This study evaluates the safety and efficacy of an analog-sedation protocol for patients with mild to moderate brain injuries in intensive care unit. Patients are randomly divided into two groups. The Analgesia-based sedation group will receive remifentanil before the addition of a sedative(Dexmedetomidine). The conventional-based sedation group will be sedated as usual(non-protocolized). Furthermore，patients in Analgesia-based sedation group will be divided into two subgroups（Analgosedation + remifentanil bolus group and Analgosedation group） depending on whether they have received an intravenous bolus of remifentanil for procedural pain relief or not during routine clinical practice.