7 Interactions involving inhalational agents

A combination of intravenous and inhalational agents to achieve a balanced anaesthetic state is common practice in modern day anaesthetic management. A recent survey of mortality in 100 000 anaesthetics revealed that the practice of combining several drugs to administer anaesthesia may be safer than the use of only one or two drugs (Cohen et al, 1988); the relative odds of dying within 7 days was 2.9 times greater when one or two anaesthetic drugs were used compared to when three or more were used. Hence, the skilful use of multiple anaesthetic agents is preferable in maintaining smooth anaesthesia and optimal patient care while reducing side-effects of the component drugs. Drug combinations may produce additive, synergistic and even antagonistic effects. Through an understanding of the pharmacodynamic interaction involving volatile anaesthetics and the pharmacokinetic processes responsible for the recovery from drug effect, optimal dosing schemes can be developed. This chapter aims to provide a review of these pharmacodynamic and pharmacokinetic principles that will allow clinicians to administer drugs to provide a more optimal anaesthetic and achieve a more rapid recovery.