Here is the design of a clinical trial:

Official Title: The TIGHT-K STUDY. Prevention of Dysrhythmias on the Cardiac Intensive Care Unit - Does Maintenance of High-normal Serum Potassium Levels Matter

Included conditions:
- Arrhythmias, Cardiac

Study Armgroups:
- {'label': 'Relaxed control', 'type': 'EXPERIMENTAL', 'description': "Those randomised to the 'Relaxed' Group will receive potassium supplementation only if their serum potassium drops below 3.6 mEq/L.", 'interventionNames': ['Drug: Potassium']}
- {'label': 'Tight control', 'type': 'ACTIVE_COMPARATOR', 'description': "Patients randomised to the 'Tight' group will receive potassium supplementation if their serum potassium falls below 4.5 mEq/L (current practice).", 'interventionNames': ['Drug: Potassium']}

Interventions:
- {'type': 'DRUG', 'name': 'Potassium', 'description': 'The trial treatment will start when patients are admitted to the intensive care unit after their surgery. The patient will undergo regular blood investigations, as per current practice. The frequency of K+ monitoring while on ICU will be according to clinician / nursing staff preference.\n\nPotassium supplementation will be according to local hospital protocols. This can be either via an intravenous infusion or as a tablet. Patients will otherwise be treated as per current hospital protocol.', 'armGroupLabels': ['Relaxed control', 'Tight control']}

Primary Outcomes:
- {'measure': 'The presence of new onset AFACS until until hour 120 after initial admission to ICU/post-operative care facility, or discharge from hospital, whichever occurs first.', 'description': 'Episode of AFACS lasting ≥30 seconds that is both clinically detected and electrocardiographically confirmed (on either a 12-lead electrocardiogram (ECG), telemetry or Holter monitoring', 'timeFrame': 'Maximum of 5 days'}

Please estimate the sample size based on the assumption: 
Assuming a 35% and 37% AFACS incidence in the tight and relaxed groups respectively, the study aims to be 90% certain that the upper limit of a one-sided 97.5% CI (or equivalently a 95% two-sided CI) will exclude a difference in favour of tight potassium control of more than 10%. A 10% loss to follow-up is also considered.
Power calculations and sample size determination
        The sample size calculation is based on a 35% incidence of new onset AFACS, a figure derived from previous large studies and is at the lower end of the published data [1,8,23]. In the pilot study for this trial, which used a similar protocol, new onset AFACS incidence was 36.9% (95% confidence interval 29.1â44.9).
        The co-applicants (from diverse backgrounds in cardiac peri-operative medicine, intensive care medicine, cardiovascular nursing, cardiac surgery, cardiology, statistics, clinical trial management with patient and public involvement) reached consensus that a clinically relevant non-inferiority margin is 10%. Assuming a 35% and 37% AFACS incidence in the tight and relaxed groups respectively, 1514 participants are required to be 90% certain that the upper limit of a one-sided 97.5% CI (or equivalently a 95% two-sided CI) will exclude a difference in favour of tight potassium control of more than 10%. Allowing for a 10% loss to follow-up means that 1684 participants should be recruited.
        The SPIRIT schedule of trial enrolment, interventions and assessments is shown in Fig 1.
        
          10.1371/journal.pone.0296525.g001
          Fig 1
          
            SPIRIT schedule of trial enrolment, interventions and assessments [24].
            * Data recorded, but collected as part of standard care.