Here is the design of a clinical trial:

Official Title: Cytokine Adsorption in Patients With Severe COVID-19 Pneumonia Requiring Extracorporeal Membrane Oxygenation - Randomized, Controlled, Open-label Intervention, Multi-center Trial (CYCOV-II-study)

Included conditions:
- Coronavirus Infection
- COVID
- SARS-CoV 2
- Respiratory Failure
- Cytokine Storm
- Extracorporeal Membrane Oxygenation

Study Armgroups:
- {'label': 'vv-ECMO + cytokine adsorption', 'type': 'EXPERIMENTAL', 'description': 'after indication of treatment with vv-ECMO in acute respiratory failure in COVID-19-disease, patients will additionally receive cytokine adsorption using a Cytosorb adsorber', 'interventionNames': ['Device: vv-ECMO + cytokine adsorption (Cytosorb adsorber)']}
- {'label': 'vv-ECMO (no cytokine adsorption)', 'type': 'OTHER', 'description': 'treatment with vv-ECMO in acute respiratory failure in COVID-19-disease (standard treatment without additional cytokine adsorption)', 'interventionNames': ['Device: vv-ECMO only (no cytokine adsorption)']}

Interventions:
- {'type': 'DEVICE', 'name': 'vv-ECMO + cytokine adsorption (Cytosorb adsorber)', 'description': 'in COVID-19-diseased vv-ECMO patients additional treatment with cytokine adsorption using a Cytosorb adsorber will be randomized (vs. control group)', 'armGroupLabels': ['vv-ECMO + cytokine adsorption']}
- {'type': 'DEVICE', 'name': 'vv-ECMO only (no cytokine adsorption)', 'description': 'COVID-19-diseased treated with vv-ECMO', 'armGroupLabels': ['vv-ECMO (no cytokine adsorption)']}

Primary Outcomes:
- {'measure': 'IL-6 reduction by 75% or more after 72 hours as compared to the baseline measurement', 'description': 'measurement of IL-6 levels in patient blood after 72 hours of cytokine adsorption (in relation to level before initiation of cytokine adsorption)', 'timeFrame': '72 hours'}
- {'measure': 'time to successful ECMO-explantation', 'description': 'time to successful ECMO-explantation within 30 days after randomization', 'timeFrame': '30 days'}

Please estimate the sample size based on the assumption: 
The statistical comparisons will be performed at a two-sided significance level alpha of 0.05. The power for detecting differences is set at 80%. No alpha correction is necessary for the individual statistical tests. The analysis for endpoint 2 will use a Fine and Gray model considering death as a competing event.
Sample size
          Sample size calculation and power considerations are based on the two primary endpoints: (1) IL-6 reduction by 75% or more after 72 hours as compared with the baseline measurement and (2) time to successful ECMO explantation within 30 days after randomisation. If there is no difference between treatment arms with respect to endpoint 1, that is, a clinically relevant IL-6 reduction, it is assumed that there is also no difference between treatment arms with respect to the clinically relevant endpoint 2. Therefore, statistical comparisons (at two-sided significance level alpha of 0.05) between treatment arms will be performed in this a priori specified sequence, that is, the statistical comparison with respect to endpoint 2 will only be performed if a difference between treatment arms with respect to endpoint 1 had been shown at a two-sided significance level alpha of 0.05. Thus, no alpha correction of the individual statistical tests is necessary.
          For sample size calculation with respect to endpoint 1, it is assumed that the probability of IL-6 reduction by 75% or more after 72 hours is 80% in the intervention group and 50% in the control group. This assumption is based on the results in the first 10 patients of the ongoing CYCOV I trial (NCT04324528 and DRKS00021300). In the intervention group, IL-6 could be reduced by 75% or more in three out of four patients; the fourth patient was considered as not representative due to pretreatment and extremely high IL-6 values at baseline. In the control group, IL-6 could be reduced by 75% or more in two out of six patients. Under this assumption, a sample size of 39 patients per treatment arm would be required to show a difference in the probability of IL-6 reduction between treatments at two-sided significance level of 0.05 with a power of 80%. This was calculated with formula â[3]â in Campbell et al33 for the Ï2 test of the hypothesis that the difference between the probabilities is equal to zero using nQuery V.8.3.1 (Module PTT0), which is adequate also for the analysis with logistic regression.34 Therefore, the 1:1 randomisation of a total of 80 patients between treatment arms is planned.
          With respect to endpoint 2, nothing is known about the expected treatment effect. It is assumed that the mortality within 30 days is high and that only a small difference between treatment arms can be expected (probability of 0.7 in the intervention group and of 0.75 in the control group). With regard to the probability of successful ECMO explantation within 30 days after randomisation, an analysis of the time to successful ECMO explantation considering death as a competing event using a Fine and Gray model will be performed. With a total of 80 patients, a difference between treatment arms can be shown at two-sided significance level of 0.05 with a power of 80 %, if the probability of successful ECMO explantation within 30 days after randomisation is 0.30 in the intervention group and 0.08 in the control group.35 This corresponds to a subdistribution HR of 4.28 and a required number of 15 patients with successful ECMO explantation.