Remifentanil has been approved by the FDA for continuation as an analgesic into the immediate postoperative period in adult patients under the direct supervision of an anesthesia practitioner in a postoperative anesthesia care unit or intensive care setting. However, National Medical Products Administration(NMPA) did not approve this indication. Therefore, the purpose of this study is to confirm the efficacy and safety of remifentanil in the analgesic therapy of critical ill patients in China.