Organization and conduct
The study protocol is drafted in accordance with the SPIRIT (Standard Protocol Items: Recommendations for Interventional Trial) guidelines[27] (see Additional file 1) and will be reported in accordance with the CONSORT (Consolidated Standards of Reporting Trials) guidelines.[28] The protocol has been assessed by the Norwegian Medicines Agency and found not to be covered by the European Union regulation 2017/745 concerning medical devices. The trial sponsor is the Clinic of Cardiology, St. Olav’s Hospital, Trondheim University Hospital, Norway. The study is coordinated by the Norwegian Air Ambulance base in Trondheim, in cooperation with KlinForsk, Clinical Research Unit, Central Norway.
Design
The primary objective of this prospective, multicentre, randomised, parallel-group, Phase II clinical trial is to assess the efficacy of REBOA as an adjunctive treatment to ACLS in patients with OHCA. The primary endpoint is the proportion of patients that achieve ROSC with a duration of at least 20 minutes. The secondary objectives are to measure 30-day survival with good neurological status, to describe the haemodynamic physiology of aortic occlusion during ACLS, and to document any adverse events. All endpoints are summarised in Table 1. Further information on the rationale for selection of endpoints can be found in the detailed study protocol, which is available as supplemental material (see Additional file 2) and on the trial website (www.reboarrest.com).
Table 1
Primary endpoint
|
Return of spontaneous circulation
|
Secondary endpoints
|
30-day survival rate with good neurological status, defined as a modified Rankin scale score of 0–3
|
|
Difference in end-tidal CO2 measurements in the control group and the intervention group after aortic occlusion
|
|
Change in blood pressures after aortic occlusion
|
|
Left ventricular ejection fraction measured by echocardiography
|
Exploratory endpoints
|
All-cause mortality one year after randomisation
|
|
Difference in organ function
|
|
Incidence of all adverse events
|
The study will enrol 200 patients (100 in each group) over a period of 3 years. A training program will be in place for all teams.[29] Planned study sites are pre-hospital service providers in Norway, Denmark, and Sweden. Other countries may be added during the trial period.
Eligibility criteria
The study population will consist of adults with OHCA assumed to be non-traumatic in origin as determined by the on-scene physician. All patients with OHCA at a study centre will be screened for inclusion. Patients who are not included in the study will be treated according to the local ACLS guideline at the study site. The inclusion and exclusion criteria are shown in Table 2.
Table 2
Inclusion and exclusion criteria
Inclusion criteria
|
Exclusion criteria
|
Estimated age 18–80 years
|
Traumatic cardiac arrest (including strangulation, electrocution, and patients rescued from avalanches)
|
Out-of-hospital cardiac arrest
|
Accidental hypothermia with temperature < 32°C
|
Non-traumatic cardiac arrest
|
Suspected non-traumatic haemorrhage as aetiology of the arrest
|
Less than 10 minutes from time of arrest to start of basic life support or ACLS
|
Pregnancy (obvious or suspected)
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ACLS is established and can be continued
|
Suspected cerebral haemorrhage as aetiology of the arrest
|
|
Patient included to the study site’s E-CPR protocol
|
|
Other factors as decided by the treatment team (environmental factors, safety factors and others)
|
ACLS, advanced cardiovascular life support; E-CPR, extracorporeal cardiopulmonary resuscitation |
Allocation and randomisation
Patients will be allocated in a 1:1 ratio between the two study arms (Fig. 1). A permuted block randomisation method stratified by site will be used to allocate eligible patients to either the control group or the intervention group. Sealed envelopes allocating patients will be opened on-scene when a patient is eligible for randomisation. The randomisation lists will be produced by KlinForsk.[30] The random allocation sequence is generated by KlinForsk and no investigator has access to the allocation sequence.
Interventions
Control group
The control group will receive ACLS as described in the guidelines published by the ERC,[5] Norwegian Resuscitation Council,[4] and other local national guidelines. Both manual compressions and a mechanical chest compression machine are allowed. Airway management includes either endotracheal intubation or a supraglottic airway device.
Intervention group
The intervention group will receive the same ACLS treatment as the control group. Additionally, intravenous or intraosseous access must be established via the upper body. This group will also receive the intervention (REBOA) as adjunctive treatment. Two types of REBOA catheter will be used in the trial: the REBOA Medical 20-mm balloon (REBOA Medical AS, Asker, Norway) and the ER-REBOA catheter (Prytime Medical Devices Inc., Boerne, TX, USA). Other catheters may be available during the trial period and will be considered for use. All catheters will be used according to their medical device approval. Use and insertion will follow the procedure described by the manufacturer.
Outline of the REBOA procedure
A detailed description of the procedure is found in the study protocol, which is available as supplemental material and on the trial website (www.reboarrest.com).
Antiseptic wash with chlorhexidine or similar solution will be performed before cannulation of the femoral artery. This will be performed under ultrasound guidance using an out-of-plane technique with insertion of a flexible guidewire. The cannulation can be performed during the ventilation phase of CPR or during a 10-20-second pause between chest compressions. After the guidewire is placed, ultrasound images of the guidewire position will be obtained and stored. A 7-Fr introducer sheath will be inserted over the guidewire and the stylet removed. A balloon sheath will be inserted through the introducer and placed at 50 cm for a zone 1 aortic occlusion[31] (Fig. 2). Zone 1 was chosen because it has the best possible haemodynamic effect.[31, 32]
If feasible, arterial pressure measurements will be recorded from the distal tip of the catheter. After insertion and before the balloon is inflated, the left radial artery will be checked for a palpable pulse. The balloon will then be inflated with sterile 0.9% sodium chloride solution, and the radial pulse check will be repeated. If a palpable pulse is present, the location of the balloon will be accepted. If a previously present pulse disappears after balloon inflation, the balloon will be deflated, the sheath withdrawn by 5 cm, and the inflation/pulse check will be repeated. The duration of resuscitation effort will be as per the standard routine, regardless of whether REBOA is used. If ROSC is achieved, the balloon will be slowly deflated over 30 seconds and left in situ. Post-ROSC treatment will then be administered as per the standard routine.
Sample size
Data to support sample size estimation for this study are scarce. A previous prospective study of REBOA in OHCA was an uncontrolled pilot study that included 10 patients, six of whom achieved ROSC.[26] In Norway, the overall ROSC rate is 32% [1]; however, the ROSC rate is reported to be only 18% in the patients with cardiac arrest who would meet the inclusion criteria for this trial.[33] We consider an increase in ROSC from 18–36% to be clinically relevant. The sample size needed to demonstrate this with 0.80 power and a significance level of 0.05 was calculated to be 94 patients in each group[34] (Fig. 3). To account for dropouts, the sample size has been set to 100 patients per arm.
Trial oversight
Data monitoring committee
An independent data monitoring committee (DMC) will be established and function as the safety board, governed by its own charter. The DMC will review recruitment, data quality, protocol deviations, safety, and adverse events at set intervals.
Monitoring
A risk-based data monitoring procedure will be in place. This allows for clinical trial monitoring by KlinForsk that fulfils all regulatory requirements and ICH–GCP guidelines without the need for 100% source verification of the patient data. The monitoring procedure includes performing a risk analysis to identify high-risk elements of the study concerning patient safety and the primary endpoint data.
Adverse Events and Device Effects
Adverse events and device effects follow ISO 14155:2020 Clinical investigation of medical devices for human subjects — Good clinical practice. Each adverse event will be assessed for seriousness, causality, severity and expectedness. For each patient, the standard period for collecting and recording adverse events will be from randomisation and until admission to hospital, with an extension up to the 30-day follow-up visit for serious adverse events.
Summary of activities
The SPIRIT schedule (Table 3) provides a summary of activities and timeline for participants in the trial. In addition to comprehensive data capture during the pre-hospital phase for the primary objective of the trial, the study collects data on all participants admitted to hospital to assess secondary and explorative endpoints.
Table 3
SPIRIT schedule with study process and data collection during study period
|
STUDY PERIOD
|
|
Enrolment
|
Randomisation
|
Post randomisation
|
TIMEPOINT
|
-T
|
T = 0
|
Hospitalization
|
T < week 2
|
T + 30 day
|
T + 1 year
|
ENROLMENT
|
|
|
|
|
|
|
Inclusion criteria
|
X
|
|
|
|
|
|
Exclusion criteria
|
X
|
|
|
|
|
|
Allocation
|
|
X
|
|
|
|
|
Informed consent
|
|
|
X
|
X
|
|
|
INTERVENTIONS
|
|
|
|
|
|
|
Intervention or control-group
|
|
X
|
|
|
|
|
ASSESSMENTS
|
|
|
|
|
|
|
ROSC
|
|
X
|
|
|
|
|
Survival
|
|
X
|
X
|
X
|
X
|
X
|
Pre-hospital registrations
|
|
|
|
|
|
|
Utstein styled documentation
|
X
|
X
|
|
|
|
|
End-tidal CO2
|
|
X
|
|
|
|
|
REBOA-procedure related data
|
|
X
|
|
|
|
|
All relevant dispatch/procedure times
|
X
|
X
|
X
|
|
|
|
In-hospital registrations
|
|
|
|
|
|
|
Blood gas from admission
|
|
|
X
|
|
|
|
Blood sample analysis
|
|
|
X
|
X
|
|
|
Urine output
|
|
|
X
|
X
|
|
|
Complications related to REBOA
|
|
|
X
|
X
|
X
|
|
Cardiac interventions
|
|
|
X
|
X
|
X
|
|
Length of stay intensive care
|
|
|
X
|
X
|
X
|
|
Length of stay hospital
|
|
|
X
|
X
|
X
|
|
Length of invasive respiratory support
|
|
|
X
|
X
|
X
|
|
Length of renal replacement therapy
|
|
|
X
|
X
|
X
|
|
Modified Rankin scale
|
|
|
|
|
X
|
|
Adverse events
|
|
X
|
X
|
X
|
X
|
|
SPIRIT, Standard Protocol Items: Recommendations for Interventional Trials; ROSC, return of spontaneous circulation; REBOA, resuscitative endovascular balloon occlusion of the aorta |
Statistical methods
A separate detailed statistical analysis plan will be developed in cooperation with the study statisticians and published before the first interim analysis.
A group sequential design with adaptive sample size modification has been chosen to allow (1) the possibility of stopping the trial early if significant between-group differences in the primary endpoint or 30-day survival rate are found and (2) re-estimation of the sample size at the interim analyses to maintain the desired statistical power. An adaptive design has been advocated and is used in clinical research for several reasons,[35–38] including cost-effectiveness, potential need for fewer study participants, ethical arguments concerning the safety and efficacy of the trial intervention, and the possibility of mimicking real-life medical practice more than a traditional randomised controlled trial.
The primary analysis will be conducted according to the intention-to-treat principle to compare the outcome between all participants randomised to the control group and the intervention group; that is, all patients in the REBOA group will be included in the analysis regardless of actual occlusion of the aorta. Per-protocol analyses will be considered if a considerable proportion of the REBOA group deviate from the protocol, thereby undermining the validity of the intention-to-treat analysis. Deviation from the protocol could be a consequence of the patient either achieving ROSC or being declared dead prior to aortic occlusion or from the procedure being aborted for whatever reason.
The primary endpoint and other dichotomous secondary endpoints will be analysed by logistic regression or hypothesis testing. Continuous secondary endpoints (end-tidal CO2 values and blood pressure) will be analysed by regression methods.
Interim analyses
Three interim analyses will be performed, after 30, 60, and 90 patients in both study groups are included. The primary endpoint and 30-day survival will be assessed. We will consider recommending the sponsor to stop the trial after an interim analysis if there is a difference in the primary endpoint or 30-day survival between the groups with a significance level following the O’Brien-Fleming approach.[39, 40]
At the second interim analysis, we will perform a sample size calculation based on the assumption that the current difference in the primary endpoint between the two groups will persist. If the sample size needed to confirm a difference is more than three times the planned sample size (with 0.80 power and a significance level of 0.05), we will consider recommending to the sponsor that the trial be stopped due to futility.
At the final interim analysis, we will re-estimate the sample size in the event of a non-significant difference in the primary endpoint. If the estimated sample size needed to confirm a difference between the groups is > 100 but ≤ 150 in each group (with 0.80 power and a significance level of 0.05), the final sample size will be modified, and we would recommend the sponsor to continue the trial until the modified sample size is reached.