Critically ill patients who require intensive care need effective analgesia and sedation to control potentially unpleasant symptoms, such as pain and anxiety. Analgesics and sedatives are also used to allow patients to tolerate nursing procedures and tracheal intubation as well as to aid mechanical ventilation. Metabolism of traditional opioids is dependent on organ function, which is abnormal among critically ill patients. The use of a score system to ensure sufficient but not excessive sedation should be mandatory. Sufentanil and remifentanil are more predictable opioids that are suitable for either sedation or analgesia in critically ill patients to achieve an adequate Ramsay score from 2 to 4.