Dialysis Access MalfunctionFLOWNCT05906550
Flow Dysfunction of Hemodialysis Vascular Access
A study testing Vascular access monitoring and Vascular access blood flow measurement in people with Dialysis Access Malfunction and Hemodialysis Access Failure, run by Maastricht University Medical Center at 13 sites in Netherlands.
Trial summary
The FLOW trial evaluates the follow-up of the vascular access for hemodialysis. In current clinical care, vascular access flow volume is periodically assessed to detect and treat asymptomatic stenosis. The FLOW trial will determine whether it is safe to abandon this practice of active surveillance. Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- Dialysis Access Malfunction, Hemodialysis Access Failure, Hemodialysis Fistula Thrombosis
- What is being tested?
- Vascular access monitoring and Vascular access blood flow measurement
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 375 participants
- Where
- 13 sitesNetherlands
- Study dates
- 1 Nov 2021to 31 Dec 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Who may be able to join
- Adult patients aged 18 years or older.
- End-stage renal disease with unlikely recovery of kidney function according to the attending nephrologist.
- Arteriovenous fistula or arteriovenous graft as hemodialysis vascular access that fulfills both of the following criteria at the time of trial enrollment:
- Vascular access flow volume of at least 500mL/min; and
- Functional vascular access: the vascular access was cannulated with 2 needles and achieved the prescribed access circuit flow in at least 6 dialysis sessions over the past 30 days. Patients who have single needle hemodialysis for reasons other than vascular access dysfunction (e.g. for nocturnal hemodialysis) but who can be cannulated with 2 needles for flow measurements and fulfill the other requirements for a functional vascular access can be enrolled as well.
- Planning to remain in one of the participating dialysis centers for at least 1 year.
Who cannot join
- Arteriovenous fistulas with multiple venous outflow paths upstream of the cannulation sites, that are not suitable for flow volume measurements using ultrasound dilution (e.g. Gracz fistulas and Ellipsys or WavelinQ endovascular fistulas).
- Home hemodialysis.
- Thrombosis of the current vascular access in the past year.
- Planned access-related intervention.
- Living donor kidney transplantation, switch to peritoneal dialysis, or switch to home hemodialysis planned within 6 months.
- Life expectancy of less than 6 months, in the opinion of the attending nephrologist.
- Unable to provide informed consent.
Trial locations and contacts
13 sites in 1 country.
13 sites in 1 country
Netherlands13 sites
Diapriva - Dialyse Centrum Amsterdam
Amsterdam
OLVG
Amsterdam
Deventer Ziekenhuis
Deventer
Medisch Spectrum Twente
Enschede
Spaarne Gasthuis
Haarlem
Zuyderland Medisch Centrum
Heerlen
Leids Universitair Medisch Centrum
Leiden
Maastricht UMC+
Maastricht
Bravis Ziekenhuis
Roosendaal
Franciscus Gasthuis & Vlietland
Rotterdam
Universitair Medisch Centrum Utrecht
Utrecht
Maxima Medisch Centrum
Veldhoven
Isala Klinieken
Zwolle
About this study
Official title: Flow Dysfunction of Hemodialysis Vascular Access: a Randomized Controlled Trial on the Effectiveness of Surveillance of Arteriovenous Fistulas and Grafts
The FLOW trial evaluates the follow-up of the vascular access for hemodialysis. In current clinical care, vascular access flow volume is periodically assessed to detect and treat asymptomatic stenosis. The FLOW trial will determine whether it is safe to abandon this practice of active surveillance. Vascular access stenosis will then be treated only when clinical problems of flow dysfunction occur during hemodialysis. The investigators expect that the intervention rate and medical costs will be reduced by 40% when correction of vascular access stenosis is triggered by clinically apparent access dysfunction rather than asymptomatic flow reduction.
Read the detailed description
Study design: Multicenter randomized controlled trial with 375 patients. Patients will be followed up for 2 to 3 years. The trial is powered to detect a reduction in the intervention rate of 0.25 per year between study groups in a superiority analysis (this is associated with cost savings of 1 million euros per year in the Netherlands). Subgroup analyses of arteriovenous fistulas and grafts and of successful and failed interventions will be done.
On 25-02-2025, the sample size was reduced from 417 to 375 patients because updated calculations based on actual event and loss to follow-up rates in the trial population showed sufficient power to detect the prespecified clinically relevant difference.
Study population: Chronic hemodialysis patients with a functioning arteriovenous fistula or graft.
Intervention group: Patients are referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present. These include physical signs, problems during dialysis, or an unexplained, sustained fall in dialysis adequacy.
Control group: Monthly surveillance of vascular access blood flow volume by ultrasound dilution measurements during hemodialysis sessions. Patients will be referred for correction of the underlying stenosis at an access flow volume <500mL/min, or when clinical signs of flow dysfunction are present.
- Conditions
- Dialysis Access Malfunction, Hemodialysis Access Failure, Hemodialysis Fistula Thrombosis, Vascular Access Malfunction
- Being tested
- Vascular access monitoring, Vascular access blood flow measurement
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Vascular access monitoringDiagnostic test
Patients are referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present. These include physical signs, problems during dialysis, or an unexplained, sustained fall in dialysis adequacy. Patients will be referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present.
Vascular access blood flow measurementDiagnostic test
Monthly surveillance of vascular access blood flow volume by ultrasound dilution measurements during hemodialysis sessions. Patients will be referred for correction of the underlying stenosis at an access flow volume <500mL/min.
| Study group | Role | What they receive |
|---|---|---|
| Intervention group | Experimental | Patients are referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present. These include physical signs, problems during dialysis, or an unexplained, sustained fall in dialysis adequacy. Receives: Diagnostic Test: Vascular access monitoring |
| Control group | Active comparator | Monthly surveillance of vascular access blood flow volume by ultrasound dilution measurements during hemodialysis sessions. Patients will be referred for correction of the underlying stenosis at an access flow volume <500mL/min, or when clinical signs of flow dysfunction are present. Receives: Diagnostic Test: Vascular access monitoring; Diagnostic Test: Vascular access blood flow measurement |
What is being measured
The primary outcome is the main question the study is designed to answer.
Access-related intervention rate
The number of interventions required for each patient-year of hemodialysis treatment
Measured: Variable follow-up time of 2-3 years
Secondary outcomes (15)
Access-related complications per patient-year (1)
Clavien-Dindo grade 2 complications (requiring pharmacological treatment)
Measured: Variable follow-up time of 2-3 years
Access-related complications per patient-year (2)
Access-related serious adverse events (Clavien-Dindo grade 4 and 5 complications, and vascular access thrombosis)
Measured: Variable follow-up time of 2-3 years
All-cause mortality
All-cause mortality
Measured: Variable follow-up time of 2-3 years
Access-related health care costs (1)
Medical Consumption Questionnaire
Measured: Every 3 months for 2-3 years from randomization (variable follow-up time)
Access-related health care costs (2)
Productivity Cost Questionnaire
Measured: Every 3 months for 2-3 years from randomization (variable follow-up time)
Patient-reported outcome measures (1)
SF-VAQ (Short-Form Vascular Access Questionnaire)
Measured: Every 3 months for 2-3 years from randomization (variable follow-up time)
Patient-reported outcome measures (2)
EQ-5D-5L
Measured: Every 3 months for 2-3 years from randomization (variable follow-up time)
Quality of the surveillance program (1)
Repeatability and reproducibility of vascular access flow volume measurements
Measured: Variable follow-up time of 2-3 years
Quality of the surveillance program (2)
Diagnostic accuracy of vascular access flow volume measurements to predict clinical signs of flow dysfunction and access thrombosis within 1 month in the intervention group
Measured: Variable follow-up time of 2-3 years
Quality of the surveillance program (3)
The percentage of vascular access balloon angioplasties resulting in technical success (residual stenosis <30%) and clinical success (increase in flow volume to >500mL/min, restoration of vascular access function and resolution of any clinical signs of flow dysfunction)
Measured: Variable follow-up time of 2-3 years
Quality of the surveillance program (4)
Vascular access patency after balloon angioplasty
Measured: Variable follow-up time of 2-3 years
Primary patency
This outcome measure will be registered for explanatory analyses
Measured: Variable follow-up time of 2-3 years
Assisted primary patency
This outcome measure will be registered for explanatory analyses
Measured: Variable follow-up time of 2-3 years
Secondary patency
This outcome measure will be registered for explanatory analyses
Measured: Variable follow-up time of 2-3 years
The number of hemodialysis sessions with cannulation difficulties
This outcome measure will be registered for explanatory analyses
Measured: Variable follow-up time of 2-3 years
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted18 Jun 2023
- Study start1 Nov 2021
- Primary completion31 Dec 2025
- Study completion31 Dec 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Dialysis Access MalfunctionStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Double blind randomized controlled trial with hybrid parallel-crossover design
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 375 participants (actual)
Sponsor and investigators
- Lead sponsor
- Maastricht University Medical Center
- Sponsor type
- University, hospital or other
- Collaborators
- ZonMw: The Netherlands Organisation for Health Research and Development
- Responsible party
- Sponsor
- Investigators
- Maarten G Snoeijs, MD PhD, Principal investigator, Maastricht University Medical Center
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT05906550
- Sponsor's protocol ID
- NL75845.068.20
- Other IDs
- NL9165
- Acronym
- FLOW
- Status last verified
- Feb 2026
- First submitted
- 23 May 2023
- Last updated
- 5 Feb 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: The size of the data collection is unknown but includes physical examination forms, Transonic flow measurement curves, angiography videos, and intervention notes. The following end products will be made available for further research and verification: data documentation; documentation of the research process, including documentation of all participants; audiovisual material / images; several versions of processed data; raw data.
Study at a glance
From the registry record, last updated by the sponsor on 5 Feb 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Flow Dysfunction of Hemodialysis Vascular Access: a Randomized Controlled Trial on the Effectiveness of Surveillance of Arteriovenous Fistulas and Grafts
- ClinicalTrials.gov ID
- NCT05906550
- Acronym / sponsor ID
- FLOW / NL75845.068.20
- Conditions
- Dialysis Access Malfunction, Hemodialysis Access Failure, Hemodialysis Fistula Thrombosis, Vascular Access Malfunction
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 375 participants (actual)
- Lead sponsor
- Maastricht University Medical CenterUniversity, hospital or other
- Collaborators
- ZonMw: The Netherlands Organisation for Health Research and Development
- Study start
- 1 Nov 2021 (actual)
- Primary completion
- 31 Dec 2025 (actual)
- Study completion
- 31 Dec 2025 (actual)
- First posted
- 18 Jun 2023 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The FLOW trial evaluates the follow-up of the vascular access for hemodialysis. In current clinical care, vascular access flow volume is periodically assessed to detect and treat asymptomatic stenosis. The FLOW trial will determine whether it is safe to abandon this practice of active surveillance. Vascular access stenosis will then be treated only when clinical problems of flow dysfunction occur during hemodialysis. The investigators expect that the intervention rate and medical costs will be reduced by 40% when correction of vascular access stenosis is triggered by clinically apparent access dysfunction rather than asymptomatic flow reduction.
Detailed description
Study design: Multicenter randomized controlled trial with 375 patients. Patients will be followed up for 2 to 3 years. The trial is powered to detect a reduction in the intervention rate of 0.25 per year between study groups in a superiority analysis (this is associated with cost savings of 1 million euros per year in the Netherlands). Subgroup analyses of arteriovenous fistulas and grafts and of successful and failed interventions will be done.
On 25-02-2025, the sample size was reduced from 417 to 375 patients because updated calculations based on actual event and loss to follow-up rates in the trial population showed sufficient power to detect the prespecified clinically relevant difference.
Study population: Chronic hemodialysis patients with a functioning arteriovenous fistula or graft.
Intervention group: Patients are referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present. These include physical signs, problems during dialysis, or an unexplained, sustained fall in dialysis adequacy.
Control group: Monthly surveillance of vascular access blood flow volume by ultrasound dilution measurements during hemodialysis sessions. Patients will be referred for correction of the underlying stenosis at an access flow volume <500mL/min, or when clinical signs of flow dysfunction are present.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 2
- Model description
- Double blind randomized controlled trial with hybrid parallel-crossover design
| Arm | Type | Receives |
|---|---|---|
| Intervention group | Experimental | Diagnostic Test: Vascular access monitoringPatients are referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present. These include physical signs, problems during dialysis, or an unexplained, sustained fall in dialysis adequacy. |
| Control group | Active comparator | Diagnostic Test: Vascular access monitoring, Diagnostic Test: Vascular access blood flow measurementMonthly surveillance of vascular access blood flow volume by ultrasound dilution measurements during hemodialysis sessions. Patients will be referred for correction of the underlying stenosis at an access flow volume <500mL/min, or when clinical signs of flow dysfunction are present. |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (6 listed)
- Adult patients aged 18 years or older.
- End-stage renal disease with unlikely recovery of kidney function according to the attending nephrologist.
- Arteriovenous fistula or arteriovenous graft as hemodialysis vascular access that fulfills both of the following criteria at the time of trial enrollment:
- Planning to remain in one of the participating dialysis centers for at least 1 year.
Key exclusion criteria (7 listed)
- Arteriovenous fistulas with multiple venous outflow paths upstream of the cannulation sites, that are not suitable for flow volume measurements using ultrasound dilution (e.g. Gracz fistulas and Ellipsys or WavelinQ endovascular fistulas).
- Home hemodialysis.
- Thrombosis of the current vascular access in the past year.
- Planned access-related intervention.
- Living donor kidney transplantation, switch to peritoneal dialysis, or switch to home hemodialysis planned within 6 months.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Vascular access monitoringPatients are referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present. These include physical signs, problems during dialysis, or an unexplained, sustained fall in dialysis adequacy. Patients will be referred for correction of the underlying stenosis when clinical signs of flow dysfunction are present. | Diagnostic test | Control group, Intervention group |
| Vascular access blood flow measurementMonthly surveillance of vascular access blood flow volume by ultrasound dilution measurements during hemodialysis sessions. Patients will be referred for correction of the underlying stenosis at an access flow volume <500mL/min. | Diagnostic test | Control group |
Primary outcome
Access-related intervention rate
Time frame: Variable follow-up time of 2-3 years
The number of interventions required for each patient-year of hemodialysis treatment
15 secondary outcomes
Access-related complications per patient-year (1)
Time frame: Variable follow-up time of 2-3 years
Access-related complications per patient-year (2)
Time frame: Variable follow-up time of 2-3 years
All-cause mortality
Time frame: Variable follow-up time of 2-3 years
Access-related health care costs (1)
Time frame: Every 3 months for 2-3 years from randomization (variable follow-up time)
Access-related health care costs (2)
Time frame: Every 3 months for 2-3 years from randomization (variable follow-up time)
Patient-reported outcome measures (1)
Time frame: Every 3 months for 2-3 years from randomization (variable follow-up time)
Patient-reported outcome measures (2)
Time frame: Every 3 months for 2-3 years from randomization (variable follow-up time)
Quality of the surveillance program (1)
Time frame: Variable follow-up time of 2-3 years
Quality of the surveillance program (2)
Time frame: Variable follow-up time of 2-3 years
Quality of the surveillance program (3)
Time frame: Variable follow-up time of 2-3 years
Quality of the surveillance program (4)
Time frame: Variable follow-up time of 2-3 years
Primary patency
Time frame: Variable follow-up time of 2-3 years
Assisted primary patency
Time frame: Variable follow-up time of 2-3 years
Secondary patency
Time frame: Variable follow-up time of 2-3 years
The number of hemodialysis sessions with cannulation difficulties
Time frame: Variable follow-up time of 2-3 years
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 5 Feb 2026.
- Individual participant dataSharing planned: Yes. The size of the data collection is unknown but includes physical examination forms, Transonic flow measurement curves, angiography videos, and intervention notes. The following end products will be made available for further research and verification: data documentation; documentation of the research process, including documentation of all participants; audiovisual material / images; several versions of processed data; raw data.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Maarten G Snoeijs, MD PhD principal investigator
Maastricht University Medical Center
13 sites in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Vascular access monitoring and Vascular access blood flow measurement in people with Dialysis Access Malfunction and Hemodialysis Access Failure, run by Maastricht University Medical Center at 13 sites in Netherlands.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 6 inclusion and 7 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 5 Feb 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 13 sites in Netherlands. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Access-related intervention rate (time frame: Variable follow-up time of 2-3 years). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 5 Feb 2026.