Efficacy of Interscalen block in shoulder surgery

INTERVENTION: Control: only General anesthesia same as the intervention group Intervention 1: Intervention; general anesthesia plus low dose interscalen block with 20 ml of lidocaine 1.5%. Intervention 2: Control: only General anesthesia same as the intervention group. Intervention; general anesthesia plus low dose interscalen block with 20 ml of lidocaine 1.5% Treatment ‐ Other CONDITION: Condition 1: post operative pain. Condition 2: post operative pain. ; Other medical procedures as the cause of abnormal reaction of the patient, or of later complication, without mention of misadventure at the time of the procedure ; Surgical operation and other surgical procedures as the cause of abnormal reaction of the patient, or of later complication, without mention of misadventure at the time of the procedure Other medical procedures as the cause of abnormal reaction of the patient, or of later complication, without mention of misadventure at the time of the procedure Surgical operation and other surgical procedures as the cause of abnormal reaction of the patient, or of later complication, without mention of misadventure at the time of the procedure PRIMARY OUTCOME: Recovery parameters. Timepoint: During PACU (post anesthetic care unit) stay. Method of measurement: Visual analogue scale for pain, Two point score for patient satisfaction, Ramsey score for agitation, eyes opening by verbal stimuli. SECONDARY OUTCOME: Patient discharge. Timepoint: duration of post anesthetic care unit. Method of measurement: hours of PACU stay. INCLUSION CRITERIA: INCLUSION CRITERIA: every adult patient who are candidate for elective shoulder surgery and can tolerate a 25% decrease in lung capacities (Forced vital capacity). Exclusion criteria: infection in site of block, coagulopathy, neuropathy, history of damage to brachial plexus and allergy to local anesthetic.