COSMIC: a core outcome set for intravenous maintenance fluid therapy trials in children.

BACKGROUND: Intravenous maintenance fluid therapy is one of the most common therapies for hospitalized children, yet the field lacks standardized outcomes to evaluate its effectiveness. Although intravenous maintenance fluid therapy has been used for nearly two centuries, existing studies show wide heterogeneity in reported endpoints, limiting the ability to perform meta-analyses and generate robust evidence. No core outcome set specific to pediatric intravenous maintenance fluid therapy currently exists, and previous initiatives have focused narrowly on fluid accumulation rather than the five components of intravenous maintenance fluid therapy prescription. This study aimed to create a comprehensive core outcome set-COSMIC-to standardize outcome reporting across research involving indications, tonicity, balanced solutions, composition, and volume of intravenous maintenance fluid therapy in children.

METHODS: The study followed the core outcome measures in effectiveness trials and core outcome set-standards for development guidelines and was prospectively registered. Four phases were undertaken: a systematic literature review (1960-2023), the extraction and classification of all reported intravenous maintenance fluid therapy-related outcomes, a two-round modified Delphi process involving international experts and non-experts, and two online consensus meetings to finalize the cost. Eligible participants included authors of intravenous maintenance fluid therapy publications and healthcare professionals. Outcomes were rated on a 9-point Likert scale, and predefined consensus thresholds determined inclusion or exclusion. Items without consensus were discussed and voted on during the final meetings.

RESULTS: The literature review identified 259 outcomes, of which 104 unique items entered Delphi round 1. Ninety participants completed round 1 and 82 round 2. Participants represented all continents. Four outcomes were deemed essential for all five PICO-based intravenous maintenance fluid therapy questions: 28-day mortality, survival free of organ dysfunction, hospital length of stay, and natremia. Additional outcomes were defined specifically for each of the five intravenous maintenance fluid therapy components, resulting in a structured and globally applicable core outcome set.

CONCLUSIONS: COSMIC is the first comprehensive core outcome set to address all core questions related to pediatric intravenous maintenance fluid therapy. It covers the full spectrum of prescription components and includes outcomes feasible across diverse healthcare settings. COSMIC adheres to the standards and provides a practical, internationally relevant framework. Its adoption will harmonize reporting, strengthen future trials, and support meta-analyses, ultimately improving evidence-based intravenous maintenance fluid therapy in children.