What is the role of propofol in ambulatory surgery?
Propofol may be used to provide sedation during a regional anesthetic, to induce general anesthesia, and to maintain general anesthesia. It is a water-insoluble, highly protein bound, lipophilic compound that has unique phar-macokinetic characteristics that render it ideal for use with ambulatory surgery. It is rapidly redistributed, and hepatic and extrahepatic clearance (pulmonary) permit rapid recovery of cognitive function with less postoperative sedation and drowsiness compared with the traditionally employed ultra-short-acting barbiturates. Depressant effects on the central nervous system are dose-dependent and range from mild sedation to sleep and unconsciousness. Neither retro-grade nor anterograde amnesia is associated with this drug. For the induction of anesthesia, propofol can be adminis-tered as a bolus dose (2–2.5 mg/kg slowly), and its effect can be maintained via a continuous intravenous infusion (0.1–0.2 mg/kg/min). Dosages are reduced for debilitated patients and for the geriatric population. For sedation during regional anesthesia, incremental doses of 10–20 mg (0.3 mg/kg) may be given, or an infusion begun. There is a known relationship between propofol (as well as other intravenous agents) serum drug levels and therapeutic effects. For propofol, the target concentration is between 3 and 6 μg/ml to provide surgical anesthesia.
When administered as the sole agent, propofol may not provide amnesia 100% of the time, and intraoperative awareness has been reported. Therefore, it is often used in conjunction with nitrous oxide, a volatile anesthetic, or midazolam. Propofol has no muscle relaxant or analgesic properties. For total intravenous anesthesia, a continuous infusion of a short-acting opioid, such as remifentanil, can be administered along with an infusion of propofol. Additional bolus doses of propofol can be infused to rap-idly deepen the level of anesthesia. Another major advan-tage of propofol appears to be a significantly diminished incidence of postoperative nausea and vomiting. Propofol’s inherent anti-emetic properties allow earlier discharge of patients, even when emesis occurs in the PACU. When used for both induction and maintenance of anesthesia in cases lasting approximately 1 hour, faster recovery time is noted when compared with a thiopental induction followed by maintenance with isoflurane and nitrous oxide. Patients anesthetized with propofol appear to awaken with a posi-tive mood, and they regain equilibrium including the ability to ambulate early. The requirement for pain medication in the postoperative period appears to be reduced, which may be related to an overall feeling of well-being.
Two disadvantages of propofol include the lack of anal-gesic properties and pain on injection. As for the former, the combination of propofol with an opioid, such as remifentanil or fentanyl, will provide required analgesia. The discomfort associated with administration can be avoided by infusion into large-bore veins as well as pre-treatment with intravenous lidocaine. Injecting lidocaine, 10–25 mg intravenously, before giving propofol or drawing up the lidocaine into the syringe after first filling it with propofol will ameliorate or eliminate completely the discomfort in most patients.
Infectious hazards associated with propofol have been well documented because the base, which is composed of an emulsion of soybean oil and egg phosphatides, serves as an excellent culture medium for the growth of bacteria. It is important to draw up the drug in an aseptic fashion and shortly before it is to be administered. Additionally, it is imperative that the syringe be discarded after single patient use. Repeated use of the same syringe throughout the day for multiple patients has been associated with clusters of cases of bacterial septicemia.