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

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.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

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.

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.

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.

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.

Platform trials for anaesthesia and perioperative medicine: a narrative review

Large randomised trials provide the most reliable evidence of effectiveness of new treatments in clinical practice. However, the time and resources required to complete such trials can be daunting. An overarching clinical trial platform focused on a single condition or type of surgery, aiming to compare several treatments, with an option to stop any or add in new treatment options, can provide greater efficiency. This has the potential to accelerate knowledge acquisition and identify effective, ineffective, or harmful treatments faster. The master protocol of the platform defines the study population(s) and standardised procedures. Ineffective or harmful treatments can be discarded or study drug dose modified during the life cycle of the trial. Other adaptive elements that can be modified include eligibility criteria, required sample size for any comparison(s), randomisation assignment ratio, and the addition of other promising treatment options. There are excellent opportunities for anaesthetists to establish platform trials in perioperative medicine. Platform trials are highly efficient, with the potential to provide quicker answers to important clinical questions that lead to improved patient care.

Circulating small extracellular vesicle-encapsulated SEMA5A-IT1 attenuates myocardial ischemia-reperfusion injury after cardiac surgery with cardiopulmonary bypass

Cardiomyocyte injury is a common complication during cardiac surgery with cardiopulmonary bypass (CPB). Studies have shown that circulating small extracellular vesicles (sEVs) are involved in the pathological process of cardiovascular diseases via delivering signaling molecules. This study aims to investigate the relationship between circulating sEV-encapsulated long noncoding RNAs (lncRNAs) and cardiac injury after CPB. Here, we found that the expression of sEV SEMA5A-IT1 in serum samples of patients after CPB was higher than that of pre-CPB serum samples. Moreover, serum-derived sEV SEMA5A-IT1 levels were negatively correlated with creatine kinase-MB (CK-MB) levels in patients who underwent CPB operation. Notably, circulating sEVs packaged with SEMA5A-IT1 could be uptaken by cardiomyocyte-like cells AC16 and increased SEMA5A-IT1 expression in AC16 cells. Upregulated SEMA5A-IT1 protected cardiomyocytes against hypoxia/reoxygenation injury, confirmed by increased cell viability, reduced cell apoptosis, and inhibited ferroptosis in AC16 cells. Mechanistically, SEMA5A-IT1 regulated the expression of B-cell CLL/lymphoma 2 (BCL2) and solute carrier family 7 member 11 (SLC7A11) through sponging miR-143-3p. Transfection of miR-143-3p mimics, BCL2, or SLC7A11 knockdown could attenuate the protective effect of SEMA5A-IT1 on cardiomyocytes. In conclusion, we propose that SEMA5A-IT1, which is transported to cardiomyocytes through circulating sEVs, is an important regulatory molecule that protects cardiomyocytes from ischemia–reperfusion injury, providing a target for the prevention and treatment of myocardial ischemia–reperfusion injury.

Coagulation and Transfusion Updates From 2021

2021 and the COVID 19 pandemic have brought unprecedented blood shortages worldwide. These deficits have propelled national efforts to reduce blood usage, including limiting elective services and accelerating Patient Blood Management (PBM) initiatives. A host of research dedicated to blood usage and management within cardiac surgery has continued to emerge. The intent of this review is to highlight this past year's research pertaining to PBM and COVID-19-related coagulation changes.

Hemodynamic Effects of Protamine Infusion in Dogs with Myxomatous Mitral Valve Disease Undergoing Mitral Valvuloplasty

Protamine, an antagonizing agent to heparin, is indispensable for dogs undergoing cardiopulmonary bypass. Protamine-induced hypotension (PIH) during cardiac anesthesia has been reported in humans. The purpose of this study was to describe the hemodynamic effect of protamine administration in dogs during cardiac surgery in clinical cases. Study design: Retrospective, clinical, cohort study. A total of 14 client-owned dogs who suffered heart failure due to medically uncontrolled myxomatous mitral valve disease (MMVD) were included in this study. The severity of MMVD was classified according to American College of Veterinary Internal Medicine staging (ACVIM: stage B2, C, D) and dogs undergoing mitral valve surgery. Records with clinical data for dogs treated between July 2019 to August 2020 were examined for age, sex, breed, body weight, concurrent diseases, hospitalization, anesthetic record, and mortality within 3 months after the operation. PIH was defined as mean arterial pressure (MAP) lowered by 20% of that before protamine infusion. To evaluate the effect of protamine on hemodynamic variables, each of the other values was compared with values at the beginning of protamine infusion. MAP decreased by 41.0 and 45.7% in two dogs (14.3%) compared with pressure before protamine infusion. Others did not show obvious alteration in hemodynamic variables. Epinephrine treatment alleviated hypotension in one dog. Another dog with systemic hypotension concomitant with elevated central venous pressure did not respond to epinephrine treatment and a reboot of extracorporeal circulation was required. Reheparinization and reinstitution of cardiopulmonary bypass successfully resuscitate the second dog. In conclusion, clinicians should alert the incidence of severe hypotension even with slow protamine infusion following canine cardiac surgery. This study also provides two effective treatments for catastrophic hypotension during protamine infusion.

Robust K-PD model for activated clotting time prediction and UFH dose individualisation during cardiopulmonary bypass

BACKGROUND AND OBJECTIVE

Activated clotting time (ACT) is a point-of-care test used to monitor the effect of unfractionated heparin (UFH) during cardiopulmonary bypass (CPB). This test sometimes returns aberrant values, which can lead to the administration of an inappropriate dosing regimen. The development of a population-robust K-PD model of UFH could allow the individualisation and automation of UFH therapy during CPB.

METHODS

We conducted a prospective observational study to collect ACT measurements from patients undergoing surgery using CPB. The ACT data were split into a development and validation cohort. The development cohort was used to estimate a standard and robust population K-PD model characterised by a residual error following a normal distribution and student's t-distribution. The ACT prediction performance using Bayesian estimates of individual K-PD parameters was evaluated by comparing predicted versus observed ACTs. Using estimates of the robust K-PD model, a Bayesian individualisation strategy to automate UFH administration was proposed and evaluated using Monte Carlo simulations.

RESULTS

A total of 295 patients were included in the study, and 1561 ACTs were collected. In patients without outlier values, Bayesian estimates (based on four ACT measurements) from both standard and robust K-PD models had similar performances, with a median prediction bias close to 0 s. In patients with outlier measurements, the use of the robust K-PD model greatly improved the prediction bias and root-mean-square error (RMSE), with a mean prediction bias of 3.25 s, IQR = [-19.9; 46.03] versus -86 s IQR = [-135.7; -63.8] for the standard model. Monte Carlo simulations showed that the robust Bayesian individualisation strategy allowed the ACT to be maintained above the target using only two to three ACT measurements.

CONCLUSIONS

The use of a robust K-PD model reduced prediction bias and RMSE in patients with outlier ACT measurements. The Bayesian individualisation strategy using robust estimates of individual parameters may help automate UFH dosing regimens. Proper clinical validation is warranted before its use in daily clinical practice.

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.