The difference between target and measured concentrations of propofol administered by TCI : an evaluation of the performance of the TCI system

Objective To determine the difference between target and measured concentrations of propofol given by target - controlled infusion (TCI) and evaluate the performance of the TCI system for Chinese. Methods Sixty-one ASA Ⅰ - Ⅱ patients (26 male, 35 female) aged 20 - 64 yr, undergoing elective lower abdominal surgery were included in this study. Body weight ranged from 43 - 81 kg and height from 143 - 185 cm. Radial artery was cannulated for BP monitoring and blood sampling.The patients were premedicated with intramuscular atropine 0.007 - 0.01 mg·kg-1 and phenobarbital 1 - 2mg·kg-1. Anesthesia was induced with fentanyl 2μg·kg-1 and TCI of propofol of which the target plasma concentration was set at 3 μg·ml-1.Intubation was facilitated with vecuronium 0.1mg·kg-1.Anesthesia was maintained with fentanyl - TCI of propofol - vecuronium. TCI of propofol was maintained for 1 h. The TCI system was composed of DellTM InspironTM 8200 computer, Graseby 3500 infusion pump, Stelpump software (Version 1.07 by JF Coetzee and R Kina) and the pharmacokinetic model and parameters by Tackley.MAP,HR,SpO2 and CVP were monitored throughout anesthesia. Blood samples were taken before induction of anesthesia (To baseline), at 2,5,10,20, 30,40,50,60,62.5,65,70,75,80,90 min after start of TCI (T1-15) for determination of plasma propofol concentration by Gas Chromatography-Mass Spectrometry (GC-MS). Comparing measured with target concentrations the median performance error (MDPE),mean absolute performance error (MDAPE),wobble and divergence were calculated.Results Compared with target concentrations,the measured concentrations of propofol were significantly higher during TCI but lower after TCI.The difference between the target and measured concentrations was significant during T1-15(P0.05).During 60 min of TCI of propofol MDPE, MDAPE, wobble and divergence were 30.02%,31.55% ,21.4% and -0.51 %·h-1 respectively. During the 30 min after TCI was discontinued,MDPE,MDAPE,wobble and divergence were - 19.71%,21.63%,13.29% and -0.26%·-1 respectively.Conclusion The performance of the TCI system for propofol is not acceptable for clinical application. The pharmacokinetic model and parameters by tackley are unsuitable for Chinese. Further study on the population phannacokinetics of Chinese is needed.