CReep and Maintenance flUid Sodium Chloride ADministration rEduction in cRitically Ill adultS

Inclusion criteria 1. At least 18 years of age 2. Patients who are admitted to the ICU for medical or surgical emergencies, including complications of elective surgery 3. The treating physician expects the patient will still require ICU care in two days, indicating a severe or complex condition at enrollment 4. The patient is expected to receive at least 300 mL of fluid creep or at least 1 liter of maintenance fluid according to study-arm during the first 24h after inclusion Exclusion Criteria: 1. A contraindication to hypotonic fluids due to risk of brain edema (including traumatic brain injury, major stroke, intracranial/subarachnoid hemorrhage, meningoencephalitis, intracranial malignancies…), with the timing and clinical judgment left at the discretion of the treating physician. 2. Hyponatremia below 131 mmol/L at admission 3. Admission solely for treatment of fluid accumulation due to cardiac decompensation, without other acute medical conditions requiring ICU-level care. Note: Patients with heart failure as a comorbidity, those on chronic diuretic therapy, or presenting with edema/bilateral lung infiltrates due to other conditions (e.g., sepsis, pneumonia) are not excluded. 4. Patient's death is deemed imminent and inevitable, admission for palliative care or admission solely for organ donation 5. Patient receiving chronic renal replacement therapy 6. Patients referred after a stay of more than 24 hours in another ICU 7. Patients randomized in CRUSADERS before 8. Patient is co-enrolled in an unapproved concomitant ICU-trial or in any trial with an intervention that affects fluid administration or fluid balance Additional exclusion criteria for the SALADIN nested substudy 1. Patients expected to require renal replacement therapy within 24 hours 2. Increased insensible fluid losses: burns, extensive wounds or skin defects or massive diarrhea,… 3. Patients without a urine catheter 4. Patients expected to require bladder irrigation within 24 hours 5. Patients on chronic treatment with loop or thiazide diuretics (including combination preparations)