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BMJ Open
BMJ Open
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bmjopen
BMJ Open
2044-6055
BMJ Publishing Group BMA House, Tavistock Square, London, WC1H 9JR

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10.1136/bmjopen-2023-079302
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Protocol
Intensive Care
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Comparison of side-hole and step-tip catheters for patients requiring continuous renal replacement therapy in intensive care units: study protocol for a randomised controlled trial
Zhou Zhifeng 10zhouzf97@163.com

Liu Chen 10flymeu@qq.com

Yang Yingying 1yingyingyangsf@163.com

Wang Fang 11106776800@qq.com

Zhang Sheng 1906930666@qq.com

http://orcid.org/0000-0003-1155-4802
Zhang Ling 1zhangling_crrt@163.com

Fu Ping 1fupinghx@scu.edu.cn

1 Department of Nephrology, Kidney Research Institute, West China Hospital of Sichuan University, Chengdu, China
DrLingZhang; zhangling_crrt@163.com
None declared.

ZZ and CL contributed equally.

2024
20 9 2024
14 9 e07930228 8 2023
02 9 2024
Copyright © Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

Abstract

Introduction

In addition to various techniques involved in catheter insertion, catheter placement location, lumen diameter and operation and management during continuous renal replacement therapy (CRRT), the design of the tip and side holes, as well as the position of the tip of the catheter, can also impact catheter function. Side-hole and step-tip catheters are commonly used during CRRT. However, there is insufficient evidence comparing their efficacy for CRRT in critically ill patients. And the optimal position of the tip of catheters is not well studied and remains controversial. This study was conducted to assess whether using a step-tip catheter could reduce the rate of catheter dysfunction compared with a side-hole catheter and whether inserting a longer catheter could reduce the incidence of catheter dysfunction and increase catheter survival time.

Methods and analysis

A prospective, open-label, three-arm, parallel-group, single-centre randomised controlled trial will be conducted at West China Hospital of Sichuan University in China. An estimated sample of 378 participants receiving CRRT treatment will be recruited. Eligible patients will be randomly assigned to three groups to receive different dialysis catheters for the initiation of CRRT at a 1:1:1 ratio via a central randomisation system: group A, side-hole catheters (11Fr, 200 mm; GDHK‐1120; Baxter International Inc., Deerfield, Illinois); group B, step-tip catheters (13Fr, 200 mm; GDHK‐1320; Baxter International Inc.) and group C, step-tip catheters (13Fr, 250 mm; GDHK‐1325; Baxter International Inc.). The femoral vein is the only vascular access. All catheters will be inserted under the guidance of ultrasound using the Seldinger method to reduce complications and trauma related to catheter insertion. The primary outcomes are the occurrence of catheter dysfunction and catheter survival time. Outcome assessors and data analysts will be blinded. All data will be analysed according to the group randomly assigned by an intention-to-treat analysis, in which catheters with missing data for the primary outcomes would be excluded.

Ethics and dissemination

The trial protocol has been approved by the Biomedical Research Ethics Committee of West China Hospital of Sichuan University (2023.1221). And the results will be published in peer-reviewed journals.

Trial registration number

ChiCTR2300075107.

Nephrology
Dialysis
Randomized Controlled Trial
Scientific and Technological Department of Sichuan Province, China 2020YFG0105 Project for Disciplines of Excellence, West China Hospital, Sichuan University ZYGD18027 Project for Disciplines of Excellence, Clinical Research Incubation Project, West China Hospital, Sichuan University 2018HXFH018
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pmcSTRENGTHS AND LIMITATIONS OF THIS STUDY

This is a randomised controlled trial comparing the effectiveness of step-tip with side-hole catheters and simultaneously exploring the optimal catheter tip position for femoral vein catheterisation during continuous renal replacement therapy.

The study was conducted in a prospective, open-label, three-arm, parallel-group design.

This is an assessment of multiple outcomes such as the incidence of catheter dysfunction, catheter survival time, average filter lifespan, all-cause mortality, length of intensive care unit or hospitalisation and adverse events.

Blinding of the study participants and treating clinicians will not be possible due to the nature of the intervention.

This study will be conducted at a single centre in southwest China, and the results will need cautious interpretation concerning region and ethnicity.

Introduction

Continuous renal replacement therapy (CRRT) is a vital blood purification therapy that is now widely used for the treatment of critically ill patients with acute kidney injury, septic shock, crush injury syndrome and even COVID-19.1 2 Continued well-functioning of the dialysis catheter during CRRT is essential for establishing sufficient reliable blood flow and complete successful therapy. In addition to the techniques of catheter insertion, catheter placement location, lumen diameter and operation and management during CRRT, the design of the tip and side holes and the position of the tip of the catheter also play an important role in prolonging catheter survival time and reducing the incidence of catheter-related complications.3 4 Currently, multiple catheter designs have been developed for clinical use. They have different characteristics in terms of catheter length, lumen diameter and shape, and tip and side-hole designs. Numerous studies have been conducted to evaluate the efficacy of these catheters in preventing thrombosis and catheter-related infections and improving catheter function in clinical treatment.5 6 However, most of these studies were observational, and the efficacy of these catheters in improving catheter survival and reducing complications is still controversial.

Side-hole and step-tip catheters are two commonly used catheters during CRRT. Side-hole catheters have multiple side holes that can support inflow in case of obstruction of the end hole.7 Side holes at the distal tip can also provide lower a shear rate and better flow on the arterial side in the short run, thus reducing blood recirculation rate.8 And a computational fluid dynamic assessment conducted by Owen et al found that the side-hole design could improve the theoretical performance of the catheters by increasing flow velocity and decreasing shear stress.9 However, side holes in the catheter may also have mechanistic and physiological disadvantages. With rough edges of side holes and instant removal of anticoagulant lock solutions, the risk of clots anchored in the side holes is significantly increased.10 And it is difficult to remove or dissolve the clots anchored in the side holes.8 Loss of anticoagulant lock solutions in the catheter tip presents a clotting risk at the catheter tip. The main flow will be dragged over the apical hole and create a large zone with low flow, which is also an important factor in favouring clot formation at the catheter tip.11 In addition, side-hole catheters facilitate an almost instantaneous wash-out of antibiotic-locking solution through side holes, which increases exposure time to intraluminal bacteria and increases the risk of catheter-related bacteraemia.12 With a staggered tip design, the step-tip catheters consist of an outflow lumen that extends several centimetres, typically 2.5 cm, below the level of the inflow tip, which is thought to reduce recirculation.13 However, there is still no firm evidence comparing the efficacy and safety of step-tip catheters to side-hole catheters for CRRT in critically ill patients. Thus, it is essential to evaluate the catheter function and catheter-related adverse events of step-tip catheters during CRRT compared with side-hole catheters.

The position of the catheter tip is also crucial for enduring adequate blood flow and reducing blood recirculation. However, the optimal position remains unclear. As for the internal jugular vein, there are guidelines for positioning it in the lower one-third of the superior vena cava, near the junction between the superior vena cava and the right atrium.14 In contrast, a randomised controlled trial (RCT) found that longer internal jugular vein catheters targeting right atrial placement yielded better extracorporeal circulation and reduced filter clotting compared with shorter catheters targeting superior vena cava placement.15 The ideal length of catheters placed in the femoral vein is also unknown, with no evidence as to whether deeper insertion results in enhanced blood flow and lower recirculation rates. In essence, there is insufficient evidence and recommendations to establish the optimal femoral vein catheter tip placement and its impact on performance.

In this trial, we intend to compare the efficacy and safety of three types of femoral vein catheterisation during CRRT. The objective of this study is to evaluate whether using a step-tip catheter for femoral vein insertion could reduce the rate of catheter dysfunction compared with a side-hole catheter. Additionally, the study aims to investigate whether the insertion of a longer catheter into the femoral vein could minimise the occurrence of catheter dysfunction and enhance catheter survival time.

Methods and analysis

Study design and setting

A single-centre, RCT will be carried out at West China Hospital of Sichuan University in China to compare the side-hole and step-tip catheters for CRRT. This study will be conducted as a prospective, open-label, three-arm, parallel-group design. The study protocol will be designed in accordance with the Standard Protocol Items: Recommendations for Interventional Trials Checklist,16 and the conduct of the study will adhere to the Declaration of Helsinki (version Fortaleza, 2010). The flowchart of the trial procedure is summarised in figure 1.

Figure 1 The summarised design of this trial. An overall outline of the design of this RCT is presented. Written informed consent was obtained by patients or persons with decisional responsibility. CRRT, continuous renal replacement therapy; RCT, randomised controlled trial.

Patient and public involvement

Patients and the public will not be involved in the design, conduct or dissemination of the study. The results will be available to the public, if necessary.

Participants

All critically ill patients in the intensive care unit (ICU) who were expected to require support with CRRT will be assessed for eligibility. The inclusion criteria include the following: (1) age between 18 and 90 years, (2) indications for CRRT according to the treating physicians, (3) intention to provide full intensive care treatment for at least 3 days and (4) written informed consent provided by the patient or a person with decisional responsibility. And the exclusion criteria comprise the following: (1) participants with coagulopathy or received systemic anticoagulation therapy for other medical reasons, (2) femoral vein anatomical abnormalities or local contraindications to catheterisation such as local skin infection in the femoral vein, (3) participants required catheter access through the jugular vein or subclavian vein, (4) participation in another clinical intervention trial within the last 1 month and (5) pregnancy or nursing or impending miscarriage.

Eligible patients will be informed clearly of the objective, procedure, expected benefits and possible risks involved. Both the patient and treating physicians are required to complete and sign the informed consent form. Confidentiality of all patient information will be maintained, and patients will have the right to withdraw from the study at any time without facing any prejudice.

Randomisation

Eligible patients will be randomly assigned to three groups to receive different dialysis catheters for the initiation of CRRT at a 1:1:1 ratio, determined by a central computer-generated randomised sequence. Group A will receive side-hole catheters (11Fr, 200 mm; GDHK‐1120; Baxter International Inc., Deerfield, Illinois), group B will receive step-tip catheters (13Fr, 200 mm; GDHK‐1320, Baxter International Inc.) and group C will receive step-tip catheters (13Fr, 250 mm; GDHK‐1325; Baxter International Inc.). The schematic diagram of the internal structures of side-hole and step-tip catheters is shown in figure 2. The randomisation process will be stratified according to the institution and will use a block randomisation design to ensure balance between groups. Due to practical considerations, blinding of patients and treating clinicians was clinically impractical during this study.

Figure 2 The schematic diagram of the internal structures of side-hole and step-tip catheters. A simple schematic diagram of the internal structures of side-hole and step-tip catheters included in this trial.

Intervention

Patients will be randomly allocated into three groups: group A, side-hole catheter (20 cm, GDHK‐1120), a double-lumen 11Fr symmetrical-tip catheter with multiple side holes; group B, step-tip catheter (200 mm, GDHK‐1320), a double-lumen 13Fr catheter with a staggered tip design and group C, step-tip catheter (250 mm, GDHK‐1325), a longer double-lumen 13Fr step-tip catheter.

Catheter insertion and care procedures

All inserted catheters will be temporary haemodialysis catheters. Catheterisation will be performed by physicians with extensive experience in catheterisation. A seven-step strategy to minimise insertion-related complications will be followed.17 First, only a well-functioning femoral vein will be selected for catheterisation. Second, the operators will perform surgical hand-scrubbing or hand-rubbing before wearing sterile gloves and wear disposable sterile surgical gowns, caps and masks. At the site of catheter placement, we will place large sterile gauze and use the same alcohol-based povidone-iodine disinfectant for skin disinfection and catheter care. The puncture site is approximately 0.5 cm medially to the point of maximal femoral artery pulsation, which is typically located below the midpoint of the inguinal ligament. After routine disinfection and drape, local infiltration anaesthesia with 2% chlorhexidine in 70% alcohol will be administered. Third, to achieve satisfactory anaesthesia, all catheters will be inserted under the guidance of ultrasound using the Seldinger method. Once the catheter is successfully inserted, it will be flushed with saline, and the sealing solution will be 4% sodium citrate or heparinised saline. Fourth, the expected catheter tip position is in the inferior vena cava (above the iliac veins and below the renal veins). We will use length estimation by anthropometric measurement and even the postprocedural X-ray examinations to further confirm the position of the catheter tip. Fifth, we will seal the exit site of the inserted catheter with cyanoacrylate adhesive. Finally, regular checks are essential to ensure the catheter’s stable placement and prevent the loosening or detachment of the securing strap. And the inserted catheters will be secured and covered with a sterile dressing. Concurrently, we will also maintain cleanliness and dryness around the catheter to minimise skin infections in the catheter’s vicinity.

The catheter is not intended for routine blood draws or medication administration but only for CRRT treatment. And before CRRT treatment, we will evaluate the catheter function through the following methods. First, using a syringe to draw blood from the catheter, if 20 mL of blood can be successfully drawn out within 6 s, it indicates that the blood flow rate of the catheter can reach 200 mL/min. Second, a recent consensus on severe blood purification nursing in China suggested a novel evaluation method: extracting 3–4 mL of needle sealing solution and blood within 1 s, confirming the catheter’s normal function.

All patients will be treated with the Prismaflex V8.0 CRRT dialysis machine (Baxter International Inc.) for CRRT. For regional citrate anticoagulation, the blood flow will initiate at 150 mL/min. And based on the treatment progress, the blood flow will be maintained at 130–150 mL/min. For low-molecular-weight heparin anticoagulation or without anticoagulants, the blood flow rate will be set at 200 mL/min. The CRRT treatment dose will be adjusted to 25 to 35 mL/kg/hour. When a catheter is no longer needed (kidney function recovery, abandonment of treatment or death) or when a new temporary catheter needs to be replaced (catheter dysfunction, catheter-related bloodstream infection or catheter-related thrombosis), the attending physician for each patient will independently decide whether to remove the catheter.

Outcome measures

This RCT will assess two coprimary outcomes: the occurrence of catheter dysfunction and catheter survival time in critically ill patients undergoing CRRT. Catheter dysfunction is defined when the following conditions occur during CRRT: inability to maintain an adequate blood flow, or continuous arterial pressure <-200 mm Hg, or continuous venous pressure >200 mm Hg, or frequent pressure alarm (>3 times/hour), or inability to aspirate blood freely.1820 Secondary outcomes include the following: (1) average filter life span; (2) all-cause mortality at ICU, hospital, 28-day and 60-day follow-ups; (3) ICU and hospital length of stay; (4) duration of CRRT treatment and (5) adverse events (intradialytic hypotension, catheter-related bloodstream infection and catheter-related thrombosis). These data will be collected throughout the study periods, and the scheduled visits and data collection are provided in detail in table 1.

Table 1 Schedule of enrolment, interventions and assessments

	V1−1D	V2D0	V3D1	V4D2	V5D3	V6D4	V7D5	V8Etc	
Patients									
 Eligibility screen	X								
 Informed consent		X							
 Demographics and medical history		X							
 Physical examination		X							
 Type of vascular access		X							
 Allocation		X							
Intervention									
 Side-hole catheters (GDHK‐1120)		X	X	X	X	X	X	X	
 Step-tip catheters (GDHK‐1320)		X	X	X	X	X	X	X	
 Step-tip catheters (GDHK‐1325)		X	X	X	X	X	X	X	
Assessment									
 Laboratory data at CRRT initiation			X						
 Occurrence of catheter dysfunction			X	X	X	X	X	X	
 Catheter survival time			X	X	X	X	X	X	
 Average filter life span			X	X	X	X	X	X	
 All-cause mortality			X	X	X	X	X	X	
 Length of stay			X	X	X	X	X	X	
 Duration of CRRT treatment			X	X	X	X	X	X	
Participant safety									
 Adverse effects			X	X	X	X	X	X	
CRRT, continuous renal replacement therapy

Sample size determination

Our hypothesis is that longer catheters with a step-tip will have superior efficacy in reducing the rate of catheter dysfunction in intensive care patients undergoing CRRT. Based on previous studies and our clinical experience, we demonstrate a catheter dysfunction incidence of approximately 15% in side-hole catheters.1922 And our hypothesis is that compared with the side-hole catheter group, the risk of catheter dysfunction in the groups of the two step-tip catheters will decrease by 20% and 30%, respectively. We performed sample size calculations with G-Power V.3.1 using an α value of 0.05 and a power of 80%. Accordingly, we require a total of 345 participants (115 per group). Taking into account a potential 10% dropout rate, we determined that we should enrol 378 participants in this study.

Monitoring

To ensure the quality and regulatory compliance of the trial, we will establish an independent data monitoring committee (DMC). The DMC will comprise five members who possess expertise in fields such as nephrology, CRRT management, nursing, trial methodology and biostatistics. The DMC meeting will be held every 2 months, and we will create a procedural document for the meetings and strictly follow the document.

Statistical analysis

Continuous variables will be presented as means with SD or medians and IQRs, while categorical variables will be presented as numbers and percentages. The comparison of categorical variables will be tested using the χ2 test, whereas, for the comparison of continuous variables, it will be determined whether they conform to a normal distribution and homogeneity of variance before appropriate methods such as t-tests, analysis of variance or Wilcoxon rank-sum tests are employed. Time to catheter dysfunction will be compared between groups by the use of Kaplan-Meier curves and log-rank test. In addition, a univariate analysis will be conducted to evaluate the impact of characteristics of included patients (such as age, body mass index, Sequential Organ Failure Assessment score, laboratory data at CRRT initiation and anticoagulants) on the incidence of catheter dysfunction. Then, a Cox regression model will be used to estimate the risk factors associated with the incidence of catheter dysfunction. All data will be analysed according to the group randomly assigned by an intention-to-treat analysis, in which catheters with missing data for the primary outcome will be excluded. P-value less than 0.05 is considered statistically significant, and all analyses will be performed using SPSS 22.0 (IBM, USA).

Strengths and limitations

To the best of our knowledge, this study will be the first RCT to compare the effectiveness of step-tip with side-hole catheters and to simultaneously explore the optimal catheter tip position for femoral vein catheterisation during CRRT. We hope that the results of this trial will support the development of catheter selection and future designs for dialysis catheters during CRRT. And in the future, based on this RCT, our team will use computer technology to develop models of these three different catheters and simulate single-fluid flow inside the catheters. Then, we will analyse the impact of the catheter tip position on the backflow ratio and determine the optimal distance. And we will conduct multiple simulations on the location, size and shape of the side holes, resulting in the optimal solution. Finally, we will incorporate all of these advantages to design a new type of catheter with superior performance.

However, there are still several limitations to this trial. First, due to the nature of the intervention and practical considerations, patients and treating clinicians will not be blinded during this study. Nevertheless, we will carefully design our methods of recruitment, randomisation, allocation, outcome assessment, data collection and analysis to minimise bias. Second, this study will be conducted in southwest China, which means that the results will need cautious interpretation concerning region and ethnicity.

Ethics and dissemination

This study has been approved by the biomedical research ethics committee, West China Hospital of Sichuan University in China (2023.1221). All participants will provide the written informed consent, which states that participation is voluntary and can be terminated at any point. The trial started recruitment in November 2023, and we aim to complete this trial by the end of 2024. Individual data will be securely stored, password-protected and accessible only by the research team. The results of this trial will be presented at national and international scientific conferences. And the final manuscript will be published in a peer-reviewed journal.

Review Process File
20 09 2024

Funding: This work was supported by the 1.3.5 Project for Disciplines of Excellence, Clinical Research Incubation Project, West China Hospital, Sichuan University (2018HXFH018); the Scientific and Technological Department of Sichuan Province, China (2020YFG0105); and the 1.3.5 Project for Disciplines of Excellence, West China 12 Hospital, Sichuan University (ZYGD18027).

Prepub: Prepublication history for this paper is available online. To view these files, please visit the journal online (https://doi.org/10.1136/bmjopen-2023-079302).

Patient consent for publication: Consent obtained from parent(s)/guardian(s).

Provenance and peer review: Not commissioned; externally peer reviewed.

Patient and public involvement: Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
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