Protamine sulfate down-regulates thrombin generation by inhibiting factor V activation

Inhibitors of Polyphosphate and Neutrophil Extracellular Traps

The contact pathway of blood clotting has received intense interest in recent years as studies have linked it to thrombosis, inflammation, and innate immunity. Because the contact pathway plays little to no role in normal hemostasis, it has emerged as a potential target for safer thromboprotection, relative to currently approved antithrombotic drugs which all target the final common pathway of blood clotting. Research since the mid-2000s has identified polyphosphate, DNA, and RNA as important triggers of the contact pathway with roles in thrombosis, although these molecules also modulate blood clotting and inflammation via mechanisms other than the contact pathway of the clotting cascade. The most significant source of extracellular DNA in many disease settings is in the form of neutrophil extracellular traps (NETs), which have been shown to contribute to incidence and severity of thrombosis. This review summarizes known roles of extracellular polyphosphate and nucleic acids in thrombosis, with an emphasis on novel agents under current development that target the prothrombotic activities of polyphosphate and NETs.

Protamine and Heparin Interactions: A Narrative Review

ABSTRACT

Protamine, first isolated from salmon fish sperm and now produced through recombinant biotechnology, is an antidote that neutralizes the anticoagulant properties of heparin. Protamine function is based on the capacity to dissociate the heparin-antithrombin III (AT III) complex (an important link that promotes blood fluidification by inhibiting coagulation), forming the inactive heparin-protamine complex. Protamine has itself dose-dependent anticoagulant properties: It interferes with coagulation factors and platelet function; it stimulates fibrinolysis; it can lead to thrombocytopenia and reduction in thrombin-related platelet aggregation; it decreases platelet response to thrombin receptor agonist in a dose-dependent manner. In this review, we will focus on protamine and its interaction with heparin. Notably, protamine is able to antagonize not only unfractionated heparin (UFH) but also low molecular weight heparins to various degrees. Protamine-allergic and anaphylactoid systemic reactions may affect up to 1 in 10 people and should be prevented and treated early.

Protamine dosing and its impact in cardiac surgery transfusion practice-A retrospective bi-institutional analysis

BACKGROUND

Bleeding after cardiac surgery is common and continues to require 10-20% of the national blood supply. Transfusion of allogeneic blood is associated with increased morbidity and mortality. Excessive protamine in the absence of circulating heparin after weaning off CPB can cause anticoagulation and precipitate bleeding. Hence, adequate dose calculation of protamine is crucial yet under evaluated.

STUDY DESIGN

Retrospective cohort study.

METHODS

We conducted a retrospective bi-institutional analysis of cardiac surgical patients who underwent cardiopulmonary bypass (CPB)-assisted cardiac surgery to assess the impact of protamine dosing in transfusion practice. Total 762 patients were identified from two institutions using electronic medical records and the Society of Thoracic Surgery (STS) database who underwent cardiac surgery using CPB. Patients were similar in demographics and other baseline characteristics. We divided patients into two groups based on mg of protamine administered to neutralize each 100 U of unfractionated heparin (UFH)-low-ratio group (Protamine: UFH ≤ 0.8) and high-ratio group (Protamine: UFH > 0.8).

RESULTS

We observed a higher rate of blood transfusion required in high-ratio group (ratio >0.8) compared with low-ratio group (ratio ≤0.8) (p < .001). The increased requirement was consistently demonstrated for intraoperative transfusions of red blood cells, plasma, platelets, and cryoprecipitate.

CONCLUSION

High protamine to heparin ratio may cause increased bleeding and transfusion in cardiac surgical patients. Protamine to heparin ratio of 0.8 or lower is sufficient to neutralize circulating heparin after weaning off cardiopulmonary bypass.

Immune-stealth VP28-conjugated heparin nanoparticles for enhanced and reversible anticoagulation

Heparins are a family of sulfated linear negatively charged polysaccharides that have been widely used for their anticoagulant, antithrombotic, antitumor, anti-inflammatory, and antiviral properties. Additionally, it has been used for acute cerebral infarction relief as well as other pharmacological actions. However, heparin's self-aggregated macrocomplex may reduce blood circulation time and induce life-threatening thrombocytopenia (HIT) complicating the use of heparins. Nonetheless, the conjugation of heparin to immuno-stealth biomolecules may overcome these obstacles. An immunostealth recombinant viral capsid protein (VP28) was expressed and conjugated with heparin to form a novel nanoparticle (VP28-heparin). VP28-heparin was characterized and tested to determine its immunogenicity, anticoagulation properties, effects on total platelet count, and risk of inducing HIT in animal models. The synthesized VP28-heparin trimeric nanoparticle was non-immunogenic, possessed an average hydrodynamic size (8.81 ± 0.58 nm) optimal for the evasion renal filtration and reticuloendothelial system uptake (hence prolonging circulating half-life). Additionally, VP28-heparin did not induce mouse death or reduce blood platelet count when administered at a high dosein vivo(hence reducing HIT risks). The VP28-heparin nanoparticle also exhibited superior anticoagulation properties (2.2× higher prothrombin time) and comparable activated partial thromboplastin time, but longer anticoagulation period when compared to unfractionated heparin. The anticoagulative effects of the VP28-heparin can also be reversed using protamine sulfate. Thus, VP28-heparin may be an effective and safe heparin derivative for therapeutic use.

Assessing the impact of different heparin dosing regimens for cardiopulmonary bypass on anticoagulation: the HepDOSE pilot study

PURPOSE

It has been suggested that a larger heparin dose during cardiopulmonary bypass (CPB) is associated with reduced perioperative coagulopathy and thromboembolic complications. We investigated the effect of different heparin doses during routine elective cardiac surgery. Our primary outcomes include blood loss and transfusion and secondary outcomes investigate the effects on coagulation biomarkers.

METHODS

In this prospective pilot trial, we allocated 60 patients undergoing cardiac surgery on CPB in a single tertiary cardiac centre into three groups to receive an initial dose of 300, 400, or 500 units (U) per kilogram of intravenous heparin prior to the commencement of CPB. Blood was sampled after induction of anesthesia, at 30 and 60 min of CPB, and three minutes after heparin reversal with protamine. Samples were analyzed for fibrinopeptide A (FPA), fibrinopeptide B (FPB), D-dimer, and thrombin-antithrombin (TAT) complexes. Postoperative blood loss and transfusion was measured for the first 24-hr period after surgery.

RESULTS

The total mean (95% CI) administered heparin dose in the 300 U·kg-1, 400 U·kg-1, and 500 U·kg-1 groups were 39,975 (36,528 to 43,421) U, 43,195 (36,940 to 49,449) U and 47,900 (44,807 to 50,992) U, respectively. There were no statistically significant differences in FPA, FPB or D-dimer levels at the measured time intervals. There was a trend towards lower TAT levels while on CPB with greater heparin dosing, which was statistically significant after the administration of protamine. The clinical significance appears to be negligible, as there is no difference in overall blood loss and amount of packed red blood cell transfusion or other blood product transfusion.

CONCLUSION

This pilot study indicates that, while larger heparin dosing for routine cardiac surgery results in subtle biochemical changes in coagulation, there is no demonstrable benefit in postoperative blood loss or transfusion requirements.

In vitro comparison of spatiotemporal fibrin clot formation dynamics in plasma treated with different protamine-heparin ratios

INTRODUCTION

Our study aim was to explore how different protamine-heparin ratios impacted enzymatic coagulation and acellular fibrin clot growth in plasma using an in vitro model. We hypothesized that a low protamine-heparin ratio would be associated with superior fibrin clot growth dynamics.

METHODS

We performed an in vitro study using 15 plasma samples from a commercial supplier. Different protamine-heparin ratios were added to each donor plasma sample: low ratio (0.7-1), traditional ratio (1-1), and high ratio (1.3-1) and clot formation dynamics were evaluated using a Thrombodynamics analyzer. Study outcomes were initial clot growth velocity and clot size at 30 min.

RESULTS

Plasma samples treated with a one-to-one protamine-heparin ratio had significantly lower mean initial clot growth velocity compared to samples treated with a low protamine-heparin ratio; mean difference -2.3 μm/min (95% CI = -4.0 to -0.7, p = .004). Plasma samples treated with a one-to-one protamine-heparin ratio also had significantly smaller mean clot size at 30 min compared to samples treated with a low protamine-heparin ratio; mean difference -54.0 μm (95% CI = -107.6 to -0.4, p = .048). There were no significant differences in mean initial clot growth velocity or clot size at 30 min between plasma samples treated with a high protamine-heparin ratio and those treated with a one-to-one or low protamine-heparin ratio (all p > .05).

CONCLUSIONS

Plasma samples treated with a low protamine-heparin ratio had superior clot growth velocity and larger clot size at 30 min compared to a one-to-one ratio, supporting the notion that a low protamine-heparin ratio may optimize enzymatic coagulation after cardiopulmonary bypass.

Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass?

BACKGROUND

Heparin rebound is a common observed phenomenon after cardiac surgery with CPB and is associated with increased postoperative blood loss. However, the administration of extra protamine may lead to increased blood loss as well. Therefore, we want to investigate the relation between heparin rebound and postoperative blood loss and the necessity to provide extra protamine to reverse heparin rebound.

METHODS

We searched PubMed, Cochrane, EMBASE, Google Scholar and Web of Science to review the question: "Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass." Combination of search words were framed within four major categories: heparin rebound, blood loss, cardiac surgery and cardiopulmonary bypass. All studies that met our question were included. Quality assessment was performed using the Cochrane risk of bias (RoB2) tool for randomized controlled trials and the risk of bias in non-randomized studies of intervention (ROBINS-I) for non-randomised trials.

RESULTS

4 randomized and 17 non-randomized studies were included. The mean incidence of heparin rebound was 40%. The postoperative heparin levels, due to heparin rebound, were often below or equal to 0.2 IU/mL. We could not demonstrate an association between heparin rebound and postoperative blood loss or transfusion requirements. However the quality of evidence was poor due to a broad variety of definitions of heparin rebound, measured by various coagulation tests and studies with small sample sizes.

CONCLUSION

The influence of heparin rebound on postoperative bleeding seems to be negligible, but might get significant in conjunction with incomplete heparin reversal or other coagulopathies. For that reason, it might be useful to get a picture of the entire coagulation spectrum after cardiac surgery, as can be done by the use of a viscoelastic test in conjunction with an aggregometry test.

What's fishy about protamine? Clinical use, adverse reactions, and potential alternatives

Protamine, a highly basic protein isolated from salmon sperm, is the only clinically available agent to reverse the anticoagulation of unfractionated heparin. Following intravenous administration, protamine binds to heparin in a nonspecific electrostatic interaction to reverse its anticoagulant effects. In clinical use, protamine is routinely administered to reverse high-dose heparin anticoagulation in cardiovascular procedures, including cardiac surgery with cardiopulmonary bypass. Despite the lack of supportive evidence regarding protamine's effectiveness to reverse low-molecular-weight heparin, it is recommended in guidelines with low-quality evidence. Different dosing strategies have been reported for reversing heparin in cardiac surgical patients based on empiric dosing, pharmacokinetics, or point-of-care measurements of heparin levels. Protamine administration is associated with a spectrum of adverse reactions that range from vasodilation to life-threatening cardiopulmonary dysfunction and shock. The life-threatening responses appear to be hypersensitivity reactions due to immunoglobulin E and/or immunoglobulin G antibodies. However, protamine and heparin-protamine complexes can activate complement inflammatory pathways and inhibit other coagulation factors. Although alternative agents for reversing heparin are not currently available for clinical use, additional research continues evaluating novel therapeutic approaches.

Smart thrombosis inhibitors without bleeding side effects via charge tunable ligand design

Current treatments to prevent thrombosis, namely anticoagulants and platelets antagonists, remain complicated by the persistent risk of bleeding. Improved therapeutic strategies that diminish this risk would have a huge clinical impact. Antithrombotic agents that neutralize and inhibit polyphosphate (polyP) can be a powerful approach towards such a goal. Here, we report a design concept towards polyP inhibition, termed macromolecular polyanion inhibitors (MPI), with high binding affinity and specificity. Lead antithrombotic candidates are identified through a library screening of molecules which possess low charge density at physiological pH but which increase their charge upon binding to polyP, providing a smart way to enhance their activity and selectivity. The lead MPI candidates demonstrates antithrombotic activity in mouse models of thrombosis, does not give rise to bleeding, and is well tolerated in mice even at very high doses. The developed inhibitor is anticipated to open avenues in thrombosis prevention without bleeding risk, a challenge not addressed by current therapies.

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.

Minimum protamine dose required to neutralize heparin in cardiac surgery: a single-centre, prospective, observational cohort study

PURPOSE

Excess protamine contributes to coagulopathy following cardiopulmonary bypass (CPB) and may increase blood loss and transfusion requirements. The primary aim of this study was to find the least amount of protamine necessary to neutralize residual heparin following CPB using the gold standard assays of anti-IIa and anti-Xa activity. Secondary objectives were to evaluate whether the post-CPB activated clotting time could be used as a surrogate marker for quantifying heparin neutralization.

METHODS

Twenty-eight consecutive patients undergoing elective cardiac surgery were enrolled. Protamine administration was standardized through an infusion pump at 25 mg·min-1. Blood samples were withdrawn prior to and following administration of 150, 200, 250, and 300 mg protamine and analyzed for activated clotting time and anti-IIa and -Xa activity.

RESULTS

Following a mean (standard deviation) cumulative heparin dose of 67,700 (19,400) units and a CPB duration of 113 (71) min, protamine requirements varied widely. Eight out of 25 (32%) patients showed complete neutralization of anti-IIa and -Xa activity at the first sampling point (150 mg protamine; protamine:heparin ratio, 0.3 [0.1]). A protamine:heparin ratio of 0.5 (0.2) was sufficient for heparin neutralization in > 90% of patients. After CPB, a low to mid-range activated clotting time correlated well with anti-IIa and -Xa activity.

CONCLUSIONS

The protamine:heparin ratio required to neutralize residual unfractionated heparin (UFH) following CPB is variable. A protamine:heparin ratio of 0.3 was sufficient to neutralize UFH in some patients, while a ratio of 0.5 is sufficient to neutralize both residual anti-IIa and -Xa activity in most patients. Larger studies are necessary to confirm these findings and evaluate their clinical implications.

STUDY REGISTRATION

ClinicalTrials.gov (NCT03787641); registered 26 December 2018.

Ultraporous Polyquaternium-Carboxylated Chitosan Composite Hydrogel Spheres with Anticoagulant, Antibacterial, and Rapid Endotoxin Removal Profiles for Sepsis Treatment

Hemoperfusion is an important method to remove endotoxins and save the lives of patients with sepsis. However, the current adsorbents for hemoperfusion have disadvantages of insufficient endotoxin adsorption capacity, poor blood compatibility, and so on. Herein, we proposed a novel emulsion templating (ET) method to prepare ultraporous and double-network carboxylated chitosan (CCS)-poly(diallyl dimethylammonium chloride) (PDDA) hydrogel spheres (ET-CCSPD), bearing both negative and positive charges. CCS was introduced to balance the strong positive charges of PDDA to improve hemocompatibility, and emulsion templates endowed the adsorbent with an ultraporous structure for enhanced adsorption efficacy. The ET-CCSPDs neither damaged blood cells nor activated complement responses. In addition, the activated partial thromboplastin time (APTT) was prolonged to 8.5 times, which was beneficial for reducing the injection of anticoagulant in patients. The ET-CCSPDs had excellent scavenging performance against bacteria and endotoxin, with removal ratios of 96.7% for E. coli and 99.8% for S. aureus, respectively, and the static removal ratio of endotoxin in plasma was as high as 99.1% (C₀ = 5.50 EU/mL, critical illness level). An adsorption cartridge filled with the ET-CCSPDs could remove 84.7% of endotoxin within 1 h (C₀ = 100 EU/mL in PBS). Interestingly, the ET-CCSPDs had a good inhibitory effect on the cytokines produced by endotoxin-mediated septic blood. By developing the ET method to prepare ultraporous and double-network adsorbents, the problems of low adsorption efficiency and poor blood compatibility of traditional endotoxin adsorbents have been solved, thus opening a new route to fabricate absorbents for blood purification.

Interaction of a Phospholipid and a Coagulating Protein: Potential Candidate for Bioelectronic Applications

In the present communication, we have investigated the interaction between a biomembrane component 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and a coagulating protein protamine sulfate (PS) using the Langmuir-Blodgett (LB) technique. The π-A isotherm, π-t characteristics, and analysis of isotherm curves suggested that PS strongly interacted with DOPC, affecting the fluidity of the DOPC layer. Electrical characterization indicates that PS as well as the PS-DOPC film showed resistive switching behavior suitable for Write Once Read Many (WORM) memory application. Trap-controlled space charge-limited conduction (SCLC) was the key mechanism behind such observed switching. The presence of DOPC affected the SCLC process, leading to lowering of threshold voltage (V _Th), which is advantageous in terms of lower power consumption.

Rheological and clot microstructure evaluation of heparin neutralization by UHRA and protamine

The current study reports the use of small amplitude oscillatory rheometry to investigate the dynamics of blood clot formation upon heparin neutralization under three different oscillatory frequencies, two of which were mimicking physiological heart rates. We utilized two different heparin antidotes, namely protamine and newly developed universal heparin reversal agent (UHRA-7), at different concentrations to determine the quality of blood clot formed upon heparin neutralization by analyzing several key rheological parameters. Scanning electron microscopy (SEM) was used to determine the morphology and microstructure of the blood clot after heparin neutralization to support the rheological observations. The current study revealed that the structure of blood clots formed had significant differences when an oscillatory frequency that mimicked the physiological heart rate was used in comparison to a lower frequency commonly used in current clinical measurements. The limited working dose range for protamine and its intrinsic anticoagulation behaviour was observed. The neutralization profile of UHRA-7 showed a large window of activity. The global assessment of rheological parameters and microstructure of the clot together revealed additional details describing anticoagulant reversal and blood coagulation dynamics by relating the blood clot's fiber thickness and the oscillatory measurements, including storage modulus and blood clot's contractile force. Additionally, a mechanical characterization was conducted to provide a further assessment of blood coagulation using the rheological data.

Transient blood thinning during extracorporeal blood purification via the inactivation of coagulation factors by hydrogel microspheres

During extracorporeal blood purification, anticoagulants are administered to prevent thrombogenesis. However, haemorrhagic complications owing to near-complete inactivation of blood coagulation and delayed recovery of haemostasis pose serious risks to patients. Here, we show in vitro and in beagle dogs that hydrogel microspheres that adsorb the coagulation factors VIII, IX and XI provide transient blood thinning when placed in the extracorporeal circuit before blood purification. The microspheres inhibited the activities of the coagulation factors by levels (~8-30%) similar to those occurring in mild haemophilia. On its reintroduction into the animal, the purified pseudo-haemophilic blood favoured faster recovery of haemostasis. The transient blood-thinning strategy may increase the safety of clinical blood-purification procedures.

Study of in vitro thrombin generation after neutralization of heparin

INTRODUCTION

Thrombin generation (TG) documents hypercoagulability. TG in platelet-poor plasma is exquisitely sensitive to heparins, which thus must be neutralized before testing. Heparinase and hexadimethrine bromide (polybrene) have been used for that purpose, but their effects per se on TG have been poorly studied so far.

METHODS

(i) TG was studied in commercial normal pooled plasma (NPP; CryoCheck^® , Cryopep) in absence or presence of neutralizing agents. (ii) NPP was spiked with increasing concentrations of unfractionated heparin (UFH; up to 1.0 IU/mL) or low-molecular-weight heparin (LMWH; enoxaparin up to 1.2 IU/mL) and TG studied after incubation of heparinase (Hepzyme^® ; 15 minutes) or polybrene (0.025 mg/mL; 10 minutes).

RESULTS

(i) With ThromboScreen reagent to initiate TG, addition of heparinase was associated with increased peak, whereas polybrene caused lengthening of lag time and time to peak, compared with nonsupplemented NPP. (ii) With polybrene, TG was completely restored over the whole range of UFH and LMWH studied. By contrast, heparinase failed to fully restore TG in presence of UFH concentrations ≥0.8 IU/mL or LMWH concentrations ≥1.0 IU/mL. Those effects were matched with detectable tiny residual amounts of non-neutralized heparin (as assessed with an anti-Xa assay) and were less pronounced with a higher picomolar concentration of tissue factor (DrugScreen reagent).

CONCLUSION

Polybrene fully restored TG of heparinized plasma at the expense of an alteration of TG, pointing to the need to use adapted reference ranges. Heparinase failed to do so in presence of high concentrations of both heparins.

Evaluation of the impact of HMS Plus on postoperative blood loss compared with ACT Plus in cardiac surgery

BACKGROUND

The standardized management of anticoagulation during the cardiopulmonary bypass seems inaccurate because of patients and surgeries variability. This study evaluates if an individualized management of heparin and protamine guided by the HMS Plus system during cardiopulmonary bypass could reduce postoperative blood loss.

METHODS

We conducted a prospective, controlled, unblinded, single-center study. 188 patients operated for cardiac surgery were included. Patients were divided in ACT Plus group (standardized approach) and HMS Plus group (individualized approach). The primary outcome was blood-loss volume during the first 24 postoperative hours. The main secondary outcomes were the need for allogeneic blood transfusions and the final protamine/heparin ratio.

RESULTS

There was no difference between the two groups for baseline characteristics. Medium bloodloss volume (±DS) in the ACT Plus group was 522 mL ±260 mL vs. 527 mL ±255 mL in the HMS Plus group (P = 0.58). The final protamine/heparin ratio (±DS) in the ACT Plus group was 0.94 ±0.1 vs. 0.58 ± 0.1 in the HMS Plus group (P < 0.0001). The transfusion rate during surgery in the ACT Plus group was 25% vs. 14% in the HMS Plus group (P = 0.09).

CONCLUSIONS

HMS Plus did not reduce the mean blood-loss volume during the first 24 postoperative hours compared with ACT Plus. Its utility for potential transfusion rate reduction remains to be proven.

Optimal protamine dosing after cardiopulmonary bypass: The PRODOSE adaptive randomised controlled trial

BACKGROUND

The dose of protamine required following cardiopulmonary bypass (CPB) is often determined by the dose of heparin required pre-CPB, expressed as a fixed ratio. Dosing based on mathematical models of heparin clearance is postulated to improve protamine dosing precision and coagulation. We hypothesised that protamine dosing based on a 2-compartment model would improve thromboelastography (TEG) parameters and reduce the dose of protamine administered, relative to a fixed ratio.

METHODS AND FINDINGS

We undertook a 2-stage, adaptive randomised controlled trial, allocating 228 participants to receive protamine dosed according to a mathematical model of heparin clearance or a fixed ratio of 1 mg of protamine for every 100 IU of heparin required to establish anticoagulation pre-CPB. A planned, blinded interim analysis was undertaken after the recruitment of 50% of the study cohort. Following this, the randomisation ratio was adapted from 1:1 to 1:1.33 to increase recruitment to the superior arm while maintaining study power. At the conclusion of trial recruitment, we had randomised 121 patients to the intervention arm and 107 patients to the control arm. The primary endpoint was kaolin TEG r-time measured 3 minutes after protamine administration at the end of CPB. Secondary endpoints included ratio of kaolin TEG r-time pre-CPB to the same metric following protamine administration, requirement for allogeneic red cell transfusion, intercostal catheter drainage at 4 hours postoperatively, and the requirement for reoperation due to bleeding. The trial was listed on a clinical trial registry (ClinicalTrials.gov Identifier: NCT03532594). Participants were recruited between April 2018 and August 2019. Those in the intervention/model group had a shorter mean kaolin r-time (6.58 [SD 2.50] vs. 8.08 [SD 3.98] minutes; p = 0.0016) post-CPB. The post-protamine thromboelastogram of the model group was closer to pre-CPB parameters (median pre-CPB to post-protamine kaolin r-time ratio 0.96 [IQR 0.78-1.14] vs. 0.75 [IQR 0.57-0.99]; p < 0.001). We found no evidence of a difference in median mediastinal/pleural drainage at 4 hours postoperatively (140 [IQR 75-245] vs. 135 [IQR 94-222] mL; p = 0.85) or requirement (as a binary outcome) for packed red blood cell transfusion at 24 hours postoperatively (19 [15.8%] vs. 14 [13.1%] p = 0.69). Those in the model group had a lower median protamine dose (180 [IQR 160-210] vs. 280 [IQR 250-300] mg; p < 0.001). Important limitations of this study include an unblinded design and lack of generalisability to certain populations deliberately excluded from the study (specifically children, patients with a total body weight >120 kg, and patients requiring therapeutic hypothermia to <28°C).

CONCLUSIONS

Using a mathematical model to guide protamine dosing in patients following CPB improved TEG r-time and reduced the dose administered relative to a fixed ratio. No differences were detected in postoperative mediastinal/pleural drainage or red blood cell transfusion requirement in our cohort of low-risk patients.

TRIAL REGISTRATION

ClinicalTrials.gov Unique identifier NCT03532594.

Impact of Transcatheter Aortic Valve Implantation on Thrombin Generation and Platelet Function

BACKGROUND

 Transcatheter aortic valve implantation (TAVI) is an evolving treatment of severe aortic valve stenosis. However, thromboembolic events such as stroke are common, predominantly early after TAVI. Optimal periprocedural antithrombotic regime is unknown. Especially, as antithrombotic medication enhances bleeding risk, thrombin generation and platelet function are crucial in the pathogenesis of ischemic events. However, the impact of the TAVI procedure on thrombin formation and platelet reactivity is not known by now.

METHODS

 We evaluated thrombin levels using thrombin-antithrombin (TAT) complexes and prothrombin fragments (PTFs) using enzyme-linked immunosorbent assay. Furthermore, platelet reactivity was measured via light transmission aggregometry before and 2 hours after TAVI in 198 patients.

RESULTS

 TAT complexes and PTF F1 + 2 substantially increased during TAVI. Postprocedurally, TAT complexes and PTF were significantly higher after TAVI compared with percutaneous coronary intervention due to acute myocardial infarction, while preprocedural TAT complexes and PTF F1 + 2 did not differ. In contrast, platelet reactivity was not altered early after TAVI. Only adenosine diphosphate-induced aggregation was reduced, reflecting preprocedural loading with clopidogrel.

CONCLUSION

 In this pilot study, we were able to demonstrate that thrombin generation is significantly increased early after TAVI, while platelet function is not affected. Increased thrombin concentrations may contribute to the high risk of postprocedural thromboembolic events. This leads to the hypothesis that extended peri-interventional anticoagulation early after TAVI may be an approach to reduce thromboembolic events.

The heparin-von Willebrand factor interaction and conventional tests of haemostasis - the challenges in predicting bleeding in cardiopulmonary bypass

Bleeding is a significant complication of cardiopulmonary bypass (CPB), despite routine anticoagulation monitoring. This is likely to be multifactorial. In this prospective, single-centre cohort study of 30 patients undergoing CPB surgery, our aim was to characterise the changes in von Willebrand factor (VWF) function, platelet interaction and the global coagulation changes during and after CPB surgery and to determine whether bleeding can be predicted. Samples were taken at six time points before, during and after CPB surgery. We observed a significant rise in VWF antigen (VWF:Ag) throughout surgery, which continued postoperatively. The absolute VWF collagen-binding assays (VWF:CB) and VWF ristocetin cofactor (VWF:RCo) rose significantly but the VWF:CB/VWF:Ag and VWF:Ag/VWF:RCo fell significantly (P = 0·0015 and P = 0·0143), suggesting loss of large multimers. We detected a non-significant trend to loss of VWF:RCo after heparinisation and a significant recovery after protamine reversal which could reflect a direct heparin effect. There was a significant increase in the R and K times with a fall in alpha angle and maximum amplitude after heparin administration, using heparinase-thromboelastography (TEG). The parameters both significantly improved following protamine (P = 0·007 and P = 0·0054). The activated clotting time (ACT) and heparin anti-Xa level correlated poorly; neither predicted clinically significant bleeding. None of these parameters had a relationship with intraoperative blood loss or requirement for blood product replacement.

A Standardized Bolus of 5 000 IU of Heparin Does not Lead to Adequate Heparinization during Non-cardiac Arterial Procedures

BACKGROUND

In non-cardiac arterial procedures (NCAP), heparin is administered to prevent arterial thromboembolic complications (ATEC). Heparin has a nonpredictable effect in the individual patient, also known as variation in heparin sensitivity. Various dosing protocols are in use, but the optimal dose is currently still unknown. A standardized bolus of 5 000 IU heparin is most frequently used by vascular surgeons and interventional radiologists. The activated clotting time (ACT) is an established method to measure the level of anticoagulation, but has, until now, not gained widespread use in NCAP. The purpose of this study was to evaluate the anticoagulant effect during NCAP of a standardized bolus of 5 000 IU heparin by measuring the ACT.

METHODS

In this prospective study, 190 patients undergoing NCAP were enrolled between December 2016 and September 2018. The ACT was measured during open and endovascular/hybrid procedures. All patients received a standardized bolus of 5 000 IU heparin. The ACT was measured by the Hemostasis Management System Plus (HMS Plus, Medtronic®), before, 5 minutes after administration of heparin, and every 30 minutes thereafter. The primary outcome was periprocedural ACT values measured. Secondary outcomes were ATEC and hemorrhagic complications.

RESULTS

A large individual patient variability in the response to heparin was found. The mean baseline ACT in all patients was 129 ± 18 s., and the mean ACT 5 minutes after the initial bolus of heparin was 191 ± 36 s. After the initial dose of 5 000 IU heparin 60 (33%) and 10 (6%) patients reached an ACT of 200 and 250 s., respectively. Despite the use of heparin, ATEC occurred in 17 patients (9%). The lowest number of ATEC occurred in the group of patients with an ACT between 200 and 250 s.

CONCLUSIONS

A standardized bolus of 5 000 IU heparin does not lead to adequate and safe heparinization in non-cardiac arterial procedures. Patient response to heparin shows a large individual variability. Therefore, routine ACT measurements are necessary to ascertain adequate anticoagulation. Further research is needed to investigate if heparin dosing based on the ACT could result in less arterial thromboembolic complications, without increasing hemorrhagic complications.

Confounding effect of therapeutic protamine and heparin levels on routine and special coagulation testing

: The management of a patient with hemophilia undergoing cardiovascular surgery relies on accurate coagulation test results. Both unfractionated heparin (UFH) and protamine sulfate used during cardiac surgery can interfere with factor and inhibitor assays. Here we describe the effects of UFH and protamine sulfate on routine coagulation, factor activity, and inhibitor assays. Pooled normal plasma (PNP) with UFH, PNP with protamine sulfate, PNP with both protamine sulfate and UFH were tested for the activated partial thromboplastin time (aPTT), prothrombin time (PT), thrombin time (TT), UFH anti-Xa, one-stage factor VIII (FVIII) activity, one-stage factor IX (FIX) activity, and Bethesda inhibitor assays for FVIII and FIX. UFH had a dose-dependent effect with TT, aPTT, and PT. On Bethesda inhibitor testing, FIX inhibition was detected at 1 U/ml UFH and 3 U/ml UFH for FVIII. Increasing protamine sulfate concentration in PNP prolonged the PT and aPTT in a dose-dependent manner, decreased FVIII and FIX activity and did not affect TT or UFH anti-Xa. At protamine sulfate doses of at least 200 μg/ml there was weak FVIII and FIX inhibition detected. At lower ratios of protamine sulfate to UFH (0.6 : 1-0.8 : 1), the aPTT decreased, suggesting reversal of UFH. However, at protamine sulfate to UFH ratios of 1.0 : 1 and higher, aPTT prolongation was observed. Inhibition of FVIII and FIX was detected at low ratios of protamine sulfate to UFH (below 0.4 : 1) and disappeared at higher ratios. UFH and protamine sulfate, alone or in combination, impact factor activity and inhibitor testing for both FVIII and FIX. Hence, factor activity and inhibitor assay results should be interpreted with caution when UFH or protamine sulfate are present.

Are We Able to Dose Protamine Accurately Yet? A Review of the Protamine Conundrum

Without anticoagulation, cardiopulmonary bypass would not have developed over the last nearly 60 years into one of the most influential innovations in medicine; without the ability to reverse anticoagulation, cardiac surgery might not have become the common intervention, which is now practiced globally. Despite the recent breathtaking developments in extracorporeal technology, heparin and protamine remain the pillars of anticoagulation and its reversal until this day. However, there is still much controversy in particular about protamine dosing regimens. A number of recent publications investigating various approaches to dosing protamine have rekindled this debate. This review is seeking to capture the current thinking about protamine dosing after cessation of cardiopulmonary bypass.

Anticoagulant and antithrombotic effects of chemically sulfated guar gum

Heparin is an extremely important and recognized anticoagulant and antithrombotic agent. Obtained from animal sources and being highly potent, risks of contamination by pathogens and bleeding are some concerns related to heparin use. In the search for alternatives to heparin, several researches have been performed with chemically sulfated polysaccharides obtained from non-animal sources. In this work, studies with guar gum led to a partially hydrolyzed and chemically sulfated derivative (hGGSL) with M_w of 15.6 kDa, DS of 1.91 and promising anticoagulant and antithrombotic properties. In vitro, hGGSL was only 4.5× less potent than unfractionated heparin, acting mainly by inhibiting thrombin via antithrombin, and had its anticoagulant activity inhibited by protamine. In vivo, hGGSL showed potential for subcutaneous use and was effective in reducing venous thrombosis. Collectively, the results provide a basis for the development of a new anticoagulant and antithrombotic agent.

Protamine stimulates platelet aggregation in vitro with activation of the fibrinogen receptor and alpha-granule release, but impairs secondary activation via ADP and thrombin receptors

Heparin and protamine are fundamental in the management of anticoagulation during cardiac surgery. Excess protamine has been associated with increased bleeding. Interaction between protamine and platelet function has been demonstrated but the mechanism remains unclear. We examined the effect of protamine on platelet function in vitro using impedance aggregometry, flow cytometry, and thrombin generation. Platelets were exposed to protamine at final concentrations of 0, 20, 40, and 80 µg/mL, alone or together with adenosine diphosphate (ADP) or thrombin PAR1 receptor-activating peptide (TRAP). We found that in the absence of other activators, protamine (80 µg/mL) increased the proportion of platelets with active fibrinogen receptor (binding of PAC-1) from 3.6% to 97.0% (p < .001) measured with flow cytometry. Impedance aggregometry also increased slightly after exposure to protamine alone. When activated with ADP or TRAP protamine at 80 µg/mL reduced aggregation, from 73.8 ± 29.4 U to 46.9 ± 21.1 U (p < .001) with ADP and from 126.4 ± 16.1 U to 94.9 ± 23.7 U (p < .01) with TRAP. P-selectin exposure (a marker of alpha-granule release) measured by median fluorescence intensity (MFI) increased dose dependently with protamine alone, from 0.76 ± 0.20 (0 µg/mL) to 10.2 ± 3.1 (80 µg/mL), p < .001. Protamine 80 µg/mL by itself resulted in higher MFI (10.16 ± 3.09) than activation with ADP (2.2 ± 0.7, p < .001) or TRAP (5.7 ± 2.6, p < .01) without protamine. When protamine was combined with ADP or TRAP, there was a concentration-dependent increase in the alpha-granule release. In conclusion, protamine interacts with platelets in vitro having both a direct activating effect and impairment of secondary activation of aggregation by other agonists.

Educational Case: The Bleeding Patient

The following fictional case is intended as a learning tool within the Pathology Competencies for Medical Education (PCME), a set of national standards for teaching pathology. These are divided into three basic competencies: Disease Mechanisms and Processes, Organ System Pathology, and Diagnostic Medicine and Therapeutic Pathology. For additional information, and a full list of learning objectives for all three competencies, see http://journals.sagepub.com/doi/10.1177/2374289517715040.¹

The Inhibitory Effect of Protamine on Platelets is Attenuated by Heparin without Inducing Thrombocytopenia in Rodents

Protamine sulfate (PS) is a polycationic protein drug obtained from the sperm of fish, and is used to reverse the anticoagulant effect of unfractionated heparin (UFH). However, the interactions between PS, UFH, and platelets are still not clear. We measured the platelet numbers and collagen-induced aggregation, P-selectin, platelet factor 4, β-thromboglobulin, prostacyclin metabolite, D-dimers, activated partial thromboplastin time, prothrombin time, anti-factor Xa, fibrinogen, thrombus weight and megakaryocytopoiesis in blood collected from mice and rats in different time points.. All of the groups were treated intravenously with vehicle, UFH, PS, or UFH with PS. We found a short-term antiplatelet activity of PS in mice and rats, and long-term platelet-independent antithrombotic activity in rats with electrically-induced thrombosis. The antiplatelet and antithrombotic potential of PS may contribute to bleeding risk in PS-overdosed patients. The inhibitory effect of PS on the platelets was attenuated by UFH without inducing thrombocytopenia. Treatment with UFH and PS did not affect the formation, number, or activation of platelets, or the thrombosis development in rodents.

Role of charge-reversal in the hemo/immuno-compatibility of polycationic gene delivery systems

As an effective and well-recognized strategy used in many delivery systems, such as polycation gene vectors, charge reversal refers to the alternation of vector surface charge from negative (in blood circulation) to positive (in the targeted tissue) in response to specific stimuli to simultaneously satisfy the requirements of biocompatibility and targeting. Although charge reversal vectors are intended to avoid interactions with blood in their application, no overall or systematic investigation has been carried out to verify the role of charge reversal in the blood compatibility. Herein, we comprehensively mapped the effects of a typical charge-reversible polycation gene vector based on pH-responsive 2,3-dimethylmaleic anhydride (DMMA)-modified polyethylenimine (PEI)/pDNA complex in terms of blood components, coagulation function, and immune response as compared to conventional PEGylated modification. The in vitro and in vivo results displayed that charge-reversal modification significantly improves the PEI/pDNA-induced abnormal effect on vascular endothelial cells, platelet activation, clotting factor activity, fibrinogen polymerization, blood coagulation process, and pro-inflammatory cytokine expression. Unexpectedly, (PEI/pDNA)-DMMA induced the cytoskeleton impairment-mediated erythrocyte morphological alternation and complement activation even more than PEI/pDNA. Further, transcriptome sequencing demonstrated that the overexpression of pro-inflammatory cytokines was correlated with vector-induced differentially expressed gene number and mediated by inflammation-related signaling pathways (MAPK, NF-κB, Toll-like receptor, and JAK-STAT) activation. By comparison, charge-reversal modification improved the hemocompatibility to a greater extent than dose PEGylation except for erythrocyte rupture. Nevertheless, it is inferior to mPEG modification in terms of immunocompatibility. These findings provide comprehensive insights to understand the molecular mechanisms of the effects of charge reversal on blood components and their function and to provide valuable information for its potential applications from laboratory to clinic. STATEMENT OF SIGNIFICANCE: The seemingly revolutionary charge reversal strategy has been believed to possess stealth character with negative charge eluding interaction with blood components during circulation. However to date, no overall or systematic investigation has been carried out to verify the role of charge-reversal on the blood/immune compatibility, which impede their development from laboratory to bedside. Therefore, we comprehensively mapped the effects of a typical charge-reversible polycationic gene vector on blood components (vascular endothelial cell, platelet, clotting factors, fibrinogen, RBCs and coagulation function) and immune response (complement and pro-inflammatory cytokines) at cellular and molecular level in comparison to PEGylation modification. These findings help to elucidate the molecular mechanisms for the effects of charge-reversal on blood components and functions, and provide valuable information for the possible application in clinical settings.

Activated platelet aggregation is transiently impaired also by a reduced dose of protamine

Objectives: Protamine reduces platelet aggregation after cardiopulmonary bypass (CPB). We studied the inhibitory effect of a reduced protamine dose, the duration of impaired platelet function and the possible correlation to postoperative bleeding. Design: Platelet function was assessed by impedance aggregometry in 30 patients undergoing cardiac surgery with CPB at baseline, before protamine administration, after 70% and 100% of the calculated protamine dose, after 20 minutes and at arrival to the intensive care unit. Adenosine diphosphate (ADP), thrombin receptor activating peptide-6 (TRAP), arachidonic acid (AA) and collagen (COL) were used as activators. Blood loss was measured during operation and three hours after surgery. Results are presented as median (25th-75th percentile). Results: Platelet aggregation decreased markedly after the initial dose of protamine (70%) with all activators; ADP 89 (71-110) to 54 (35-78), TRAP 143 (116-167) to 109 (77-136), both p < .01; AA 25 (16-49) to 17 (12-24) and COL 92 (47-103) to 60 (38-81) U, both p < .05. No further decrease was seen after 100% protamine. The effect was transient and after twenty minutes platelet aggregation had started to recover; ADP 76 (54-106), TRAP 138 (95-158), AA 20 (10-35), COL 70 (51-93) U. Blood loss during operation correlated to aggregometry measured at baseline and after protaminization. Conclusions: Protamine after CPB induces a marked decrease in platelet aggregation already at a protamine-heparin ratio of 0.7:1. The impairment seems to be transient and recovery had started after 20 minutes.

The role of evidence-based algorithms for rotational thromboelastometry-guided bleeding management

Rotational thromboelastometry (ROTEM) is a point-of-care viscoelastic method and enables to assess viscoelastic profiles of whole blood in various clinical settings. ROTEM-guided bleeding management has become an essential part of patient blood management (PBM) which is an important concept in improving patient safety. Here, ROTEM testing and hemostatic interventions should be linked by evidence-based, setting-specific algorithms adapted to the specific patient population of the hospitals and the local availability of hemostatic interventions. Accordingly, ROTEM-guided algorithms implement the concept of personalized or precision medicine in perioperative bleeding management (‘theranostic’ approach). ROTEM-guided PBM has been shown to be effective in reducing bleeding, transfusion requirements, complication rates, and health care costs. Accordingly, several randomized-controlled trials, meta-analyses, and health technology assessments provided evidence that using ROTEM-guided algorithms in bleeding patients resulted in improved patient’s safety and outcomes including perioperative morbidity and mortality. However, the implementation of ROTEM in the PBM concept requires adequate technical and interpretation training, education and logistics, as well as interdisciplinary communication and collaboration.

Spontaneous spinal subdural haematoma in a patient on apixaban

A 68-year-old man on apixaban presented to the emergency department with back pain following a long-haul flight. Investigations for pulmonary embolus and aortic dissection were negative and he was discharged with analgesia for mechanical back pain. He presented three more times with worsening back pain, third time with urinary retention and the fourth time with lower limb weakness and loss of coordination. He was found to have a spinal subdural haematoma on MRI and transferred to a tertiary centre, where he was managed conservatively and discharged for rehabilitation with good neurological recovery.

Clinical Impact of Protamine Titration-Based Heparin Neutralization in Patients Undergoing Coronary Bypass Grafting Surgery

OBJECTIVES

A hemostasis management system (HMS) is a point-of-care method for heparin and protamine titration. The authors hypothesized that protamine dosing over the HMS estimate would be associated with elevated activated clotting time (ACT), increased bleeding, and transfusion owing to protamine's anticoagulant activity.

DESIGN

A retrospective cohort study.

SETTING

Single-center university hospital.

PARTICIPANTS

One hundred eighty-nine patients undergoing elective coronary artery bypass grafting surgery.

INTERVENTIONS

Patients were stratified into 3 groups per ratio of actual total administered protamine versus the HMS-derived protamine estimate: (1) low-ratio (≤66% of HMS estimate), (2) moderate-ratio (66%-100% of HMS estimate), and (3) high-ratio (>100% of HMS estimate).

MEASUREMENTS AND MAIN RESULTS

The primary endpoints were post-protamine ACT, and residual heparin levels on HMS among the 3 groups in addition to bleeding and transfusion. There were 54 (28.6%) patients in the low, 95 (50.3%) in the moderate, and 40 (21.2%) in the high-ratio group. The high-ratio patients who were overdosed with protamine relative to the HMS estimate had elevated ACT, international normalized ratio, and activated partial thromboplastin time values, and subsequently received more red blood cell (RBC) and non-RBC transfusions compared to lower-ratio groups. Higher actual/HMS protamine ratios were associated independently with post-protamine ACT elevations after adjustment for sex, body mass index (BMI), and cardiopulmonary bypass (CPB) time.

CONCLUSION

Most patients received the protamine dose sufficiently close to the HMS estimate, but protamine dosing above the HMS estimate occurred in both obese and nonobese patients, which was associated independently with prolonged ACT after adjusting for sex, BMI, and CPB time.

Approaches to prevent bleeding associated with anticoagulants: current status and recent developments

Anticoagulants are widely used for the prophylaxis and treatment of cardiovascular disorders and to prevent blood clotting during surgeries. However, the major limitation associated with anticoagulant therapy is bleeding; all the current anticoagulants do have a bleeding risk. The propensity to bleed is much higher among the elderly population and patients with renal insufficiency. Therefore, there is an utmost and urgent clinical need for a highly efficient, nontoxic antidote with excellent anticoagulant reversal activity. This will significantly improve the safety of anticoagulation therapy. This review summarizes the current options and approaches to reverse anticoagulation activity of clinically used anticoagulants. We start with an introduction to thrombosis and then summarize the details of current clinically available anticoagulants and their mechanisms of action and limitations. This is followed by current practices in anticoagulant neutralization including the details of the only clinically approved unfractionated heparin antidote, protamine; recent advances in the development of antidotes against heparin-based drugs; and direct oral anticoagulants (DOACs).

Heparin-protamine balance after neonatal cardiopulmonary bypass surgery

Essentials Heparin-protamine balance (HPB) modulates bleeding after neonatal cardiopulmonary bypass (CPB). HPB was examined in 44 neonates undergoing CPB. Post-operative bleeding occurred in 36% and heparin rebound in 73%. Thrombin-initiated fibrin clot kinetic assay and partial thromboplastin time best assessed HPB.

SUMMARY

Background Neonates undergoing cardiopulmonary bypass (CPB) are at risk of excessive bleeding. Blood is anticoagulated with heparin during CPB. Heparin activity is reversed with protamine at the end of CPB. Paradoxically, protamine also inhibits blood coagulation when it is dosed in excess of heparin. Objectives To evaluate heparin-protamine balance in neonates undergoing CPB by using research and clinical assays, and to determine its association with postoperative bleeding. Patients/Methods Neonates undergoing CPB in the first 30 days of life were studied. Blood samples were obtained during and after surgery. Heparin-protamine balance was assessed with calibrated automated thrombography, thrombin-initiated fibrin clot kinetic assay (TFCK), activated partial thromboplastin time (APTT), anti-FXa activity, and thromboelastometry. Excessive postoperative bleeding was determined by measurement of chest tube output or the development of cardiac tamponade. Results and Conclusions Of 44 neonates enrolled, 16 (36%) had excessive postoperative bleeding. The TFCK value was increased. By heparin in neonatal blood samples, but was only minimally altered by excess protamine. Therefore, it reliably measured heparin in samples containing a wide range of heparin and protamine concentrations. The APTT most closely correlated with TFCK results, whereas anti-FXa and thromboelastometry assays were less correlative. The TFCK and APTT assay also consistently detected postoperative heparin rebound, providing an important continued role for these long-established coagulation tests in the management of postoperative bleeding in neonates requiring cardiac surgical repair. None of the coagulation tests predicted the neonates who experienced postoperative bleeding, reflecting the multifactorial causes of bleeding in this population.

Calculation Algorithm Reduces Protamine Doses Without Increasing Blood Loss or the Transfusion Rate in Cardiac Surgery: Results of a Randomized Controlled Trial

OBJECTIVES

The aim of the study was to investigate whether the HeProCalc algorithm affects heparin and protamine dosage, postoperative blood loss, and transfusion rate.

DESIGN

Randomized controlled trial.

SETTING

University hospital.

PARTICIPANTS

The study comprised 210 cardiac surgery patients undergoing cardiac surgery with cardiopulmonary bypass. Twenty patients were excluded because of re-exploration for localized surgical bleeding (n = 9), violation of protocol (n = 2), aprotinin use (n = 3 and nadir body temperature <32°C (n = 6).

INTERVENTIONS

Study participants were randomly assigned to either traditional heparin and protamine dosage based on body weight only (control group) or dosage based on the HeProCalc algorithm (intervention group).

MEASUREMENTS AND MAIN RESULTS

The initial median heparin dose was 32,500 IU (interquartile range [IQR] 30,000-35,000) in the intervention group compared with 35,000 IU (IQR 30,000-37,500) (p = 0.025) in the control group. The total heparin dose in the intervention group was 40,000 IU (IQR 32,500-47,500) compared with 42,500 IU (IQR 35,000-50,000) in the control group (p = 0.685). The total protamine dose was 210 mg (IQR 190-240) in the intervention group compared with 350 mg (IQR 300-380) (p < 0.001) in the control group. The ratio of total protamine to initial dose of heparin in the intervention group was 0.62 compared with 1.0 (p < 0.001). The amount of chest tube bleeding after 12 postoperative hours was 320 mL (IQR 250-460) in the intervention group compared with 350 mL (IQR 250-450) (p = 0.754) in the control group. Neither the transfusion rate nor postoperative blood loss differed significantly between the 2 groups.

CONCLUSION

Use of the HeProCalc algorithm reduced protamine dosage and the protamine/heparin ratio after cardiopulmonary bypass compared with conventional dosage based on weight without significant effect on postoperative blood loss or the transfusion rate.

Perioperative management of the bleeding patient

Perioperative bleeding remains a major complication during and after surgery, resulting in increased morbidity and mortality. The principal causes of non-vascular sources of haemostatic perioperative bleeding are a preexisting undetected bleeding disorder, the nature of the operation itself, or acquired coagulation abnormalities secondary to haemorrhage, haemodilution, or haemostatic factor consumption. In the bleeding patient, standard therapeutic approaches include allogeneic blood product administration, concomitant pharmacologic agents, and increasing application of purified and recombinant haemostatic factors. Multiple haemostatic changes occur perioperatively after trauma and complex surgical procedures including cardiac surgery and liver transplantation. Novel strategies for both prophylaxis and therapy of perioperative bleeding include tranexamic acid, desmopressin, fibrinogen and prothrombin complex concentrates. Point-of-care patient testing using thromboelastography, rotational thromboelastometry, and platelet function assays has allowed for more detailed assessment of specific targeted therapy for haemostasis. Strategic multimodal management is needed to improve management, reduce allogeneic blood product administration, and minimize associated risks related to transfusion.

Calcium content mediated hemostasis of calcium-modified oxidized microporous starch

Blood coagulates are closely related to calcium ions (coagulation factor IV), and calcium-doped biomaterials have been reported to be effective in hemostasis. However, the effects exerted by calcium on hemostatic agents have not been previously investigated. The aims of this work were to develop calcium-modified oxidized microporous starch (CaOMS) with controllable calcium contents and to explore the relationship between calcium content and hemostatic effects. The results showed that low calcium content promoted coagulation, while high calcium content inhibited coagulation. CaOMS3 with 2.2 mg/g calcium content was optimal because of its excellent water absorption performance that enhanced physical coagulation, the rapid initiation of coagulation cascade reactions, and the enhanced chemical coagulation by RBC aggregation and platelet activation. The synergistic effects of chemical activation and physical absorption endowed CaOMS with the potential to control internal organ bleeding. These results suggested that CaOMS may be a promising hemostatic agent with wide spread applications.

The effect of protamine dosing variation on bleeding and transfusion after heparinisation for cardiopulmonary bypass

INTRODUCTION

Accurate dosing of protamine reversal following on-pump cardiac surgical procedures is challenging, with both excessive and inadequate administration recognised to increase bleeding risk. We aimed to examine the relationship between three ratios for heparin reversal and markers of haemostasis.

METHODS

A retrospective analysis of a prospectively collected database was undertaken at a single tertiary cardiac unit, reviewing all cases of on-pump coronary artery bypass grafts and single valve replacements from 01/01/2011 to 31/12/2015. The ratio between total intra-operative heparin and protamine was stratified to three groups (low: ≤0.6 mg per 100 IU of heparin, moderate: 0.6-1.0 and high: >1.0) and related to the primary outcome of red blood cell (RBC) transfusion, with secondary outcomes being the number of units transfused, the haemoglobin differential and mediastinal drain output at 4 hours.

RESULTS

Of the 803 patients identified, 338 received a blood transfusion, with 1035 units being used. Eighteen percent of individuals (145) received a low ratio, 50% (404) received a moderate ratio and 32% (254) a high ratio. Using the moderate group as a reference, the low dose group was 56.5% less likely to have received a RBC transfusion (OR 0.435; 95% CI 0.270:0.703 p=0.001) while the high dose group carried a 241% increased association with transfusion (OR 3.412; 95% CI 2.399:4.853 p<0.001). For those transfused, a lower protamine:heparin ratio was associated with a lower number of units transfused, lesser haemoglobin differential and less mediastinal drain output.

CONCLUSION

Higher doses of intra-operative protamine relative to heparin are associated with greater risk of transfusion and post-operative bleeding.

Effect of high or low protamine dosing on postoperative bleeding following heparin anticoagulation in cardiac surgery

While experimental data state that protamine exerts intrinsic anticoagulation effects, protamine is still frequently overdosed for heparin neutralisation during cardiac surgery with cardiopulmonary bypass (CPB). Since comparative studies are lacking, we assessed the influence of two protamine-to-heparin dosing ratios on perioperative haemostasis and bleeding, and hypothesised that protamine overdosing impairs the coagulation status following cardiac surgery. In this open-label, multicentre, single-blinded, randomised controlled trial, patients undergoing on-pump coronary artery bypass graft surgery were assigned to a low (0.8; n=49) or high (1.3; n=47) protamine-to-heparin dosing group. The primary outcome was 24-hour blood loss. Patient haemostasis was monitored using rotational thromboelastometry and a thrombin generation assay. The low protamine-to-heparin dosing ratio group received less protamine (329 ± 95 vs 539 ± 117 mg; p<0.001), while post-protamine activated clotting times were similar among groups. The high dosing group revealed increased intrinsic clotting times (236 ± 74 vs 196 ± 64 s; p=0.006) and the maximum post-protamine thrombin generation was less suppressed in the low dosing group (38 ± 40% vs 6 ± 9%; p=0.001). Postoperative blood loss was increased in the high dosing ratio group (615 ml; 95% CI 500–830 ml vs 470 ml; 95% CI 420–530 ml; p=0.021) when compared to the low dosing group, respectively. More patients in the high dosing group received fresh frozen plasma (11% vs 0%; p=0.02) and platelet concentrate (21% vs 6%; p=0.04) compared to the low dosing group. Our study confirms in vitro data that abundant protamine dosing is associated with increased postoperative blood loss and higher transfusion rates in cardiac surgery.