Fluid Therapy in Mechanically Ventilated Critically Ill Adult Patients

Importance: Fluid therapy is ubiquitous in the intensive care unit (ICU) but carries risks, especially in mechanically ventilated patients. Contemporary global practice across dose, indication, and type is unknown. Objective: To characterize ICU fluid practices in mechanically ventilated adults. Design, Setting, and Participants: International prospective observational cohort study between April 2024 and July 2025, across 206 ICUs in 41 countries on 6 continents. Consecutive adult patients receiving invasive mechanical ventilation within 3 days of ICU admission and ventilated 24 hours or more. Exclusion criteria were age younger than 16 years and transfer under mechanical ventilation from another ICU. Exposures: Fluid volume, indication, and type after intubation. Main Outcomes and Measures: Key measures included (1) total infused volume and daily fluid balance over 7 days after intubation; (2) the indication for fluid therapy over the first 3 days after intubation; (3) the proportion of total administered fluid volume attributable to each fluid type over the first 3 days after intubation. Results: Among 2454 patients analyzed (median age, 63 years [IQR, 49-73 years]; 63.6% [1560] male), median daily fluid input peaked on day 1 at 3.0 L (IQR, 2.2-4.0 L) and declined to 2.6 L (IQR, 1.8-3.5 L) through day 6. Daily fluid balance (median, 0.9 L; IQR, 0.1-1.9 L on day 1) decreased to less than 0.3 L (IQR, -0.5 to 1.2 L) by day 3 and remained near-neutral through day 6. Maintenance and replacement fluids (to meet daily requirements and to correct ongoing losses; 31.9%) and creep fluids (to deliver medications and maintain catheter patency; 30.9%) were the primary indications, whereas resuscitation (to restore circulating blood volume; 16.0%) accounted for a smaller proportion. Isotonic balanced crystalloids (48.9%) and isotonic saline (0.9% sodium chloride) (27.0%) were common; colloids were rare (1.3%). Substantial between-site variation persisted after adjustment for case-mix. Conclusions and Relevance: In this prospective international cohort study, fluid therapy varied widely among mechanically ventilated critically ill patients, with maintenance and creep fluids-rather than resuscitation fluids-accounting for most total volume.