Here is the design of a clinical trial:

Official Title: Safety and Efficacy Evaluation of S (+) -Ketamine for Postoperative Acute Pain in Children in Perioperative Settings: A Multicenter, Randomized, Open-label, Active Controlled Pragmatic Clinical Trial

Included conditions:
- S-ketamine
- Esketamine
- Acute Pain
- Postoperative Pain
- Analgesia
- Hyperalgesia
- Delirium
- Depression, Anxiety
- Children

Study Armgroups:
- {'label': 'S (+)-Ketamine group', 'type': 'EXPERIMENTAL', 'description': 'Patients who undergo general anesthesia using S(+)-ketamine hydrochloride for anesthesia induction, maintenance or postoperative analgesia.', 'interventionNames': ['Drug: Conventional therapy + S (+)-Ketamine']}
- {'label': 'Control group', 'type': 'ACTIVE_COMPARATOR', 'description': 'Patients who undergo conventional therapy without S (+)-Ketamine hydrochloride injection during perioperative period.', 'interventionNames': ['Drug: Conventional therapy']}

Interventions:
- {'type': 'DRUG', 'name': 'Conventional therapy + S (+)-Ketamine', 'description': 'In principle, there are no specific restrictions on the dosage, mode of administration, timing, and compatibility of S-ketamine hydrochloride injection, but the recommended dosage is given, which is lower than the dosage specified in the instructions.\n\nRecommended use and dosage of S (+)-Ketamine:\n\n1. Intravenous injection：Bolus intravenous injection before skin incision, the dose is 0.1\\~0.25 mg/kg; Bolus intravenous injection (dose 0.1\\~0.25 mg/kg) before skin incision + continuous intravenous infusion (dose of 0.1\\~0.25 mg/kg/h) during operation; Continuous intravenous infusion after surgery with a dose of 0.02\\~0.1 mg/kg/h for 24\\~48 h.\n2. Intramuscular injection：The dose is 2\\~4 mg/kg.', 'armGroupLabels': ['S (+)-Ketamine group'], 'otherNames': ['Conventional therapy + S-ketamine', 'Conventional therapy + Esketamine']}
- {'type': 'DRUG', 'name': 'Conventional therapy', 'description': 'Receiving conventional therapy without S (+)-Ketamine hydrochloride injection. There is no restrictions in drugs, doses and incompatibility, the researchers can choose appropriate medication regimens based on clinical practice, but other NMDA receptor antagonists are not be allowed to use, such as dextromethorphan and amantadine.', 'armGroupLabels': ['Control group'], 'otherNames': ['Routine treatment']}

Primary Outcomes:
- {'measure': 'The area under the broken line of FLACC scale score', 'description': 'Only for children aged 0\\~7 years. The score of FLACC Scale is 0-10, the higher the score, the more severe the pain.', 'timeFrame': 'Hour 0-48 after surgery'}
- {'measure': 'The area under the broken line of Numerical Rating Scale score', 'description': 'Only for children aged 8\\~17years. The score of Numerical Rating Scale(NRS) is 0-10, the higher the score, the more severe the pain.', 'timeFrame': 'Hour 0-48 after surgery'}
- {'measure': 'Opioid consumption', 'description': 'Total opioid consumption(conversion to equivalent morphine)', 'timeFrame': 'Hour 0-48 after surgery'}

Please estimate the sample size based on the assumption: 
The assumptions include a power of 80%, a two-sided significance level of 0.025, and a 2:1 ratio of S(+)-ketamine hydrochloride group to the conventional group.
Power and sample size determination
        This study hypothesis that S(+)-ketamine hydrochloride could significantly reduce pain scores and/or opioid consumption within 48 h after surgery compared with routine clinical practice. Due to the lack of reference for primary endpoint, the sample size will be evaluated under different effect size assumption. Assuming power is 80%, two-sided significant level 0.025, and the ratio of S(+)-ketamine hydrochloride group to conventional group is 2:1, the sample size under different effect sizes is shown in Table 1. As shown, about 687 patients will be powerful enough to detect an effect size of 0.25. The effect size d is defined as d = (Î¼1âÎ¼2)/Ï, and Cohen (1988) gave the interpretation of d=0.25 as 25% of Ï and defines d = 0.2, 0.5, and 0.8 as small, medium, and large effect size. In our study, the used effect size of 0.25 is a relatively small effect size. By considering 4 types of surgery, we decide to include 3000 patients. Patients will stratify by age and surgical approach, and enrolled in a competitive enrollment way until the total number of research centers reached the expected sample size.Table 1The sample sizes under different effect sizesControl group(N)S(+)-ketamine hydrochloride group (N)Total subjects(N)Effect sizes581161740.5001302603900.3332294586870.25035771410710.200514102815420.167699139820970.143913182627390.1251155231034650.1111426285242780.100Sample size under different effect sizes assuming power is 80%, two-sided significant level of 0.025, and the ratio of S(+)-ketamine hydrochloride group to conventional group is 2:1