The placebo group will receive continuous saline NaCl 50 ml/day for 6 days as a continuous infusion (excluding additional infusion therapy). Patients will be further divided into subgroups according to OI on the day of admission to ICU. The oxygenation index (OI) PaO2/FiO2 (partial pressure of oxygen in arterial blood/ fraction of inspired oxygen) ratio in patients will be calculated daily.