The clinical effects of different target concentrations during closed-loop anesthesia with propofol administered by TCI

Objective During TCI of propofol anesthesiologist still has to rely on depth of anesthesia and blood pressure (BP) to alter the target concentration. In this study depth of anesthesia was monitored by BIS and TCI was controlled by feedback from BP and BIS monitoring. The purpose of this study was to determine the best target concentration during closed-loop anesthesia with propofol administered by TCI in terms of cardiovascular stability.Methods Twenty-four ASA I -II patients (12 male, 12 female) aged 20-50 years weighing 45-70 kg presenting for laparoscopic cholecystectomy were randomly divided into 3 groups of eight patients according to target concentration of propofol entered into the TCI system : group A 3 .0μg·ml-1 ; group B 3.5μg·ml-1 and group C 4.0μg·ml-1 . The patients were premedicated with intramuscular atropine 0.5mg and phenobarbital 0.1g. Propofol was administered by Graseby 3 500 which was connected to BIS and BP monitor (HXD-1) via RS 232 connector. Anesthesia was induced with fentanyl 5 μg·kg-1 and propofol given by TCI. Intubation was facilitated with vecuronium 0.1 mg##kg-1 when patients lost consciousness. During maintenance of anesthesia TCI of propofol was controlled by feedback from BIS and BP monitoring. Propofol infusion was stopped whenever BIS was 50 or MAP 80% of the baseline value and restarted when BIS 50 or MAP 80% of the baseline value. Radial artery was cannulated for direct BP monitoring. BP, HR, SpO2 and BIS were monitored throughout anesthesia. Blood samples were taken from radial artery for determination of blood propofol concentration before induction of anesthesia, 1, 2, 3, 4, 5 min after TCI of propofol was started, 10, 20, 30 rnin after intubation, when patient regained consciousness and at extubation. Results During induction of anesthesia the decrease in BIS was significantly less in group A than that in group B and C (P 0.05). The amount of propofol infused for induction was significantly different among the three groups ( P 0.05). During maintenance of anesthesia the propofol dose was significantly less in group A than that in group B and C ( P 0.05) . The fluctuation in MAP and HR was significantly greater in group A than in group B and C ( P 0.05). During induction of anesthesia the magnitude of decrease in MAP was significantly greater in group C than that in group B ( P 0.05) . The measured blood propofol concentrations were lower than the predicted concentrations at all time points after start of TCI. There was a close negative correlation between BIS and predicted target concentration. Conclusion 3.5 μg·ml-1 is the appropriate target concentration needed with TCI of propofol administered by Graseby 3500 for laparoscopic cholecystectomy.