Here is the design of a clinical trial:

Official Title: Paraplegia Prevention in Aortic Aneurysm Repair by Thoracoabdominal Staging With 'Minimally-Invasive Segmental Artery Coil-Embolization': A Randomized Controlled Multicentre Trial - PAPAartis

Included conditions:
- Aortic Aneurysm, Thoracoabdominal

Study Armgroups:
- {'label': 'MISACE arm', 'type': 'EXPERIMENTAL', 'description': 'Minimally-Invasive Segmental Artery Coil-Embolization\n\nMISACE procedure prior to aneurysm repair\n\nsegmental arteries are occluded with coils or plugs in one to three MISACE sessions (staged procedure)', 'interventionNames': ['Procedure: Minimally-Invasive Segmental Artery Coil-Embolization']}
- {'label': 'control arm', 'type': 'NO_INTERVENTION', 'description': 'receives treatment of aneurysm as usual: open surgical repair or endovascular repair without MISACE'}

Interventions:
- {'type': 'PROCEDURE', 'name': 'Minimally-Invasive Segmental Artery Coil-Embolization', 'description': 'During one single MISACE session 3-7 segmental arteries will be occluded. The procedure is conducted through a peripheral artery access in local anaesthesia. Microcoils or vascular plugs will be used for the occlusion itself.', 'armGroupLabels': ['MISACE arm']}

Primary Outcomes:
- {'measure': 'The primary objective is to greatly reduce incidence of ischaemic spinal cord injury and mortality.', 'description': 'Successful treatment of the aneurysm is a binary variable. All of the following criteria must be met for this composite endpoint to count as a success:\n\n* The patient is alive and without substantial spinal cord injury 30 days after treatment, and\n* the aneurysm did not rupture and has been excluded within six months of randomization. Substantial spinal cord injury will be determined with a modified Tarlov scale (see below).', 'timeFrame': '30 days after TAAA repair'}

Please estimate the sample size based on the assumption: 
Group-sequential design with two interim analyses, power of just over 87%, very few dropouts expected, and loss to follow-up not expected to be a major factor.
Sample size and recruitment
        Estimates of effect size are difficult for several reasons. Foremost, there are large discrepancies between outcome rates quoted in the literature. Moreover, the impact of recent improvements in techniques on outcomes cannot yet be quantified accurately, and finally, the effect size depends on the improvement due to the trial intervention which, in turn, depends on anatomy, postrepair management and other complex factors. Taking a random effects model of the data from large recent publications for open10 28â30 and endovascular repair,31â33 one finds an estimated incidence of 18% (95% prediction interval 15% to 23%) for open repair and a very uncertain 24% (2% to 79%) for endovascular repair. The prediction interval as opposed to the CI provides the correct bounds for what can be expected in the trial.34 The resources and time available to the study allow for the recruitment of 500 patients. Assuming success rates of 80% in the control arm and 90% in the intervention arm and using a group-sequential design35 with two interim analyses, this then implies a power of just over 87%.36 The definitions of the primary endpoint and the full analysis set imply that only very few dropouts are to be expected for this analysis and that compliance will not be a problem. The severity of the therapy and recovery times mean that loss to follow-up is not expected to be a major factor.
        The planned recruitment is between 8 and 9 patients per site per year. This is roughly half the number of patients that meet the inclusion criteria. However, slow recruitment plagues many trials and mitigation strategies have already been developed. A list of interested recruitment sites (n>10) is being collected to expand the consortium. Statistical monitoring will be used to identify reasons for screened patients not being included in the trial so that minor and clinically justified amendments to the trial protocol can address these issues, for example, through adjustments to the inclusion and exclusion criteria. Finally, a newsletter including recruitment by site will be distributed at regular intervals to spawn healthy competition among the team members.