Efficacy and safety of haemadsorption combined with continuous renal replacement therapy for rhabdomyolysis and acute kidney injury: a single-center, open-label, randomised controlled trial protocol

Abstract

Introduction

Myoglobin (Mb) exerts both direct and indirect nephrotoxic effects, contributing to the progression of kidney injury. For patients with rhabdomyolysis (RM) and acute kidney injury (AKI) requiring renal replacement therapy (RRT), Mb clearance is a critical therapeutic goal. Recent studies have indicated that haemoadsorption (HA) combined with continuous renal replacement therapy (CRRT) is an effective strategy for removing circulating Mb. However, clinical data regarding the efficiency of Mb clearance and long-term patient outcomes with this approach remain limited. This study aims to evaluate the efficacy and safety of HA combined with CRRT in treating severe RM and AKI.

Methods and analysis

This single-center, open-label, randomised controlled trial will be conducted at West China Hospital of Sichuan University. A total of 60 patients with severe RM and AKI will be enrolled and randomly assigned in a 1:1 ratio to either the CRRT group or the CRRT+HA group. Randomisation will be conducted by drawing lots, performed by the patient’s legal representative (with ‘0’ indicating the CRRT group and ‘1’ indicating the CRRT+HA group).

The primary outcome of the study is the plasma clearance of Mb. Secondary outcomes include the plasma clearance of creatine kinase, haemodynamic changes, changes in acute physiology and chronic health II (APACHE) II score and sequential organ failure assessment (SOFA) score, renal function recovery, length of hospital stay, all-cause mortality, and pre- and post-treatment changes in albumin, platelet and haemoglobin counts. Data will be analysed using both intention-to-treat and per-protocol analysis methods.

Ethics and dissemination

The study will comply with the Declaration of Helsinki and the Chinese Clinical Trials Act. The study protocol has been approved by the Biomedical Research Ethics Committee of West China Hospital of Sichuan University (2024.1914). Written informed consent will be obtained from all participants. The study results will be presented at academic meetings and in peer-reviewed academic journals.

Trial registration number

ChiCTR2400092176.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• This study is the first to directly evaluate the clearance efficiency of haemadsorption combined with continuous renal replacement therapy on myoglobin. It also explores the impact of this treatment modality on patients’ long-term prognosis.

• Incomplete data may exist due to factors such as clotting in the dialysis circuit, patient withdrawal or resuscitation efforts preventing completion of the 10 hour treatment regimen. However, we minimised bias through intention-to-treat and per-protocol analyses.

• This study is a single-center, open-label investigation.

• The primary endpoint comprises five repeated measurements.

• We cannot determine the optimal timing for initiating renal replacement therapy to maximise benefits for patients.

Introduction

Acute kidney injury (AKI) is the most common late complication of rhabdomyolysis (RM).¹ Statistics show that approximately 13–50% of patients with RM develop AKI, with 26% requiring renal replacement therapy (RRT) and 10%–50% facing mortality associated with RM and AKI.^{2 3} Myoglobin (Mb), a 17 kDa protein, is the principal pathogenic substance in AKI. During RM, Mb contributes to AKI through the formation of obstructive casts in renal tubules and direct nephrotoxic effects. Rapid and effective removal of Mb is therefore crucial to preventing the progression of RM and AKI.⁴

Extracorporeal techniques for the efficient clearance of Mb from circulation have been a key focus of clinical research for decades.⁵ Studies have demonstrated that Mb elimination is feasible with haemodialysis or haemofiltration using high cut-off filters and high fluid volumes.⁶,⁸ However, commonly employed techniques in intensive care units (ICU), such as continuous veno-venous haemodialysis (CVVHD) or continuous veno-venous haemofiltration (CVVH), have been found to be suboptimal for Mb clearance.⁷⁹,¹¹

Recent evidence suggests that haemoadsorption (HA), either alone or in combination with continuous veno-venous haemodiafiltration (CVVHDF), may offer an effective approach to Mb removal. Case reports,¹¹,¹³ retrospective studies^{8 14} and small prospective tests¹⁵ have reported promising results for Mb clearance using HA.

A previous retrospective study involving 111 patients further demonstrated that continuous renal replacement therapy (CRRT) combined with HA therapy not only reduced ICU and in-hospital mortality rates among patients with RM and AKI but also exhibited a clearance effect on creatine kinase (CK).¹⁶ Although these findings suggest the potential clinical value of HA therapy for RM and AKI, the precise efficacy and safety of combining HA with CRRT in treating RM and AKI remain to be further clarified due to the current lack of high-quality randomised controlled trials supporting this approach. To address this gap, we have designed a single-center, open-label, randomised controlled trial. The primary objective is to compare the plasma clearance of Mb at various time points between CVVHDF combined with HA and CVVHDF alone. Secondary outcomes include plasma clearance of CK, changes in haemodynamic parameters, acute physiology and chronic health (APACHE) II score and sequential organ failure assessment (SOFA) score, all-cause mortality, recovery of renal function and other relevant laboratory markers before and after treatment.

This study aims to provide robust evidence on the most effective RRT modality for patients with RM and AKI, ultimately serving as a valuable reference for managing RM-induced acute kidney injury.

Methods and analysis

Study design and setting

This study is a single-center, open-label, prospective, parallel-group randomised controlled trial designed to evaluate the efficacy and safety of HA combined with CRRT for severe RM and AKI conducted at West China Hospital of Sichuan University.

The study protocol has been developed in alignment with the Standard Protocol Items: Recommendations for Interventional Trials Checklist¹⁷ and adheres to the principles outlined in the Declaration of Helsinki (Fortaleza, 2013 version). A detailed flowchart summarising the trial procedures is presented in figure 1.

Figure 1. Summarised design of this trial. APACHE II, acute physiology and chronic health II; CK, creatine kinase; CRRT, continuous renal replacement treatment; HA, haemoadsorption; Mb, myoglobin; SOFA, sequential organ failure assessment.

Patient and public involvement

Patients and 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

The study recruitment period is from 24 November 2024 to 20 April 2026. All patients diagnosed with RM and AKI requiring RRT will be evaluated for eligibility. The inclusion criteria are as follows: (1) patients diagnosed with RM (CK >1000 IU/L or more than five times the upper limit of normal, accompanied by a significant increase in serum Mb) and CK ≥5000IU/L¹⁸ and Mb ≥3000 ng/mL; (2) patients diagnosed with AKI, meeting one of the following: serum creatinine (SCr) increase >26.5 µmol/L within 48 hours or >50% of baseline value within 7 days; or urine volume <0. mL/kg/h for more than 6 hours¹⁹; (3) clinical evaluation indicates the need for RRT; and (4) patients were admitted to the ICU.

The exclusion criteria include (1) patients who have received other forms of blood purification therapy before enrolment, (2) patients or their representatives who refuse to participate in the study or decline to sign the informed consent form, (3) patients with a history of chronic kidney disease, (4) patients with RM caused by myositis or myopathy and (5) patients who are pregnant or have undergone organ transplantation.

Withdrawal from the study: (1) patients or their families requesting withdrawal from the study and (2) RRT duration falling below 2 hours for any reason.

Eligible patients will receive detailed information about the study’s objectives, procedures, anticipated benefits and potential risks. Written informed consent will be obtained from both patients and treating physicians. Confidentiality of patient data will be strictly maintained, and participants can withdraw from the study at any time without repercussions.

Randomisation

This study employs a randomised controlled trial design. Eligible patients will be randomly assigned to two groups in a 1:1 ratio. The specific randomisation procedure is as follows: a researcher not involved in patient recruitment (Researcher 1) will prepare 60 cards in advance, with 30 labelled ‘0’ (CRRT group, receiving CVVHDF therapy) and 30 labelled ‘1’ (CRRT+HA group, receiving HA combined with CVVHDF therapy). Each card was sealed in an opaque, identical envelope. Subsequently, another independent researcher (Researcher 2) provided these envelopes to eligible patients’ family members for selection. Each patient selected one envelope; upon opening, their group assignment was determined, and the envelope was not returned. Due to the nature of the interventions, blinding of patients and clinicians is not feasible in this trial.

Intervention

CRRT group

Patients in the CRRT group will undergo CVVHDF using the AN69-ST150 haemofilter (Gambro Renal Products, Lakewood, CO, USA) with the Prismaflex CRRT System (Baxter, Deerfield, IL, USA) (figure 2A). Key parameters include:

Figure 2. Diagram of continuous renal replacement treatment (CRRT) or CRRT+ haemoadsorption (HA) and specimen collection points. (A) Device connection diagram and specimen collection points for the CRRT group; (B) device connection diagram and specimen collection points for the CRRT+HA group. HA380, a secondary crosslinked polystyrene neutral macroporous adsorption resin device. AN 69-ST150, refers to the filter membrane material and membrane area. The polyacrylonitrile membrane used in AN69ST features a polyimide coating on its surface, with 150 indicating an effective polyimide area of 1.5 m².

Blood flow rate: 150–250 mL/min.

Haemofilter replacement: Every 72 hours to prevent premature clotting.

Therapeutic dose: 25–35 mL/kg/h.

Replacement solution: bicarbonate solution (Chengdu Qingshan Likang Pharmaceutical Co., Ltd., Chengdu, China) administered post-dilution with a replacement fluid-to-dialysate ratio of 1:1 (v/v).

Anticoagulation: determined based on Kidney Disease: Improving Global Outcome guidelines.

CRRT+HA group

In addition to CRRT, the CRRT+HA group will receive HA therapy using the HA380 adsorption device integrated with the CVVHDF setup for the first 10 hours. Subsequent continuation of HA therapy will be evaluated based on clinical needs (figure 2B).

The HA380 adsorption device uses a secondary cross-linked polystyrene neutral macroporous adsorbent resin with the following specifications:

Filling volume: 380 mL.

Adsorption surface area: ~54 000–64 000 m².

Molecular weight range: selectively adsorbs solutes of 5–60 kDa.

This setup aims to maximise the removal of Mb and other pathological solutes, providing a comprehensive approach for managing RM-induced acute kidney injury.

Primary outcomes

The primary outcomes are the plasma clearance of Mb at 2, 4, 8 and 10 hours following RRT (table 1).

Table 1. Timing of visits and data collection.

	Screening	Baseline period: -1 hours	Visiting time
			Treatment period Follow-up period: 3 months
Patients
Eligibility screen	×
Informed consent		×
Demographics and medical history		×
Physical examination		×
Disease diagnosis and aetiology		×
Urine output during first 24 hours		×
Randomisation		×
Intervention
CRRT+HA group			×	×
Comparison
CRRT group			×	×
Assessment
Routine blood test		×	×
Blood biochemical examination*		×	×
Vital Signs*		×	×
Severe Disease Severity Scores*		×	×
Assist mechanical ventilation		×	×
Outcomes
Substance-specific clearances			×
Hospital stays				×
All-cause mortality				×
Renal function				×
Participant safety
Adverse effects			×	×

^*Blood biochemical examination includes liver function (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, albumin, TB and DB), renal function (serum creatinine and blood urea nitrogen), electrolytes (blood calcium and phosphorus), blood lipids (total cholesterol, triglycerides, low-density lipoprotein and high-density lipoprotein); vital signs include blood pressure, heart rate and blood oxygen saturation; Severe Disease Severity Scores include acute physiology and chronic health II, sequential organ failure assessment and vasoactive-inotropic score.

CRRT, continuous renal replacement therapy ; HA, haemoadsorption.

Secondary outcomes

The secondary outcomes are as follows (table 1):

1. All-mortality rates: 28-day mortality, 60-day mortality and 90-day mortality.

2. Renal function recovery: full recovery is defined as the absence of AKI criteria 90 days post-treatment.²⁰ Partial recovery is indicated by sustained abnormal SCr levels and/or persistent proteinuria and haematuria, without the need for haemodialysis.²¹ Dialysis dependency is defined as ongoing haemodialysis requirements after 90 days.²²

3. Changes in haemodynamics: changes in heart rate, mean arterial pressure and vasoactive-inotropic scores (VIS) at 10 and 24 hours of treatment. VIS is calculated using the following formula:VIS=dopamine (ug/kg/min)+dobutamine (ug/kg/min)+100×epinephrine (ug/kg/min)+100×norepinephrine (ug/kg/min)+10×milrinone (ug/kg/min)+10 000×vasopressin (U/kg/min).²³

4. APACHE II score and SOFA score: changes in APACHE II score and SOFA score at 10 and 24 hours of treatment.

5. Length of stay: ICU length of stay and total length of stay.

6. The plasma clearance of CK: the plasma clearance of CK at 2, 4, 8 and 10 hours following RRT.

Safety outcomes

Evaluate changes in haemoglobin, platelet and albumin counts before and after CRRT and CRRT+HA treatment.

Patient safety

All adverse events associated with RRT will be meticulously documented, including the type, severity, actions taken and the relationship of the adverse event to the treatment.

Sample size determination

Sample size calculations were based on 10 h Mb clearance for the primary outcome. We used a superiority test for sample size estimation. According to the pre-test, the mean value of Mb clearance at 10 hours after treatment was 12.6 in the CRRT+HA group and 4.6 in the CRRT group. Based on previous studies, the SD of Mb clearance was 6.75, using 1.85 mL/min as the defining value (the defining value is one-sixth of the SD).¹⁰ A one-sided test was used with an alpha value of 0.025, a power of 90% and a sample size of 1:1 for both groups. The sample size was estimated to be 25 cases in each group by calculating the test of superiority using the PASS 2008 software. Given a potential dropout rate of 20%, we determined that 60 participants should be recruited for this study.

Endpoints and calculations

Measurements

Concentrations of Mb (17 kDa) and CK (82 kDa) will be assessed before (Cpre) and after (Cpost) the dialyser or HA adsorption device at 2, 4, 8 and 10 hours post-treatment (figure 2).

Avoiding bias

Ultrafiltration will be paused for 10 min before sampling to prevent haemoconcentration effects.

Substance clearance for HA

The substance-specific plasma clearance (Cl_p) is calculated at the sampling times for HA²⁴: Cl_p (ml/min) = (Q_b × ((1 - Hct) ÷ 100)) × ((C_pre - C_post.) ÷ C_pre), where Q_b is the blood flow of the extracorporeal circuit, Hct is the haematocrit level of the patient, C_pre is the concentrations before the HA adsorption device and C_post is the concentrations after the HA adsorption device.

Substance clearance for CVVHDF

Cl_p is calculated by multiplying the sieving coefficient (SC)²⁵ and the ultrafiltration rate (QUF)²⁶: Cl_p (ml/min) =SC×QUF. SC is calculated from SC=(2×CUF)/(C_pre+C_post). QUF is calculated from QUF=QR_post+QR_pre+Q_NETUF where CUF is the ultrafiltrate substance-specific concentration, QR_post is the post-replacement fluid flow rate, QR_pre is the pre-displacement fluid flow rate, QNETUF is the net ultrafiltration flow, C_pre is the concentrations before the dialyser and C_post is the concentrations after the dialyser.

Specimens taken

Specimens will be collected at multiple time points for analysis. At 2, 4, 8 and 10 hours after the initiation of RRT treatment, we will collect pre-dialyser, post-dialyser, pre-HA adsorbent device, post-HA adsorbent device and ultrafiltrate specimens (figure 2).

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, dialysis nursing, trial methodology and biostatistics. The DMC meeting will be held every 3 months, and we will create a procedural document for the meetings and strictly follow the document.

Data collection and statistical analysis

Upon enrolment, physicians will comprehensively collect patients’ medical history, including diagnosis, aetiology, physical examination findings, past medical history, medication history, as well as urine output, laboratory test results and vital signs (including blood pressure, heart rate, oxygen saturation, etc) within 24 hours before treatment. Following treatment initiation, vital signs, disease severity scores, ventilator usage and corresponding treatment parameters will be recorded at three time points: 0 hours, 10 hours and 24 hours. Concurrently, biological samples will be collected at 2, 4, 8 and 10 hours post-treatment. Primary endpoints include length of hospital stay (total days and ICU days), clinical outcomes at discharge and 3 months post-discharge and renal function recovery (table 1).

Continuous variables will be presented as means with SD or as medians with 25th and 75th quantiles in square brackets, depending on the results of the normality test (Shapiro–Wilk test). Categorical variables will be reported as n (%). Normally distributed variables will be analysed using the Student’s t-test, while the Mann-Whitney U test will be used for non-normally distributed variables. Categorical variables will be assessed using the X² test (two-sided), with results expressed as frequencies and percentages.

In cases where patients do not complete the 10 hour treatment due to shedding or other reasons, we will perform both intent-to-treat and per-protocol analyses to assess the efficacy of plasma clearance of Mb and CK.

Statistical analysis will be conducted using IBM SPSS version 27 (Minneapolis, USA). Graphs will be generated using GraphPad Prism 10. The significance level for all tests is set at 5% for two-tailed tests. Data were independently double-entered by two researchers, coded in Excel software and saved.

Discussion

This study is a single-center, open-label, prospective, parallel-group randomised controlled trial designed to identify extracorporeal circulatory treatment modalities capable of rapidly and effectively removing Mb, by comparing the Mb clearance efficiency of different RRT approaches.

Fast elimination of Mb is crucial due to its direct and indirect toxic effects on the kidneys.²⁷ Mb is endocytosed by renal tubular cells, where it is oxidised, generating reactive oxygen species that damage DNA and proteins. This process activates an inflammatory response and promotes vasoconstriction, exacerbating kidney injury. Mb can also be filtered by the glomerulus, precipitating in the renal tubules, and binding to Tamm–Horsfall proteins, which may form tubular casts and contribute to acute tubular obstruction.^{27 28} Elevated Mb levels have been linked to AKI and higher mortality rates.²⁹ A retrospective analysis revealed that AKI occurred in 68.9% of elderly patients with RM.³⁰

Haemofiltration is recommended for eliminating Mb in patients with myoglobinuric AKI requiring RRT.³¹ Mikkelsen and Toft were the first to report the effective elimination of Mb using CVVHDF in cases of RM.³² However, previous studies have indicated that the conventional CRRT modes are inefficient at removing Mb.³³ For example, a prospective study showed that CVVH of AV600 filter had a Mb screening coefficient of 0.28 at 2 hours of treatment and 0.11 at 24 hours of treatment.³⁴ The screening coefficient of Mb by CVVHDF with an AN69S filter was 0.21.³⁵ It has also been suggested that CVVH with a high-cutoff dialyser is superior to CVVHDF with a high-flux dialyser for Mb.¹⁰ However, older studies have reported initial albumin loss during CVVH using a high-cutoff dialyser.³⁶

Recent case reports,¹¹,¹³ retrospective studies⁸,¹⁴ and small prospective trials¹⁵ have shown that CytoSorb (Cytosorbents Corporation, Monmouth Junction, NJ, USA) is effective in removing Mb. Despite these findings, there remains a lack of high-quality randomised controlled trials to determine the efficiency of HA for Mb clearance. Therefore, this study aims to compare the effects of HA, CVVHDF combined with HA and CVVHDF alone on Mb clearance efficiency and long-term prognosis to determine the most suitable clinical treatment for patients with RM and AKI.

However, this study has several limitations. First, due to the use of different cardiopulmonary bypass circuits in the two groups, a double-blind design was not feasible, necessitating an open-label study. Second, this was a single-center study. Third, we could not determine the optimal timing for initiating RRT to maximise patient benefit. Finally, the primary endpoint included five repeated measurements, which may have contributed to variability in the results.

Ethics and dissemination

This trial is approved by the Biomedical Research Ethics Committee, West China Hospital of Sichuan University (no. 2024.1914). Written informed consent will be obtained from all participants. Data will be securely stored, and results disseminated through conferences and peer-reviewed publications.

Data availability statement

Data are available upon reasonable request.