Fluid overload is a frequent and harmful complication in critically ill, mechanically ventilated children, contributing to prolonged ventilation, organ dysfunction, and increased mortality. Standard maintenance fluid therapy based on the Holliday–Segar formula often overestimates requirements in this population due to reduced insensible losses, systemic inflammation, non-osmotic ADH release, and impaired fluid elimination. Although conservative fluid strategies have shown benefits in adults and limited paediatric cohorts, optimal maintenance fluid management in critically ill children remains inadequately defined.

This open-label, randomized controlled trial will compare standard maintenance fluids (80–90% of Holliday–Segar) versus conservative maintenance fluids (50–60%) in hemodynamically stable, mechanically ventilated children aged 1–18 years admitted to the PICU of Kalawati Saran Children’s Hospital. Randomization will use variable permuted block sizes (2, 4, 6) with allocation concealment via opaque, sequentially numbered envelopes.

The primary outcome is fluid overload percentage (FO%) at Day 7 or extubation, calculated as:
 [(Fluid Intake – Fluid Output) / Admission Weight] × 100.
Secondary outcomes include the proportion developing FO% more than 10%, Ventilator-Free Days, PICU-Free Days at 28 days, and PELOD-2 scores over 7 days. All fluid inputs (IV fluids, boluses, blood products, drug diluents, feeds) and outputs (urine, GI aspirates, surgical drains) will be recorded. Nutrition will follow ASPEN 2017 paediatric guidelines.

Safety triggers permit deviation from assigned fluid strategy if hemodynamic instability occurs. A sample size of 70 (35 per arm) was selected based on feasibility. Data will be analysed using t-test/Mann–Whitney U for continuous variables and chi-square/Fisher’s exact test for categorical variables.

The study aims to generate paediatric-specific evidence to optimize maintenance fluid strategies and reduce fluid overload in critically ill ventilated children.