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. 2024 May 9;19(5):e0302830. doi: 10.1371/journal.pone.0302830

Predictors of bleeding complications during catHeter-dirEcted thrombolysis for peripheral arterial occlusions (POCHET)

Barend M Mol 1, Maarten C Verwer 1, Rob Fijnheer 2, Jasper Florie 3, Oscar A Groot 4, Falco Hietbrink 5, Mathilde Nijkeuter 6, Evert-Jan P A Vonken 7, Vincent van Weel 8, Dominique P V de Kleijn 1, Gert J de Borst 1,*; on behalf of the POCHET study group
Editor: Eyüp Serhat Çalık9
PMCID: PMC11081216  PMID: 38722842

Abstract

Introduction

The risk of major bleeding complications in catheter directed thrombolysis (CDT) for acute limb ischemia (ALI) remains high, with reported major bleeding complication rates in up to 1 in every 10 treated patients. Fibrinogen was the only predictive marker used for bleeding complications in CDT, despite the lack of high quality evidence to support this. Therefore, recent international guidelines recommend against the use of fibrinogen during CDT. However, no alternative biomarkers exist to effectively predict CDT-related bleeding complications. The aim of the POCHET biobank is to prospectively assess the rate and etiology of bleeding complications during CDT and to provide a biobank of blood samples to investigate potential novel biomarkers to predict bleeding complications during CDT.

Methods

The POCHET biobank is a multicentre prospective biobank. After informed consent, all consecutive patients with lower extremity ALI eligible for CDT are included. All patients are treated according to a predefined standard operating procedure which is aligned in all participating centres. Baseline and follow-up data are collected. Prior to CDT and subsequently every six hours, venous blood samples are obtained and stored in the biobank for future analyses. The primary outcome is the occurrence of non-access related major bleeding complications, which is assessed by an independent adjudication committee. Secondary outcomes are non-major bleeding complications and other CDT related complications. Proposed biomarkers to be investigated include fibrinogen, to end the debate on its usefulness, anti-plasmin and D-Dimer.

Discussion and conclusion

The POCHET biobank provides contemporary data and outcomes of patients during CDT for ALI, coupled with their blood samples taken prior and during CDT. Thereby, the POCHET biobank is a real world monitor on biomarkers during CDT, supporting a broad spectrum of future research for the identification of patients at high risk for bleeding complications during CDT and to identify new biomarkers to enhance safety in CDT treatment.

Introduction

Acute limb ischemia (ALI) is a potentially lethal condition in which the viability of the limb is threatened due to an acute decrease in limb perfusion [1]. Following the Rutherford classification for ALI [2], catheter directed thrombolysis (CDT) is generally the preferred treatment strategy in viable (Rutherford I) or marginally threatened (Rutherford IIa) ALI [1]. The benefit of CDT should be counterbalanced with the inherent associated risk of bleeding complications which remain a major concern when applying CDT. Bleeding complications rates range from 11% to 56%, with an average complication rate of 18% with almost half of these being major [3]. One of the most severe CDT related major complication is haemorrhagic stroke, which may occur in up to 4% of patients undergoing CDT for ALI [4].

Periprocedural prediction of bleeding complications during CDT has been topic of research since long.

Standard operating procedures (SOP) of CDT for ALI are heterogeneous, which makes it challenging to compare results of previous single centre cohort studies [3,5]. This heterogeneity is not caused by negligence, but by a lack of research on the best treatment standards for CDT, as most SOP are still based on landmark trials like the ‘Surgery versus Thrombolysis for Ischemia of the Lower Extremity’ (STILE, 1994) trial and the ‘Thrombolysis Or Peripheral Arterial Surgery’ (TOPAS, 1998) trial [6,7]. These studies have been performed nearly thirty years ago and included patients are likely not representable for the current CDT-population. Duration of ALI for STILE inclusions was up to 6 months and patients enrolled in the TOPAS trial were treated with intravenous heparin up to two times the baseline level of activated partial thromboplastin time (aPTT) plus intra-arterially CDT, causing a high rate major bleeding complications. Despite the heterogeneity in SOP, plasma fibrinogen level (PFL) monitoring has been widely used to predict the occurrence of major bleeding complications, as depicted by a recent survey among physician members of the Society of Interventional Radiology [8]. This practice is mainly based on the observed association between low PFL and the occurrence of major bleeding complications in the STILE trial, although PFL measurement in this study was done only after CDT [6]. Furthermore, a recent systematic review described the predictive value of PFL for major bleeding during CDT and stated that it could not be clarified for which threshold PFL is associated with haemorrhagic complications. Moreover, the role of PFL, in general, as predictor for haemorrhagic complications during CDT remains unproven [9]. Currently, the European Society for Vascular Surgery (ESVS) guidelines on ALI do not recommend routine monitoring of PFL during thrombolysis, mainly due to the lack of high quality evidence underlying its practice [1]. This finding advocates the necessity to prospectively investigate the predictive value of PFL, as well as a need for identification of other potential predictors.

The aim of POCHET biobank (Predictors Of bleeding Complications during catHeter dirEcted Thrombolysis for peripheral arterial occlusions) is to prospectively collect data of ALI patients treated with CDT to assess the rate and etiology of bleeding complications during CDT and to establish a prospective biobank of blood samples taken prior and during CDT to investigate current and potential new biomarkers that predict bleeding complications.

Methods and design

Study design

The POCHET biobank is a multicentre prospective biobank study including all consecutive patients eligible for CDT for the treatment of ALI of the lower limb. All patients are treated according to the standard operating procedure for CDT which is aligned in each participating centre. Patients are treated with either Urokinase or Alteplase, as effects and risks are similar [10]. Results will be corrected for thrombolytic medication given. The standard operating procedure is further elaborated in the (S1 File) Written informed consent is collected and included patients donate venous blood samples prior to CDT and simultaneous to standard blood collection every six hours for the duration of thrombolysis. With a maximum CDT-duration of 72 hours, the number of blood collections are maximised at 13 times. As the nature of this study is an observational biobank study, registration as a clinical trial is not applicable [11].

Ethical approval

This biobank is conducted with approval of the Biobank Research Ethics Committee (BREC) of the University Medical Center (UMC) Utrecht (approval number 19–731, date of approval 30 march 2021). Within this ethical approval, donating a maximum of 136.5 ml blood to the biobank is considered safe and does not affect standard healthcare [12]. For all participating hospitals, a transfer of human material and associated personal data agreement is signed in order to store all collected samples in the central biobank in the UMC Utrecht, the Netherlands. Before plasma samples and its corresponding clinical data can be analysed for a specific research question, approval of the BREC is necessary.

Inclusion and exclusion criteria

When the treating physician decides CDT is the treatment of choice for ALI, patients must fulfil the following inclusion criteria for the POCHET study:

  • Subacute (<6 weeks) thrombotic occlusion of a native artery, bypass or stent in the iliac or femorodistal artery.

  • 18 years of age.

  • Written informed consent.

Exclusion criteria

A patient is not able to participate in this biobank study if one of the following criteria is present:

  • No treatment indication for CDT

  • Not willing to or not able to provide written informed consent

  • Absolute or relative contra-indication for thrombolytic therapy (see S1 File)

Treatment location

In all participating centres, a dedicated angio suite is used for all angiograms made throughout the CDT process: for confirmation of the occlusion, for (mechanical) thrombectomy prior to CDT if deemed necessary and for evaluation of CDT treatment. Patients are being monitored in at least a medical care unit facility during CDT (See S1 File, sub 4, 7 and 9).

Sample size

The POCHET biobank is an ongoing biobank storing blood samples of patients undergoing thrombolytic therapy for future biomarker research questions. As knowledge develops on predicting biomarkers on bleeding complications during CDT, new research questions are likely to arise constantly. As such, a sample size calculation on a biobank is not possible. The first blood sample assessments on bleeding biomarkers will be done at 100 inclusions. Currently, POCHET biobank has approval for 500 participants, but is likely to expand after the first biomarkers on bleeding complications are explored and higher statistical power might be needed. For this, it is anticipated that the POCHET biobank will become the biggest cohort of plasma samples of patients which are treated with CDT for ALI.

Endpoint definitions

The primary endpoint is the occurrence of non-acces site related major bleeding during CDT. Major bleeding complication is defined as bleeding related death, intracranial bleeding, intra-organ bleeding, surgical -, radiological—or endoscopic intervention related to bleeding or necessity of inotropic medication.

Secondary endpoints consists of non-major bleeding complications leading to early cessation of thrombolysis, other bleeding complications, and treatment related complications such as trash, compartment syndrome, 30 day re-intervention,30 day major amputation and non-bleeding related death. A list of all endpoint definitions is available in the (S2 File).

An independent clinical adjudication committee is constructed for the assessment of bleeding complications and consists of a trauma surgeon, haematologist and internal medicine physician. The committee will independently determine the presence of bleeding complications, its location and clinical implications with a standardized form and based on anonymized patient data. In this way, all relevant bleeding classifications for thrombolysis can be deducted and evaluated in a blinded fashion on their clinical implications. In case of disagreement between the three members, discrepancies will be discussed until unanimous decision (See Fig 1).

Fig 1. The independent adjudication committee will define and score presence and severity of bleeding complications in a blinded fashion.

Fig 1

Lab manual for blood samples

For the duration of CDT, simultaneous to standard procedures, venous blood samples will be collected every 6 hours consisting of an extra 6 ml EDTA and 4.5 ml Citrate tube, starting with the first blood collection before the enhancement of the CDT treatment (See Fig 2). When CDT stops, blood collections for the biobank will stop immediately. Venous blood collection is done by a second peripheral venous catheter which will not be used for fluid or medication administration. Blood samples are not collected by using the sheath or thrombolysis catheter, as thrombolytic medication might interfere with the coagulation biomarkers used for future analysis. Blood samples are centrifuged at 2000g for 10 minutes at room temperature and plasma is stored in 0.5ml tubes within two hours after collection at -80° C. These samples are then transported from participating centres to a central biobank of the University Medical Center Utrecht and again stored at -80° C awaiting future analysis (See Fig 3). All future analysis will be done in a single laboratory facility,

Fig 2. Blood sample collection protocol.

Fig 2

Fig 3. Processing of blood samples.

Fig 3

Data collection

Data will be prospectively collected from electronic medical records and pseudo-anonymized by the study data manager. Only the data manager will have access to the pseudo-anonymisation key. Data regarding patient characteristics at presentation such as comorbidities, medication use, occlusion specifics and data of hospital admission and follow-up will all be collected and stored in the data management system Castor EDC. Pseudo-anonymized blood samples will be stored and analysed later by trained laboratory personnel. All laboratory outcome data will be digitally stored in a secured location at the University Medical Center Utrecht. The anonymized and encrypted data is only available for authorized research personnel. A list of all included variables is available in the (S3 File). See Fig 4 for a summary of the POCHET biobank.

Fig 4. Summary of POCHET study.

Fig 4

Patient and public involvement

Currently, in the explorative phase of the POCHET biobank we have chosen not to involve patients with the establishment of the biobank. But, when the POCHET biobank has stored blood samples of many different enrolled patients, the database can be used to contribute in a broad spectrum of research questions, for which both patient—or national cardiovascular associations can play a key role in formulating and designing future research.

Statistical analysis

Baseline characteristics will be presented as mean ± standard deviation in case of normally distributed data and as median ± interquartile range for skewed data. Categorical variables will be stated as absolute numbers and percentages. Groups will be made according to bleeding or no bleeding complication during thrombolytic treatment and baseline characteristics will be compared using T-Tests, Wilcoxon Rank-sum test and Pearson’s Chi Square tests when applicable. The predictive value of different haemostatic components on bleeding complications will be analysed by regression analysis. The discriminative power will be measured by C-statistics and Net Reclassification Index. Univariate and Multivariate Cox Regression analysis will be used to test for predictors for bleeding complications, mortality and limb salvage. Proportional hazard assumption will be used to correct for competing interest.

Discussion

POCHET is the first large scale prospective biobank including patients with ALI undergoing CDT treatment. By prospectively collecting data from patients and obtaining sequential blood samples, it is possible to provide contemporary characteristics and outcomes of nowadays ALI-patients undergoing CDT and investigate the role of potential (new) biomarkers to predict major bleeding complications during CDT for ALI.

The assessment of new biomarkers to predict bleeding complications requires a uniform definition of a bleeding complication, classification in major or minor and access versus non access related bleeding complications. Although multiple bleeding classifications are available, none are specifically appropriate for CDT in ALI because they are derived from non-surgical cohorts and differ when calling a bleeding complication major [1316]. The international society of thrombosis and haemostasis (ISTH), for instance, considers a drop of haemoglobin of 1,24 mmol/L (2g/dL) related to haemorrhage a major bleeding, although this might not have any clinical consequence to the CDT therapy [16]. Other bleeding classifications like the Thrombolysis In Myocardial Infarction (TIMI) and Bleeding Academic Research Consortium (BARC) are developed in patients with cardiac diseases and anti-coagulation therapies and thereby not reflecting patients with ALI [13,14]. The Clavien-Dindo classification, although widely used among surgical patients, is a very well defined grading classification for complications in general, but not specific for bleeding complications [17]. Therefore, an independent adjudication committee is implemented to this study, to assess bleeding complications from a basic clinical perspective such as bleeding location, haemoglobin drop, therapy needed and the necessity to seize thrombolytic therapy. In this way, bleeding complications are descriptive and different existing bleeding classifications can be deducted separately. Furthermore, for the definition of the primary endpoint of this study, non-access site related major bleeding complication, the commonly used criterion “necessity of transfusion of 2 or more units of blood” is intentionally not used as it is highly linked to the type of surgery or intervention in the surgical population [18]. A criterion covering events of excessive and unexpected blood loss are marked with the type of intervention that was implemented. That is why these events were incorporated in the definition of major bleeding complication for the POCHET trial, such as re-intervention. Nevertheless, blood transfusion in relation to any bleeding complication is relevant information and will be collected. With this information, different bleeding classifications can then be analysed for which classification is most clinically relevant for the population of patients receiving CDT.

The POCHET biobank has a broad scope of future research that can be conducted with the available samples and data. With an aligned thrombolytic therapy for every patient, existing risk factors for bleeding complications can be verified. Obviously, the usefulness of fibrinogen catches the eye as one of the first research questions to be answered when trying to end the debate on this matter, as its absolute value or degradation speed remains unproven in the prediction of bleeding complications during CDT [9,19,20]. Furthermore, clinical risk factors for bleeding complications, such as an older age, cardiac history, limb sensibility and/or motor deficit on presentation, platelet count, and occluded synthetic grafts, can be verified with this biobank [21,22].

Several potential biomarkers could be hold promise as a predictor for major bleeding during CDT. For instance Von Willebrand Factor (VWF), the platelet adhesion protein. VWF-platelet complexes are heavily degraded in tissue plasminogen activator therapy, such as alteplase, leading to fibrinolysis [23]. The subsequent inability for thrombus formation by plasminogen activation elsewhere can thereby lead to bleeding complications [24].

Furthermore, anti-plasmin and plasminogen activator inhibitor both serve as the main down regulators in fibrinolysis. These regulators must be surmounted during thrombolytic therapy around the thrombus for effective lysis, but still be effective in systemic circulation to avoid bleeding [25]. Low baseline levels before CDT or degradation of these down regulators during treatment might lead to bleeding complications.

Another promising marker is D-dimer, a major fibrin degradation product that is released upon cleavage of crosslinked fibrin by plasmin. Widely used in the screening for embolic disease such as deep venous thrombosis, a recent review showed potential prognostic value for D-dimer on safety and outcome in thrombolysis [26].

A recent addition in biomarkers are the proteins in plasma extra-cellular vesicles (EVs), bilayer lipid membrane particles excreted by each cell, containing important information concerning coagulation [27]. For instance, platelet-derived and red blood cell-derived EVs both support factor XII dependent thrombin generation and thereby enhancing the coagulation cascade [28]. Degradation of these vesicles during CDT might impede coagulation and thereby increase the risk of bleeding.

Furthermore, fundamental human research on coagulation and fibrinolysis is possible with the POCHET biobank, with both samples within one individual patient prior to thrombolysis and samples on which the homeostasis is completely shifted towards anti-coagulation. For instance, little is known about the effect of lipoprotein Lp(a), a risk factor for atherosclerotic disease, and induced thrombolysis. One effect might be that Lp(a) may compete with plasminogen and thereby increase thrombolysis time [29]. With increased thrombolysis time with high levels of Lp(a), bleeding complications might be more frequent in these patients and merits further analysis.

In summary, POCHET will be the first large scale biobank collecting consecutive blood samples of patients with ALI that undergo CDT. Related to its design, POCHET will 1) help characterise the consecutive ALI population treated with CDT, 2) help identify novel biomarkers to predict major bleeding complications and hence aid physicians and research scientists to create a safer thrombolytic therapy and 3) support a wide range of diverse research projects in the field of coagulation and related interventions.

Supporting information

S1 File. Standard thrombolytic treatment of the lower limb.

(DOCX)

pone.0302830.s001.docx (21.9KB, docx)
S2 File. Endpoint definitions of the POCHET study.

(DOCX)

pone.0302830.s002.docx (15KB, docx)
S3 File. All variables included in the POCHET study.

(DOCX)

pone.0302830.s003.docx (22.2KB, docx)

Acknowledgments

Members of the POCHET study group:

G. J. de Borst Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

M.K. Dinkelman Department of Vascular Surgery, Elisabeth TweeSteden Hospital, Tilburg, The Netherlands

D.E.J.G.J. Dolmans Department of Vascular Surgery, Diakonessenhuis Hospital, Utrecht, The Netherlands

W.M. de Fijter Department of Vascular Surgery, Elisabeth TweeSteden Hospital, Tilburg, The Netherlands

D.P.V. de Kleijn Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

E.S. van Hattum Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

C.E.V.B. Hazenberg Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

J.A. van Herwaarden Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

J.M.M. Heyligers Department of Vascular Surgery, Elisabeth TweeSteden Hospital, Tilburg, The Netherlands

A. Jansze Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

M.C. Loubert Department of Vascular Surgery, Meander Medical Center, Amersfoort, The Netherlands

B.M. Mol Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

S.K. Nagesser Department of Vascular Surgery, Diakonessenhuis Hospital, Utrecht, The Netherlands

B.J. Petri Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

M. Teraa Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

R.J. Toorop Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, The Netherlands

W.J. Thijsse Vascular Surgery, Meander Medical Center, Amersfoort, The Netherlands

P.W.H.E. Vriens Department of Vascular Surgery, Elisabeth TweeSteden Hospital, Tilburg, The Netherlands

M. de Vries Department of Vascular Surgery, Diakonessenhuis Hospital, Utrecht, The Netherlands

V. van Weel Vascular Surgery, Meander Medical Center, Amersfoort, The Netherlands

Lead author of the POCHET Study Group: G.J. de Borst. E-mail address: G.J.deBorst-2@umcutrecht.nl

All figures were created with www.biorender.com.

Data Availability

No datasets were generated or analysed during the current study. All relevant data from this study will be made available upon study completion

Funding Statement

The author(s) received no specific funding for this work.

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Decision Letter 0

Eyüp Serhat Çalık

23 Jan 2024

PONE-D-23-42662Predictors Of bleeding Complications during catHeter-dirEcted Thrombolysis for peripheral arterial occlusions (POCHET)PLOS ONE

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Academic Editor

PLOS ONE

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When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at 

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2. Please include “Protocol” in the manuscript  title.

3. Please include a copy of the ethics committee approval, which should include the date of approval, the approval number, and signature or stamp from the ethics committee, and English translation, as an "Other" file.

In the Methods section of your revised manuscript, please include the full name of the institutional review board or ethics committee that approved the protocol, the approval or permit number that was issued, and the date that approval was granted.

4. One of the noted authors is a group or consortium: The POCHET study group

In addition to naming the author group, please list the individual authors and affiliations within this group in the acknowledgments section of your manuscript. Please also indicate clearly a lead author for this group along with a contact email address.

Additional Editor Comments:

I read the manuscript on this important topic with interest. I think that the study protocol is generally well written and will provide important contributions to those interested in the subject when the study is completed. The manuscript has been reviewed by three reviewers and their concerns are as follows. Please edit your manuscript according to the reviewers' suggestions and provide point-by-point responses. In particular, please provide the ethics committee approval of the study and the clinical trials register.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: No

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

You may also provide optional suggestions and comments to authors that they might find helpful in planning their study.

(Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Overall evaluation: The order of work in this study protocol should be reversed. First full ethical approval, then Clinical Trials registration, then submission of study protocol including statements of full ethical approval and Clinical trial registration number.

It should be clear from the protocol that some data will be collected and interpreted as part of the emergency intervention for proper patient care while some blood samples will be collected for “the future”.

One large problem you will encounter is that most bleeding events, also major, is related to access-site related bleeding that has nothing to do with anticoagulation, coagulation or fibrinolytic disturbances. Have you thought of that? Your primary endpoint should be major non-introducer-related major bleeding, and your estimated sample size should be based on assumption upon this endpoint, and not all major bleeding complications.

Specific comments:

1. Abstract. Add how many centers.

2. Add Clinical Trials registration number

3. Abstract – define major bleeding already here

4. The full ethical approval of this study is missing and should be included before the study protocol is submitted to a journal. In this ethical approval, the maximal amount of extra blood taken from the patient outside of clinical routine should be stated, and a reference given that it is ok to withdraw a certain amount of blood without any clinical consequences.

5. Some kind of power calculation would benefit this study protocol. How many patients would be needed to have some clue whether fibrinogen is a marker of major bleeding?

6. Data collection. The clinical biochemistry assays for example for fibrinogen may differ across centers. Have you checked that? How do you intend to calibrate between assays?

7. Data collection. No use of for instance REDCap data management system?

8. Definition of major bleeding – you should add necessity of transfusion of at least 2 units of blood during the in-hospital stay. Give reference: Schulman et al. J Thromb Haemostat 2010; 8: 202-204. Even though you argue against this, it is clinically relevant since many patients with ALI also have concomitant anemia at admission (around 30%).

9. Statistics. Can you expand on how you will be able to correct for competing interest? I mean if a patient dies, there will be no possibility of major amputation.

10. Limb salvage. Do you mean major amputation? Please define.

11. Ref 12 and 15 are the same.

Reviewer #2: The present study protocol aims to investigate the possible biomarkers to identify patients with high bleeding risk associated with catheter directed thrombolysis. The topic is clinically relevant although the multiple treatment protocols add to the challenge of clinical trial. The use of either Alteplase or Urokinase would make study more standardized. However if target 500 patients will be reached the post hoc comparation between regimen and biomarkers might be possible.

Only some minor notes on the manuscript:

Since present study is a clinical trial it would be logical to be registered as clinical trial at for example web registry ClinicalTrials.gov and registry number to be added to the manuscript.

Study design it would be more informative to add a nice flow chart. The reference to S1 is ok, but nice flow chart would make manuscript more interesting. Also figures 1-4 are nice but flow chart would be more accurate and present figures could support the flow chart?

Allergy against Alteplase or Urokinase not contraindication according S1? Please check absolute and relative contraindications.

Figure 3 one might get impression that the blood samples are collected from introduction sheet close to thrombus, which might even be interesting addition considering the aim of the study?

Biobank approval number available? If it would be nice to add it to the text.

Reviewer #3: Dear authors

Thanks for sharing your protocol. I have some few suggestions/doubts that may improve your data.

1)Title and abstract are interesting and highlight main points of the study. I think abstract must draw attention to the readers. I suggest report which biomarkers will be included at your research at the abstract.

2) Inclusion criteria: How severe were the included patients related to the limb perfusion? Only ALI Rutherford I and IIa patients were included? Please, answer - You must be very clear as this is a very crucial feature to take in accout. Explain

3) Exlusion criteria: IIB and II Rutherford ALI categories. Yes or not? Please, explain

4) About potential biomarkers: I suggest you describe how they will be measured at blood samples - your protocol and findings must be reproductible for other groups , mainly anti-plasmin, plasminogen activator inhibitor and VES.

5) Will fibinolytic agent be standartized? Is alteplase? Or other agents will be allowed? Please , be as clearer as possible.

6) Both ischemic upper and lower limbs will be included? Pleases, specify it.

7) I suggest define 02(two) groups of endopoints: efficacy endpoints and safety endpoints (besides bleeding complications, I suggest reporting "limb salvage"). All your variables MUST be reported.

8) Is your protocol registered (or being registered) on a platform like clinical trials.gov?

Please pay attention, mainly at question 2. It is very important to define your inclusion (and exclusion) criteria - it may be a potential source of bias

**********

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

**********

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PLoS One. 2024 May 9;19(5):e0302830. doi: 10.1371/journal.pone.0302830.r002

Author response to Decision Letter 0


28 Mar 2024

Response to Reviewers

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at .

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

The manuscript has been revised to the PLOS ONE’s style requirements

2. Please include “Protocol” in the manuscript title.

“Protocol” has been added to the manuscript title

3. Please include a copy of the ethics committee approval, which should include the date of approval, the approval number, and signature or stamp from the ethics committee, and English translation, as an "Other" file.

In the Methods section of your revised manuscript, please include the full name of the institutional review board or ethics committee that approved the protocol, the approval or permit number that was issued, and the date that approval was granted.

The original letter of approval of the Biobank Research Ethics Committee and it’s English translation has been included as an “other” file with the latest submission.

Under the “ethical approval” header within the “Methods and Design” section, the approval number and the date of approval is added.

4. One of the noted authors is a group or consortium: The POCHET study group

In addition to naming the author group, please list the individual authors and affiliations within this group in the acknowledgments section of your manuscript. Please also indicate clearly a lead author for this group along with a contact email address.

The affiliation of the members of the POCHET study group have been added in the acknowledgment section. Also the lead author of the POCHET study group is indicated with a contact email address.

Additional Editor Comments:

I read the manuscript on this important topic with interest. I think that the study protocol is generally well written and will provide important contributions to those interested in the subject when the study is completed. The manuscript has been reviewed by three reviewers and their concerns are as follows. Please edit your manuscript according to the reviewers' suggestions and provide point-by-point responses. In particular, please provide the ethics committee approval of the study and the clinical trials register.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

________________________________________

2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

________________________________________

3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

________________________________________

4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: No

________________________________________

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

________________________________________

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

You may also provide optional suggestions and comments to authors that they might find helpful in planning their study.

(Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Overall evaluation: The order of work in this study protocol should be reversed. First full ethical approval, then Clinical Trials registration, then submission of study protocol including statements of full ethical approval and Clinical trial registration number.

It should be clear from the protocol that some data will be collected and interpreted as part of the emergency intervention for proper patient care while some blood samples will be collected for “the future”.

One large problem you will encounter is that most bleeding events, also major, is related to access-site related bleeding that has nothing to do with anticoagulation, coagulation or fibrinolytic disturbances. Have you thought of that? Your primary endpoint should be major non-introducer-related major bleeding, and your estimated sample size should be based on assumption upon this endpoint, and not all major bleeding complications.

Dear reviewer,

The authors would like to thank you for your elaborate evaluation of the study and your very thorough comments. We adjusted the manuscript on these topics and clarify why we made certain decisions. Before we answer the list below, let us please answer your general comments.

• The nature of this study is observational and does not assign patients to one or different interventions which are compared between groups. For this study, all included patients are treated according to the predefined and standardized treatment protocol. The assessment of the best type of thrombolysis protocol falls beyond the scope of this study. Also because there are many variables to be studied to define the optimal protocol i.e. type of thrombolysis; dosage; access routing; duration of therapy, additional heparinization; interval of control angio etc etc.

• Donated blood samples are stored in the biobank for future analysis. Based on these future analysis, a new study can be conducted which can analyse possible new biomarkers that predict bleeding complications during thrombolysis. Because of the observational setting of the study, our study is not a clinical trial as defined by the International Committee of Medical Journal Editors (ICMJE) as there is no intervention. The definitions states:

“The ICMJE defines a clinical trial as any research project that prospectively assigns people or a group of people to an intervention, with or without concurrent comparison or control groups, to study the relationship between a health-related intervention and a health outcome”

https://www.icmje.org/recommendations/browse/publishing-and-editorial-issues/clinical-trial-registration.html

For this, the authors believe that a registration as a clinical trial is not applicable. To clarify this, we added “ As the nature of this study is an observational biobank study, registration as a clinical trial is not applicable“ to the study design section in line 120-121 ( the clean revised manuscript.

• Reviewer #1 stated that the order of work in this study protocol should be reversed, but since the registration as a clinical trial is not applicable, it is of our believe that the suggested order is no longer applicable. To clarify this, we added “ As the nature of this study is an observational biobank study, registration as a clinical trial is not applicable“ to the study design section in line 120-121 of the clean revised manuscript.

• The suggestion about the major bleeding complications definition is a very important recommendation. There is a very significant difference between access site related bleedings and any other bleeding during catheter direct thrombolysis. This difference was not clearly stated in the manuscript and therefore, the definition of the primary endpoint is edited to “non- access site related major bleeding” in line 165 (clean revised manuscript) in the endpoint definition section and in line 40 (clean revised manuscript) of the abstract.

Specific comments:

1. Abstract. Add how many centers. We thank the reviewer for this important comment because the number of including centers is important information. The reason we have not included the number of including centers is because the possibility for other centers to join later on in including patients for the POCHET trial. By stating the number of including centers at this point in time, this information will be incorrect when other authors will reference to this protocol paper. It is of course very important information to state the number of including centers when the results of the POCHET biobank are published. Currently, we have two centers including patients and expect more centers to include patients in the year 2024.

2. Add Clinical Trials registration number. See first bullet point above.

3. Abstract – define major bleeding already here. As mentioned above, the primary endpoint has been changed in the abstract as ‘non-access related major bleeding” as mentioned above.

4. The full ethical approval of this study is missing and should be included before the study protocol is submitted to a journal. In this ethical approval, the maximal amount of extra blood taken from the patient outside of clinical routine should be stated, and a reference given that it is ok to withdraw a certain amount of blood without any clinical consequences. The comment is on the ethical approval is a very significant recommendation. This study was approved by the Biobank Research Ethics Committee of the University Medical Center Utrecht, which is the central organ for reviewing new biobank protocols. It’s approval letter of the biobank protocol, including English translation, is submitted with this revised manuscript. In this biobank protocol it is stated that during thrombolysis, along with general blood collections every 6 hours, blood collections for the biobank were performed, consisting of a 6 ml EDTA and a 4,5ml citrate tube. With a maximum duration of thrombolysis of 72 hours and an extra donation to the biobank before thrombolysis would start, the maximum blood collections for the biobank per patient will add up to a maximum of 13 separate donations of 10,5 ml per donation. Blood donations to the biobank would stop when thrombolysis stops, which means that in general practice, a lot of patients will donate less than 13 times. This is further clarified in the Method section under sub header “Study design” and “lab manual for blood samples” in lines 122 (clean revised manuscript) and 198 (clean revised manuscript) and stated below.

Line 122: “With a maximum CDT-duration of 72 hours, the number of blood collections are maximised at 13 times”

Line 198: “When CDT stops, blood collections for the biobank will stop immediately.”

A total maximum of 136,5 ml per patient is taken. Amrein et al (doi 10.1016/j.blre.2011.09.003) reviewed the risks of blood donation, which were mainly vena puncture related or had to do with vasovagal collapses. For this study, these risks are not applicable, as blood samples are collected by a venous catheter. Long term risks of blood donation would mainly be iron deficiency syndrome, which was more seen in people who donated blood more frequently. The patients in our study, only donate blood to the biobank during thrombolysis treatment and the total amount of blood taken is only one third when compared to a regular blood donation (max 136,5ml vs 500 ml). This contributes to the safety of the blood donation for the POCHET biobank, which is very important. This is why it is further elaborated in the manuscript (line 126 of clean revised manuscript, “donating a maximum of 136.5 ml blood to the biobank is considered safe and does not affect standard healthcare”.) and in this letter.

5. Some kind of power calculation would benefit this study protocol. How many patients would be needed to have some clue whether fibrinogen is a marker of major bleeding?

Thank you for this important recommendation. A power calculation in clinical research aids researchers in the risk of under or over inclusion. However, the POCHET study is not a clinical study, but a biobank. As previous studies mostly had a retrospective analysis as design, there is a broad range of expected endpoints, which also differed in their definitions amongst studies. As such, the prospective POCHET registry using strict defined endpoints and standardized protocol will help to set the new outcome parameters which can subsequently be used to perform power calculations for future thrombolysis based studies.

The most important value of a biobank is that it holds tissue or blood for future research for all kinds of research questions. Every research question can have its own effect and thereby have its own power calculation. This is further elaborated in the subheader “Sample size” in the “Methods and design” section.

6. Data collection. The clinical biochemistry assays for example for fibrinogen may differ across centers. Have you checked that? How do you intend to calibrate between assays?

This is a very important remark. All plasma samples will be stored temporarily in the participating centers at -80° Celsius. No biochemistry assay is being done in different centers. Samples are transported on dry ice every few months to the central biobank in Utrecht where they again will be stored at -80° Celsius. All biochemistry assays will then be done in a single laboratory. This is further elaborated in the subheader “Lab manual for blood samples” in the “methods and design “ section in line 194 of the clean revised manuscript and stated below.

“All future analysis will be done in a single laboratory facility,”

7. Data collection. No use of for instance REDCap data management system?

Thank you for this comment. Although it is stated that the data is securely stored, the way it is stored is not mentioned in the manuscript. This is changed in the revised manuscript in line 203 of the clean revised manuscript and stated below

“Data regarding patient characteristics at presentation such as comorbidities, medication use, occlusion specifics and data of hospital admission and follow-up will all be c

Attachment

Submitted filename: 20240314 Response to Reviewers.docx

pone.0302830.s004.docx (160.7KB, docx)

Decision Letter 1

Eyüp Serhat Çalık

15 Apr 2024

Predictors Of bleeding Complications during catHeter-dirEcted Thrombolysis for peripheral arterial occlusions (POCHET)

PONE-D-23-42662R1

Dear Dr. Mol,

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Eyüp Serhat Çalık

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Acceptance letter

Eyüp Serhat Çalık

26 Apr 2024

PONE-D-23-42662R1

PLOS ONE

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Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 File. Standard thrombolytic treatment of the lower limb.

    (DOCX)

    pone.0302830.s001.docx (21.9KB, docx)
    S2 File. Endpoint definitions of the POCHET study.

    (DOCX)

    pone.0302830.s002.docx (15KB, docx)
    S3 File. All variables included in the POCHET study.

    (DOCX)

    pone.0302830.s003.docx (22.2KB, docx)
    Attachment

    Submitted filename: 20240314 Response to Reviewers.docx

    pone.0302830.s004.docx (160.7KB, docx)

    Data Availability Statement

    No datasets were generated or analysed during the current study. All relevant data from this study will be made available upon study completion


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