Intravenous Anesthetics

INTRAVENOUS ANESTHETICS

Intravenous nonopioid anesthetics play an important role in the practice of modern anesthesia. They are widely used to facilitate rapid induction of anesthesia and have replaced inhalation as the preferred method of anesthesia induction in most settings except for pediatric anesthesia. Intravenous agents are also commonly used to provide sedation during monitored anesthesia care and for patients in intensive care (ICU) settings. With the introduction of propofol, intravenous anesthesia also became an option for the maintenance of anesthesia. However, similar to the inhaled agents, the currently avail-able intravenous anesthetics are not ideal anesthetic drugs in the sense of producing all and only the five desired effects (unconsciousness, amnesia, analgesia, inhibition of autonomic reflexes, and skeletal muscle relaxation). Therefore, balanced anesthesia with multiple drugs (inhaled anesthetics, sedative-hypnotics, opioids, neuromuscular blocking drugs) is generally used to minimize unwanted side effects.

The intravenous anesthetics used for induction of general anes-thesia are lipophilic and preferentially partition into highly per-fused lipophilic tissues (brain, spinal cord), which accounts for their rapid onset of action. Regardless of the extent and speed of their metabolism, termination of the effect of a single bolus is determined by redistribution of the drug into less perfused and inactive tissues such as skeletal muscle and fat. Thus, all drugs used for induction of anesthesia have a similar duration of action when administered as a single bolus dose despite significant differences in their metabolism. Figure 25–6 shows the chemical structures of common clinically used intravenous anesthetics. Table 25–2 lists pharmacokinetic properties of these and other intravenous agents.