Median Sevoflurane Concentration for Hypotension Between Young and Elderlypatients: Adaptive Clinical Trial

Median Sevoflurane Concentration for Hypotension Between Young and Elderlypatients: Adaptive Clinical Trial

Comparison of Median Alveolar Sevoflurane Concentration for Hypotension Between Young and Elderly Patients: Adaptive Clinical Trial

Two arms: elder group, young group. Dixon's up and down adaptive methodology for ED50. Executed after Anesthesia induction for 10min without touching the patient after starting mechanical ventilation.

This adaptive clinical trial will vary target end tidal sevoflurane by 0.4, then by 0.2 and by 0.1 thereafter in order to minimize sample size.

Adaptive up and down methodology. Anesthesia will be induced using etomidate, rocuronium and remifentanil. After intubation and mechanical ventilation, a high fresh gas flow and variable vaporizer target concentration will be used to stabilize the patient's target end tidal sevoflurane in less than two minutes. Each patient's target end tidal sevoflurane is determined by the concentration used in the previous patient of the same group and by the incidence of hypotension. If the previous patient suffered hypotension, next patient's target concentration will drop. If there was no hypotension, next patient's target concentration will rise. The first patient on each group will be 2%. Target end tidal will vary 0.4% until the first crossover, then drop to 0.2% until the second crossover and will vary 0.1% thereafter.

Participant will not know allocation (sevoflurane concentration) and will be under general anesthesia

Inclusion Criteria: Understands experiment, is voluntary, signs informed consent; Does not take medication that influences arterial pressure; Normotensive. Exclusion Criteria: Received any medication that influences arterial pressure before experiment;