Fluid Management Surgical Patients in Intensive Care Unit.

maintenance fluid e.g. Ringer or Ringer acetate plus replacement fluid with crystalloids e.g. Ringer,or Ringer acetate or saline 0.9%, 500ml / 30 min. guided by ScVO2 with target value ≥ 70% versus lactate clearance (LCR) with target value ≤ 2mmol/L (or decline ≥ 10%) by the end of the study in group A \& group B respectively. Maintenance fluid without replacement will be initiated if ScVO2 or lactate value normalized.