery patients undergoing isolated OPCAB. Aspirin or clopidogrel was discontinued at least 4 days preoperatively. All patients had baseline investigations and were operated on only when these were within the normal range (except in cases of known renal disease and diabetes). Their mean age was 56.75 9.72 years, and 80% were male. The mean body mass index was 25.15 4.12 kgm2. The majority of patients had ejection fractions of 40%–54%; 7 had a low ejection fraction of less than 40%. The most common risk factor was hypertension followed by diabetes. The mean values of all hematological and biochemical parameters were within the normal ranges. All operations were performed under general anesthesia via a median sternotomy. Postoperative management in the intensive care unit consisted of maintaining good perfusion of organs and tissues. Mean arterial pressure was kept between 60 and 70 mm Hg, and ionotropic support was provided as required. Demographic data, pre- and postoperative laboratory investigations, ventilator requirement, ionotropic requirement, intensive care unit and hospital stay, fever, wound infection, and transfusion requirement were recorded. Sampling was carried out after the patient reached the intensive care unit. A 360-mL sample of arterial blood was taken, and the test was performed at 37 C immediately after
taking the sample and before transfusion of any blood products. Postoperative blood loss was recorded at 1 h, 6 h, and at chest drain removal (total blood loss). Statistical analysis was performed using SPSS version 15.0 software (SPSS, Inc., Chicago, IL, USA). Values are represented as number (percentage) and mean standard deviation. The following statistical formulas were used: mean, standard deviation, Student’s t test, the paired t test, receiver operator characteristic curve analysis, and bivariate correlation. A value of p < 0.05 was considered significant.
Results The lowest recorded hemoglobin level was 9.4 gdL1. The mean hematocrit was 37.6% 4.7%. Platelet counts in all patients were above 100,000/mL with a mean of 1.78 0.41 105/mL. The mean prothrombin time and international normalized ratio were 14.3 0.7 s and 1.0 0.1 s, respectively. Bleeding times ranged from 2:30 to 3:45 min, and the clotting time ranged from 4:30 to 6:30 min. The mean serum creatinine was 1.1 0.2 gdL1; the highest recorded value was 1.7 gdL1. No jaundice was seen in any patient and the liver enzymes showed no evidence of hepatic dysfunction. The total mediastinal drainage ranged from 170 to 1200 mL with a mean of 525.64 197.39 mL. The majority of patients (n ¼ 35) did not require a transfusion. The duration of postoperative ventilatory support in the intensive care unit was 11.13 3.79 h (range from 6–18 h). Reintubation was required in 2 (3.6%) cases. No patient had a fever. Intensive care unit stay >3 days was required in only 9 (16.4%) cases. Most patients were discharged from the hospital before the 8th postoperative day. The TEG findings are shown in Table 1. The mean values of reaction time (RT) and kinetic time (KT) were higher, while those of a-angle, maximum amplitude (MA), and clot lysis at 30 and 60 min were lower in patients with blood loss >500 mL compared to those with blood loss 500 mL. Of the TEG variables, MA had the highest sensitivity as well as specificity, while RT had the lowest sensitivity and KT had the lowest specificity (Table 4).
Discussion The value of TEG in the management of patients undergoing orthotopic liver transplantation has been
established.2–4 On the other hand, although studies have reported that viscoelastic point-of-care coagulation devices may predict excessive bleeding after cardiopulmonary bypass (CPB), the findings are not consistent, and evidence supporting its usefulness as a predictor of bleeding is minimal.5–7 An increasing number of patients have impaired baseline platelet function due to administration of antiplatelet drugs. Because of the complex process of anticoagulation with heparin and antagonism with protamine (routine in CABG), there is a potential to predict postoperative hemostatic disturbances and guide transfusion,8 and while the use of TEG has been investigated in various general surgeries and orthopaedics, evaluation in a broad range of patients is clearly needed before recommending its routine use in cardiac surgery.9,10
Table 4. Regressed cut-off and predicted sensitivity and specificity of thromboelastography variables. Variable
Regressed cut-off
Predicted sensitivity
Predicted specificity
Reaction time (mm) Kinetic time (mm) Alpha angle Maximum amplitude (mm)
>9.50 >6.50
