Hemostasis changes during cardiopulmonary bypass surgery

Accurate protamine:heparin matching (not just smaller protamine doses) decreases postoperative bleeding in cardiac surgery; results from a high-volume academic medical center

BACKGROUND

A multidisciplinary Quality Assurance/Performance Improvement study to identify the incidence of "heparin rebound" in our adult cardiac surgical population instead detected a thromboelastometry pattern suggestive of initial protamine overdose in 34% despite Hepcon-guided anticoagulation management. Analysis of our practice led to an intervention that made an additional lower-range Hepcon cartridge available to the perfusionists.

METHODS

One year later, an IRB-approved retrospective study was conducted in >500 patients to analyze the effects of the intervention, specifically focusing on the impact of the initial protamine dose accuracy and 18-h mediastinal chest tube drainage (MCTd).

RESULTS

No differences were observed between group demographics, surgical procedures, duration of CPB or perioperative blood product transfusion. Both groups were managed using the same perfusion and anesthesia equipment, strategies, and protocols. The median initial protamine dose decreased by 19% (p < .001) in the intervention group (170 [IQR 140-220] mg; n = 295) versus the control group (210 [180-250] mg; n = 257). Mean 18-h MCTd decreased by 13% (p < .001) in the intervention group (405.15 ± 231.54 mL; n = 295) versus the control group (466.13 ± 286.73 mL; n = 257). Covariate-adjusted mixed effects model showed a significant reduction of MCTd in the intervention group, starting from hour 11 after surgery (group by time interaction p = .002).

CONCLUSION

Though previous investigators have associated lower protamine doses with less MCTd, this study demonstrates that more accurately matching the initial protamine dose to the remaining circulating heparin concentration reduces postoperative bleeding.

Review of Thromboelastography (TEG): Medical and Surgical Applications

Thromboelastography (TEG) is a laboratory assay utilized to evaluate hemostatic properties of blood, identify coagulopathy, and guide blood product administration. While the clinical use of TEG started in the care of surgical patients, the assay has now been incorporated more routinely in the care of the medical patient as well. In this review, we explore the evolution of TEG from the historical perspective of its inception to the current state of the art of the assay. The TEG procedure and its measurements are illustrated along with a table that summarizes recommendations from across the medical and surgical literature. After each section, we review salient learning points to provide the busy clinician with information that can be immediately integrated at the bedside. We conclude with a series of summary questions to check for comprehension and direct the reader to additional resources to improve their knowledge of TEG.

Heparin Rebound: An In-Depth Review

The common conception of "heparin rebound" invokes heparin returning to circulation in the postoperative period after apparently adequate intraoperative reversal with protamine. This is believed to portend increased postoperative bleeding and provides the rationale for administering additional empiric doses of protamine in response to prolonged coagulation tests and/or bleeding. However, the relevant literature of the last 60+ years provides only a weak level of evidence that "rebounded" heparin itself is a significant etiology of postoperative bleeding after cardiac surgery with cardiopulmonary bypass. Notably, many of the most frequently cited heparin rebound investigators ultimately concluded that although exceedingly low levels of heparin activity could be detected by anti-Xa assay in some (but not all) patients postoperatively, there was no correlation with actual bleeding. An understanding of the literature requires a careful reading of the details because the investigators lacked standardized definitions for "heparin rebound" and "adequate reversal" while studying the phenomenon with significantly different experimental methodologies and laboratory tests. This review was undertaken to provide a modern understanding of the "heparin rebound" phenomenon to encourage an evidence-based approach to postoperative bleeding. Literature searches were conducted via PubMed using the following MeSH terms: heparin rebound, heparin reversal, protamine, platelet factor 4, and polybrene. Relevant English language articles were reviewed, with subsequent references obtained from the internal citations. Perspective is provided for both those who use HepCon-guided management and those who do not, as are practical recommendations for the modern era based on the published data and conclusions of the various investigators.

A systematic review of the evidence supporting post-operative antithrombotic use following cardiopulmonary bypass in children with CHD

OBJECTIVES

To determine the optimal antithrombotic agent choice, timing of initiation, dosing and duration of therapy for paediatric patients undergoing cardiac surgery with cardiopulmonary bypass.

METHODS

We used PubMed and EMBASE to systematically review the existing literature of clinical trials involving antithrombotics following cardiac surgery from 2000 to 2020 in children 0-18 years. Studies were assessed by two reviewers to ensure they met eligibility criteria.

RESULTS

We identified 10 studies in 1929 children across three medications classes: vitamin K antagonists, cyclooxygenase inhibitors and indirect thrombin inhibitors. Four studies were retrospective, five were prospective observational cohorts (one of which used historical controls) and one was a prospective, randomised, placebo-controlled, double-blind trial. All included were single-centre studies. Eight studies used surrogate biomarkers and two used clinical endpoints as the primary endpoint. There was substantive variability in response to antithrombotics in the immediate post-operative period. Studies of warfarin and aspirin showed that laboratory monitoring levels were frequently out of therapeutic range (variably defined), and findings were mixed on the association of these derangements with bleeding or thrombotic events. Heparin was found to be safe at low doses, but breakthrough thromboembolic events were common.

CONCLUSION

There are few paediatric prospective randomised clinical trials evaluating antithrombotic therapeutics post-cardiac surgery; most studies have been observational and seldom employed clinical endpoints. Standardised, validated endpoints and pragmatic trial designs may allow investigators to determine the optimal drug, timing of initiation, dosing and duration to improve outcomes by limiting post-operative morbidity and mortality related to bleeding or thrombotic events.

Hyperglycemia and Thrombocytopenia - Combinatorially Increase the Risk of Mortality in Patients With Acute Myocardial Infarction Undergoing Veno-Arterial Extracorporeal Membrane Oxygenation

Background: Patients with cardiogenic shock due to acute myocardial infarction (AMI) can rapidly undergo veno-arterial extracorporeal membrane oxygenation (VA-ECMO) therapy to recover cardiac output and decrease mortality. However, the clinical indicators predictive of mortality in these patients remain unknown.

Methods and Results: We conducted a single-center retrospective cohort study targeting AMI patients undergoing VA-ECMO. All 63 patients undergoing VA-ECMO for AMI at the Japanese Red Cross Kumamoto Hospital between January 1, 2010 and June 30, 2020 were enrolled. An exploratory analysis was conducted using a survival tree model and variables selected in a univariate Cox proportional hazard model. The median survival time from the start of VA-ECMO was 6.3 days, and 77.8% (n=49) of patients died. Survival analysis divided patients into 3 groups based on 2 parameters at the initial medical examination: Group 1, patients with neither hyperglycemia (blood glucose ≥213 mg/dL) nor thrombocytopenia (platelets ≤145,100/μL); Group 2, patients with hyperglycemia; and Group 3, patients with hyperglycemia plus thrombocytopenia. Relative to Group 1, the risk of in-hospital mortality was significantly increased in Group 2 (hazard ratio [HR] 2.25; 95% confidence interval [CI] 1.13–4.46), and that risk further increased in Group 3 (HR 7.60; 95% CI 3.21–17.95).

Conclusions: Hyperglycemia plus thrombocytopenia on initial medical examination combinatorially increase the risk of mortality in patients with cardiogenic shock due to AMI undergoing VA-ECMO.

Adequacy of hemostatic resuscitation improves therapeutic efficacy of recombinant activated factor VII and reduces reexploration rate for bleeding in postoperative cardiac surgery patients with refractory hemorrhage

Background:

Excessive bleeding and surgical reexploration are common complications that increase the risk of multi-organ failure and prolonged hospitalization after cardiac surgery. Off-label use of recombinant activated factor VII (rFVIIa) is a recommended treatment for refractory bleeding.

Objective:

The objective of the study is to determine if the adequacy of hemostatic resuscitation enhances the efficacy of rFVIIa.

Methods:

This retrospective, observational, cohort study included patients who received rFVIIa for refractory postoperative bleeding after cardiac surgery. Patients were divided into two groups based on the presence or absence of adequate coagulation resuscitation before rFVIIa administration, defined as international ratio (INR) ≤1.5, platelet count ≥100 K/mL, and fibrinogen ≥200 mg/dL. The failure of rFVIIa treatment was defined as surgical reexploration within 24 h, thoracostomy drainage >400 mL/h within 6 h or transfusion of additional blood products or another rFVIIa dose within 6 h after initial rFVIIa dose.

Results:

Of the 3833 patients, screened who underwent cardiothoracic surgery procedures, 58 patients received rFVIIa for refractory postoperative bleeding. Successful hemostasis with rFVIIa was more likely in patients who were adequately resuscitated compared with those who were not (20 [71.4%] vs. 10 [33.3%], respectively; P = 0.0046). Multiple logistic regression analysis indicated that patients who were adequately resuscitated before rFVIIa were less likely to fail treatment (odds ratio, 0.16; 95% confidence interval [0.04–0.62]; P = 0.007).

Conclusions:

The therapeutic efficacy of rFVIIa is dependent on the adequacy of hemostatic resuscitation; restoration of normal serum fibrinogen, INR, and platelet counts >100 K/mL may provide an adequate substrate for rFVIIa to be effective in managing refractory postoperative cardiac surgical bleeding.

The N-terminal lectin-like domain of thrombomodulin reduces acute lung injury without anticoagulant effects in a rat cardiopulmonary bypass model

OBJECTIVES

Systemic inflammation evoked by cardiopulmonary bypass (CPB) leads to acute lung injury (ALI) and respiratory failure. Although recombinant human soluble thrombomodulin (rTM) consists of three domains (D1-3), is reported to attenuate systemic inflammation through the N-terminal lectin-like domain (D1), anticoagulant domain (D2) may exacerbate coagulopathy after CPB. We investigated the potential of selective D1 against CPB-mediated ALI free from anticoagulant effects using a rat CPB model.

METHODS

Rats were divided into three groups: control (CPB alone, n = 5), D1 (CPB + D1, n = 4), and D123 (CPB + D123, n = 6). D1 or D123 was administrated to the rats of each group before CPB establishment. Blood samples are collected before, during and after CPB. Blood coagulability was assessed by a coagulation analyzer. Lung samples are collected at 1 h after the termination of CPB for histological analyses.

RESULTS

D123 group exhibited significantly prolonged glass beads-activated clotting time with heparinase after CPB compared to that in control group, whereas no significant prolongation in control and D1 group (control vs. D1 vs. D123: 65.4 ± 9.2 vs. 65.3 ± 10.9 vs. 83.5 ± 4.6 s, p = 0.036 [control vs. D123], 0.99 [control vs. D1]) indicating the absence of anticoagulant activities of D1. Histological studies revealed less congestion, edema, inflammation, and hemorrhage in both D1 and D123 groups compared to those in control group indicating protective effects of both D1 and D123 against ALI mediated by CPB.

CONCLUSIONS

N-terminal lectin-like domain of rTM may reduce the risk of ALI without anticoagulant effects.

Short-term recovery pattern of plasma fibrinogen after cardiac surgery: A prospective observational study

Low plasma fibrinogen level is common after cardiopulmonary bypass (CPB). Current substitution practice with fibrinogen concentrate generally follows a single measurement and cut-off values from the literature, whereas early postoperative endogenous fibrinogen kinetics is incompletely described and widely disregarded. The aim of this study was to determine the short-term recovery pattern of plasma fibrinogen after CPB weaning. Our hypothesis was that in the absence of surgical bleeding, CPB-induced hypofibrinogenemia would resolve spontaneously and predictably within a few hours. In a prospective, observational study of 26 patients undergoing conventional CPB (cCPB) or minimally invasive extracorporeal circulation (MiECC), Clauss fibrinogen level (C-FIB) was determined at 10 closely spaced time points after protamine administration. Primary endpoint was the time to recovery of post-CPB fibrinogen levels to ≥1.5 g/L. C-FIB reached its nadir after protamine administration corresponding to 62 ± 5% (mean ± SD) of the baseline level after cCPB and 68 ± 7% after MiECC (p = 0.027 vs. cCPB). C-FIB recovered spontaneously at a nearly constant rate of approximately 0.08 g/L per hour. In all patients, C-FIB was ≥1.5 g/L at 4 hours and ≥2.0 g/L at 13 hours after CPB weaning. Following cardiac surgery with CPB and in the absence of surgical bleeding, spontaneous recovery of normal endogenous fibrinogen levels can be expected at a rate of 0.08 g/L per hour. Administration of fibrinogen concentrate triggered solely by a single-point measurement of low plasma fibrinogen some time after CPB is not justified.

Blood - Artificial Surface Interactions during Cardiopulmonary Bypass

Evaluation of the biocompatibility of four different types of oxygenator (bubble, membrane, hollow fibre and ‘hybrid’) was performed on 26 patients undergoing cardiopulmonary bypass during elective coronary surgery. More platelet derangement and an increased degree of hemolysis, revealed by higher plasmatic concentration of beta-thromboglobulin, platelet factor 4 and plasmatic free hemoglobin (p < 0.05), was seen when using the bubble oxygenator. Damage to blood cells was minimal with the membrane oxygenator while the ‘hybrid’ and the hollow fibre oxygenators proved to rank at an intermediate level. Complement activation at the beginning of the cardiopulmonary bypass occurred via the alternative pathway as demonstrated by C3adesarg increase (up to nine times) without a concomitant elevation of C4adesarg. Cardiopulmonary bypass complement activation was quantitatively similar with all the oxygenators. A further activation via the classical pathway occured in all the patients after protamine injection. Consistent differences as far as clinical and biological effects exist among the various commercially available cardiopulmonary bypass apparatus; our study provides guidelines for the evaluation and selection of devices which might reduce postoperative sequelae.

Elevated preoperative von Willebrand factor is associated with perioperative thrombosis in infants and neonates with congenital heart disease

Essentials Perioperative thrombosis is a major cause of morbidity and mortality in congenital heart disease. Neonates and infants undergoing repair of congenital heart lesions were prospectively followed. Elevated von Willebrand factor (VWF) to ADAMTS-13 activity ratios typified the postoperative period. Thrombosis was associated with preoperative VWF activity and cryoprecipitate transfusion SUMMARY: Background The surgical repair of congenital heart malformations is frequently complicated by perioperative thrombosis of unclear etiology. An imbalance between von Willebrand factor (VWF) and ADAMTS-13 is an emerging variable in thrombosis. Objectives To describe perioperative changes to VWF, ADAMTS-13 and NETosis, and evaluate clinical and biochemical associations with postoperative thrombosis. Methods Neonates and infants undergoing palliation or definitive surgical repair of congenital heart malformations were recruited (n = 133). Preoperative and postoperative plasma levels of VWF, ADAMTS-13 and markers of NETosis were determined. Patients were followed for up to 30 days for the occurrence of thrombosis. Univariate and multivariate logistic regression analyses were conducted to identify variables associated with thrombosis. Results We identified significant postoperative increases in VWF activity, VWF level, DNA-histone complexes and cell-free DNA with an overall decrease in ADAMTS-13 activity. Patients experiencing postoperative thrombotic events (9%) were characterized by surgery performed at a lower intraoperative temperature, higher preoperative lactic acid levels, and higher preoperative VWF activity and level. A multivariate logistic regression model identified preoperative VWF activity (odds ratio (OR) 8.39 per IU mL-1 , 95% confidence interval [CI] 1.73-40.55) and transfusion of cryoprecipitate (OR 1.10 per mL kg-1 , 95% CI 1.03-1.17) as being associated with thrombosis. Conclusions Pediatric patients undergoing surgical repair of congenital heart malformations are exposed to high levels of VWF with diminished or minimal change to ADAMTS-13 in the immediate postoperative period. Elevated preoperative VWF activity is associated with postoperative thrombosis in pediatric congenital heart disease.

The acute effect of the antioxidant drug "U-74389G" on mean platelet volume levels during hypoxia reoxygenation injury in rats

Background

This experimental study examined the effect of the antioxidant drug "U-74389G", on a rat model and particularly in a hypoxia - reoxygenation protocol. The effects of that molecule were studied hematologically using blood mean platelets volume (MPV) levels.

Methods

40 rats of mean weight 231.875 g were used in the study. MPV levels were measured at 60 min of reoxygenation (groups A and C) and at 120 min of reoxygenation (groups B and D). The drug U-74389G was administered only in groups C and D.

Results

U-74389G administration kept significantly increased the predicted MPV levels by 12.77 ± 3.07% (p = 0.0001). Reoxygenation time non-significantly decreased the predicted MPV levels by 2.55 ± 3.71% (p = 0.4103). However, U-74389G administration and reoxygenation time together kept significantly increased the predicted MPV levels by 7.09 ± 1.91% (p = 0.0005).

Conclusions

U-74389G administration whether it interacted or not with reoxygenation time kept significantly increased the predicted MPV levels. This finding has great clinical interest in blood clotting and coagulation pathophysiology.

Cardiopulmonary Bypass Using Centrifugal Pump

Centrifugal pumps are nonocclusive pumps that offer centrifugal blood pumping known as the constrained force vortex principle.

Of 2405 open heart procedures, 370 (15.4%) were performed with a centrif ugal pump (CP). In the rest of the cases extracorporeal circulation (ECC) was established with conventional roller pump (RP). The operations performed with a CP were: 34 reoperations, 11 ascending aortic aneurysms + coronary artery bypass graft (CABG), 47 multivalve replacements, 125 CABG + left ventricu lar aneurysmectomies, and 153 CABGs alone.

This prospective study consisted of two groups, each group including 50 patients undergoing CABG surgery. In group I ECC was established with a CP and in group II with a conventional RR The two selected groups of patients were considered to be similar in terms of clinical, hemodynamic, and angio graphic data. Hemodynamic study concerned flow rate, systemic vascular re sistance (SVR), and urinary output. No difference was found between the CP and RP hemodynamically. Nevertheless, the alteration of the flow rate in re sponse to variation of SVR is accepted as an advantage.

As for hemolytic effect during ECC of CP compared with RP: Plasma free hemoglobin, hemotocrit, platelet count, platelet factor 4, and fibrinogen levels, were investigated. These parameters revealed that there was significant hemoly sis and trauma to the blood components in the RP group when compared with the CR (p < 0.05, p < 0.01).

There was no significant difference in psychoneurologic complications, but behavioral and sensory disorders were encountered sevenfold more in the RP group. This might be due to spoliation of the tubing set or to microair embo lism.

Compared with the conventional RP the CP proved to have no hemodynamic advantage. The effects on blood components showed significant trauma to the RP group. Postoperative drainage verified this observation (p < 0.05).

In this study the CP appears to be superior to the RP especially in compli cated and prolonged ECC.

Blood Conservation Strategies in Cardiac Surgery

Perioperative bleeding in cardiac surgery is related to both surgical trauma of blood vessels and defects in the hemostatic mechanism caused, in part, by cardiopulmonary bypass. Blood transfusion therefore remains a significant risk of cardiac surgery with important health and economic consequences. Blood conservation strategies for cardiac surgery have advanced over the years and the following discussion will focus on the current practices at Toronto General Hospital.

Optimal Management of Bleeding Complications After Cardiac Surgery

Patients undergoing cardiac surgery with cardiopulmo nary bypass (CPB) are at increased risk for excessive perioperative blood loss requiring transfusion of blood products. Point-of-care evaluation of platelets, coagu lation factors, and fibrinogen can enable physicians to assess bleeding abnormalities rapidly. They also can facilitate the optimal administration of pharmacologic and transfusion-based therapy and allow physicians to identify patients with surgical bleeding. The ability to reduce the unnecessary use of blood products in this setting has important implications for emerging issues in blood inventory and blood costs. The ability to de crease operative time along with re-exploration rates has important consequences for health care costs in an increasingly managed health care environment. Copyright© 2001 by W.B. Saunders Company.

Transient hypercoagulability in adult patients following open-heart surgery

The technique of thrombelastography was used to assess whether the phenomenon of hypercoagulability (accelerated coagulation) occurred in adult patients (n = 20) undergoing consecutive open-heart surgical procedures. Standard haematological investigations (pre- and 2 hours postop) were also performed and comparisons made with thrombelastographic parameters. Thrombelastographic hypercoagulability was identified in 12/20 (60%) cases but this event was transient occurring immediately postprotamine administration, and normalizing at 2h postoperation. The standard postoperative haematological assessments routinely made 2h after operation failed to detect this phenomenon. Hypercoagulability following cardiac surgery in adult patients merits further evaluation in order that the clinical significance may be determined.

Thrombocytopenia in the Intensive Care Unit Setting

Thrombocytopenia is a commonly encountered labora tory abnormality in the intensive care unit setting. Al though moderate degrees of thrombocytopenia may be dismissed as clinically trivial, severe thrombocytopenia can have catastrophic consequences. This review di vides the potential pathogenesis of thrombocytopenia into three pathophysiological categories: (1) produc tive, (2) consumptive, and (3) distributional. The im portant etiologies and appropriate therapies for throm bocytopenia in each of these categories are discussed. We have attempted to emphasize the underlying patho genic mechanisms as well as highlight the diagnostic dilemmas likely to be faced by intensive care unit physi cians. Although this review stresses those thrombocyto penic disorders most likely to be encountered in the intensive care unit, chronic etiologies of thrombocy topenia are also discussed because preexistent throm bocytopenia will further complicate the care of any acutely ill intensive care unit patient.

Approach to the Assessment of Platelet Function: Comparison between Optical-based Platelet-rich Plasma and Impedance-based Whole Blood Platelet Aggregation Methods

Platelet aggregation studies play an important role in the assessment of hereditary and acquired platelet function defects. The first aggregation test introduced into laboratory practice used platelet-rich plasma (PRP) where aggregation was detected by an optical method. The assessment of platelet function using whole blood (WB) aggregation by an impedance method followed up nearly 20 years later. The WB impedance aggregation assay appears to be superior to the optical method because it 1) evaluates platelets in a physiologic milieu in the presence of red and white blood cells, which are known to modulate platelet function; 2) is faster; 3) has higher sensitivity; and 4) does not require centrifugation, thus avoiding injury to platelets and loss of giant thrombocytes. These two assays were compared. Clearly, the WB impedance aggregation methodology has many advantages over the optical PRP assay for the assessment of the hyperactive platelet syndrome and the effects of anti-platelet drugs.

C1-esterase inhibitor following cardiopulmonary bypass: evaluation of coagulation parameters - a preliminary report

This study was designed to evaluate the effects of C1-esterase inhibitor (C1-INH) on haemostasis and blood loss in routine cardiopulmonary bypass (CPB). To determine whether or not C1-INH reduces blood loss or transfusion requirements after routine CPB, we randomized 20 patients to receive double-blind either C1-INH (15 IU/kg over 10 minutes intravenously) or placebo following heparin administration. The two groups were similar in age, sex, prior salicylate use and time on CPB.

At 30 minutes from the beginning of CPB and postprotamine, factor XII, factor XI, C1-INH and prekallikrein activity were significantly higher ( p < 0.05) than in the placebo group. No manifestations of hypercoagulability were seen in either group. Despite this haemostatic effect, patients treated with C1-INH had similar postoperative blood loss to the placebo group and similar blood transfusion requirements.

We conclude that routine use of C1-INH in CPB is unwarranted.

Point of care testing in children undergoing cardiopulmonary bypass

BACKGROUND

Excessive hemorrhage is a major complication after cardiac surgery requiring cardiopulmonary bypass (CPB). The aim of this study was to define the potential role of the cone and platelet analyzer (CPA) and the rotating thromboelastogram (ROTEM) point of care tests in children undergoing CPB.

PROCEDURE

We prospectively studied 15 pediatric patients aged 1 month to 10 years. Blood count, blood coagulation tests (prothrombin time [PT], activated partial thromboplastin time, fibrinogen, thrombin time), CPA and ROTEM parameters were measured before and after CPB. Demographic and surgical data were recorded as were those on perioperative blood loss and blood product transfusion.

RESULTS

Low body weight, longer duration on CPB and lower core body temperature were associated with an increased bleeding risk. The ROTEM test showed a significant prolongation of clotting time and decreased maximal clot firmness (MCF) postoperatively in children with increased bleeding. The coagulation parameters associated with increased bleeding were: prolonged PT, lower fibrinogen levels, prior to surgery, and lower MCF after surgery. CPA test findings were not associated with postoperative bleeding in our patients.

CONCLUSIONS

CPA did not serve as a prognostic tool for predicting bleeding risk in children undergoing CPB. The change in ROTEM's post-CPB results associated with bleeding tendency, and they may predict for poorer clot formation and stability.

Coagulation considerations for infants and children undergoing cardiopulmonary bypass

Cardiac surgery involving cardiopulmonary bypass imposes a significant pathophysiologic burden on patients. Pediatric patients are especially predisposed to the adverse effects of surgery and bypass on the coagulation system, with resultant bleeding, transfusion, and poor outcomes. These risks accrue to pediatric patients in inverse proportion to their weight and are attributable to hematologic immaturity, coagulation defects associated with congenital heart disease, bypass equipment, and the nature of congenital heart surgery. Standard anticoagulation does not completely inhibit thrombin generation, and continuous consumption of coagulation factor continues throughout bypass. Conventional measurements of anticoagulation during bypass poorly reflect this incomplete anticoagulation, and alternate methods may improve anticoagulant therapy. Emerging therapies for blocking the effects of bypass on the coagulation system hold promise for decreasing bleeding and related complications, and improving outcomes in congenital heart surgery.

Coagulation and fibrinolytic protein kinetics in cardiopulmonary bypass

The development of Cardiopulmonary Bypass (CPB) catopulted the field of cardiothoracic surgery into a new dimension--one that changed the lives of individuals with congenital and acquired heart disease worldwide. Despite its contributions, CPB has clear limitations and creates unique challenges for clinicians and patients alike, stemming from profound hemostatic pertubations and accompanying risk for bleeding and possibly thrombotic complications.

Antithrombin levels, morbidity, and mortality in a surgical intensive care unit

BACKGROUND

Antithrombin (AT) levels have been suggested as being predictive of outcome in intensive care unit (ICU) patients with septic shock. We investigated the time course of AT levels in a surgical ICU and tested the hypothesis that AT levels may be associated with morbidity and increased mortality rates in a cohort of surgical ICU patients.

METHODS

Three-hundred-twenty-seven consecutive patients admitted to the ICU with an estimated length of stay more than 48 h were included. AT levels were measured daily.

RESULTS

On admission to the ICU, AT levels were below the lower limit of normal in 84.1% (n = 275) of patients and increased significantly by 48 h after admission to reach normal values by the 7th ICU day in patients who never had sepsis (n = 208). This increase in AT levels was delayed in patients with sepsis. Patients with severe sepsis (n = 55) had consistently lower AT levels compared with other patients. Patients with lower AT levels were more likely to need blood products and had a greater maximum degree of organ dysfunction in the ICU than did other patients. The ICU length of stay was similar, regardless of the AT level on admission. Admission AT levels were not associated with increased ICU mortality in a multivariable analysis.

CONCLUSIONS

AT levels are low on admission to the ICU, regardless of the presence of sepsis. Although associated with the degree of organ dysfunction and the severity of sepsis, AT levels were not independently associated with worse outcome in this group of surgical ICU patients.

Warfarin cessation before cardiopulmonary bypass: lessons learned from a randomized controlled trial of oral vitamin K

BACKGROUND

No standard protocol of warfarin cessation and bridging for cardiac surgery exists. This study examined a single institution's protocol with respect to timing of cessation and low molecular weight heparin bridging. The recovery of vitamin K-dependent factors and the effects of cardiopulmonary bypass on coagulation factors were explored. Administration of preoperative oral vitamin K was investigated in a randomized, placebo-controlled trial. A post hoc analysis examined residual anti-Xa activity of enoxaparin bridging.

METHODS

Forty patients on warfarin undergoing cardiopulmonary bypass were randomized to receive 5 mg of oral vitamin K or placebo 6 days before surgery. Blood samples were acquired at six times and assayed for prothrombin time, anti-Xa activity, and functional levels of factors II, V, VII, and IX and of protein C. Measures of bleeding and transfusion were also collected.

RESULTS

No difference in bleeding or transfusion was observed between the treatment groups. Appropriate recovery of coagulation factors was observed with warfarin cessation irrespective of treatment group. The coagulation factors decreased by an average of 0.36 units/mL during the period of surgery. Enoxaparin 1 mg/kg until the evening before surgery resulted in 70% of patients entering the operating room with therapeutic anti-Xa activity (0.6 +/- 0.3 units/mL).

CONCLUSIONS

The cessation of warfarin 6 days preoperatively is sufficient for functional recovery of vitamin K-dependent factors, which undergo significant changes during the operative course. A 5-mg dose of vitamin K with warfarin discontinuation did not enhance recovery of vitamin K-dependent factors and is unnecessary. With the observation that enoxaparin up until the night before surgery resulted in high residual anti-Xa levels in the operating room, our center now administers the last dose of enoxaparin 24 hours before surgery.

Effect of Clopidogrel Premedication in Off-Pump Cardiac Surgery

Background— Premedication with clopidogrel has reduced thrombotic complications after percutaneous coronary revascularization procedures. However, because of the enhanced and irreversible platelet inhibition by clopidogrel, patients requiring surgical revascularization have a higher risk of bleeding complications and transfusion requirements. A principal benefit of surgical coronary revascularization without cardiopulmonary bypass is its lower hemorrhagic sequelae. The purpose of this study was to evaluate the effect of preoperative clopidogrel administration in the incidence of hemostatic reexploration, blood product transfusion rates, morbidity, and mortality in patients undergoing off-pump coronary artery bypass graft surgery using a large patient sample and a risk-adjusted approach.

Methods and Results— Two hundred eighty-one patients (17.9%) did and 1291 (82.1%) did not receive clopidogrel before their surgery, for a total of 1572 patients undergoing isolated off-pump coronary artery bypass graft surgery between January 2000 and June 2002. Risk-adjusted logistic regression analyses and a matched pair analyses by propensity scores were used to assess the association between clopidogrel administration and reoperation as a result of bleeding, intraoperative and postoperative blood transfusions received, and the need for multiple transfusions. Hemorrhage-related preoperative risk factors identified in the literature and those found significant in a univariate model were used. The clopidogrel group had a higher likelihood of hemostatic reoperations (odds ratio [OR], 5.1; 95% confidence interval [CI], 2.47 to 10.47; P <0.01) and an increased need in overall packed red blood cell (OR, 2.6; 95% CI, 1.94 to 3.60; P <0.01), multiple unit (OR, 1.6; 95% CI, 1.07 to 2.48; P =0.02), and platelet (OR, 2.5; 95% CI, 1.77 to 3.66; P <0.01) transfusions. Surgical outcomes and operative mortality (1.4% versus 1.4%; P =1.00) were not statistically different.

Conclusions— Clopidogrel administration in the cardiology suite increases the risk for hemostatic reoperation and the requirements for blood product transfusions during and after off-pump coronary artery bypass graft surgery.

Autologous blood transfusion for cardiopulmonary bypass: effects of storage conditions on platelet function

OBJECTIVES

Cardiopulmonary bypass impairs formation of large stable platelet aggregates (macroaggregation), although formation of small aggregates (microaggregation) is preserved. A factor in the uncertain benefits of intraoperative autologous blood transfusion may be the effects of storage on platelet function. The effects of citrate preservative and heparinization before storage on platelet function was therefore assessed.

METHODS

Twenty-seven patients undergoing elective coronary artery bypass grafting were randomly allocated to have 450 to 1,000 mL of blood taken into CPDA anticoagulant bags either before (n = 14) or after heparinization (n = 13). Samples from the patients and stored blood were anticoagulated with rhirudin, 200 U/mL. The macroaggregatory response to submaximal collagen was measured by impedance aggregometry and microaggregation by single platelet counting.

RESULTS

During macroaggregation, before cardiopulmonary bypass, the ex vivo median (interquartile range) response was 16.3 (12.4-18.7) Omega. This decreased 10 minutes after heparin to 8.9 (3.3-11.0) Omega (p < 0.0001). In the blood bags (in vitro), the initial response for nonheparinized blood was 4.8 (0.1-7.5) Omega (p < 0.002 v ex vivo) and at end-cardiopulmonary bypass was 2.4 (1.6-8.2) Omega. During microaggregation, in vivo heparinization decreased microaggregation both ex vivo and in vitro in CPDA blood; the in vitro response of nonheparinized blood at end-cardiopulmonary bypass was greater than that seen after in vivo heparinization (p < 0.007). No difference in bleeding or transfusion requirements was seen.

CONCLUSIONS

Collecting blood into CPDA anticoagulant caused a marked deterioration in platelet function. This was worse after in vivo heparinization and included depression of microaggregation.

A Double-Blind, Placebo-Controlled Trial of Epsilon-Aminocaproic Acid for Reducing Blood Loss in Coronary Artery Bypass Grafting Surgery

BACKGROUND

Epsilon-aminocaproic acid is a plasmin inhibitor that potentially reduces perioperative bleeding when administered prophylactically to cardiac surgery patients. To evaluate the efficacy of epsilon-aminocaproic acid, a prospective placebo-controlled trial was conducted in patients undergoing primary coronary artery bypass grafting surgery.

STUDY DESIGN

One hundred patients were randomly assigned to receive either epsilon-aminocaproic acid (100 mg/kg before skin incision followed by 1 g/hour continuous infusion until chest closure, 10 g in cardiopulmonary bypass circuit) or placebo, and the efficacy of epsilon-aminocaproic acid was evaluated by the reduction in postoperative thoracic-drainage volume and in donor-blood transfusion up to postoperative day 12.

RESULTS

Postoperative thoracic-drainage volume was significantly lower in the epsilon-aminocaproic acid group compared with the placebo group (epsilon-aminocaproic acid, 649 +/- 261 mL; versus placebo, 940 +/- 626 mL; p=0.003). There were no significant differences between the epsilon-aminocaproic acid and placebo groups in the percentage of patients requiring donor red blood cell transfusions (epsilon-aminocaproic acid, 24%; versus placebo, 18%; p=0.62) or in the number of units of donor red blood cells transfused (epsilon-aminocaproic acid, 2.2 +/- 0.8 U; versus placebo, 1.9 +/- 0.8 U; p=0.29). Epsilon-aminocaproic acid did not reduce the risk of donor red blood cell transfusions compared with placebo (odds ratio: 1.2, 95% confidence interval; 0.4 to 3.2, p=0.63).

CONCLUSIONS

Prophylactic administration of epsilon-aminocaproic acid reduces postoperative thoracic-drainage volume by 30%, but it may not be potent enough to reduce the requirement and the risk for donor blood transfusion in cardiac surgery patients. This information is useful for deciding on a therapy for hemostasis in cardiac surgery.

Activated recombinant factor VII after cardiopulmonary bypass reduces allogeneic transfusion in complex non-coronary cardiac surgery: randomized double-blind placebo-controlled pilot study

BACKGROUND

Receiving an allogeneic transfusion may be an independent predictor of mortality for patients undergoing cardiac surgery. Furthermore, these patients utilize 15% of all donated blood in the UK. In our unit, 80% of patients undergoing complex non-coronary cardiac surgery requiring cardiopulmonary bypass (CPB) receive an allogeneic transfusion. Activated recombinant FVII (rFVIIa) may be effective in reducing this need for transfusion.

METHODS

Twenty patients undergoing complex cardiac surgery were randomized to receive rFVIIa or placebo after CPB and reversal of heparin.

RESULTS

Two patients in the rFVIIa group received 13 units of allogeneic red cells and coagulation products compared with eight patients receiving 105 units of allogeneic red cells and coagulation products in the placebo group (relative risk of any transfusion 0.26; confidence interval 0.07-0.9; P=0.037). The groups did not differ for adverse events.

CONCLUSION

Despite major limitations (underpowered study and prone to type I error), we have shown that rFVIIa significantly reduces the need for allogeneic transfusion in complex non-coronary cardiac surgery without causing adverse events.

Tranexamic acid and early saphenous vein graft patency in conventional coronary artery bypass graft surgery: a prospective randomized controlled clinical trial

OBJECTIVE

Use of antifibrinolytic agents reduces the risk of bleeding and decreases the need for blood product use in patients undergoing cardiac surgery. The purpose of this study was to determine whether perioperative use of tranexamic acid decreases the rate of saphenous vein graft patency in the early postoperative period after conventional coronary artery bypass grafting surgery.

METHODS

A total of 312 patients scheduled for elective coronary artery bypass grafting surgery with cardiopulmonary bypass were randomized to receive either tranexamic acid 100 mg/kg (n = 147) or placebo (n = 165) in a double-blinded fashion before the initiation of cardiopulmonary bypass. Saphenous vein graft patency was assessed with magnetic resonance imaging 5 to 30 days after surgery.

RESULTS

Both groups were comparable with respect to baseline demographic data and surgical characteristics. A total of 237 (76%) patients underwent magnetic resonance imaging assessment. A total of 297 saphenous vein grafts were performed and 253 (85.2%; 95% confidence interval, 83.5%-86.9%) were seen in the tranexamic acid group, and 265 saphenous vein grafts were performed and 231 (87.2%; 95% confidence interval, 85.5%-88.9%) were seen in the placebo group (P = .4969). The blood loss and blood product transfusion rates in the tranexamic acid group were significantly lower than in the placebo group. There was no difference between groups with respect to postoperative morbidity and mortality.

CONCLUSIONS

The administration of tranexamic acid before cardiopulmonary bypass did not seem to compromise early venous graft patency rates but reduced perioperative blood product transfusion rates. Consequently, tranexamic acid could be advocated for routine use in patients undergoing conventional coronary artery bypass grafting surgery.

Effects of protamine and heparin can be detected and easily differentiated by modified thrombelastography (Rotem ® ): an in vitro study

BACKGROUND

Precise coagulation monitoring might help prevent heparin-protamine mismatch and thus decrease postoperative blood loss. We therefore measured coagulation time (CT) by modified thrombelastography (Rotem) as a possible differential monitor of the effects of heparin and protamine.

METHODS

Undiluted and diluted blood samples from 26 healthy volunteers were spiked with increasing concentrations of heparin (0.1, 0.2, 0.4, 0.8 and 1 U ml(-1)). In addition, undiluted blood was spiked with protamine hydrochloride (0.1, 0.2, 0.4, 0.8 and 1.6 U ml(-1)), and we tested the effect of protamine on the reversal of heparin 0.4 U ml(-1). Heparin-containing samples were analysed using the heparin-sensitive INTEM test and the heparinase-containing HEPTEM test; protamine series were also analysed with the EXTEM test (tissue factor activation).

RESULTS

CT by the INTEM test [CT-INTEM; median (min/max)] increased significantly and dose-dependently with increasing concentrations of heparin [control, 175 s (146/226); heparin, 1.0 U ml(-1) 1320 s (559/2100); P<0.001] and protamine [control, 172 s (150/255); protamine, 1.6 U ml(-1) 527 s (300/1345); P<0.0001]. Up to heparin concentrations of 0.4 U ml(-1), results were similar in undiluted and diluted blood samples. As expected, CT-HEPTEM remained within the normal range for all tested heparin concentrations (median 180-183 s), but increased similarly to CT-INTEM for increasing protamine concentrations.

CONCLUSION

CT measurement using the Rotem technique appears to be a valuable tool for heparin-protamine management. For detection of heparin alone, protamine alone and the two combined, the ratio of CT-INTEM:CT-HEPTEM can be used to distinguish the effects of heparin excess (CT-INTEM:CT-HEPTEM>1) from those of protamine excess (CT-INTEM:CT-HEPTEM=1).

Clinical Outcomes in Cardiac Surgery: Conventional Surgery versus Bloodless Surgery

Bleeding during and after cardiac operations and the effects of cardiopulmonary bypass hemodilution commonly result in blood transfusions. Excessive microvascular bleeding can result in re-exploration and prolonged hospitalization. Nearly 20% of all blood transfusions in the United States are associated with cardiac surgery. The risks associated with the use of allogeneic blood product transfusion include mistransfusion, immunologic complications, and transmission of infectious diseases. The large demand for blood products places significant pressure on the national blood supply, resulting in frequent shortages. The variability in transfusion practice of cardiac surgery patients suggests that sound blood management and a conservative approach to this population can result in reduced transfusions without increasing morbidity or mortality and avoiding complications associated with allogeneic blood transfusion.