One of the main factors to keep in mind for drug selection for the sedation of a critical patient is its foreseen duration. We have denominated by consent, short sedation that whose duration is less than 72 h. We advise the existence and application of a protocol of short sedation in all intensive care units. This protocol must guarantee the patient's analgesia at all times and its application must not increase the times of waking up and weaning of the mechanical ventilation. In this chapter the pharmacology and the comparative studies of the drugs more used for this aim are revised and the clinical recommendations are settle down. Some recommendations for specific situations are also settle down and a role is assigned to less habitual drugs such as ketamine.