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

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 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.

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.

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.

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.

Perioperative outcomes of combined heart surgery and lung tumor resection: a systematic review and meta-analysis

Objective

The prevalence of patients with concomitant heart and lung lesions requiring surgical intervention is increasing. Simultaneous cardiac surgery and pulmonary resection avoids the need for a second operation. However, there are concerns regarding the potentially increased mortality and complication rates of simultaneous surgery and the adequacy of lung exposure during heart surgery. Therefore, we performed a meta-analysis to evaluate the perioperative mortality and complication rates of combined heart surgery and lung tumor resection.

Methods

A comprehensive literature search was performed in July 2020. The PubMed, Embase, and Web of Science databases were searched to identify studies that reported the perioperative outcomes of combined heart surgery and lung tumor resection. Two reviewers independently screened the studies, extracted data, and assessed the risk of bias of included studies. Pooled proportions and 95% confidence intervals (95% CI) were calculated by R version 3.6.1 using the meta package.

Results

A total of 536 patients from 29 studies were included. Overall, the pooled proportion of operative mortality was 0.01 (95% CI: 0.00, 0.03) and the pooled proportion of postoperative complications was 0.40 (95% CI: 0.24, 0.57) for patients who underwent combined cardiothoracic surgery. Subgroup analysis by lung pathology revealed that, for patients with lung cancer, the pooled proportion of anatomical lung resection was 0.99 (95% CI: 0.95, 1.00) and the pooled proportion of systematic lymph node dissection or sampling was 1.00 (95% CI: 1.00, 1.00). Subgroup analysis by heart surgery procedure found that the pooled proportion of postoperative complications of patients who underwent coronary artery bypass grafting (CABG) patients using the off-pump method was 0.17 (95% CI: 0.01, 0.43), while the pooled proportion of complications after CABG using the on-pump method was 0.61 (95% CI: 0.38, 0.82).

Conclusion

Combined heart surgery and lung tumor resection had a low mortality rate and an acceptable complication rate. Subgroup analyses revealed that most patients with lung cancer underwent uncompromised anatomical resection and mediastinal lymph node sampling or dissection during combined cardiothoracic surgery, and showed off-pump CABG may reduce the complication rate compared with on-pump CABG. Further researches are still needed to verify these findings.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

BACKGROUND

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

METHODS AND FINDINGS

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

CONCLUSIONS

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

TRIAL REGISTRATION

ClinicalTrials.gov Unique identifier NCT03532594.

Managing the coagulopathy associated with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) has allowed for significant surgical advancements, but accompanying risks can be significant and must be expertly managed. One of the foremost risks is coagulopathic bleeding. Increasing levels of bleeding in cardiac surgical patients at the time of separation from CPB are associated with poor outcomes and mortality. CPB-associated coagulopathy is typically multifactorial and rarely due to inadequate reversal of systemic heparin alone. The components of the bypass circuit induce systemic inflammation and multiple disturbances of the coagulation and fibrinolytic systems. Anticipating coagulopathy is the first step in managing it, and specific patient and procedural risk factors have been identified as predictors of excessive bleeding. Medication management pre-procedure is critical, as patients undergoing cardiac surgery are commonly on anticoagulants or antiplatelet agents. Important adjuncts to avoid transfusion include antifibrinolytics, and perfusion practices such as red cell salvage, sequestration, and retrograde autologous priming of the bypass circuit have varying degrees of evidence supporting their use. Understanding the patient's coagulation status helps target product replacement and avoid larger volume transfusion. There is increasing recognition of the role of point-of-care viscoelastic and functional platelet testing. Common pitfalls in the management of post-CPB coagulopathy include overdosing protamine for heparin reversal, imperfect laboratory measures of thrombin generation that result in normal or near-normal laboratory results in the presence of continued bleeding, and delayed recognition of surgical bleeding. While challenging, the effective management of CPB-associated coagulopathy can significantly improve patient outcomes.

A 0.6-protamine/heparin ratio in cardiac surgery is associated with decreased transfusion of blood products

OBJECTIVES

In cardiac surgery, adequate heparinization is necessary to prevent thrombus formation in the cardiopulmonary bypass (CPB). To counteract the heparin effect after weaning from CPB, protamine is administered. The optimal protamine/heparin ratio is still unknown.

METHODS

In this before-after study, we evaluated the effect of a 0.6/1-protamine/heparin ratio implementation as of May 2017 versus a 0.8/1-protamine/heparin ratio on the 12-h postoperative blood loss and the amount of blood and blood component transfusions (fresh frozen plasma, packed red blood cells, fibrinogen concentrate, platelet concentrate and prothrombin complex concentrate) after cardiac surgery. A total of 2051 patients who underwent cardiac surgery requiring CPB between May 2016 and May 2018 were included.

RESULTS

In the 0.6/1-protamine/heparin ratio group, only 28.8% of the patients received blood component transfusion, compared to 37.9% of the patients in the 0.8/1-ratio group (P < 0.001). The median 12-h postoperative blood loss was 230 ml (interquartile range 140-320) in the 0.6/1-ratio group versus 260 ml (interquartile range 155-365) in the 0.8/1-ratio group (P < 0.001).

CONCLUSIONS

A 0.6/1-protamine/heparin ratio after weaning from CPB is associated with a significantly reduced 12-h postoperative blood loss and blood components transfusion.

Thrombotic risk in central venoarterial extracorporeal membrane oxygenation post cardiac surgery

Introduction:

Post-cardiotomy cardiogenic shock is an accepted indication for venoarterial extracorporeal membrane oxygenation. The true incidence and risk factors for the development of thrombosis in this setting remain unclear.

Methods:

Patients supported with central venoarterial extracorporeal membrane oxygenation due to ventricular dysfunction precluding weaning from cardiopulmonary bypass were retrospectively identified. Electronic records from a single institution spanning a 4-year period from January 2015 to December 2018 were interrogated to assess the incidence of thrombosis. The relationship to exposures including intracardiac stasis and procoagulant usage was explored.

Results:

Twenty-four patients met the inclusion criteria and six suffered major intracardiac thrombosis. All cases of thrombosis occurred early, and none survived to hospital discharge. The lack of left ventricular ejection conferred a 46% risk of developing thrombosis compared to 0% if ejection was maintained (p = 0.0093). Aprotinin use was also associated with thrombus formation (p = 0.035). There were no significant differences between numbers of patients receiving other procoagulants when grouped by thrombosis versus no thrombosis.

Conclusion:

Stasis is the predominant risk factor for intracardiac thrombosis. This occurs rapidly and the outcome is poor. As a result, we suggest early left ventricular decompression. Conventional management of post-bypass coagulopathy seems safe if the aortic valve is opening.

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.

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

OBJECTIVES

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

DESIGN

Randomized controlled trial.

SETTING

University hospital.

PARTICIPANTS

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

INTERVENTIONS

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

MEASUREMENTS AND MAIN RESULTS

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

CONCLUSION

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