The recent advent of computer-assisted IV drug administration has made more practical the maintenance of anesthesia with anesthetics with relatively short half-lives (e.g., propofol and short-acting phenylpiperidine opioids).The technique called total intravenous anesthesia (TIVA) is done with short-acting drugs so that rapid recovery occurs even after long infusions. The loading and maintenance doses of each agent can be programmed by taking their individual pharmacokinetic profiles into consideration. Thus, dosage is automatically adjusted for factors that may alter drug distribution, parameters controlling drug clearance, and the duration of the procedure, to maintain a plasma level that is just adequate for the appropriate depth of anesthesia. Many practitioners, however, still prefer to titrate the infusion of intravenous drugs to effect without the use of computer programming.
The shorter-acting drugs seem to have increasing applications in outpatient surgery, which now accounts for nearly 60% of all elective procedures, and for minor inpatient procedures (e.g., wound repair, bronchoscopy, angiography). Patients generally receive lower doses of drugs so that operative procedures are tolerable, avoiding the substantial depression of cardiorespiratory systems that may occur with the higher doses required for hypnosis. Sedative doses of benzodiazepines and propo-fol are among the most common; they are frequently administered in combination with short-acting opioids. The term for such a technique is conscious sedation. Other techniques may also be employed. For example, when an opioid is combined with a neuroleptic drug, such as the butyrophenone droperidol (Inapsine), the technique is called neuroleptanalgesia. An inhalational drug, such as nitrous oxide (N2O), may be added during intervals of the operative procedure when complete anesthesia is desired (i.e., neuroleptanesthesia).
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