Here is the design of a clinical trial:

Official Title: Impact of Prone Position in Patients Under Spontaneous Breathing on Intubation or Non-invasive Ventilation or Death Incidence During COVID-19 Acute Respiratory Distress

Included conditions:
- COVID19
- Oxygen Therapy
- Prone Position
- Spontaneous Ventilation
- Respiratory Distress Syndrome

Study Armgroups:
- {'label': 'Conventional positioning', 'type': 'NO_INTERVENTION', 'description': 'semi-seated in bed or seated in a chair during the day. The prone position is not allowed during the day (it is allowed at night if it is the natural sleeping position).'}
- {'label': 'Interventional positioning : prone position', 'type': 'EXPERIMENTAL', 'description': 'Two sessions minimum of prone position over the day. With a total objective of at least 2h30 of cumulated duration over the day. The objective is to spend as much time as possible in prone position if the patient tolerates it well.', 'interventionNames': ['Other: prone position']}

Interventions:
- {'type': 'OTHER', 'name': 'prone position', 'description': 'Two sessions minimum of prone position over the day. With a total objective of at least 2h30 of cumulated duration over the day. The objective is to spend as much time as possible in prone position if the patient tolerates it well.', 'armGroupLabels': ['Interventional positioning : prone position']}

Primary Outcomes:
- {'measure': 'Percent age of patients who will have endotracheal intubation or non-invasive ventilation at two pressure levels and/or die, in each of the 2 randomization groups.', 'description': 'To show that PP in spontaneously ventilation patients could reduce the risk of acquiring the following event (composite endpoint):\n\n* Endotracheal intubation\n* Or non-invasive ventilation (NIV) with two pressure levels\n* And/or death', 'timeFrame': 'Day 28'}

Please estimate the sample size based on the assumption: 
A two-sided alpha risk is set at 5%, statistical power at 80%, and a lost to follow-up rate of less than 2%.
Sample size
        There are few studies in COVID-19 patients in medical wards comparing awake prone position to usual care. In two small studies in hypoxaemic COVID-19 patients in medical wards, the rate of intubation was 0% and mortality was 0% or 3.7% in both groups (prone position and usual care).21 35 In a small, cluster randomised study, the rate of transfer to ICU was 0% in the usual care group and 10% in the prone position group.26 In a randomised controlled trial on prone position versus standard of care, the rate of intubation was 13% in both groups and the rate of mortality was 6.7% in prone position vs 10% in usual care group.5
        In the above small-sized studies in non-severe COVID-19 patients hospitalised in medical wards, the most useful information was that patients were frequently capable to self-prone positioning. Overall, data on intubation rate in non-severely hypoxaemic COVID-19 patients are scarce. Therefore, despite the progression of the pandemic since the beginning of our project, the calculation of a necessary number of subjects remains highly speculative.
        We initially planned to enrol 400 patients (200 in each group) assuming a global treatment failure rate of 15%, an 8% difference in treatment failure rate between groups and a lost to follow-up rate of 10%. In the beginning of October 2021, while the spread of COVID-19 was dramatically slowing down, we anticipated that the targeted number of 400 patients would be difficult to reach in a reasonable time. Therefore, we asked the data manager to let us know the lost to follow-up rate in the 232 included patients on 1 October 2021, for whom outcomes were available in the centralised CRF and to estimate the global rate of treatment failure (without unblinding the group of randomisation), as to recalculate a target number of patients to enrol. Lost to follow-up rate was 0% and the global rate of treatment failure was 12.5%, that is, both lower than anticipated. Based on these new data, we hypothesised that the treatment failure rate will be 4% and 14% in the intervention and usual care group, respectively. With a two-sided alpha risk set at 5% and a statistical power of 80%, 134 patients in each group were needed to demonstrate a difference of 10% in treatment failure rate (use of noninvasive ventilation, intubation or death) between the two groups with a lost to follow-up rate of less than 2%. This calculation slightly overestimates the necessary sample size because it does not consider the stratified design. This new enrolment target of 268 patients was approved by the ethics committee on 9 November 2021.