Michel Struys

Strategies to Prevent Awareness

The objective of any intravenous anaesthetic drug administration is to obtain the desired clinical level of anaesthesia or sedation. Nowadays, in clinical practice, most anaesthetic drugs are given using standard dosing guidelines without applying the knowledge of their pharmacokinetics and dynamics to control their administration. Drugs are sometimes administered with the rationale: “Give some drug and observe your patient to see what happens”. The ultimate goal when administering a particular dose of a drug is to obtain the desired clinical effect, for which a specific therapeutic concentration of the drug at the site of action (= the receptor) is necessary. For most anaesthetic agents, this effect-site (or bio-phase) is not the plasma but the central nervous system and the effect-site concentration is not measurable. Therefore, the relation between the therapeutic plasma concentration and the clinical effect can be considered instead. Based on this concentration-effect relationship, it is possible to select a target plasma concentration. This target concentration can be defined as the plasma concentration which, on the basis of available information, is most likely to yield the desired effect1.