Intrathecal Magnesium for Same-day-surgery

5% hyperbaric lidocaine has lost its usefulness for same-day-surgery (SDS) anaesthesia because it has been blamed responsible for the so-called transitory neurological syndrome (TNS). This entity appears particularly in patients operated on lithotomy and knee arthroscopy position and obese patients. It is a benign, moderately painful (grade 3-4 out of 10) and self-limited in time, but disturbing enough to be avoided in same-day-surgery cases. Other local anesthetics are not competitive with general anesthesia in time to be discharged home from the SDS unit. The magnesium ion is well-known for its protective properties on cells with electrical activity. The objective is to confirm that the magnesium ion added as adjuvant to intrathecal (IT) lidocaine may antagonize TNS incidence. If this hypothesis could be confirmed, the practical and theoretical consequences would be far-reaching. The method to achieve our objective would be a double-blinded randomized clinical trial considering two groups of intrathecal lidocaine: with and without added IT magnesium.