With changes in health-care delivery systems in the last 20 years,
there has been increasing use of intravenous drugs in anesthesia,
both as adjuncts to inhaled anesthetics and in techniques that do not
include inhaled anesthetics (e.g., total intravenous anesthesia).
Unlike inhaled anesthetics, intravenous agents do not require specialized
vaporizer equipment for their delivery or expensive facilities for
the recovery and disposal of exhaled gases. Intravenous drugs such
as thiopental, etomidate, ketamine, and propofol have an onset of
anesthetic action faster than the fastest of the inhaled gaseous
agents such as desflurane and sevoflurane. Therefore, intravenous
agents are commonly used for induction of anesthesia. Recovery is
sufficiently rapid with many intravenous drugs to permit short ambulatory
(outpatient) surgical procedures. In the case of propofol, recovery
times are similar to those seen with the shortest-acting inhaled
anesthetics. The anesthetic potency of intravenous anesthetics,
including thiopental, ketamine, and propofol, is adequate to permit
their use as the sole anesthetic in short surgical procedures when
combined with nitrous oxide and opioid analgesics. Adjunctive use
of potent opioids (e.g., fentanyl and related compounds) contributes
cardiovascular stability, enhanced sedation, and profound analgesia.
Other intravenous agents such as the benzodiazepines (e.g., midazolam,
diazepam) have slower onset and recovery features and are rarely
used for induction of anesthesia. However, preanesthetic administration
of benzodiazepines can be used to provide a basal level of sedation
and amnesia when used in conjunction with other anesthetic agents.
The characteristics of selected intravenous anesthetics are summarized
in Table 15–3.