In ICU and operating theatre, fluid expansion is the main hemodynamic therapeutic. The objective of fluid expansion is to increase cardiac output thus arterial oxygen delivery to match patient's oxygen consumption. To date, it has been shown that all fluid expansion solutions may have side effects (hydro-electrolytic disorder, renal failure, hydro-sodium overload, etc.) that may limit their use.

Human digestive system physiologically ensures the absorption of oral water and hydration of the human body. Water is quickly absorbed by the digestive tract with a peak between 15 and 20 minutes. It has demonstrated that oral water remains the best hydration solution that have an effect on plasma volume expansion and cardiovascular system during exercise. While the cardiovascular effect of fluid expansion by saline serum is well known (venous return, preload and cardiac output), that of oral water vary in the literature depending on the physiological state of the patient and the clinical state. Oral water can change cardiac output and blood pressure through various physiological effects: increased blood volume, recruitment of splanchnic blood volume, and peripheral vasoconstriction. Usually, ICU patients have feeding through nasogastric tube.

To date, no study has studied the effect of a given amount of enteral cardiovascular system in ICU patients. The objective of this study is to describe the effect of oral water administration on the cardiovascular system of patients during the optimization and/or hemodynamic stabilization phase. The comparison of groups (water/ physiological saline) would allow us: (1) to describe the cardiovascular effects of water in the resuscitation patient, (2) to compare these cardiovascular effects with those of saline solution, (3) to have the data to design further study.

Inclusion Criteria:

• Close family member has given written consent for patient included in emergency
• Intubated-ventilated patient in controlled volume mode
• Normothermal patient (36.5-37.5°C)
• Adult patient in intensive care for whom the attending physician has decided to give fluid expansion because of acute circulatory failure (systolic blood pressure < 90 mmHg, and/or mean blood pressure < 65 mmHg, and/or the need for infusion of vasopressor amines, and/or skin mottles, and/or diuresis < 0.5 mL/kg/h for a duration of ≥ 2 hours, and/or arterial lactate level > 2 mmol/L) (21),
• Patient with a variation OF SV over 10% with PLR,
• Echogenic patient,
• Patient with a regular sinus rhythm,
• Patient with a nasogastric tube.

Exclusion Criteria:

• Person subject to a legal protection measure (curatorship, guardianship)
• Person subject to a measure to safeguard justice
• Condition contraindicating the use of the oral route,
• Patient not affiliated or not covered by the national health system,
• Pregnant, parturient or breastfeeding woman,
• Hemodynamically unstable patient (variation of more than 10% in blood pressure),
• Arrhythmia-like rhythm disorder by atrial fibrillation,
• Modification of therapies (sedation, catecholamines) during the study period,
• Modification of the ventilatory parameters.
• Heart failure
• Oedemato-ascitic insufficiency of cirrhosis
• Changes in drug doses