Sedative and Anxiolytic Drugs
Sedation is best considered as a continuum between normal consciousness and general anaesthesia. The most frequently cited description of the varying levels of sedation utilized in clinical practice is that from the American Society of Anesthesiologists (Table 7.1).
TABLE 7.1
Continuum of Depth of Sedation: Definition of General Anaesthesia and Levels of Sedation/ Analgesia. American Society of Anesthesiologists, 2009
The difference between sedative and anaesthetic drugs is largely one of usage. Many anaesthetic drugs may be used at reduced dosage to produce sedation and, similarly, agents used primarily as sedatives will produce a form of anaesthesia if given in sufficiently high doses. The usual target is to produce conscious sedation, i.e. to titrate drug therapy so the patient is free of anxiety, free of pain and responding purposefully to command. In adults, this corresponds to the levels of sedation from anxiolysis to moderate sedation as described in Table 7.1.
INDICATIONS FOR THE USE OF SEDATIVE DRUGS
Sedative Drugs
Most sedative drugs may be categorized into one of three main groups: benzodiazepines, antipsychotics and α2-adrenoceptor agonists. Drugs classified more usually as intravenous anaesthetic agents, particularly propofol and ketamine, are also used as sedatives in subanaesthetic doses; the pharmacology of these drugs is discussed in Chapter 3. Similarly, remifentanil, which is used increasingly as part of a sedative regimen, is described fully in Chapter 5. Inhaled anaesthetics (see Ch 2) are also used occasionally as sedatives (e.g. sevoflurane to an end-tidal concentration of 0.3–0.5 kPa, or nitrous oxide).