Anticoagulant and side-effects of protamine in cardiac surgery: a narrative review

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.

Individualized heparin monitoring and management reduces protamine requirements in cardiac surgery on minimal invasive extracorporeal circulation; A prospective randomized study

INTRODUCTION

Individualized heparin and protamine management is increasingly used as a strategy to reduce coagulation activation and bleeding complications. While it is associated with increased heparin requirements during Cardiopulmonary Bypass (CPB), the impact on protamine administration remains controversial. We aim to investigate the effect of heparin level-guided monitoring on protamine dosing during cardiac surgery where low-anticoagulation protocols are implemented.

METHODS

This is a prospective, randomized, controlled trial. A total of 132 patients undergoing elective full-spectrum cardiac surgery with Minimal Invasive Extracorporeal Circulation (MiECC) were recruited. All patients were managed by the same anaesthetic, surgical and perfusion team. Patients were randomly allocated in two groups; the individualized heparin-protamine titration (IHPT) group and the conventional heparinization and reversal group by using ACT (cACT) with a 0.75:1, protamine: heparin ratio. Titration was accomplished with the Hepcon HMS Plus (Medtronic, Minneapolis, MN) system. The primary outcome of the study was the total protamine dose used. Secondary outcomes comprised of the total heparin dose, the percentage of patients achieving target ACT, 24-h transfusion requirements, postoperative bleeding, duration of mechanical ventilation, major morbidity and length of hospital stay. Patients in each group were divided in two subgroups according to the target ACT; those operated for coronary artery bypass grafting (CABG) using a target ACT >300 s and the rest (non-CABG) patients operated with a target ACT >400 s, respectively.

RESULTS

Protamine requirements were significantly reduced when IHPT was implemented; CABG (118 ± 24 mg vs 163 ± 61 mg; p < 0.001) and non-CABG cases (151 ± 46 mg vs 197 ± 45 mg; p < 0.001). Moreover, heparin requirements were significantly higher in the non-CABG subgroup managed with IHPT (34,539 ± 7658 IU vs 29,893 ± 9037 IU; p = 0.02). In overall, no significant differences were detected with respect to postoperative bleeding, transfusion of RBC or other blood products.

CONCLUSIONS

Individualized heparin monitoring and management reduces protamine requirements in cardiac surgery with MiECC implementing reduced anticoagulation strategy.

TRIAL REGISTRATION

clinicaltrials.gov; NCT04215588.

Development of substrate-independent heparin coating to mitigate surface-induced thrombogenesis: efficacy and mechanism

Heparin coatings are widely applied on blood-contact materials to reduce the use of anticoagulants during blood treatment. However, the previous heparin coatings formed via covalent binding or electrostatic bonding commonly require complex surface premodification, and the blood coagulation pathway was significantly inhibited to potentially increase the bleeding risk. This contradicts the intended purpose and deviates from the anticoagulation mechanism of the heparin coatings. Herein, we present a facile and substrate-independent coating, achieved through the co-deposition of dopamine/chitosan followed by electrostatic interaction between heparin and the immobilized chitosan, which could be prepared within 1 hour. This coating prolonged the plasma re-calcification time (PRT) to over 60 minutes, effectively preventing surface-induced thrombosis. Favorable hemocompatibility was reflected in a hemolysis ratio of less than 2%, low levels of platelet adhesion and activation, and low levels of fibrinogen adhesion. We also systematically elucidate the anticoagulant mechanism of the coating, demonstrating why the coating can prevent thrombogenesis without the bleeding risk. Our work not only offers a promising and readily available heparin coating for blood-contact materials, but more importantly, the mechanism exploration supports the practical feasibility of heparin coating in various applications.

The Crucial Triad: Endothelial Glycocalyx, Oxidative Stress, and Inflammation in Cardiac Surgery-Exploring the Molecular Connections

Since its introduction, the number of heart surgeries has risen continuously. It is a high-risk procedure, usually involving cardiopulmonary bypass, which is associated with an inflammatory reaction that can lead to perioperative and postoperative organ dysfunction. The extent of complications following cardiac surgery has been the focus of interest for several years because of their impact on patient outcomes. Recently, numerous scientific efforts have been made to uncover the complex mechanisms of interaction between inflammation, oxidative stress, and endothelial dysfunction that occur after cardiac surgery. Numerous factors, such as surgical and anesthetic techniques, hypervolemia and hypovolemia, hypothermia, and various drugs used during cardiac surgery trigger the development of systemic inflammatory response and the release of oxidative species. They affect the endothelium, especially endothelial glycocalyx (EG), a thin surface endothelial layer responsible for vascular hemostasis, its permeability and the interaction between leukocytes and endothelium. This review highlights the current knowledge of the molecular mechanisms involved in endothelial dysfunction, particularly in the degradation of EG. In addition, the major inflammatory events and oxidative stress responses that occur in cardiac surgery, their interaction with EG, and the clinical implications of these events have been summarized and discussed in detail. A better understanding of the complex molecular mechanisms underlying cardiac surgery, leading to endothelial dysfunction, is needed to improve patient management during and after surgery and to develop effective strategies to prevent adverse outcomes that complicate recovery.

Synthesis, Biological Evaluation and Reversal of Sulfonated Di- and Triblock Copolymers as Novel Parenteral Anticoagulants

Despite targeting different coagulation cascade sites, all Food and Drug Administration-approved anticoagulants present an elevated risk of bleeding, including potentially life-threatening intracranial hemorrhage. Existing studies have not thoroughly investigated the efficacy and safety of sulfonate polymers in animal models and fully elucidate the precise mechanisms by which these polymers act. The activity and safety of sulfonated di- and triblock copolymers containing poly(sodium styrenesulfonate) (PSSS), poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPS), poly(ethylene glycol) (PEG), poly(sodium methacrylate) (PMAAS), poly(acrylic acid) (PAA), and poly(sodium 11-acrylamidoundecanoate) (PAaU) blocks are synthesized and assessed. PSSS-based copolymers exhibit greater anticoagulant activity than PAMPS-based ones. Their activity is mainly affected by the total concentration of sulfonate groups and molecular weight. PEG-containing copolymers demonstrate a better safety profile than PAA-containing ones. The selected copolymer PEG47-PSSS32 exhibits potent anticoagulant activity in rodents after subcutaneous and intravenous administration. Heparin Binding Copolymer (HBC) completely reverses the anticoagulant activity of polymer in rat and human plasma. No interaction with platelets is observed. Selected copolymer targets mainly factor XII and fibrinogen, and to a lesser extent factors X, IX, VIII, and II, suggesting potential application in blood-contacting biomaterials for anticoagulation purposes. Further studies are needed to explore its therapeutic applications fully.

Routine Protamine Administration for Bleeding in Transcatheter Aortic Valve Implantation: The ACE-PROTAVI Randomized Clinical Trial

Importance

Vascular complications after transfemoral transcatheter aortic valve implantation (TAVI) remain an important cause of procedure-related morbidity. Routine reversal of anticoagulation with protamine at the conclusion of transfemoral TAVI could reduce complications, but data remain scarce.

Objective

To evaluate the efficacy and safety of routine protamine administration after transfemoral TAVI.

Design, Setting, and Participants

The ACE-PROTAVI trial was an investigator-initiated, double-blind, placebo-controlled randomized clinical trial performed at 3 Australian hospitals between December 2021 and June 2023 with a 1-year follow-up period. All patients accepted for transfemoral TAVI by a multidisciplinary heart team were eligible for enrollment.

Interventions

Eligible patients were randomized 1:1 between routine protamine administration and placebo.

Main Outcomes and Measures

The coprimary outcomes were the rate of hemostasis success and time to hemostasis (TTH), presented as categorical variables and compared with a χ2 test or as continuous variables as mean (SD) or median (IQR), depending on distribution. The major secondary outcome was a composite of all-cause death, major and minor bleeding complications, and major and minor vascular complications after 30 days, reported in odds ratios (ORs) with 95% CIs and P values.

Results

The study population consisted of 410 patients: 199 patients in the protamine group and 211 in the placebo group. The median (IQR) patient age in the protamine group was 82 (77-85) years, and 68 of 199 patients receiving protamine (34.2%) were female. The median (IQR) patient age in the placebo group was 80 (75-85) years, and 89 of 211 patients receiving the placebo (42.2%) were female. Patients receiving up-front protamine administration had a higher rate of hemostasis success (188 of 192 patients [97.9%]) than patients in the placebo group (186 of 203 patients [91.6%]; absolute risk difference, 6.3%; 95% CI, 2.0%-10.6%; P = .006); in addition, patients receiving up-front protamine had a shorter median (IQR) TTH (181 [120-420] seconds vs 279 [122-600] seconds; P = .002). Routine protamine administration resulted in a reduced risk of the composite outcome in the protamine group (10 of 192 [5.2%]) vs the placebo group (26 of 203 [12.8%]; OR, 0.37; 95% CI, 0.1-0.8; P = .01). This difference was predominantly driven by the difference in the prevalence of minor vascular complications. There were no adverse events associated with protamine use.

Conclusions and Relevance

In the ACE-PROTAVI randomized clinical trial, routine administration of protamine increased the rate of hemostasis success and decreased TTH. The beneficial effect of protamine was reflected in a reduction in minor vascular complications, procedural time, and postprocedural hospital stay duration in patients receiving routine protamine compared with patients receiving placebo.

Trial Registration

anzctr.org.au Identifier: ACTRN12621001261808.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Effect of nitric oxide delivery via cardiopulmonary bypass circuit on postoperative oxygenation in adults undergoing cardiac surgery (NOCARD trial): a randomised controlled trial

BACKGROUND

Cardiac surgery involving cardiopulmonary bypass induces a significant systemic inflammatory response, contributing to various postoperative complications, including pulmonary dysfunction, myocardial and kidney injuries.

OBJECTIVE

To investigate the effect of Nitric Oxide delivery via the cardiopulmonary bypass circuit on various postoperative outcomes.

DESIGN

A prospective, single-centre, double-blinded, randomised controlled trial.

SETTING

Rabin Medical Centre, Beilinson Hospital, Israel.

PATIENTS

Adult patients scheduled for elective cardiac surgery were randomly allocated to one of the study groups.

INTERVENTIONS

For the treatment group, 40 ppm of nitric oxide was delivered via the cardiopulmonary bypass circuit. For the control group, nitric oxide was not delivered.

OUTCOME MEASURES

The primary outcome was the incidence of hypoxaemia, defined as a p a O2 /FiO 2 ratio less than 300 within 24 h postoperatively. The secondary outcomes were the incidences of low cardiac output syndrome and acute kidney injury within 72 h postoperatively.

RESULTS

Ninety-eight patients were included in the final analysis, with 47 patients allocated to the control group and 51 to the Nitric Oxide group. The Nitric Oxide group exhibited significantly lower hypoxaemia rates at admission to the cardiothoracic intensive care unit (47.1 vs. 68.1%), P  = 0.043. This effect, however, varied in patients with or without baseline hypoxaemia. Patients with baseline hypoxaemia who received nitric oxide exhibited significantly lower hypoxaemia rates (61.1 vs. 93.8%), P  = 0.042, and higher p a O2 /FiO 2 ratios at all time points, F (1,30) = 6.08, P  = 0.019. Conversely, this benefit was not observed in patients without baseline hypoxaemia. No significant differences were observed in the incidence of low cardiac output syndrome or acute kidney injury. No substantial safety concerns were noted, and toxic methaemoglobin levels were not observed.

CONCLUSIONS

Patients with baseline hypoxaemia undergoing cardiac surgery and receiving nitric oxide exhibited lower hypoxaemia rates and higher p a O2 /FiO 2 ratios. No significant differences were found regarding postoperative pulmonary complications and overall outcomes.

TRIAL REGISTRATION

NCT04807413.

Protamine titration to optimize heparin antagonization after cardiopulmonary bypass

OBJECTIVES

To optimize protamine titration for heparin antagonization after weaning from cardiopulmonary bypass (CPB).

DESIGN

A prospective, observational trial.

SETTING

Single-center, non-university teaching hospital.

PARTICIPANTS

Forty patients presenting for elective on-pump coronary artery bypass grafting with or without single valve surgery.

INTERVENTIONS

At the end of CPB, the residual amount of heparin in the patient was estimated using a Bull-curve. The total protamine dose was calculated as 1 unit of protamine for 1 unit of heparin. Protamine was administered as 5 aliquots containing 20% of the total protamine dose each, with 2-min intervals.

MEASUREMENTS AND MAIN RESULTS

Activated Clotting Time (ACT) values were measured 2 min after administration of each aliquot. ROTEM(®)-analysis was performed after the full dose of protamine had been administered. After 60% of the total protamine dose had been administered, ACT values were normalized in 86.5% of patients. After the complete dose of protamine had been administered, 61.1% of patients displayed signs of protamine overdose on ROTEM(®)-analysis.

CONCLUSIONS

In patients who present for on-pump coronary artery bypass grafting with or without single valve surgery, a 0.6-to-1 ratio of protamine-to-heparin to antagonize heparin may be sufficient and beneficial for patients.

Assessment of Perioperative Protamine Reactions in Patients With Fish Allergies: A Retrospective Observational Study

OBJECTIVES

To retrospectively assess the incidence and severity of perioperative protamine reactions in adult patients with documented history of fish allergy.

DESIGN

Retrospective observational study.

SETTING

Large academic tertiary referral center.

PARTICIPANTS

Adults with fish allergies undergoing surgeries involving protamine, between January 1, 2008, and March 1, 2018.

INTERVENTIONS

Perioperative protamine administration in patients with documented fish allergy.

MEASUREMENTS AND MAIN RESULTS

Perioperative protamine and anaphylactic reactions were reviewed. A diagnosis of anaphylaxis or protamine reaction was based on clinical suspicion, perioperative events, and postoperative evaluations. Among 214 patients, 2 cases (<1%) of anaphylaxis or protamine reactions occurred. Cardiac procedures were most common (67%). The median intraoperative heparin dosage was 46,000 IU, and the median protamine dosage was 310 mg. Nearly all patients (99%) were admitted to the intensive care unit postoperatively, with a median hospital stay of 6.5 days (interquartile range, 5.2-14.6 days). There were 3 deaths (1%) within 30 days, and 15 (7%) within 1 year.

CONCLUSIONS

The study findings suggest that in patients with a history of fish allergy, cross-reactivity with protamine is unlikely, as anaphylaxis and/or protamine reactions were rare in this patient population in the perioperative environment. Based on these findings, this study does not recommend avoiding protamine solely based on a history of fish allergy when heparin reversal is required during surgery.

External Trigger Free Charge Switchable Cationic Ligands in the Design of Safe and Effective Universal Heparin Antidote

Thrombosis, the formation of blood clots within a blood vessel, can lead to severe complications including pulmonary embolism, cardiac arrest, and stroke. The most widely administered class of anticoagulants is heparin-based anticoagulants such as unfractionated heparin, low-molecular weight heparins (LMWHs), and fondaparinux. Protamine is the only FDA-approved heparin antidote. Protamine has limited efficacy neutralizing LMWHs and no reversal activity against fondaparinux. The use of protamine can lead to complications, including excessive bleeding, hypotension, and hypersensitivity, and has narrow therapeutic window. In this work, a new concept in the design of a universal heparin antidote: switchable protonation of cationic ligands, is presented. A library of macromolecular polyanion inhibitors (MPIs) is synthesized and screened to identify molecules that can neutralize all heparins with high selectivity and reduced toxicity. MPIs are developed by assembling cationic binding groups possessing switchable protonation states onto a polymer scaffold. By strategically selecting the identity and modulating the density of cationic binding groups on the polymer scaffold, a superior universal heparin reversal agent is developed with improved heparin-binding activity and increased hemocompatibility profiles leading to minimal effect on hemostasis. The activity of this heparin antidote is demonstrated using in vitro and in vivo studies.

The association between heparin sensitivity index and postoperative blood loss in Chinese patients undergoing elective off-pump coronary artery bypass grafting: a single center retrospective study

BACKGROUND

The heparin sensitivity index (HSI) is closely associated with perioperative ischemic events and increased blood loss in cardiac surgery. Previous studies have produced conflicting results. Therefore, this study aimed to investigate the relationship between HSI and postoperative blood loss specifically in Chinese patients undergoing elective off-pump coronary artery bypass grafting (OPCAB).

METHODS

Patients underwent OPCAB between March 2021 and July 2022 were retrospectively included. Enrolled patients were classified into Low-HSI (HSILOW; HSI < 1.3) and Normal-HSI (HSINORM; HSI ≥ 1.3) groups. HSI = [(activated clotting time (ACT) after heparin) - (baseline ACT)] / [loading dose of heparin (IU/kg)]. Primary outcome included postoperative blood loss at 24 h. Secondary outcomes were total postoperative blood loss, transfusion requirement of red blood cell (RBC), fresh frozen plasma (FFP), platelet concentrates (PC), and other complications.

RESULTS

We retrospectively analyzed 303 Chinese OPCAB patients. HSILOW group had higher preoperative platelet (PLT) count (221 × 109/L vs. 202 × 109/L; P = 0.041) and platelet crit (PCT) value (0.23% vs. 0.22%; P = 0.040) compared to HSINORM group. Two groups showed no significant differences in postoperative blood loss at 24 h (460 mL vs. 470 mL; P = 0.252), total blood loss (920 mL vs. 980 mL; P = 0.063), RBC transfusion requirement (3.4% vs. 3.1%; P = 1.000), FFP transfusion requirement (3.4% vs. 6.2%; P = 0.380), and other complications. Preoperative high PLT count was associated with low intraoperative HSI value (odds ratio: 1.006; 95% confidence interval: 1.002, 1.011; P = 0.008).

CONCLUSIONS

Intraoperative HSI value was not associated with postoperative blood loss in Chinese patients undergoing OPCAB. Preoperative high PLT count was an independent predictor of low intraoperative HSI value.

A functional RNA-origami as direct thrombin inhibitor with fast-acting and specific single-molecule reversal agents in vivo model

Injectable anticoagulants are widely used in medical procedures to prevent unwanted blood clotting. However, many lack safe, effective reversal agents. Here, we present new data on a previously described RNA origami-based, direct thrombin inhibitor (HEX01). We describe a new, fast-acting, specific, single-molecule reversal agent (antidote) and present in vivo data for the first time, including efficacy, reversibility, preliminary safety, and initial biodistribution studies. HEX01 contains multiple thrombin-binding aptamers appended on an RNA origami. It exhibits excellent anticoagulation activity in vitro and in vivo. The new single-molecule, DNA antidote (HEX02) reverses anticoagulation activity of HEX01 in human plasma within 30 s in vitro and functions effectively in a murine liver laceration model. Biodistribution studies of HEX01 in whole mice using ex vivo imaging show accumulation mainly in the liver over 24 h and with 10-fold lower concentrations in the kidneys. Additionally, we show that the HEX01/HEX02 system is non-cytotoxic to epithelial cell lines and non-hemolytic in vitro. Furthermore, we found no serum cytokine response to HEX01/HEX02 in a murine model. HEX01 and HEX02 represent a safe and effective coagulation control system with a fast-acting, specific reversal agent showing promise for potential drug development.

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.

Surfactant-based supramolecular dye assembly: A highly selective and economically viable platform for quantification of heparin antidote

Herein, we have employed a supramolecular assembly of a cationic dye, LDS-698 and a common surfactant sodium dodecyl sulfate (SDS) as a turn-on fluorescent sensor for protamine (Pr) detection. Addition of cationic Pr to the solution of dye-surfactant complex brings negatively charged SDS molecules together through strong electrostatic interaction, assisting aggregation of SDS way before its critical micellar concentration (CMC). These aggregates encapsulate the dye molecules within their hydrophobic region, arresting non-radiative decay channels of the excited dye. Thus, the LDS-698•SDS assembly displays substantial enhancement in fluorescence intensity that follows a nice linear trend with Pr concentration, providing limit of detection (LOD) for Pr as low as 3.84(±0.11) nM in buffer, 124.4(±6.7) nM in 1% human serum and 28.3(±0.5) nM in 100% human urine. Furthermore, high selectivity, low background signal, large stokes shift, and emission in the biologically favorable deep-red region make the studied assembly a promising platform for Pr sensing. As of our knowledge it is the first ever Pr sensory platform, using a very common surfactant (SDS), which is economically affordable and very easily available in the market. This innovative approach can replace the expensive, exotic and specialized chemicals considered for the purpose and thus showcase its potential in practical applications.

Effect of rt-PA on Shear Wave Mechanical Assessment and Quantitative Ultrasound Properties of Blood Clot Kinetics In Vitro

OBJECTIVE

The consequences associated with blood clots are numerous and are responsible for many deaths worldwide. The assessment of treatment efficacy is necessary for patient follow-up and to detect treatment-resistant patients. The aim of this study was to characterize the effect of treatment on blood clots in vitro using quantitative ultrasound parameters.

METHODS

Blood from 10 pigs was collected to form three clots per pig in gelatin phantoms. Clots were subjected to 1) no treatment, 2) rt-PA (recombinant tissue plasminogen activator) treatment after 20 minutes of clotting, and 3) rt-PA treatment after 60 minutes of clotting. Clots were weighted before and after the experiment to assess the treatment effect by the mass loss. The clot kinetics was studied over 100 minutes using elastography (Young's modulus, shear wave dispersion, and shear wave attenuation). Homodyne K-distribution (HKD) parameters derived from speckle statistics were also studied during clot formation and dissolving (diffuse-to-total signal power ratio and intensity parameters).

RESULTS

Treated clots loosed significantly more mass than non-treated ones (P < .005). A significant increase in Young's modulus was observed over time (P < .001), and significant reductions were seen for treated clots at 20 or 60 minutes compared with untreated ones (P < .001). The shear wave dispersion differed for treated clots at 60 minutes versus no treatments (P < .001). The shear wave attenuation decreased over time (P < .001), and was different for clots treated at 20 minutes versus no treatments (P < .031). The HKD intensity parameter varied over time (P < .032), and was lower for clots treated at 20 and 60 minutes than those untreated (P < .001 and P < .02).

CONCLUSION

The effect of rt-PA treatment could be confirmed by a decrease in Young's modulus and HKD intensity parameter. The shear wave dispersion and shear wave attenuation were sensitive to late and early treatments, respectively. The Young's modulus, shear wave attenuation, and HKD intensity parameter varied over time despite treatment.

Anticoagulation in renal replacement therapies: Why heparin should be abandoned in critical ill patients?

Extracorporeal circuits used in renal replacement therapy (RRT) can develop thrombosis, leading to downtimes and reduced therapy efficiency. To prevent this, anticoagulation is used, but the optimal anticoagulant has not yet been identified. Heparin is the most widely used anticoagulant in RRT, but it has limitations, such as unpredictable pharmacokinetics, nonspecific binding to plasma proteins and cells, and the possibility of suboptimal anticoagulation or bleeding complications, specifically in critically ill patients with acute renal failure who are already at high risk of bleeding. Citrate anticoagulation is a better alternative, being considered a standard for continuous renal replacement therapy, since it is associated with a lower risk of bleeding complications and better efficacy, even in patients with acute renal failure or liver disease. The aim of this article is to provide an updated review of the different strategies of anticoagulation in renal replacement therapies that can be implemented in critical scenarios, focusing on the advantages and disadvantages of each one and the beneficial aspects of using citrate over heparin in critical ill patients.

The effect of heparins on plasma concentration of heparin-binding protein: a pilot study

Background

Neutrophil-derived heparin-binding protein (HBP) plays a role in the pathophysiology of impaired endothelial dysfunction during inflammation. HBP has been suggested as a predictor of organ dysfunction and disease progression in sepsis. We investigated the effects of heparins on plasma concentrations of HBP in patients undergoing surgery.

Methods

We studied three groups of patients receiving heparins during or after surgery. The vascular surgery group received 3000-7500 U, whereas the cardiac surgery group received 27 500-40 000 U. After major general surgery, the third group received 5000 U of low-molecular-weight heparin (LMWH) subcutaneously. Serial plasma HBP concentrations were measured after these treatments with two different methods: Axis-Shield ELISA and Joinstar FIC-Q100. In addition, plasma myeloperoxidase and syndecan-1 were measured in the cardiac surgery group.

Results

During vascular surgery, heparin induced a six-fold increase in HBP within 2 min, from 3.6 (2.4-5.4) to 21.4 (9.0-35.4) ng ml-1 (P<0.001). During cardiac surgery, the higher dose of heparin elevated HBP concentrations from 5.3 (2.7-6.1) to 48.7 (38.4-70.1) ng ml-1 (P<0.0001) within 3 min. Patients receiving LMWH showed an increase from a baseline of 5.7 (3.7-12.1) ng ml-1 to a peak HBP concentration of 14.8 (9.5-18.1) ng ml-1 (P<0.0001) after 3 h. Plasma concentrations of myeloperoxidase, but not syndecan-1, also responded with a rapid increase after heparin. There was a strong correlation between the two methods for HBP analysis (r=0.94).

Conclusions

Plasma concentrations of HBP increased rapidly and dose-dependently after heparin administration. Subcutaneous administration of LMWH increases plasma HBP, but to a lesser degree.

Clinical trial registration

ClinicalTrials.gov identifier: NCT04146493.

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.

In vitro assessment of protamine toxicity with neural cells, its therapeutic potential to counter chondroitin sulfate mediated neuron inhibition, and its effects on reactive astrocytes

Multiple therapies have been studied to ameliorate the neuroinhibitory cues present after traumatic injury to the central nervous system. Two previous in vitro studies have demonstrated the efficacy of the FDA-approved cardiovascular therapeutic, protamine (PRM), to overcome neuroinhibitory cues presented by chondroitin sulfates; however, the effect of a wide range of PRM concentrations on neuronal and glial cells has not been evaluated. In this study, we investigate the therapeutic efficacy of PRM with primary cortical neurons, hippocampal neurons, mixed glial cultures, and astrocyte cultures. We show the threshold for PRM toxicity to be at or above 10 μg/ml depending on the cell population, that 10 μg/ml PRM enables neurons to overcome the inhibitory cues presented by chondroitin sulfate type A, and that soluble PRM allows neurons to more effectively overcome inhibition compared to a PRM coating. We also assessed changes in gene expression of reactive astrocytes with soluble PRM and determined that PRM does not increase their neurotoxic phenotype and that PRM may reduce brevican production and serpin transcription in cortical and spinal cord astrocytes. This is the first study to thoroughly assess the toxicity threshold of PRM with neural cells and study astrocyte response after acute exposure to PRM in vitro.

Factors Influencing Anti-Xa Assays: A Multicenter Prospective Study in Critically Ill and Noncritically Ill Patients Receiving Unfractionated Heparin

BACKGROUND

 The presence of dextran sulfate (DS) in reagents and the type of blood collection tube (citrate/citrated-theophylline-adenosine-dipyridamole [CTAD]) can lead to discrepancies between unfractionated heparin (UFH) anti-Xa levels.

OBJECTIVES

 To evaluate the extent of the effect (1) of different reagents containing or not containing DS and (2) of the blood collection tubes, on UFH anti-Xa levels, in various clinical situations (NCT04700670).

METHODS

 We prospectively included patients from eight centers: group (G)1, cardiopulmonary bypass (CPB) after heparin neutralization (n = 39); G2, cardiothoracic intensive care unit (ICU) after CPB (n = 35); G3, medical ICU (n = 53); G4, other medical inpatients (n = 38). Blood was collected into citrated and CTAD tubes. Chromogenic anti-Xa assays were centrally performed, using seven reagent/analyzer combinations including two without DS. The association between anti-Xa levels and covariates was tested using a linear mixed-effects model.

RESULTS

 We analyzed 4,546 anti-Xa values from 165 patients. Median anti-Xa levels were systematically higher with reagents containing DS, whatever the patient group, with the greatest effect observed in G1 (0.32 vs. 0.05 IU/mL). Anti-Xa levels were slightly higher in CTAD than in citrate samples, irrespective of the assay. The model showed: (1) a significant dextran-patient group interaction (p < 0.0001), the effect of DS on anti-Xa levels varying from 30.9% in G4 to 296% in G1, and (2) a significant effect of CTAD, varying between patient groups (p = 0.0302).

CONCLUSION

 The variability of anti-Xa levels with a great overestimation of the values, using a reagent containing DS, can lead to different treatment decisions, especially after heparin neutralization by protamine. Clinical consequences of these differences remain to be demonstrated.

Perioperative hemostatic management of patients with type A aortic dissection

Coagulopathy is common in patients undergoing thoracic aortic repair for Stanford type A aortic dissection. Non-critical administration of blood products may adversely affect the outcome. It is therefore important to be familiar with the pathologic conditions that lead to coagulopathy in complex cardiac surgery. Adequate care of these patients includes the collection of the medical history regarding the use of antithrombotic and anticoagulant drugs, and a sophisticated diagnosis of the coagulopathy with viscoelastic testing and subsequently adapted coagulation therapy with labile and stable blood products. In addition to the above-mentioned measures, intraoperative blood conservation measures as well as good interdisciplinary coordination and communication contribute to a successful hemostatic management strategy.

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.

Management of an unintentional enoxaparin overdose: A case report and literature review

PURPOSE

The aim of this article is to describe a case in which protamine was used for a low-molecular-weight heparin (LMWH) overdose and present an up-to-date review of the literature on the management of LMWH overdose in adults.

SUMMARY

An unintentional administration of enoxaparin 900 mg occurred in a 73-year-old man with coronavirus disease 2019-related pulmonary embolism. Management of the overdose included a protamine bolus followed by an infusion. Anti-factor Xa levels and activated partial thromboplastin time were monitored. Anti-factor Xa levels declined in a linear fashion irrespective of protamine administration. No bleeding or further thrombotic complications occurred in the patient. A review of the literature revealed that the optimal strategy to treat an LMWH overdose is unknown, with treatment of overdoses ranging from clinical observation to aggressive protamine dosing in reported cases. Although protamine effectively neutralizes unfractionated heparin, it is unable to completely reverse LMWH activity and has variable effects on laboratory measures of LMWH anticoagulant activity.

CONCLUSION

The current case report provides additional data to previous literature suggesting that protamine may have a limited effect in decreasing anti-factor Xa levels in LMWH overdose. Continued reporting on the management of LMWH overdoses is warranted to clarify the optimal treatment strategy.

Novel strategies in antithrombotic therapy: targeting thrombosis while preserving hemostasis

Antithrombotic therapy is a delicate balance between the benefits of preventing a thrombotic event and the risks of inducing a major bleed. Traditional approaches have included antiplatelet and anticoagulant medications, require careful dosing and monitoring, and all carry some risk of bleeding. In recent years, several new targets have been identified, both in the platelet and coagulation systems, which may mitigate this bleeding risk. In this review, we briefly describe the current state of antithrombotic therapy, and then present a detailed discussion of the new generation of drugs that are being developed to target more safely existing or newly identified pathways, alongside the strategies to reverse direct oral anticoagulants, showcasing the breadth of approaches. Combined, these exciting advances in antithrombotic therapy bring us closer than we have ever been to the "holy grail" of the field, a treatment that separates the hemostatic and thrombotic systems, preventing clots without any concurrent bleeding risk.

Unfractionated heparin and the activated clotting time in non-cardiac arterial procedures

INTRODUCTION

Unfractionated heparin is administered during non-cardiac arterial procedures (NCAP) to prevent thromboembolic complications. In order to achieve a safe level of anticoagulation, the effect of heparin can be measured. The aim of this review was to provide an overview on what is known about heparin, suggested tests to monitor the effect of heparin, including the activated clotting time (ACT), and the factors that could influence that ACT.

EVIDENCE ACQUISITION

A literature search in PubMed was performed. Articles reporting on heparin, clotting time tests (including thrombin time, activated partial thromboplastin time, anti-activated factor X and ACT), and ACT measurement devices were selected.

EVIDENCE SYNTHESIS

Heparin has a non-predictable effect in the individual patient, which could be measured using the ACT. However, ACT values can be influenced by many factors, such as hemodilution, hypothermia and thrombocytopenia. In addition, a high variation in ACT outcomes is found between measurement devices of different brands. In the sparse literature on the role of ACT during NCAP, no consensus has been reached on optimal target ACT values. An ACT >250 seconds leads to more bleeding complications. Females have a longer ACT after heparin administration, with a higher risk of bleeding complications.

CONCLUSIONS

The effect of heparin is unpredictable. ACT can be used to monitor the effect of heparin and achieve individualized anticoagulation, tailored to the patient and the specifics of the operative procedure. However, the ACT itself can be affected by several factors and caution must be present, as measured ACT values differ between measurement devices.

Bacterial-Nanocellulose-Based Biointerfaces and Biomimetic Constructs for Blood-Contacting Medical Applications

Understanding the interaction between biomaterials and blood is critical in the design of novel biomaterials for use in biomedical applications. Depending on the application, biomaterials can be designed to promote hemostasis, slow or stop bleeding in an internal or external wound, or prevent thrombosis for use in permanent or temporary medical implants. Bacterial nanocellulose (BNC) is a natural, biocompatible biopolymer that has recently gained interest for its potential use in blood-contacting biomedical applications (e.g., artificial vascular grafts), due to its high porosity, shapeability, and tissue-like properties. To promote hemostasis, BNC has been modified through oxidation or functionalization with various peptides, proteins, polysaccharides, and minerals that interact with the coagulation cascade. For use as an artificial vascular graft or to promote vascularization, BNC has been extensively researched, with studies investigating different modification techniques to enhance endothelialization such as functionalizing with adhesion peptides or extracellular matrix (ECM) proteins as well as tuning the structural properties of BNC such as surface roughness, pore size, and fiber size. While BNC inherently exhibits comparable mechanical characteristics to endogenous blood vessels, these mechanical properties can be enhanced through chemical functionalization or through altering the fabrication method. In this review, we provide a comprehensive overview of the various modification techniques that have been implemented to enhance the suitability of BNC for blood-contacting biomedical applications and different testing techniques that can be applied to evaluate their performance. Initially, we focused on the modification techniques that have been applied to BNC for hemostatic applications. Subsequently, we outline the different methods used for the production of BNC-based artificial vascular grafts and to generate vasculature in tissue engineered constructs. This sequential organization enables a clear and concise discussion of the various modifications of BNC for different blood-contacting biomedical applications and highlights the diverse and versatile nature of BNC as a natural biomaterial.

Protamine dose to neutralize heparin at the completion of cardiopulmonary bypass can be reduced significantly without affecting post-operative bleeding

BACKGROUND

Systemic anticoagulation with heparin during cardiopulmonary bypass (CPB) should be neutralized by protamine administration to restore normal hemostasis. Our previous study showed the protamine-to-heparin ratio (P-to-H) of 1:1 (1 mg protamine:100 IU circulating heparin; 1.0 Ratio) is likely an overestimation. Thus, we reduced the P-to-H in the HMS Plus Hemostasis Management System to 0.9:1 (0.9 Ratio) for 5 months and then to 0.8:1 (0.8 Ratio). We monitored post-operative (post-op) bleeding in the setting of reduced protamine dose (PD).

METHODS

We performed a retrospective study of 632 patients (209 for the 1.0 Ratio, 211 for 0.9 Ratio, 212 for 0.8 Ratio group) who underwent cardiac surgery to measure the reduction of PD and how it affects 24-hour (24 h) post-op chest tube output. We also analyzed the entire data set to explore whether further reduction of P-to-H is warranted.

RESULTS

While there was no difference in the indexed heparin dose among the three groups, we achieved a significant reduction in the indexed actual protamine dose (APDi) by 24% (0.9 Ratio) and 31% (0.8 Ratio) reductions compared to the 1.0 Ratio group. On average, APDi was 88 ± 22, 67 ± 18, and 61 ± 15 mg/m2 in the 1.0, 0.9, and 0.8 Ratio groups, respectively. We found no significant difference in 24 h post-op bleeding among the three groups.

CONCLUSION

1.0 Ratio at the completion of CPB is likely an excessive administration of protamine. With the stepwise reduction of PD, we observed no increase in post-op bleeding, which may indicate that no meaningful increase in heparin rebound occurred. In addition, further analysis of the entire data set demonstrates that a 0.75 Ratio is likely sufficient to neutralize the heparin completely.

Prognostic Factors for Postoperative Bleeding Complications and Prolonged Intensive Care after Percutaneous Hepatic Chemosaturation Procedures with Melphalan

Percutaneous hepatic melphalan perfusion (chemosaturation) in patients with liver metastases is known to be associated with procedure-related hemodynamic depression and coagulation impairment, which may cause bleeding complications and/or a prolonged intensive care unit length of stay (ICU LOS). We retrospectively analyzed possible predictive factors for bleeding complications and an ICU LOS > 1 d in a cohort of 31 patients undergoing 90 chemosaturation procedures. Using a multivariable mixed-model approach, we identified the amount of perioperative fluid volume (OR 12.0, 95% CI 2.3-60.0, p = 0.003) and protamine (OR 0.065, 95% CI 0.007-0.55, p = 0.012) to be associated with bleeding complications. Furthermore, the amount of perioperative fluid volume was associated with an ICU LOS > 1 d (OR 5.2, 95% CI 1.4-19.0, p = 0.011). Heparin dosage, melphalan dosage, extracorporeal circulation time, and noradrenaline dosage had no significant effects on outcomes. Protamine use was not associated with anaphylactic or thromboembolic complications. Despite the limited sample size, these results suggest a restrictive perioperative fluid regime to be beneficial, and support the use of protamine for heparin reversal after chemosaturation procedures. Further prospective randomized trials are needed to confirm these findings.

Heparin reversal with protamine sulfate after Percutaneous Hepatic Perfusion (PHP): is less more?

PURPOSE

Percutaneous hepatic perfusion (PHP) is a palliative intraarterial therapy for unresectable hepatic malignancies. During PHP, high-dose melphalan is infused via the hepatic artery to saturate tumor in the liver with the chemotherapeutic substance. The venous hepatic blood is filtered by an extracorporeal melphalan specific filtration system. Blood clotting in the extracorporeal filter system is prevented by administering unfractionated heparin (UFH) in high doses, which might be reversed with protamine sulfate after the procedure. Aim of this retrospective two-center-study was to analyze the potential effect of UFH reversal with protamine sulfate on complication rates following PHP.

MATERIALS AND METHODS

All patients receiving PHP treatment between 10/2014 and 04/2021 were classified according to their intraprocedural coagulation management: 92 patients/192 PHP received full UFH reversal with protamine (group_PROTAMINE); 13 patients/21 PHP in group_{REDUCED_PROTAMINE} received a reduced amount of protamine, and 28 patients/43 PHP did not receive UFH reversal with protamine (group_{NO_PROTAMINE}). Periinterventional clinical reports, findings and laboratory values were retrospectively evaluated. Complications and adverse events were classified according to Common Terminology Criteria for Adverse Events (CTCAEv5.0).

RESULTS

Thromboembolic events were recorded after 10 PHP procedures (5%) in group_PROTAMINE, six of which (3%) were major events (CTCAE grade 3-5). No (0%) thromboembolic events were recorded in group_{REDUCED_PROTAMINE} and group_{NO_PROTAMINE}. Hemorrhagic events were registered after 24 PHP (13%) in group_PROTAMINE, two of which (1%) were major (CTCAE grade 3-4). In group_{REDUCED_PROTAMINE}, only minor bleeding events were recorded, and one major hemorrhagic event was documented in group_{NO_PROTAMINE} (2%). There was a significant difference between the percentage of post-interventional thrombopenia in group_PROTAMINE (39%) and group_{REDUCED_PROTAMINE} (14%) versus group_{NO_PROTAMINE} (23%) (p=.00024). In group_PROTAMINE one patient suffered from a severe anaphylactic shock after the administration of protamine.

CONCLUSION

Our retrospective study implies that there might be a link between the practice of protamine sulfate administration to reverse the full hemodilutive effect of UFH after PHP and the post-interventional risk of thromboembolic events as well as clinically significant thrombopenia. Our data suggest that the standard use of protamine sulfate after PHP in low-risk patients without clinical signs of active bleeding should be critically re-evaluated.

In house synthesized novel distyryl-BODIPY dye and polymer assembly as deep-red emitting probe for protamine detection

In this contribution, we designed and synthesized a deep-red emitting distyryl-BODIPY dye (dye 3) which is non-fluorescent in aqueous solution due to the formation of non-emissive aggregates. However, in presence of an amphiphilic polymer (polystyrene sulfonate, PSS), the aggregated dye molecules de-aggregate and form dye 3-PSS complex, which significantly modulates the optical features of the bound dye. Interestingly, the dye 3-PSS complex shows turn-on fluorescence response in deep-red region in presence of protamine (Pr) due to the formation of dye 3-PSS-Pr ternary complex. Such enhancement follows a linear trend in the dynamic range of 0-8.75 μM of Pr which has been utilized to determine Pr with limit of detection (LOD) of 15.04(±0.5) nM in phosphate buffer. Furthermore, excellent selectivity of the dye 3-PSS system towards Pr allows us to determine Pr even in complex biological matrix like 1% human serum. Thus, dye 3-PSS system can be applied as a very effective tool for the detection and quantification of Pr in deep-red region, overcoming several limitations encountered with the probes in the shorter wavelength region. This is the first report on BODIPY dye based supramolecular assembly for sensing and quantification of protamine.

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.

Efficacy and Safety of Low-Dose Protamine in Reducing Bleeding Complications during TAVI: A Propensity-Matched Comparison

OBJECTIVES

We aimed to evaluate the efficacy and safety of low-dose protamine in reducing access site-related complications during Transcatheter Aortic Valve Implantation (TAVI) as compared to full-dose protamine.

BACKGROUND

Access site-related complications represent an independent predictor of poor outcomes of TAVI. Data regarding heparin reversal with protamine and the dosage needed to prevent bleeding complications are scarce among patients undergoing TAVI.

METHODS

A total of 897 patients were retrospectively included in the study. Patients who underwent percutaneous coronary intervention within 4 weeks before or concomitantly with TAVI (n = 191) were given 0.5 mg protamine for each 100 units of unfractionated heparin. All other patients (n = 706) were considered as a control group and 1 mg protamine for each 100 units of heparin was administered.

RESULTS

The combined intra-hospital endpoint of death, life-threatening major bleeding, and major vascular complications were significantly more frequent in patients receiving low-dose protamine [29 (15.2%) vs. 50 (7.1%), p < 0.001]. After propensity matching (n = 130 for each group) for relevant clinical characteristics including anti-platelet therapy [19 (14.6%) vs. 6 (4.6%), p = 0.006], low-dose protamine predicted the combined endpoint (OR 3.54, 95%-CI 1.36-9.17, p = 0.009), and even in multivariable analysis, low-dose protamine continued to be a predictor of the combined endpoint in the matched model (OR 3.07, 95%-CI 1.17-8.08, p = 0.023) alongside baseline hemoglobin.

CONCLUSIONS

In this propensity-matched retrospective analysis, a low-dose protamine regime is associated with a higher rate of major adverse events compared to a full-dose protamine regime following transfemoral TAVI.

The anesthesiologist's perspective on emergency aortic surgery: Preoperative optimization, intraoperative management, and postoperative surveillance

The management of emergencies related to the aorta requires a multidisciplinary approach involving various health care professionals. Despite technological advancements in treatment methods, the risks and mortality rates associated with surgery remain high. In the emergency department, definitive diagnosis is usually obtained through computed tomography angiography, and management focuses on controlling blood pressure and treating symptoms to prevent further deterioration. Preoperative resuscitation is the main focus, followed by intraoperative management aimed at stabilizing the patient's hemodynamics, controlling bleeding, and protecting vital organs. After the operation, factors such as organ protection, transfusion management, pain control, and overall patient care must be taken into account. Endovascular techniques are becoming more common in surgical treatment, but they also present new challenges in terms of complications and outcomes. It is recommended that patients with suspected ruptured abdominal aortic aneurysms be transferred to facilities with both open and endovascular treatment options and a track record of successful outcomes to ensure the best patient care and long-term results. To achieve optimal patient outcomes, close collaboration and regular case discussions between health care professionals are necessary, as well as participation in educational programs to promote a culture of teamwork and continuous improvement.

The contemporary role of protamine in the cardiac catheterization laboratory

Access to the arterial circulation and full anticoagulation carries a risk of serious bleeding during and after percutaneous coronary intervention. Important sources of bleeding include the arterial access site and coronary artery perforation. Prompt and effective management of hemorrhagic complications is an essential interventional skill. Protamine sulfate is well-known as a heparin reversal agent. Despite this, there is heterogeneity in the use of protamine during interventional procedures. While protamine is generally well-tolerated, it is associated with a risk of hypersensitivity reaction, including anaphylaxis, among others. The purpose of this review is to summarize the existing evidence about and experience with the use of protamine sulfate in the setting of percutaneous coronary and structural interventional procedures.

New intra-conduit thrombus detected using transesophageal echocardiography immediately after weaning from cardiopulmonary bypass during the Fontan procedure: a case report

This study reports a case wherein a new thrombus was detected by transesophageal echocardiography in the conduit during extracardiac conduit Fontan procedure. Immediately after weaning from the cardiopulmonary bypass and administration of protamine, a thrombus was noted in the conduit by transesophageal echocardiography. Since the patient was hemodynamically stable, anticoagulation therapy was initiated after admission to the intensive care unit. One week post-surgery, imaging results showed residual thrombus, but the patient was safely discharged. Even during Fontan procedure, careful observation with transesophageal echocardiography is important because of the possibility of thrombus formation in the conduit.

Protamine use in transcarotid arterial revascularization

OBJECTIVE

The literature suggests that heparin reversal with protamine in transcarotid arterial revascularization (TCAR) decreases postoperative bleeding complications without an increase in stroke or death. However, the dosing of protamine in TCAR has not yet been evaluated. We aimed to evaluate our experience with intraoperative heparin reversal with protamine.

METHODS

This was a single-center, retrospective, observational study that evaluated the heparin and protamine doses used during TCAR. All adult patients who underwent TCAR between 9/1/2019 and 4/2/2021 were included. Demographic data was obtained from the Vascular Quality Initiative and protamine/heparin doses were obtained from a chart review. Multivariate logistic regression models were used to assess the association between the protamine/heparin dose ratio and other variables.

RESULTS

Sixty-two patients were included. The average protamine/heparin dose ratio used was 0.96 ± 0.12 mg/U; seven had a ratio less than 0.8 mg/U, and one was greater than 1.2 mg/U. Two patients experienced bleeding complications, which were managed non-operatively. No patient with a protamine/heparin ratio greater than 0.8 mg/U had postoperative bleeding. Postoperative bradycardia was observed in 32.3% of patients and hypotension in 35%, with 19% requiring vasopressors. No relationship was identified between the protamine/heparin ratio and bleeding, bradycardia, or hypotension. No 30-day myocardial infarction, stroke or death occurred.

CONCLUSIONS

We identified a near 1:1 ratio of a protamine/heparin dosing regimen for the reversal of heparin during TCAR, with postoperative bleeding complications similar to those reported in the literature. However, patients who received a lower protamine/heparin ratio did not experience bleeding complications. In the era of protamine shortages, a future larger-scale study is needed to evaluate the impact of a lower protamine dose on postoperative complications.

Increasing obesity is associated with lower postoperative bleeding in coronary bypass patients

OBJECTIVE

Despite inherent comorbidities, obese cardiac surgical patients paradoxically had shown lower morbidity and mortality, although the nature of this association is still unclear. Thus, the authors intended in this large registry-based study to investigate the impact of obesity on short- and long-term postoperative outcomes, focusing on bleeding and transfusion requirements.

DESIGN

Retrospective registry study.

SETTING

Three university hospitals.

PARTICIPANTS

A cohort of 12,330 prospectively compiled data from coronary bypass grafting patients undergoing surgery between 2007 to 2020 were retrieved from the Western Denmark Heart Registry.

INTERVENTIONS

The parameters were analyzed to assess the association between body mass index (BMI) and the selected outcome parameters.

MEASUREMENTS AND MAIN RESULTS

The crude data showed a clear statistically significant association in postoperative drainage from 637 (418-1108) mL in underweight patients with BMI <18.5 kg/m² to 427 (295-620) mL in severely obese patients with BMI ≥40 kg/m² (p < 0.0001, Kruskal-Wallis). Further, 50.0% of patients with BMI <18.5 received an average of 451 mL/m² in red blood cell transfusions, compared to 16.7% of patients with BMI >40 receiving 84 mL/m². The obese groups were less often submitted to reexploration due to bleeding, and fewer received perioperative hemostatics, inotropes, and vasoconstrictors. The crude data showed increasing 30-day and 6-month mortality with lower BMI, whereas the one-year mortality showed a V-shaped pattern, but BMI had no independent impact on mortality in logistic regression analysis.

CONCLUSION

Patients with high BMI may carry protection against postoperative bleeding after cardiac surgery, probably secondary to an inherent hypercoagulable state, whereas underweight patients carry a higher risk of bleeding and worse outcomes.

Association of postoperative atrial fibrillation with higher dosing ratios of protamine-to-heparin

Background: Postoperative atrial fibrillation (POAF) is defined as new-onset AF in the immediate postoperative period. The relatively high incidence of POAF after cardiac surgery is well described, but pathophysiological mechanisms underlying the initiation, maintenance, and progression of POAF may be multifactorial and have not yet been comprehensively characterized. One of the mechanisms includes altered Ca2+ kinetics. Accumulating evidence has suggested that altered atrial cytosolic calcium handling contributes to the development of POAF, protamine reversibly modulates the calcium release channel/ryanodine receptor 2 (RyR2) and voltage-dependent cardiac RyR2. However, it is currently unknown whether such abnormalities contribute to the arrhythmogenic substrate predisposing patients to the development of POAF. Methods: We have retrospectively analyzed 147 patients who underwent cardiac surgery with cardiopulmonary bypass support. Of these, 40 patients were excluded from the analysis because of pre-existing AF. All patients received heparin followed by protamine at different dosing ratios of protamine-to-heparin, depending on the periods studied. Results: The dosing ratio of protamine-to-heparin = 1.0 was compared with higher dosing ratios of protamine-to-heparin >1.0 up to 1.7. POAF developed in 15 patients (15/107 = 14%), of these, 5 out of 57 patients (33.3%) in the dosing ratio of protamine-to-heparin = 1.0 and 10 out of 35 patients (66.7%) in the higher dosing ratios of protamine-to-heparin. Statistical significance was observed in patients with higher dosing ratios of protamine-to-heparin, compared with the dosing ratio of protamine-to-heparin = 1.0 (odds ratio = 3.890, 95% CI = 1.130–13.300, p-value = 0.031). When types of diseases were analyzed in terms of higher dosing ratios of protamine-to-heparin, only valvular disorders were significantly associated with POAF (p = 0.04). Conclusions: Protamine is clinically utilized to reverse heparin overdose and has been shown to display immunological and inflammatory alterations. However, its association with POAF has not been reported. Our results provide evidence that higher dosing ratios of protamine-to-heparin may increase the incidence of POAF.

Transcaval Access and Closure Best Practices

Transcaval aortic access is a versatile electrosurgical technique for large-bore arterial access through the wall of the abdominal aorta from the adjoining inferior vena cava. Although counterintuitive, its relative safety derives from the recognition that interstitial hydraulic pressure exceeds venous pressure, so arterial bleeding harmlessly decompresses into the nearby caval venous hole. Transcaval access has been performed in thousands of patients for transcatheter aortic valve replacement and endovascular thoracic aneurysm repair and to avoid limb ischemia in percutaneous mechanical circulatory support. Transcaval access may have value compared with transaxillary or subclavian access and with surgical transcarotid access when standard transfemoral access is not optimal. The dissemination of transcaval access and closure techniques has been hampered by the unavailability of commercially marketed devices. This state-of-the-art review details exemplary transcaval technique, patient selection, computed tomographic planning, step-by-step access and closure, management of complications, and procedural troubleshooting in special situations. These contemporary best practices can help operators gain or maintain proficiency.

Suicide left ventricle following protamine: A case report

A patient with severe aortic stenosis and left ventricular hypertrophy underwent a transcatheter aortic valve replacement. The patient's blood pressure significantly dropped after protamine administration. A diagnosis of suicide left ventricle post-valve replacement was made. The diagnosis and management of the protamine reaction are detailed. This case highlights the need to slowly infuse protamine sulfate and monitor for adverse events.

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.

Durably antibacterial cotton fabrics coated by protamine via Schiff base linkages

The development of antibacterial cotton fabrics with an overall performance is critical but remains challenging. In this study, we propose a facile method to prepare durable antibacterial cotton fabric without significant sacrifices of wearing comfortability. Cotton fabric is firstly oxidated to obtain dialdehyde groups, then treated with PM molecules to establish a PM coating on the fiber surfaces via Schiff base linkages. The resultant cotton fabrics show durably antibacterial activity, realizing high bacterial reduction rates against both E. coli and S. aureus higher than 99.99 %, and offering remarkable durabilities tolerable 50 washing cycles and 500 rubbing times. These fabrics also show reliable safety for human skin that proofed by a series of cytotoxicity tests with positive results. This work demonstrates an example of versatile strategy to impart effective antibacterial function with durable activity to cotton textiles, showing great potential for practical applications in functional textile fields.

Anaesthesia for vascular emergencies - a state of the art review

In this state-of-the-art review, we discuss the presenting symptoms and management strategies for vascular emergencies. Although vascular emergencies are best treated at a vascular surgical centre, patients may present to any emergency department and may require both immediate management and safe transport to a vascular centre. We describe the surgical and anaesthetic considerations for management of aortic dissection, aortic rupture, carotid endarterectomy, acute limb ischaemia and mesenteric ischaemia. Important issues to consider in aortic dissection are extent of the dissection and surgical need for bypasses in addition to endovascular repair. From an anaesthetist's perspective, aortic dissection requires infrastructure for massive transfusion, smooth management should an endovascular procedure require conversion to an open procedure, haemodynamic manipulation during stent deployment and prevention of spinal cord ischaemia. Principles in management of aortic rupture, whether open or endovascular treatment is chosen, include immediate transfer to a vascular care centre; minimising haemodynamic changes to reduce aortic shear stress; permissive hypotension in the pre-operative period; and initiation of massive transfusion protocol. Carotid endarterectomy for carotid stenosis is managed with general or regional techniques, and anaesthetists must be prepared to manage haemodynamic, neurological and airway issues peri-operatively. Acute limb ischaemia is a result of embolism, thrombosis, dissection or trauma, and may be treated with open repair or embolectomy, under either general or local anaesthesia. Due to hypercoagulability, there may be higher numbers of acutely ischaemic limbs among patients with COVID-19, which is important to consider in the current pandemic. Mesenteric ischaemia is a rare vascular emergency, but it is challenging to diagnose and associated with high morbidity and mortality. Several peri-operative issues are common to all vascular emergencies: acute renal injury; management of transfusion; need for heparinisation and reversal; and challenging postoperative care. Finally, the important development of endovascular techniques for repair in many vascular emergencies has improved care, and the availability of transoesophageal echocardiography has improved monitoring as well as aids in surgical placement of endovascular grafts and for post-procedural evaluation.

How to Solve the Conundrum of Heparin-Induced Thrombocytopenia during Cardiopulmonary Bypass

Heparin-induced thrombocytopenia (HIT) is a major issue in cardiac surgery requiring cardiopulmonary bypass (CPB). HIT represents a severe adverse drug reaction after heparin administration. It consists of immune-mediated thrombocytopenia paradoxically leading to thrombotic events. Detection of antibodies against platelets factor 4/heparin (anti-PF4/H) and aggregation of platelets in the presence of heparin in functional in vitro tests confirm the diagnosis. Patients suffering from HIT and requiring cardiac surgery are at high risk of lethal complications and present specific challenges. Four distinct phases are described in the usual HIT timeline, and the anticoagulation strategy chosen for CPB depends on the phase in which the patient is categorized. In this sense, we developed an institutional protocol covering each phase. It consisted of the use of a non-heparin anticoagulant such as bivalirudin, or the association of unfractionated heparin (UFH) with a potent antiplatelet drug such as tirofiban or cangrelor. Temporary reduction of anti-PF4 with intravenous immunoglobulins (IvIg) has recently been described as a complementary strategy. In this article, we briefly described the pathophysiology of HIT and focused on the various strategies that can be applied to safely manage CPB in these patients.

The emerging role of adopting protamine for reducing the risk of bleeding complications during the percutaneous coronary intervention: A meta-analysis

BACKGROUND

The safety and the benefits of reducing the risk of bleeding complications via protamine administration during the percutaneous coronary intervention (PCI) remains unclear. This study aimed to systematically assessed the efficacy and safety of using protamine in PCI.

METHOD

Potential academic studies were identified from PubMed, Cochrane Library, EMBASE, and Web of Science. The time range we retrieved from was that from the inception of electronic databases to March 31, 2022. Gray studies were identified from the references of included literature reports. Stata version 12.0 statistical software (StataCorp LP) was used to analyze the pooled data.

RESULTS

A total of seven studies were involved in our study. The overall participants of the protamine group were 4983, whereas it was 1953 in the nonprotamine group. This meta-analysis indicated that protamine was preferable for PCI as its lower value of major bleeding (odds ratio [OR] = 0.489, 95% confidence interval [CI]: 0.362-0.661, p < .001) and minor bleeding (OR = 0.281, 95% CI: 0.123-0.643, p = .003). Additionally, the protamine did not tend to be related a higher incidence of mortality (p = .143), myocardial infarction (p = .990), and stent thrombosis (p = .698).

CONCLUSIONS

Based on available evidence, use of protamine may reduce the risk of bleeding complications without increasing the risk of mortality, myocardial infarction, and stent thrombosis. Given the relevant possible biases in our study, adequately powered and better-designed studies with long-term follow-up are required to reach a firmer conclusion.