Tidal Volume Challenge During Prone position for Assessing Fluid Responsiveness. A Interventional Prospective Trial

The TVC has been proposed as novel hemodynamic test to assess fluid responsiveness in ICU patients. TVC consists in the transient increase of Tidal Volume from 6ml/kg to 8ml/kg for 1 minute. The TVC-related changes of stroke volume variation (SVV) and pulse pressure variation (PPV) are highly predictive of fluid responsiveness. The aim of the present study is to assess TVC reliability in a population of neurosurgical patients scheduled for prone or supine surgery. Brief description of TVC: 1) TVC is a transient increase in the Tidal Volume used to ventilate the patient from 6 to 8 ml/kg of predicted body weight 2) The duration is 1 minute 3) The attending anesthetist will modify the setting of the ventilation in operating room 4) The decision of administer fluids because of transient hypotension (defined as a reduction of >20% of systolic blood pressure recorded at the beginning of the operation) is the indication to perform first the TVC 5) Only the first fluid challenge will be recorded. The frequency of administration will be decided by the attending anesthetist according to the occurrence of hemodynamic instability, for the entire duration of the operation. The end-expiratory occlusion test is a hemodynamic test aiming to assess fluid responsiveness by means of a interruption of mechanical ventilation. In order to compare TVC with EEO, the EEO will be also performed in all the patients at predefined time points (before and after TVC, when the patient is ventilated with 6ml/kg and 8 lm/kg respectively).