Monitoring Hemostatic Function during Cardiac Surgery with Point-of-Care Viscoelastic Assays: A Narrative Review

Bleeding is a well-known and severe complication of cardiac surgery. Cardiopulmonary bypass, along with heparinization and hemodilution, is thought to affect all pathways of the hemostatic process, leading to excessive bleeding and worsened morbidity and mortality. The traditionally used standard laboratory tests (SLTs) were not designed for the surgical setting, have long turnaround times, and are poor predictors of bleeding. This review aims to give an overview of viscoelastic assays (VEAs), compare VEAs to conventional testing methods, and summarize the evidence for VEAs in cardiac surgery. A search of Medline via Pubmed, Scopus, and Embase yielded 2,868 papers, which we reviewed and summarized the key findings. VEAs such as rotational thromboelastometry and thromboelastography provide a quick turnaround, graphical, global impression of hemostasis in whole blood. VEAs allow for the analysis of specific contributors to the coagulation process and may facilitate cause-oriented hemostatic treatment and the development of treatment algorithms. VEAs have been found to have a high specificity and high negative predictive value for coagulopathic bleeding. Patients treated with VEA-based algorithms have been shown to have lower rates of bleeding, transfusion requirements, and exposure to allogeneic blood products. However, VEA-based algorithms have not demonstrated a mortality benefit and evidence for outcomes such as surgical re-exploration and hospital length of stay remains equivocal. In conclusion, VEAs have been shown to be comparable if not superior to SLTs in cardiac surgery. Further large-scale studies are needed to better evaluate the impact of VEAs on clinical outcomes.

Predictive Factors for Bleeding Risk in Patients Undergoing Valvular Surgery

BACKGROUND

The postoperative period of heart valve surgery is challenging due to the risk of bleeding, leading to complications and increased morbidity and mortality.

OBJECTIVE

To develop a risk score to predict bleeding in patients after valve surgery.

METHODS

Retrospective study of patients operated on between 2021 and 2022. Patients with major bleeding were selected based on the BARC and Bojar criteria. A logistic regression analysis was performed for factors related to bleeding and a nomogram of scores was created. For statistical significance, p<0.05 and a 95% confidence interval were considered. The study was approved by the CEP.

RESULTS

525 patients were analyzed, with a mean age of 56 years and a predominance of females. The most common valve disease was mitral insufficiency, 8.8% had increased bleeding and 4.3% had surgical reoperations. The variables with statistical significance were tricuspid insufficiency (OR 3.31, p < 0.001), chronic kidney disease/acute kidney injury (OR 2.97, p = 0.006), preoperative hemoglobin (OR 0.73, p < 0.001), reoperations (OR 2, 5, p = 0.003), cardiopulmonary bypass (CPB) time (OR 1.12, p < 0.001), 2-valve approach OR of 2.23 (p = 0.013), use of packed red blood cells OR of 2.8 (p = 0.001). In the multiple model, tricuspid insufficiency, CPB time and preoperative hemoglobin reached statistical significance.

CONCLUSION

CPB time, preoperative hemoglobin and tricuspid insufficiency were independently associated with postoperative bleeding. The proposed scale is plausible and can help predict the risk of bleeding.

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.

Imaging the dynamics and microstructure of fibrin clot polymerization in cardiac surgical patients using spectrally encoded confocal microscopy

During cardiac surgery with cardiopulmonary bypass (CPB), altered hemostatic balance may disrupt fibrin assembly, predisposing patients to perioperative hemorrhage. We investigated the utility of a novel device termed spectrally-encoded confocal microscopy (SECM) for assessing fibrin clot polymerization following heparin and protamine administration in CPB patients. SECM is a novel, high-speed optical approach to visualize and quantify fibrin clot formation in three dimensions with high spatial resolution (1.0 μm) over a volumetric field-of-view (165 × 4000 × 36 μm). The measurement sensitivity of SECM was first determined using plasma samples from normal subjects spiked with heparin and protamine. Next, SECM was performed in plasma samples from patients on CPB to quantify the extent to which fibrin clot dynamics and microstructure were altered by CPB exposure. In spiked samples, prolonged fibrin time (4.4 ± 1.8 to 49.3 ± 16.8 min, p < 0.001) and diminished fibrin network density (0.079 ± 0.010 to 0.001 ± 0.002 A.U, p < 0.001) with increasing heparin concentration were reported by SECM. Furthermore, fibrin network density was not restored to baseline levels in protamine-treated samples. In CPB patients, SECM reported lower fibrin network density in protaminized samples (0.055 ± 0.01 A.U. [Arbitrary units]) vs baseline values (0.066 ± 0.009 A.U.) (p = 0.03) despite comparable fibrin time (baseline = 6.0 ± 1.3, protamine = 6.4 ± 1.6 min, p = 0.5). In these patients, additional metrics including fibrin heterogeneity, length and straightness were quantified. Note, SECM revealed that following protamine administration with CPB exposure, fibrin clots were more heterogeneous (baseline = 0.11 ± 0.02 A.U, protamine = 0.08 ± 0.01 A.U, p = 0.008) with straighter fibers (baseline = 0.918 ± 0.003A.U, protamine = 0.928 ± 0.0006A.U. p < 0.001). By providing the capability to rapidly visualize and quantify fibrin clot microstructure, SECM could furnish a new approach for assessing clot stability and hemostasis in cardiac surgical patients.

Detection of hypofibrinogenemia during cardiac surgery: a comparison of resonance-based thrombelastography with the traditional Clauss method

: Bleeding after cardiac surgery is associated with significant morbidity and mortality. Hypofibrinogenemia is a crucial factor for bleeding in this setting and may be rapidly detected using point-of-care viscoelastic tests (POC-VET). However, the correlation of POC-VET with conventional coagulation assays is still unclear. The current study aimed to correlate resonance-based POC-VET assays (Haemonetics TEG 6s) with the traditional nonrapid Clauss method. Another aim was to identify a cut-off value for the detection of hypofibrinogenemia (fibrinogen plasma level below 150 mg/dl) focusing on the maximum amplitude of the TEG 6s citrated functional fibrinogen (CFF) assay. Adult patients undergoing cardiac surgery were screened for inclusion in this single-centre retrospective cohort study. Inclusion criteria were the availability of a TEG assay and timely corresponding laboratory results. Calculation of a CFF-maximum amplitude (CFF-MA) cut-off value was performed using receiver operating curve analysis in the baseline cohort and validated in the control cohort. The best correlation with the Clauss method was observed for the CFF-MA (r = 0.77; P < 0.0001) compared with the citrate kaolin maximum amplitude assay (r = 0.57; P < 0.0001) and the citrate kaolin heparinase maximum amplitude assay (r = 0.67; P < 0.0001). A cut-off value of 19.9 mm for the CFF-MA was calculated [area under the curve 0.87 (95% confidence interval: 0.82-0.92; P < 0.0001)]. This cut-off value had a sensitivity of 81.8% and a specificity of 71.1% for identification of hypofibrinogenemia in the control cohort. The resonance-based thrombelastography analyser can identify hypofibrinogenemia. Future clinical studies should investigate whether cut-off value guided coagulation therapy with POC-VET may improve patient outcomes in patients who suffer from bleeding complications.

Compact Grating-Coupled Biosensor for the Analysis of Thrombin

A compact optical biosensor for direct detection of thrombin in human blood plasma (HBP) is reported. This biosensor platform is based on wavelength spectroscopy of diffraction-coupled surface plasmons on a chip with a periodically corrugated gold film that carries an antifouling thin polymer layer consisting of poly[(N-(2-hydroxypropyl)methacrylamide)-co-(carboxybetaine methacrylamide)] (poly(HPMA-co-CBMAA)) brushes. This surface architecture provides superior resistance to nonspecific and irreversible adsorption of abundant compounds in the analyzed HBP samples in comparison to standard surface modifications. The carboxylate groups along the polymer brushes were exploited for the covalent immobilization of aptamer ligands. These ligands were selected to specifically capture the target thrombin analyte from the analyzed HBP sample in a way that does not activate the coagulatory process at the biosensor surface with poly(HPMA-co-CBMAA) brushes. Direct label-free analysis of thrombin in the medically relevant concentration range (1-20 nM) is demonstrated without the need for diluting the HBP samples or using additional steps for signal enhancement. The reported platform constitutes the first step toward a portable and sensitive point-of-care device for direct detection of thrombin in human blood.

Using flowable gelatin in anterior cervical spine surgery in real-world practice: a retrospective cohort study

AIM

To assess the clinical and economic impact of flowable gelatin hemostatic matrix (FGHM) in anterior cervical spine surgery (ACSS).

PATIENTS & METHODS

A total of 451 patients with performed ACSS were included to compare FGHM with conventional hemostatic methods for clinical and cost outcomes using propensity score matching method.

RESULTS

The comparisons of the matched 125 pairs observed that FGHM was associated with significantly lower blood transfusion volume (11.2 vs 36.3 ml; p = 0.039), shorter postsurgery hospital stay length (3.7 vs 4.7 days; p = 0.002), shorter operation time (103.5 vs 117.7 min; p = 0.004), lower drainage placement rate (51.2 vs 89.6%; p < 0.001) and also lower total hospital costs (median ¥64,717 vs ¥65,064; p = 0.035).

CONCLUSION

Use of FGHM in ACSS improved perioperative outcomes without increasing hospital costs.

Comparison of Coagulation Parameters in Arterial and Venous Blood in Cardiac Surgery Measured Using the Quantra System

Objective:

Perioperative coagulation testing often is performed with arterial samples even though device reference ranges typically are established in venous samples. Although limited studies exist comparing coagulation parameters across sampling sites, viscoelastic testing devices have demonstrated some differences. The objective of this study was to compare coagulation parameters determined using the Quantra System for venous and arterial samples.

Design:

Prospective, observational study.

Setting:

Tertiary care university hospital.

Participants:

The study comprised 30 adult patients undergoing cardiac surgery.

Interventions:

Paired arterial and venous samples were obtained at 2 of the following time points: baseline, during bypass, or after protamine reversal of heparin. Quantra measurements included Clot Time (CT), Heparinase Clot Time (CTH), Clot Time Ratio (CTR), Clot Stiffness (CS), and Fibrinogen (FCS) and Platelet (PCS) Contributions to clot stiffness.

Measurements and Main Results:

The relationship and agreement between matched data pairs were established and statistical analysis was performed via paired t tests. CTR, CS, FCS, and PCS were unaffected by the sampling site, whereas CT and CTH demonstrated statistically significant differences between arterial and venous samples (p < 0.001). Arterial clot times were prolonged relative to the venous ones with a mean percent error of 14.2 % and 11.9 %, respectively. These results are in general agreement with those reported for other viscoelastic testing devices.

Conclusions:

This study demonstrates that Quantra clot stiffness-based parameters (CS, FCS, PCS) are unaffected by sampling site, whereas the clot time parameters (CT and CTH) show good correlation in the presence of a bias. CTR, a ratio of CT and CTH, also is unaffected.

Zika Virus and Patient Blood Management

Sporadic Zika virus infections had only occurred in Africa and Asia until an outbreak in Micronesia (Oceania) in 2007. In 2013 to 2014, several outer Pacific Islands reported local outbreaks. Soon thereafter, the virus was likely introduced in Brazil from competing athletes from French Polynesia and other countries that participated in a competition there. Transmission is thought to have occurred through mosquito bites and spread to the immunologically naive population. Being also a flavivirus, the Zika virus is transmitted by the Aedes mosquito that is endemic in South and Central America that is also the vector of West Nile virus, dengue, and chikungunya. In less than a year, physicians in Brazil reported a many-fold increase in the number of babies born with microcephaly. Despite initial skepticism regarding the causal association of the Zika virus epidemic and birth defects, extensive basic and clinical research evidence has now confirmed this relationship. In the United States, more than 4000 travel-associated infections have been reported by the middle of 2016 to the Centers for Disease Control and Prevention. Furthermore, many local mosquito-borne infections have occurred in Puerto Rico and Florida. Considering that the virus causes a viremia in which 80% of infected individuals have no symptoms, the potential for transfusion transmission from an asymptomatic blood donor is high if utilizing donor screening alone without testing. Platelet units have been shown to infect 2 patients via transfusion in Brazil. Although there was an investigational nucleic acid test available for testing donors, not all blood centers were initially required to participate. Subsequently, the US Food and Drug Administration issued a guidance in August 2016 that recommended universal nucleic acid testing for the Zika virus on blood donors.In this report, we review the potentially devastating effects of Zika virus infection during pregnancy and its implication in cases of Guillain-Barre syndrome in adults. Furthermore, we urge hospital-based clinicians and transfusion medicine specialists to implement perisurgical patient blood management strategies to avoid blood component transfusions with their potential risks of emerging pathogens, illustrated here by the Zika virus. Ultimately, this current global threat, as described by the World Health Organization, will inevitably be followed by future outbreaks of other bloodborne pathogens; the principles and practices of perioperative patient blood management will reduce the risks from not only known, but also unknown risks of blood transfusion for our patients.

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.

Heparin monitoring during cardiac surgery. Part 1: validation of whole-blood heparin concentration and activated clotting time

There is limited published data on the agreement between techniques for monitoring heparin levels. The aim of this study was to validate the Hepcon/HMS, with particular focus on the agreement with laboratory anti-Xa assay. The performances of two ACT instruments - Hemochron and HemoTec - were also evaluated, including an assessment for interchangeability. Blood samples from 42 adult cardiopulmonary bypass (CPB) patients were analysed for activated clotting time (ACT), whole-blood heparin concentration (Hepcon/HMS) and anti-factor Xa (anti-Xa) plasma heparin concentration. Agreement between measures was determined using the method of Bland and Altman. Simple analysis of agreement between the Hepcon and anti-Xa heparin revealed the Hepcon has a mean bias of -0.46 U/mL, with the limits of agreement ±1.12 U/mL. The comparison between ACT instruments indicated a mean difference of -96 seconds for the HemoTec, with limits of ±265 seconds. The Hepcon/HMS instrument displayed satisfactory agreement with anti-Xa plasma heparin concentration, as the expected variation would not be expected to cause problems in the clinical setting. Agreement between the two measurements of ACT may be satisfactory, provided each is assigned a different target value.

Point of Care: Diagnostics in Hemostasisthe Wrong Direction?

Point-of-care-testing (POCT) is performance of a laboratory assay outside the laboratory by nontrained personnel. The advantages of POCT are: more rapid medical decisions, avoidance of long sample transports, and small samples. The disadvantages of POCT are: no laboratory personnel, insufficient calibration, quality control and maintenance, poor documentation, high costs, difficult comparability POCT/central laboratory. Therefore, disposing of a 24-hour central laboratory, the POCT spectrum should be limited to the vital parameters: K+, Ca++, Na+, glucose, creatinine, blood gases, hemoglobin or hematocrit, NH3, lactate. POCT offers no advantages, if the hospital has a rapid transport system such as a pneumatic delivery to the central laboratory. The rapid diagnosis of the acute hemostasis state of a patient should be performed in the 24-hour central laboratory that is connected to all hospital wards via a good pneumatic delivery.

Rotational thromboelastometry in prediction of bleeding after cardiac surgery

Background

Reexploration and its associated complications significantly affect hospital mortality and morbidity. Therefore, to prevent postoperative bleeding and its related complications, using an appropriate modality is essential during cardiac surgery.

Methods

Four hundred patients (296 males and 104 females, mean age 60.8 ± 9 years) scheduled for first-time coronary artery bypass graft surgery were prospectively enrolled. Blood samples were obtained for ROTEM testing before surgery and 30 min after heparin reversal. The patients were divided into 2 groups: group 1 was patients with no abnormal postoperative bleeding and group 2 was patients who required reexploration for abnormal postoperative bleeding. Group 2 patients were divided into 2 subgroups: 2a was patients with surgical bleeding and group 2b was patients with nonsurgical bleeding. Variables were compared between groups.

Results

Among the 400 patients, 42 were reexplored. Hospital stay was significantly longer and hospital deaths more frequent in group 2 patients ( p < 0.001 and p = 0.010, respectively). Ten (2.8%) patients had abnormal preoperative results of ROTEM in group 1 compared to 14 (33.3%) in group 2 ( p < 0.001). After surgery, the number of patients with abnormal ROTEM results was significantly different between the 2 groups: 6 (1.7%) in group 1 vs. 14 (33.3%) in group 2 ( p < 0.001). Four (12.5%) patients in group 2a had abnormal preoperative ROTEM results compared to 10 (100%) in group 2a ( p < 0.001).

Conclusion

Measuring coagulation factors by ROTEM both before surgery and after heparin reversal can identify patients at increased risk of postoperative bleeding.

Coagulation testing in the perioperative period

Perioperative coagulation management is a complex task that has a significant impact on the perioperative journey of patients. Anaesthesia providers play a critical role in the decision-making on transfusion and/or haemostatic therapy in the surgical setting. Various tests are available in identifying coagulation abnormalities in the perioperative period. While the rapidly available bedside haemoglobin measurements can guide the transfusion of red blood cells, blood product administration is guided by many in vivo and in vitro tests. The introduction of newer anticoagulant medications and the implementation of the modified in vivo coagulation cascade have given a new dimension to the field of perioperative transfusion medicine. A proper understanding of the application and interpretation of the coagulation tests is vital for a good perioperative outcome.

Marked changes in platelet count and function following pediatric congenital heart surgery

BACKGROUND

Reduced hemostatic capacity is common following congenital heart surgery using cardiopulmonary bypass (CPB). The etiology is multifactorial with dilutional coagulopathy, as well as platelet adhesion and activation in the CPB circuit and oxygenator. The purpose of the present study was to evaluate platelet count and function in children following CPB.

METHODS

In a prospective, observational study comprising 40 children, platelet count and function (Multiplate Analyzer(®)) were measured before surgery, immediately after bypass, and on the first postoperative day. Furthermore, conventional coagulation analysis and thromboelastometry (ROTEM(®)) were carried out.

RESULTS

A significant decrease in platelet count was observed immediately after coming of bypass (P < 0.001) and persisted to the first postoperative day (P = 0.002). Platelet function was reduced immediately after bypass after induction with ADP (P < 0.001) or TRAP (P = 0.03). The duration of CPB correlated significantly with the decrease in platelet count (r = -0.62, P = 0.0001) and reduction in platelet function (r = -0.42-0.63; P < 0.01). Moderate to deep hypothermia during CPB was associated with a decreased platelet function (P = 0.01-0.12), whereas cyanosis or previous heart surgery caused no further changes in platelet function following CPB.

CONCLUSION

Both platelet count and platelet function were significantly reduced after CPB in children undertaken correctional heart surgery. Duration of CPB and hypothermia was associated with significant changes in platelet function.

Polyion selective polymeric membrane-based pulstrode as a detector in flow-injection analysis

A method for the detection of polyions using fully reversible polyion selective polymeric membrane type pulstrodes as detectors in a flow-injection analysis (FIA) system is examined. The detection electrode consists of a plasticized polymeric membrane doped with 10 wt % of tridodecylmethylammonium-dinonylnaphthalene sulfonate (TDMA/DNNS) ion-exchanger salt. The pulse sequence used involves a short (1 s) galvanostatic pulse, an open-circuit pulse (0.5 s) during which the EMF of the cell is measured, and a longer (15 s) potentiostatic pulse to return the membrane to its original chemical composition. It is shown that total pulse sequence times can be optimized to yield reproducible real-time detection of injected samples of protamine and heparin at up to 20 samples/h. Further, it is shown that the same membrane detector can be employed for FIA detection of both polycations at levels ≥10 μg/mL and polyanions at levels of ≥40 μg/mL by changing the direction of the galvanostatic pulse. The methodology described may also be applicable in the detection of polyionic species at low levels in other flowing configurations, such as in liquid chromatography and capillary electrophoresis.

Improved blood utilization using real-time clinical decision support

BACKGROUND

We analyzed blood utilization at Stanford Hospital and Clinics after implementing real-time clinical decision support (CDS) and best practice alerts (BPAs) into physician order entry (POE) for blood transfusions.

STUDY DESIGN AND METHODS

A clinical effectiveness (CE) team developed consensus with a suggested transfusion threshold of a hemoglobin (Hb) level of 7 g/dL, or 8 g/dL for patients with acute coronary syndromes. The CDS was implemented in July 2010 and consisted of an interruptive BPA at POE, a link to relevant literature, and an "acknowledgment reason" for the blood order.

RESULTS

The percentage of blood ordered for patients whose most recent Hb level exceeded 8 g/dL ranged at baseline from 57% to 66%; from the education intervention by the CE team August 2009 to July 2010, the percentage decreased to a range of 52% to 56% (p = 0.01); and after implementation of CDS and BPA, by end of December 2010 the percentage of patients transfused outside the guidelines decreased to 35% (p = 0.02) and has subsequently remained below 30%. For the most recent interval, only 27% (767 of 2890) of transfusions occurred in patients outside guidelines. Comparing 2009 to 2012, despite an increase in annual case mix index from 1.952 to 2.026, total red blood cell (RBC) transfusions decreased by 7186 units, or 24%. The estimated net savings for RBC units (at $225/unit) in purchase costs for 2012 compared to 2009 was $1,616,750.

CONCLUSION

Real-time CDS has significantly improved blood utilization. This system of concurrent review can be used by health care institutions, quality departments, and transfusion services to reduce blood transfusions.

Accuracy and clinical utility of a point-of-care HbA1c testing device

BACKGROUND

Point-of-care testing (POCT) is widely used to measure blood glucose levels in people with diabetes, although its use in measuring glycated hemoglobin (HbA1c) levels is less common, perhaps due to perceived performance issues and access to the technology.

METHODS

Forty blood samples were analyzed in duplicate using Bayer's A1CNow + ® Multi-Test A1C system (A1CNow + ) with 3 different reagent lots; HbA1c levels of the samples spanned the clinically relevant range of 4% to 10%. Corresponding samples were sent to a National Glycohemoglobin Standardization Program (NGSP) secondary reference laboratory (University of Missouri Secondary Reference Laboratory #9), which analyzed the samples with a Tosoh Automated Glycohemoglobin Analyzer HLC-723G8 (Tosoh G8; Tosoh Bioscience, Inc).

RESULTS

Glycated hemoglobin levels measured with the A1CNow + aligned with measurements obtained using the laboratory method, with correlation coefficients of 0.985, 0.987, and 0.989 for the 3 lots, respectively. The 95% CIs for the differences between the A1CNow + levels and the mean HbA1c levels were within -0.55% to +0.50% for the 3 reagent lots, which is well within the currently acceptable limits of ±0.75% HbA1c required by the NGSP. Results were further analyzed per the new tighter NGSP performance criteria effective September 1, 2012, requiring that 37 of 40 results be within ±7% (relative bias) of the NGSP reference laboratory measures. All 3 lots met the tighter NGSP criteria.

CONCLUSION

The A1CNow + provides accuracy and precision when performing POCT of HbA1c as an aid in diabetes management. Ongoing improvements in this and other HbA1c POCT devices may lead to a greater global acceptance of the role of POCT of HbA1c in diabetes management.

Use of point-of-care testing for plasma therapy

Use of point-of-care testing (POCT) has been driven by limitations of laboratory-based testing as a tool for decisions for transfusions of blood components. Clinical settings such as liver transplantation, cardiothoracic surgery, and trauma are particularly in need of such diagnostic tests because of the complex coagulopathies that can develop in these settings of substantial hemorrhage and need for blood component support. Successful implementation of POCT requires collaboration between surgery, anesthesia, critical care, and the laboratory to ensure proper quality control of equipment, operator training and competency, medical records test results, billing procedures, and consensus-derived transfusion algorithms for cost-effective, targeted blood component transfusion support. In this review we summarize clinical evidence for the effectiveness of POCT, along with some future directions for this strategy.

Can RoTEM® analysis be applied for haemostatic monitoring in paediatric congenital heart surgery?

BACKGROUND

Successful management of bleeding disorders after congenital heart surgery requires detection of specific coagulation disturbances. Whole-blood rotation thromboelastometry (RoTEM®) provides continuous qualitative haemostatic profiles, and the technique has shown promising results in adult cardiac surgery.

SETTING

To compare the performance of RoTEM® with that of conventional coagulation tests in children, we conducted a descriptive study in children undergoing congenital cardiac surgery. For that purpose, 60 children were enrolled and had blood samples taken before, immediately after, and 1 day after surgery. Conventional coagulation tests included: activated partial thromboplastin time, prothrombin time, fibrinogen, fibrin D-dimer, thrombin clotting time, factor XIII, and platelet count.

RESULTS

Post-surgical haemostatic impairment was present to some degree in all children, as seen by pronounced changes in activated partial thromboplastin time, prothrombin time, thrombin clotting time, and platelet count, as well as RoTEM® analysis. RoTEM® showed marked changes in clotting time - prolonged by 7-18% - clot formation time - prolonged by 46-71% - maximum clot firmness - reduced by 10-19%, and maximum velocity - reduced by 29-39%. Comparison of the two techniques showed that conventional coagulation tests and RoTEM® performed equally well with regard to negative predictive values for excessive post-operative drain production - more than 20 millilitres per kilogram per 24 hours after surgery - with an area under the curve of approximately 0.65.

CONCLUSION

RoTEM® can detect haemostatic impairments in children undergoing cardiac surgery and the method should be considered as a supplement in the perioperative care of the children where targeted transfusion therapy is necessary to avoid volume overload.

When do new biomarkers make economic sense?

Cost-effectiveness and cost-utility studies are commonly used to make payment decisions for new drugs and expensive interventions. Such studies are relatively rare for evaluating the cost-utility of clinical laboratory tests. As medical costs continue to increase in the setting of decreased resources it is likely that new biomarkers may increasingly be examined with respect to their economic benefits in addition to clinical utility. This will represent an additional hurdle for routine use of new biomarkers. Before reaching the final economic hurdle new biomarkers will still need to demonstrate clinical usefulness. Thus a new biomarker will never make economic sense if it is not clinically useful. Once diagnostic accuracy and potential clinical usefulness is established there are several types of economic studies that new biomarkers may undergo. The most common of these are cost-utility studies which estimate the ratio between the cost of an intervention or test and the benefit it produces in the number of years gained in full health. The quantity used most often to describe this is amount of money per quality adjusted life year (QALY) gained. The threshold for being considered cost-effective is generally USD 50,000 per QALY gained. Examples of biomarkers that have been subjected to economic analyses will be provided.

Impact of platelet count on results obtained from multiple electrode platelet aggregometry (Multiplate)

OBJECTIVES

Use of potent antiplatelet drugs requires evaluation of platelet function. While platelet function in elective cases is usually assessed in a central laboratory environment, there is also an urgent need for rapid perioperative point-of-care assessment. Recently, multiple electrode platelet aggregometry has been developed and assumed to measure platelet function independent from platelet count. We tested the hypothesis that results of multiple electrode platelet aggregometry are affected by platelet count, in particular if platelet count is below normal range.

METHODS

Whole blood samples from 20 healthy volunteers were prepared containing platelet concentrations of 50,000, 100,000, 150,000, 200,000, and 250,000 microl(-1) while maintaining hematocrit. Platelet aggregation was induced by collagen, thrombin receptor activating peptide 6 (TRAP-6), adenosine-diphoshate (ADP), and arachidonic acid, respectively, and aggregation was measured by multiple electrode platelet aggregometry (Multiplate).

RESULTS

Results of multiple electrode platelet aggregometry significantly decreased in blood samples with platelet count below normal range. Compared to results measured in blood samples with platelet count within normal range, aggregometry results decreased by 18.4 % (p<0.001) and 37.2 % (p<0.001) in blood samples with a platelet count of 100.000 and 50.000 microl(-1), respectively. On the other hand, large interindividual variation has been observed and some blood samples showed normal results even with platelet counts of 50.000 microl(-1).

CONCLUSION

The results obtained with Multiplate. Analyzer are influenced by platelet function as well as platelet count thus displaying the overall platelet aggregability within the blood sample rather than platelet function alone.

Point-of-care coagulation testing and transfusion algorithms

Patients with cardiovascular disease have an array of haemostasis disorders that predispose to the development of thrombotic and embolic disease states. These patients are often maintained on anti-thrombotic medication to prevent adverse cardiovascular events. Patients undergoing cardiac surgery also have haemostatic disorders that include their intrinsic disease state, adjunctive medication, and the coagulation disturbances induced by cardiopulmonary bypass. The following review introduces the monitors that are available for monitoring perioperative coagulation, with an emphasis on cardiovascular surgery. Heparin monitors, platelet function monitors for use in transfusion algorithms, and monitoring anti-platelet drugs will be discussed.

Perspectives on cost and outcomes for point-of-care testing

Point-of-care testing (POCT) is usually more expensive on a unit-cost basis than testing performed in a central laboratory. It is difficult to manage POCT and to maintain regulatory compliance, especially in large institutions. However, some POCT technologies have improved patient outcomes (patient self-glucose monitoring in the home, tight glycemic control in intensive care settings) or hospital or emergency department operations (whole-blood cardiac-marker testing and D-dimer testing in emergency departments). In some cases, these outcomes result simply from making a new test available, rather than performing the test at the point of care. In most cases, the rapid turnaround time provided by POCT is the main factor that is ultimately responsible for the improvement in outcomes.

Perioperative Coagulopathy, Bleeding, and Hemostasis During Cardiac Surgery

Cardiac surgery patients use 10%-25% of the blood products transfused annually in the United States. The transfusion of red blood cells or blood products has been the subject of intense scrutiny over the past 10 years. Bleeding after cardiac surgery can be surgical or nonsurgical and lead to hemodynamic compromise and surgical reexploration. Because hemorrhage and blood product transfusions are associated with multiple negative outcomes, including increased mortality, it is prudent to understand the mechanisms responsible for nonsurgical bleeding. This review focuses on the physiology of the normal coagulation and fibrinolysis, risk factors associated with patients presenting for cardiac surgery, impairments of normal hemostasis associated with cardiac surgery and cardiopulmonary bypass (CPB), and potential interventions to reduce perioperative blood loss and blood transfusion.

Global hemostasis testing thromboelastography: old technology, new applications

Thromboelastography (TEG) as a method of assessing global hemostatic and fibrinolytic function has existed for more than 60 years. Improvements in TEG technology have led to increased reliability and thus increased usage. The TEG has been used primarily in the settings of liver transplant and cardiac surgery, with proven utility for monitoring hemostatic and fibrinolytic derangements. In recent years, indications for TEG testing have expanded to include managing extracorporeal membrane oxygenation (ECMO) therapy, assessing bleeding of unclear etiology, and assessing hypercoagulable states. In addition, TEG platelet mapping has been utilized to monitor antiplatelet therapy. Correlation between TEG platelet mapping and other platelet function tests such as the PFA-100 or platelet aggregation studies, however, has not been evaluated fully for clinical outcomes, and results may not be comparable. In general, the advantages of the TEG include evaluation of global hemostatic function using whole blood, a quick turn-around-time, the possibility of both point-of-care-testing and performance in central laboratories, the ability to detect hyperfibrinolysis, monitoring therapy with recombinant activated factor VII, and detection of low factor XIII activity. Potential applications include polycythemia and dysfibrinogenemia. Disadvantages of TEG include a relatively high coefficient of variation, poorly standardized methodologies, and limitations on specimen stability of native whole blood samples. In the pediatric setting, an additional advantage of the TEG is a relatively small sample volume, but a disadvantage is the difference in normal ranges between infants, especially newborns, and adults. In summary, TEG is an old concept with new applications that may provide a unique perspective on global hemostasis in various clinical settings.

The surgical application of point-of-care haemostasis and platelet function testing

Background

Disordered coagulation complicates many diseases and their treatments, often predisposing to haemorrhage. Conversely, patients with cardiovascular disease who demonstrate antiplatelet resistance may be at increased thromboembolic risk. Prompt identification of these patients facilitates optimization of haemostatic dysfunction. Point-of-care (POC) tests are performed ‘near patient’ to provide a rapid assessment of haemostasis and platelet function.

Methods

This article reviews situations in which POC tests may guide surgical practice. Their limitations and potential developments are discussed. The paper is based on a Medline and PubMed search for English language articles on POC haemostasis and platelet function testing in surgical practice.

Results

POC tests identifying perioperative bleeding tendency are already widely used in cardiovascular and hepatic surgery. They are associated with reduced blood loss and transfusion requirements. POC tests to identify thrombotic predisposition are able to determine antiplatelet resistance, predicting thromboembolic risk. So far, however, these tests remain research tools.

Conclusion

POC haemostasis testing is a growing field in surgical practice. Such testing can be correlated with improved clinical outcome.

Quality and timeliness in medical laboratory testing

In terms of testing, modern laboratory medicine can be divided into centralized testing in central laboratories and point-of-care testing (POCT). Centralized laboratory medicine offers high-quality results, as guaranteed by the use of quality management programs and the excellence of the staff. POCT is performed by clinical staff, and so such testing has moved back closer to the patient. POCT has the advantage of shortening the turnaround time, which potentially benefits the patient. However, the clinical laboratory testing expertise of clinical staff is limited. Consequently, when deciding which components of laboratory testing must be conducted in central laboratories and which components as POCT (in relation to quality and timeliness), it will be medical necessity, medical utility, technological capabilities and costs that will have to be ascertained. Provided adequate quality can be guaranteed, POCT is preferable, considering its timeliness, when testing vital parameters. It is also preferred when the central laboratory cannot guarantee the delivery of results of short turn-around-time (STAT) markers within 60 or (even better) 30 min. POCT should not replace centralized medical laboratory testing in general, but it should be used in cases where positive effects on patient care have been clearly demonstrated.

The use of desmopressin in open-heart surgery

Desmopressin (l-deamino-8-D-arginine vasopressin, DDAVP) is a synthetic analogue of the antidiuretic hormone vasopressin. Like the natural antidiuretic hormone, desmopressin increases the plasma levels of factor VIII and von Willebrand factor (vWF), with the advantage, compared to vasopressin, that it produces little or no vasoconstriction, no increase in blood pressure, and no contraction of the uterus or gastrointestinal tract, so that it is well tolerated when administered to humans. In 1977, desmopressin was used for the first time in patients with mild hemophilia A and von Willebrand disease (vWD) for the prevention and treatment of bleeding, first during dental extractions and then during major surgical procedures. The clinical indications for desmopressin rapidly expanded beyond hemophilia and vWD. The compound was shown to be efficacious even in bleeding disorders not involving a deficiency or dysfunction of factor VIII or vWF, including congenital and acquired defects of platelet function and such frequent abnormalities of hemostasis as those associated with chronic kidney and liver diseases. Desmopressin has also been used prophylactically in patients undergoing surgical operations characterized by large blood loss and transfusion requirements.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

Response characteristics of a reversible electrochemical sensor for the polyion protamine

We describe here in detail the first reversible electrochemical sensors for the polyion protamine. Potentiometric sensors were proposed in recent years, mainly for the determination of the polyions heparin and protamine. Such potentiometric polyion sensors functioned on the nonequilibrium extraction of polyions into a hydrophobic membrane phase via ion pairing with lipophilic ion exchangers. This made it difficult to design sensors that operate in a truly reversible fashion. The reversible sensors described here utilize the same basic response mechanism as their potentiometric counterparts, but the processes of extraction and ion stripping are now fully controlled electrochemically. Spontaneous polyion extraction is avoided by using membranes containing highly lipophilic electrolytes that possess no ion-exchange properties. Reversible extraction of polyions is induced if a constant current pulse of fixed duration is applied across the membrane, followed by a baseline potential pulse. The key theoretical response principles of this new class of polyion sensors are discussed here and compared to those of its classical potentiometric counterpart. The electrochemical sensing system is characterized in terms of optimal working conditions, membrane composition, selectivity, and influence of sample stirring and organic-phase diffusion coefficient on the response characteristics. Excellent potential stability and reversibility of the sensors are observed, and measurements of heparin concentration in whole blood samples via protamine titration are demonstrated.

Significant reduction in blood loss in patients undergoing minimal extracorporeal circulation

Several recent studies have shown differences in blood loss and allogeneic transfusion requirements between on-pump and off-pump coronary artery bypass grafting (CABG). Recently a new concept, the mini-extracorporeal circulation, was introduced to minimize the side effects of extracorporeal circulation. Therefore, there are no data comparing the three techniques with special emphasis to blood loss and transfusion requirements. Two hundred and eighty-five patients undergoing first-time coronary artery bypass grafting were retrospectively matched for number of grafts, age and sex. Ninety-five patients underwent surgery with the off-pump CABG (OPCAB) technique, 97 patients using conventional CABG with cold cardioplegia (CCABG) and 93 patients with the mini-extracorporeal circuit with warm blood cardioplegia (MCABG). Blood loss for the CCABG group with a mean loss of 819 +/- 557 mL and the OPCAB group with a mean loss of 870 +/- 768 mL was significant different compared to the MCABG group with a mean loss of 679 +/- 290 mL. The use of units red blood cell units was significantly higher for CCABG group and OPCAB group compared to the MCABG group. On the day of operation the use of platelet concentrate was significantly higher for the CCABG group compared to MCABG group. As a consequence of improvements of several components of the mini heart lung machine, significantly less blood products are needed in MCABG patients. The expected reduced need for transfusion when the pump was completely avoided could not be confirmed in this single retrospective cohort study.

A novel antidote-controlled anticoagulant reduces thrombin generation and inflammation and improves cardiac function in cardiopulmonary bypass surgery

Heparin and protamine are the standard anticoagulant-antidote regimen used in almost every cardiopulmonary bypass (CPB) procedure even though both are associated with an array of complications and toxicities. Here we demonstrate that an anticoagulant aptamer-antidote pair targeting factor IXa can replace heparin and protamine in a porcine CPB model and also limit the adverse effects on thrombin generation, inflammation, and cardiac physiology associated with heparin and protamine use. These results demonstrate that targeting clotting factors upstream of thrombin in the coagulation cascade can potentially reduce the perioperative pathologies associated with CPB and suggest that the aptamer-antidote pair to FIXa may improve the outcome of patients undergoing CPB. In particular, this novel anticoagulant-antidote pair may prove to be useful in patients diagnosed with heparin-induced thrombocytopenia or those who have been sensitized to protamine, particularly patients who have insulin-dependent diabetes.