MAAS Method (Minimal-flow Auto-control Anesthesia System) for the Administration of Desflurane and Sevoflurane

"Phase sevo 1)~* Moment 1 (M1): from OTI until end-tidal sevoflurane (etSEVO%) exceeds ettSEVO% by 10%. Deliver of sevoflurane to the system (SEVOdel) carried out by completely opening sevoflurane vaporizer (8%).~* M2) once etSEVO% surpass ettSEVO% by 10%: turn off sevoflurane vaporizer and observe the progressive fall etSEVO%. When etSEVO% approaches ettSEVO% (0.1-0.2 points above ettSEVO%), the investigators will turn on the sevoflurane vaporizer following the MAAS method to ensure stability in inspired and expired concentrations of sevoflurane.~Phase sevo 2) Objective: to maintain etSEVO% = ettSEVO% ±5% When the etSEVO% increases above the mentioned levels \>\> reduce SEVOdel by 0.25-0.5%.~When the etSEVO% decreases below the mentioned levels\>\> increase SEVOdel by 0.25-0.5%."

The investigators will close the sevoflurane vaporizer and will start the administration of Propofol in intravenous perfusion; the investigators will then open the FGF sequentially at 2\>5\>10 liters per minute (LPM), until the etSEVO% is \<0.2 MAC.

"Phase desflu 1)~* Moment 1 (M1): from the end of Washout phase until end-tidal desflurane (etDESFLU%) exceeds ettDESFLU% by 10%. Deliver of desflurane to the system (DESFLUdel) carried out by completely opening the desflurane vaporizer (18%).~* M2) once etDESFLU% surpass ettDESFLU% by 20%: turn off the desflurane vaporizer and observe the progressive fall etDESFLU%. When etDESFLU% approaches ettDESFLU% (0.8-1.2 points above ettDESFLU%), the investigators will turn on the desflurane vaporizer following the MAAS method to ensure stability in inspired and expired concentrations of desflurane.~Phase desflu 2) Objective: to maintain etDESFLU% = ettDESFLU% ±5% When the etDESFLU% increases above the mentioned levels \>\> reduce DESFLUdel by 0.25-0.5%.~When the etDESFLU% decreases below the mentioned levels\>\> increase DESFLUdel by 0.25-0.5%."

"From the end of Phase desflu 2 until the end of the intervention. Maintenance of anesthesia with desflurane following the principles of MAAS Method.~Between 15-20 minutes before the end of the intervention, the investigators will stop the administration of desflurane, registering the time until the reaching etDESFLU% \< 0.2 MAC."