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.

HEMA-Lysine-Based Cryogels for Highly Selective Heparin Neutralization.

Unfractionated heparin (UFH) and its low-molecular-weight fragments (LMWH) are widely used as anticoagulants for surgical procedures and extracorporeal blood purification therapies such as cardiovascular surgery and dialysis. The anticoagulant effect of heparin is essential for the optimal execution of extracorporeal blood circulation. However, at the end of these procedures, to avoid the risk of bleeding, it is necessary to neutralize it. Currently, the only antidote for heparin neutralization is protamine sulphate, a highly basic protein which constitutes a further source of serious side events and is ineffective in neutralizing LMWH. Furthermore, dialysis patients, due to the routine administration of heparin, often experience serious adverse effects, among which HIT (heparin-induced thrombocytopenia) is one of the most severe. For this reason, the finding of new heparin antagonists or alternative methods for heparin removal from blood is of great interest. Here, we describe the synthesis and characterization of a set of biocompatible macroporous cryogels based on poly(2-hydroxyethyl methacrylate) (pHEMA) and L-lysine with strong filtering capability and remarkable neutralization performance with regard to UFH and LMWH. These properties could enable the design and creation of a filtering device to rapidly reverse heparin, protecting patients from the harmful consequences of the anticoagulant.

Isolation and Purification of Protamine from the Cultured Takifugu flavidus and Its Physicochemical Properties.

Protamine is a cationic peptide derived from fish sperm and has several important functional properties: antibacterial properties, acting as a carrier for injectable insulin and as a heparin antagonist, combatting fatigue, etc. Thus, it has been widely used in medicinal applications and food products. Cultured Takifugu flavidus is a type of pufferfish with a delicious taste that is popular in China, and its production is increasing significantly. Therefore, protamine was extracted via acid extraction from the sperm of Takifugu flavidus and further isolated and purified via sephadex gel chromatography, ion exchange chromatography, and desalination chromatography. Furthermore, the physicochemical properties of protamine were investigated. The results showed that the sperm of the cultured T. flavidus were non-toxic, and the extracted and purified protamine had high contents of arginine (36.90%) and lysine (27.02%), respectively. The secondary structure of protamine was mainly ß-folded and irregularly curled. Additionally, protamine exhibited high thermal stability with a denaturation temperature of 176 °C. This study would provide a theoretical basis for the structural analysis, bioactivity, and resource development of pufferfish protamine and help to promote the development of the pufferfish industry.

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.

Evaluation of Activated Clotting Times With a Heparin Reversal Protocol Designed to Conserve Protamine During Drug Shortages: A Retrospective, Cohort Study.

OBJECTIVE: To retrospectively evaluate a protamine conservation approach to heparin reversal implemented during times of critical shortages. This approach was aimed at maintaining access to cardiac surgical services. SETTING: In-patient hospital setting. PARTICIPANTS: Eight hundred-one cardiac surgical patients>18 years old. INTERVENTIONS: Patients undergoing cardiac surgery who received >30,000 U of heparin were given a single fixed vial protamine dose of 250 mg or a standard 1 mg of protamine to 100 U of heparin ratio-based dose to reverse heparin. MEASUREMENTS AND MAIN RESULTS: The primary endpoint was differences in post-reversal activated clotting times between the 2 groups. The secondary endpoint was differences in the number of protamine vials used between the 2 reversal strategies. The first activated clotting times values measured after initial protamine administration were not different between the Low Dose and Conventional Dose groups (122.3 s v 120.6 s, 1.47 s, 99% CI -1.47 to 4.94, p = 0.16). The total amount of protamine administered in the Low Dose group was less than that in the Conventional Dose group (-100.5 mg, 99% CI -110.0 to -91.0, p < 0.0001), as were the number of 250 mg vials used per case (-0.69, 99% CI -0.75 to -0.63, p < 0.0001). The mean initial protamine doses between groups were 250 mg and 352 mg, p < 0.0001. The mean protamine vials used were 1.33 v 2.02, p < 0.0001. When the calculations were based on 50 mg vials, the number of vials used per case in the Low Dose group was even less (-2.16, 99% CI -2.36 to -1.97, p < 0.0001).) CONCLUSIONS: Conservation measures regarding critical medications and supplies during times of shortages can maintain access to important services within a community.

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.

Protamine-Induced Coronary Graft Thrombosis: A Review.

Perioperative myocardial infarction is a serious complication affecting a significant portion of patients undergoing coronary artery bypass graft surgery. This may arise due to coronary graft thrombosis, a rare but potentially fatal phenomenon associated with both congenital and acquired risk factors. Multiple case reports implicate the role of protamine in the development of such thromboses. The role of protamine in facilitating the regulation of hemostasis by reversing the anticoagulant effects of heparin in patients undergoing cardiopulmonary bypass is well-recognized. However, discussion of its potential contribution to coronary graft thrombosis and mechanisms by which this may occur is lacking. Furthermore, its narrow therapeutic index and side effect profile are such that its appropriateness as a universal reversal agent to heparin requires reconsideration. This article reviews the current body of evidence regarding the use of protamine in cardiac surgery and the limited case reports pertaining to its potential role in the pathophysiology of coronary graft thrombosis.

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.

Protamine use in transfemoral carotid artery stenting is not associated with an increased risk of thromboembolic events.

BACKGROUND: Protamine use in carotid endarterectomy has been shown to be associated with fewer perioperative bleeding complications without higher rates of thromboembolic events. However, the effect of protamine use on complications after transfemoral carotid artery stenting (CAS) is unclear, and concerns remain about thromboembolic events. METHODS: A retrospective review was performed for patients undergoing transfemoral CAS in the Vascular Quality Initiative from March 2005 to December 2018. We assessed in-hospital outcomes using propensity score-matched cohorts of patients who did and did not receive protamine. The primary outcome was in-hospital stroke or death. Secondary outcomes included bleeding complications, stroke, death, transient ischemic attack, myocardial infarction, and congestive heart failure exacerbation. Bleeding complications were categorized as bleeding resulting in intervention or blood transfusions. RESULTS: Of the 17,429 patients undergoing transfemoral CAS, 2697 (15%) patients received protamine. We created 2300 propensity score-matched pairs of patients who did and did not receive protamine. There were no statistically significant differences in stroke or death between the two cohorts (protamine, 2.5%; no protamine, 2.9%; relative risk [RR], 0.85; 95% confidence interval [CI], 0.60-1.21; P = .37). Protamine use was not associated with statistically significant differences in perioperative bleeding complications resulting in interventional treatment (0.9% vs 0.5%; RR, 2.10; 95% CI, 0.99-4.46; P = .05) or blood transfusion (1.2% vs 1.2%; RR, 0.92; 95% CI, 0.53-1.61; P = .78). There were also no statistically significant differences for the individual outcomes of stroke (1.8% vs 2.3%; RR, 0.78; 95% CI, 0.52-1.16; P = .22), death (0.9% vs 0.8%; RR, 1.17; 95% CI, 0.62-2.19; P = .63), transient ischemic attack (1.4% vs 1.3%; RR, 1.10; 95% CI, 0.67-1.82; P = .70), myocardial infarction (0.5% vs 0.4%; RR, 1.20; 95% CI, 0.52-2.78; P = .67), or heart failure exacerbation (1.0% vs 0.9%; RR, 1.05; 95% CI, 0.58-1.90; P = .88). Protamine use in patients presenting with symptomatic carotid stenosis was associated with lower risk of stroke or death (3.0% vs 4.3%; RR, 0.69; 95% CI, 0.47-0.998; P = .048), whereas there were no statistically significant differences in stroke or death with protamine use in asymptomatic patients (1.6% vs 1.0%; RR, 1.63; 95% CI, 0.67-3.92; P = .28). CONCLUSIONS: Heparin reversal with protamine after transfemoral CAS is not associated with an increased risk of thromboembolic events, and its use in symptomatic carotid disease is associated with a lower risk of stroke or death.

Andexanet Alfa, the Possible Alternative to Protamine for Reversal of Unfractionated Heparin.

The recent shortage of protamine prompted an investigation of alternatives for reversal of unfractionated heparin. Heparin is an anticoagulant utilized in the hospital setting. Available options for anticoagulation include direct oral anticoagulants, vitamin K antagonists, thrombin inhibitors, low-molecular-weight heparins, and heparin. Protamine is the approved reversal agent for heparin with few alternatives under investigation. Although andexanet was designed as an antidote for apixaban and rivaroxaban, in vitro studies show that in a dose-dependent technique, andexanet had near full reversal of heparin, reversed anti-factor Xa activity, and neutralized anticoagulant effects of activated partial thromboplastin time and thrombin time induced by heparin.

Can the Minimum Protamine Dose to Neutralize Heparin at the Completion of Cardiopulmonary Bypass be Significantly Lower than the Conventional Practice?

Systemic anticoagulation with heparin during cardiopulmonary bypass (CPB) should be neutralized by protamine administration to restore normal hemostasis. However, protamine has potentially serious side effects and excessive protamine can cause increased postoperative bleeding. Thus, our goal is to appropriately dose protamine at the completion of CPB to neutralize heparin so that neither residual heparin nor excessive protamine is present. We performed a retrospective study of 216 patients who underwent cardiac surgery to search for a safe minimum protamine dose (PD) when measuring heparin concentration (HC). In addition, we developed a formula to determine PD using total heparin dose (THD) and CPB time without measuring HC. When protamine-to-heparin ratio (P-to-H) is set at 1 mg protamine to 100 international unit (IU) heparin in HMS Plus Hemostasis Management System (HMS), we determined that 75% of the calculated total PD is a safe minimum PD to sufficiently neutralize circulating heparin after CPB. On average, this translates into either .37 mg protamine/100 IU heparin of THD or .54 mg/100 IU of the first heparin bolus. The formula we developed to calculate PD without measuring HC can provide a PD that strongly agrees with the safe minimum PD when measuring HC. The safe minimum PD to neutralize circulating heparin after CPB can be significantly lower than conventional dosing practices. Reduction of PD may decrease the risk of postoperative bleeding and protamine-related adverse events. Based on our data, we decreased P-to-H in HMS to examine whether it is possible to reduce PD further than the safe minimum PD determined in this study.

Reversal Activity and Toxicity of Heparin-Binding Copolymer after Subcutaneous Administration of Enoxaparin in Mice.

Uncontrolled bleeding after enoxaparin (ENX) is rare but may be life-threatening. The only registered antidote for ENX, protamine sulfate (PS), has 60% efficacy and can cause severe adverse side effects. We developed a diblock copolymer, heparin-binding copolymer (HBC), that reverses intravenously administered heparins. Here, we focused on the HBC inhibitory activity against subcutaneously administered ENX in healthy mice. BALB/c mice were subcutaneously injected with ENX at the dose of 5 mg/kg. After 110 min, vehicle, HBC (6.25 and 12.5 mg/kg), or PS (5 and 10 mg/kg) were administered into the tail vein. The blood was collected after 3, 10, 60, 120, 360, and 600 min after vehicle, HBC, or PS administration. The activities of antifactors Xa and IIa and biochemical parameters were measured. The main organs were collected for histological analysis. HBC at the lower dose reversed the effect of ENX on antifactor Xa activity for 10 min after antidote administration, whereas at the higher dose, HBC reversed the effect on antifactor Xa activity throughout the course of the experiment. Both doses of HBC completely reversed the effect of ENX on antifactor IIa activity. PS did not reverse antifactor Xa activity and partially reversed antifactor IIa activity. HBC modulated biochemical parameters. Histopathological analysis showed changes in the liver, lungs, and spleen of mice treated with HBC and in the lungs and heart of mice treated with PS. HBC administered in an appropriate dose might be an efficient substitute for PS to reverse significantly increased anticoagulant activity that may be connected with major bleeding in patients receiving ENX subcutaneously.

Protamine use in transcarotid artery revascularization is associated with lower risk of bleeding complications without higher risk of thromboembolic events.

OBJECTIVE: Recent studies have found that transcarotid artery revascularization (TCAR) is associated with lower risk of stroke or death compared with transfemoral carotid artery stenting but higher risk of bleeding complications, presumably associated with the need for an incision. Heparin anticoagulation is universally used during TCAR, so protamine use may reduce bleeding complications. However, the safety and effectiveness of protamine use in TCAR are unknown. We therefore evaluated the impact of protamine use on perioperative outcomes after TCAR in the Vascular Quality Initiative TCAR Surveillance Project. METHODS: We performed a retrospective review of patients undergoing TCAR in the Vascular Quality Initiative TCAR Surveillance Project from September 2016 to April 2019. We assessed in-hospital outcomes using propensity score-matched cohorts of patients who did and did not receive protamine. The primary efficacy end point was access site bleeding complications, and the primary safety end point was in-hospital stroke or death. Secondary end points included the individual end points of stroke, death, transient ischemic attack, myocardial infarction, congestive heart failure exacerbation, and hemodynamic instability. RESULTS: Of the 5144 patients undergoing TCAR, all patients received heparin and 4072 (79%) patients received protamine. We identified 944 matched pairs of patients who did and did not receive protamine. Protamine use was associated with a significantly lower risk of bleeding complications (2.8% vs 8.3%; relative risk [RR], 0.33; 95% confidence interval [CI], 0.21-0.52; P < .001), including bleeding that resulted in interventional treatment (1.0% vs 3.6%; RR, 0.26; 95% CI, 0.13-0.54; P < .001) and in blood transfusion (1.2% vs 3.9%; RR, 0.30; 95% CI, 0.15-0.58; P <.001). There were no statistically significant differences in in-hospital stroke or death for patients who received protamine and those who did not (1.6% vs 2.2%; RR, 0.71; 95% CI, 0.37-1.39; P = .32); however, there was a trend toward lower risk of stroke for patients who received protamine (1.1% vs 2.0%; RR, 0.53; 95% CI, 0.24-1.13; P = .09). There were also no statistically significant differences in the rates of transient ischemic attack (0.4% vs 1.1%; RR, 0.40; 95% CI, 0.13-1.28; P = .11), myocardial infarction (0.4% vs 0.8%; RR, 0.50; 95% CI, 0.15-1.66; P = .25), heart failure exacerbation (0.4% vs 0.3%; RR, 1.33; 95% CI, 0.30-5.96; P = .71), or postoperative hypotensive hemodynamic instability (16% vs 15%; RR, 1.06; 95% CI, 0.83-1.35; P = .50) with protamine use. CONCLUSIONS: Protamine can be safely used in TCAR to reduce the risk of perioperative bleeding complications without increasing the risk of thrombotic events.

Editor's Choice - Protamine Reduces Serious Bleeding Complications Associated with Carotid Endarterectomy in Asymptomatic Patients without Increasing the Risk of Stroke, Myocardial Infarction, or Death in a Large National Analysis.

OBJECTIVE: Controversy persists regarding the use of protamine during carotid endarterectomy (CEA), despite real world evidence to support its use. The purpose of this study was to determine the impact of protamine reversal of heparin anticoagulation on the outcome of CEA in the USA. METHODS: A prospective national registry (Society for Vascular Surgery Vascular Quality Initiative) of 72 787 patients undergoing elective asymptomatic CEA by 1879 surgeons from 316 centres in the USA and Canada from 2012 to 2018 was reviewed. Protamine use varied by both surgeon (20% rare use [< 10%], 30% variable use [11%-79%], 50% routine use [> 80% cases]) and geographical region (44% vs. 96%). Temporal trends in protamine use were also determined. End points included post-operative re-operation for bleeding, as well as potential protamine related thrombotic complications, including stroke, death, and myocardial infarction (MI). Predictors of end points were determined by multivariable logistic regression. Propensity matching was additionally used to control for differences between groups. RESULTS: Of the 72 787 patients who underwent CEA, 69% received protamine, while 31% did not. Protamine use increased over time from 60% (2012) to 73% (2018). In total, 378 patients (0.7%) in the protamine treated group underwent re-operation for bleeding vs. 342 patients (1.4%) in the untreated cohort (p < .001). Protamine use did not affect the rate of MI (0.7% vs. 0.8%; p = .023), stroke (1.1% vs. 1.0%; p = .20), or in hospital death (0.2% vs. 0.2%; p = 0.70) between treated and untreated patients, respectively. On multivariable analysis, protamine use was independently associated with reduced risk of re-operation for bleeding (odds ratio 0.5, 95% confidence interval 0.39-0.55; p < .001). Independent of protamine exposure, the consequences of a return to the operating room (RTOR) for bleeding were statistically significant, with a sevenfold increase in MI (RTOR 4.9% vs. no RTOR 0.7%; p < .001), an eightfold increase in stroke (RTOR 7.2% vs. no RTOR 0.9%; p < .001), and a 13 fold increase in death (RTOR 2.4% vs. no RTOR 0.2%; p < .001). CONCLUSION: Protamine reduces serious bleeding complications at the time of CEA without increasing the risk of MI, stroke, or death, in this large North American analysis. Based on this and previous regional work regarding protamine use in CEA, it is believed that there is now sufficient evidence to support its routine use, and it should be considered as a benchmark for quality during CEA.

Verification of a thrombus induction method at the target point inside the blood pump using a fibrinogen coating for a thrombus detection study.

Although the magnetically levitated centrifugal blood pump (mag-lev pump) is considered superior to other pumps in antithrombogenicity, thrombotic complications are still reported. Research into thrombus detection inside a mag-lev pump is very important for solving this problem. Our research group has already proposed a method to detect a thrombus inside a mag-lev pump in real time without an additional sensor, which is named the impeller vibration method. To efficiently advance our research with reproducibility, a preconditioning method to induce thrombus inside the pump was thought to be necessary. Therefore, this study aimed to develop a preconditioning method that induces thrombus formation. To verify this method, in vitro experiments for thrombus detection were performed. A mag-lev pump developed at Tokyo Institute of Technology was used. A fibrinogen solution was coated on the inner surfaces of the bottom housing to induce thrombus formation at the target point inside the pump. The thrombus is detected by utilizing the phenomenon that the phase difference between the impeller displacement and input current to the magnetic bearing increases when a thrombus is formed inside a pump. Five hundred mL of porcine blood anticoagulated with heparin sodium was circulated in the mock circuit, and protamine sulfate was administered. Flow rate (1 L/min), impeller vibrational frequency (70 Hz), and vibrational amplitude (30 µm) were set to constant. The experiment was terminated when the phase difference increased by over 2° from the minimum value. The experiments were performed in fibrinogen-coated (group F, n = 5) and non-coated pumps (group N, n = 5). In group F, thrombus formation was observed at the fibrinogen-coated point of the housing. In contrast, a relatively small thrombus was observed in varying locations such as the housing or the impeller in group N. Thrombus formation time (the time from when the phase difference takes the minimum value to when the experiment is terminated) was different between the two groups. The mean time was significantly shorter in group F (44 ± 29 minutes) than in group N (143 ± 38 minutes; p = 0.0019). Therefore, a preconditioning method that induced thrombus formation at the target point inside a blood pump was successfully developed.

Protamine Induced Anaphylactic Shock after Peripheral Vascular Surgery.

Anaphylactic reactions to protamine are quite rare and almost exclusively reported during cardiac surgery. In this report, we illustrate a rare case of protamine reaction after peripheral vascular surgery a couple of months after cardiac surgery and how the patient survived this critical complication.

In Vivo Protamine Titration Using Activated Coagulation Time to Neutralize Heparin Anticoagulation in Cardiac Surgery: Proof of Concept.

OBJECTIVE: In vivo protamine titration (IVPT) is based on the observation of a plateau on the decay curve of the celite activated clotting times (ACTs) during protamine infusion for heparin reversal. The aim of the present study was to determine the optimal protamine/heparin ratio to reverse anticoagulation using IVPT curves. DESIGN: Prospective, randomized study. SETTING: Tertiary care university hospital. PARTICIPANTS: The study comprised 138 patients undergoing elective cardiac surgery requiring cardiopulmonary bypass. INTERVENTIONS: The control group was given a protamine infusion of 1.3 mg per 1 mg (100 U) of heparin over 21 minutes. ACT was measured every 3 minutes. In the test group, the protamine dose was prepared using the same ratio as for the control group, and ACT values were measured every 3 minutes until a plateau was reached (2 consecutive ACT values <160 s), at which time the protamine infusion was stopped. The protamine/heparin ratio, blood losses, transfusions, and heparin concentrations were recorded. RESULTS: The protamine dose was lower in the test group (456.00 ± 105.66 mg [control group] v 295.25 ± 100.60 mg [test group]; p < 0.0001). The mean protamine/heparin ratios were 1.30 ± 0.10 (control group) and 0.81 ± 0.22 (test group) (p < 0.0001). Heparin concentrations were greater in the test group 15 minutes (0.10 [0-0.2] U/mL v 0 [0-0.1] U/mL; p = < 0.0001) and 3 hours (0 [0-0.1] U/mL v 0 [0-0] U/mL; p = 0.0002) after protamine infusion. There was no difference in the blood losses and transfusion requirements. CONCLUSIONS: IVPT is safe and efficient in this low-risk population.

Protamine sulfate use during tibial bypass does not appear to increase thrombotic events or affect short-term graft patency.

OBJECTIVES: While the use of protamine sulfate as a heparin reversal agent has been extensively reviewed in patients undergoing carotid endarterectomy and coronary artery bypass grafting, there is a lack of literature on protamine's effects on lower extremity bypasses. The purpose of this study was to determine the risk of protamine sulfate dosing after tibial bypass on thrombotic or bleeding events, including early bypass failure. METHODS: We performed a retrospective review of our institutional database for patients undergoing primary distal peripheral bypass from January 2009 through December 2015 (contralateral bypass was considered to be a new primary bypass). Primary endpoints include composite thrombotic events (myocardial infarction, stroke, amputation at 30 days and patency less than 30 days) and composite bleeding events (bleeding or transfusion). RESULTS: A total of 152 tibial or peroneal bypasses in 136 patients with critical limb ischemia were identified. Of these, 78 (57.4%) patients received protamine sulfate intraoperatively and 58 (42.6%) did not. There were no differences in composite thrombotic or hemorrhagic outcomes. Protamine use had no effect on the rates of perioperative MI (9.0% versus 3.5%, p = 0.20), stroke (1.3% versus 1.7%, p = 0.83), or perioperative mortality (5.1% versus 3.5%, p = 0.64). There was no significant difference in composite post-operative bleeding events (20.7% versus 14.1%, p = 0.31) or composite thrombotic events (17.2% versus 18.0%, p = 0.91). Patients who received protamine undergoing bypass with non-autogenous conduit had significantly higher-recorded median operative blood loss (250 mL versus 150 mL, p = 0.0097) and median procedure lengths (265 min versus 201 min, p = 0.0229). No difference in 30-day amputation-free survival was noted (91.0% versus 91.4%, p = 0.94). Follow-up Kaplan-Meier estimation did not demonstrate a difference in 30-day patency (91.7% versus 88.5%, p = 0.52). CONCLUSIONS: Heparin reversal with protamine sulfate after tibial or peroneal bypass grafting is not associated with higher cardiovascular morbidity, bypass thrombosis, amputation, or mortality. Additionally, there was no statistically significant difference in post-operative bleeding or thrombosis complications for patients who did not receive protamine, although the findings are suggestive of a potential difference in a more adequately powered study. Our results suggest that protamine sulfate is safe for intraoperative use without increased risk of thrombotic complications or early tibial bypass graft failure.

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.

Mid-term Clinical Outcomes of Immediate Protamine Use Following Elective Percutaneous Coronary Interventions.

Bleeding complication has been considered as a serious problem in current percutaneous coronary interventions (PCI). Fortunately, several groups have already reported the effectiveness of protamine use just after PCI to immediately remove any arterial sheath. However, there is a concern that protamine reversal may increase non-occlusive thrombus and, in turn, lead to mid-term cardiovascular events such as target vessel revascularization (TVR) or stent thrombosis. Thus, the purpose of this study was to evaluate whether protamine use following elective PCI was associated with mid-term clinical outcomes. In total, 472 patients were included in this study; subsequently, they were divided into protamine group (n = 142) and non-protamine group (n = 330). The primary endpoint was the composite of ischemia-driven TVR and stent thrombosis. The median follow-up period was determined to be at 562 days. In total, 32 primary endpoints were observed during the study period, and the incidence of primary endpoints tended to be greater in the protamine group than in the non-protamine group (P = 0.056). However, the lesion length, the degree of calcification, and the prevalence of hemodialysis were significantly determined greater in the protamine group than in the non-protamine group. In the multivariate Cox proportional hazards model, the use of protamine (versus non-protamine: hazard ratio 0.542 and 95% confidence interval 0.217-1.355, P = 0.191) was deemed not to be associated with the primary endpoint after controlling legion length, calcification, and hemodialysis. In conclusion, immediate protamine use following elective PCI did not increase mid-term ischemia-driven TVR or stent thrombosis. However, immediate protamine use after PCI should be discussed further for the safety of the patient.