The effect of ultrasound-guided interscalene brachial plexus block on post-hepatectomy shoulder pain: a prospective, randomized, double-blind, controlled study

INTERVENTION: Control group(C group):ultrasound‐guided interscalene brachial plexus block;Ropivacaine group(R group):ultrasound‐guided interscalene brachial plexus block; CONDITION: post‐hepatectomy shoulder pain PRIMARY OUTCOME: ?VAS; SECONDARY OUTCOME: the time to the first analgesic request;Assessment of respiratory function before and 30min after block;Number of patients who did not require analgesics within 48h after surgery;Total consumption of analgesics ( for shoulder pain only ) and adverse reactions;Pain score (before block, 15min after block, 24h and 48h after operation);Complications related to the procedure;Patient's satisfaction; INCLUSION CRITERIA: patients with age between 18 and 75 years, American Society of Anesthesiologists status ? to ?, undergoing hepatectomy,BMI<35