Here is the design of a clinical trial:

Official Title: Clinical Effectiveness of Hypertonic Sodium Lactate Infusion for Intraoperative Brain Relaxation in Patients Undergoing Scheduled Craniotomy for Supratentorial Brain Tumor Resection: Study Protocol of a Single Center Double-blind Randomized Controlled Phase II Pilot Trial

Included conditions:
- Sodium Lactate
- Intracranial Hypertension
- Brain Relaxation

Study Armgroups:
- {'label': 'Sodium Lactate', 'type': 'EXPERIMENTAL', 'description': 'Intravenous Molar Sodium Lactate is administered during the first surgical incision. The dose is 2.5mL/kg.', 'interventionNames': ['Drug: Sodium Lactate']}
- {'label': 'Mannitol 20%', 'type': 'ACTIVE_COMPARATOR', 'description': 'Intravenous mannitol 20% is administered during the first surgical incision. The dose is 5mL/kg (1g/kg).', 'interventionNames': ['Drug: Mannitol 20% Infusion']}

Interventions:
- {'type': 'DRUG', 'name': 'Sodium Lactate', 'description': 'Sodium lactate is administered at 2.5mL/kg during the first surgical incision. Neurosurgeon will evaluate the brain relaxation using a validated scale once the dura is open. A stage 1(perfectly relaxed) or 2((acceptably relaxed) is considered satisfactory.\n\nSodium Lactate and Mannitol 20% are used at an equimolar dose', 'armGroupLabels': ['Sodium Lactate']}
- {'type': 'DRUG', 'name': 'Mannitol 20% Infusion', 'description': 'Mannitol 20% is administered intravenously at a dose of 5mL/kg, so 1g/kg, during the first surgical incision. Neurosurgeon will evaluate the brain relaxation using a validated scale once the dura is open. A stage 1(perfectly relaxed) or 2((acceptably relaxed) is considered satisfactory.', 'armGroupLabels': ['Mannitol 20%']}

Primary Outcomes:
- {'measure': 'Quality of brain relaxation', 'description': 'An adequate brain relaxation is evaluated by the neurosurgeon with a stage 1 (perfectly relaxed) or 2 (acceptably relaxed) of the brain swelling score validated by Todd et al. The brain swelling score is a four-point-scale: 1 (normal brain; no swelling); 2 (minimal swelling, but acceptable); 3 (serious swelling but no specific change in management required); or 4 (severe brain swelling requiring some intervention). Todd et al. reported a significant Relationship between intracranial pressure and the brain swelling score. The brain swelling score is the consensual tool used in clinical trials to assess the clinical effectiveness of brain relaxative therapy.', 'timeFrame': 'intraoperative'}

Please estimate the sample size based on the assumption: 
Measurement accuracy of the primary outcome is set at 20% for the interventional group.
3.11. Sample size calculation
        No previous study has assessed the clinical effectiveness of hypertonic sodium lactate infusion for intraoperative brain relaxation in patients undergoing scheduled craniotomy for supratentorial brain tumor resection. Thus, no assumption can be made on the expected difference in primary outcome between groups. The sample size calculation was based on the expected measurement accuracy of the primary outcome in the interventional group.
        Seo et al reported a satisfactory brain relaxation (primary outcome) in 65% of patients who received the same dose of 20% mannitol as in the conventional group.[8] We hypothesized that the primary outcome will be at least 55% in the interventional group to consider that hypertonic lactate sodium infusion provides a clinically relevant brain relaxation for supratentorial brain tumor resection.
        A sample size of 25 patients was calculated to achieve a measurement accuracy of the primary outcome of 20% in the interventional group. In this phase II pilot study, 2 groups of patients are included to check whether the expected rate of the primary outcome is the same in the conventional group as in the study from Seo et al[8] and to provide reliable data for further studies. Thus, the inclusion of a total sample size of 50 patients (25 patients per group) is planned.