Pharmacology of drugs for conscious sedation

In endoscopic monitoring and treatment of gastrointestinal disease, it is important that patients will accept repeated examination. They are less likely to do so if the procedure is remembered as distressing or uncomfortable, as is likely when it is performed under topical anaesthesia alone. The aim of conscious sedation is a lightly sedated patient, who is awake, cooperative on demand, amnesic, and free from anxiety and fear. Various drugs in low doses can be used to meet these criteria. Among these are phenothiazines, butyrophenones, barbiturate and non-barbiturate hypnotics, benzodiazepines, and the hypno-analgesic, ketamine. As benzodiazepines offer both sedative and profound amnesic and anxiolytic effects, these drugs are used for conscious sedation worldwide. Diazepam has been the 'gold standard' of sedation, but the more modern benzodiazepines, particularly midazolam, are now more commonly used. In general, benzodiazepines demonstrate a broad therapeutic range. In accordance with dose, however, sedative drugs may induce side-effects, such as drowsiness, lowering of blood pressure, and respiratory depression. In addition, some may induce more wide-ranging side-effects, such as histamine liberation and anaphylactic reactions, thrombophlebitis, and pain on injection. They may have severe drug interactions when used in combination with local anaesthetics, hypnotics and opioids. In older patients, lower doses are necessary for sedation. Sedative drugs should be administered slowly, to avoid haemodynamic and respiratory side-effects.