To determine the plasma concentrations of propofol required to achieve different levels of sedation during monitored anesthesia care.
Sixty ASA I-II, 18-65 yr-old patients, received a target-controlled continuous iv infusion of propofol. The target plasma concentration of propofol (Cpt) was initially set at 0.4 microg x ml(-1). Two minutes after calculated equilibrium between plasma and effect-site concentrations, the Cpt of propofol was increased by 0.2 microg x ml(-1) steps until the patient showed no reaction to squeezing the trapezius. The level of sedation was assessed immediately before each increase in propofol Cpt using the Observer's Assessment of Alertness/Sedation (OAA/S) scale.
The Cpt of propofol required to induce lethargic response to name was 1.3 microg x ml(-1) (5 degrees and 95 degrees percentiles: 1.0 - 1.8 microg x ml(-1)), to obtain response after loud and repeated calling name was 1.7 microg x ml(-1) (1.2 - 2.2 microg x ml(-1)), to obtain response after prodding or shaking was 2.0 microg x ml(-1) (1.6 - 2.6 microg x ml(-1)), to obtain response after squeezing the trapezius was 2.4 microg x ml(-1) (1.8 - 3.0 microg x ml(-1)). Patients showed no response after squeezing the trapezius at 2.8 microg x ml(-1) (2.0 - 3.6 microg x ml(-1)). Correlation between Cpt propofol and sedation scores were r = 0.76, P < 0.0001.
Target-controlled infusion of propofol provided easy and safe management of intraoperative sedation, allowing fast and predictable deepening in the level of sedation, while minimizing systemic side effects of intravenous sedation due to the minimal risk of overdosing the drug.