Rationale: Fluid overload is a common complication in children who are admitted to the pediatric intensive care for mechanical ventilation. Acute lung infection is a frequent cause for admission to the PICU and forms an uniform group with a single organ failure. In these critically ill children, fluid overload is associated with adverse outcome. Restricting the volume of fluids already in an early stage of ICU admission may prevent fluid overload during mechanical ventilation and thus improve clinical outcome. However, at the same time fluid restriction may interfere with appropriate energy and macronutrient intake that is needed for recovery.

Objective: The main goal of this pilot study is to evaluate the feasibility of a restrictive fluid management protocol and investigate its effect on the occurrence of fluid overload in mechanically ventilated children with acute infectious lung disease.

Study design: Single-center prospective randomized feasibility and pilot study in preparation of a multi-center randomized controlled trial (RCT).

Study population: Mechanically ventilated children with (suspicion of) acute infectious lung disease admitted to the pediatric intensive care unit (PICU) of the Emma Children's Hospital, Academic Medical Center, Amsterdam.

Intervention: Patients receive either liberal (control group) or a restrictive (experimental group) fluid treatment, while ensuring appropriate caloric intake.

Main study parameters/endpoints: Primary outcomes are cumulative fluid balance and body weight during the first week of mechanical ventilation. Secondary outcomes (in preparation of the larger multi-center RCT) include: mortality, duration of mechanical ventilation and oxygenation indices. To determine the feasibility, in- and exclusion rate, adherence to treatment arms, need for fluid bolus, need for diuretics and hemodynamic indices as well as energy and protein intake are studied.

Both fluid management protocols reflect a variant of current clinical practice, hence will not provide extra burden or risk to patients included in the study. Patients will be randomized to either of the fluid protocol arms on admission to the PICU (at start of mechanical ventilation). Patients included in the restrictive fluid treatment arm might have direct benefit from the study if indeed fluid overload is less common in this group.

Inclusion Criteria:

• Signed informed consent by parents or legal caretakers
• Admitted to the PICU of the Emma Children's Hospital, Academic Medical Center, Amsterdam, The Netherlands
• Intubated and mechanically ventilated, with an anticipated duration of mechanical ventilation of at least 72 hours at enrolment (as judged by investigator or pediatrician on duty)
• Patients with an acute infectious lung disease, including (suspected) viral, bacterial or fungal infection

Exclusion Criteria:

• Patients in need of a particular fluid regimen (either restrictive or liberal) due to their medical history (e.g. cardiovascular disease and/or congenital (cyanotic) heart disease)
• Use of previous and/or maintenance diuretic treatment
• Ongoing (fluid) resuscitation on admission
• Acute kidney injury with need for renal replacement therapy