The difference between target and measured concentration of remifentanil administered by target-controlled infusion: an evaluation of the performance of a new type-I TCI system

Objective To determine the difference between target and measured concentration of remifentanil given by target-controlled infusion (TCI) and evaluate the performance of a new type Ⅰ TCI system for Chinese. Methods Thirty-six ASA Ⅰ or Ⅱ patients aged 40-60 yr weighing 50-70 kg undergoing elective lung resection were randomly divided into 2 groups according to target remifentanil concentration: group Ⅰ 6 ng · ml-1 and group Ⅱ 8 ng·ml-1. The patients were premedicated with intramuscular midazolam 0.05 mg·kg-1 and atropine 0.5 mg. Anesthesia was induced with remifentanil and propofol both given by TCI. The target concentration of propofol (effect-site concentration) was set at 3 μg·ml-1 and remifentanil (plasma concentration) at 6 or 8 ng· ml-1. When the patients lost consciousness, vecuronium 0.1 mg·kg-1 was given i. v. to facilitate intubation. The patients were mechanically ventilated and PETCO2 was maintained at 30-40 mm Hg. Anesthesia was maintained with TCI of propofol and remifentanil and intermittent i. v. boluses of vecuronium. Target plasma concentration of remifentanil remained unchanged during anesthesia. BIS value was maintained at 45-55 by modifying target propofol concentration. Arterial blood samples were taken before and 5, 10, 20, 40, 60, 90 and 120 min after TCI remifentanil was started for determination of blood remifentanil concentration by high performance liquid chromatography.The performance error (PE) was determined for each measured blood remifentanil concentration. The performance in the population was determined by median absolute performance error (MDAPE), median performance error (MDPE) and the wobble (the median absolute deviation of each PE from the MDPE). Results The measured concentrations (Cm) of remifentanil were significantly lower than the target plasma concentration (Cp) at5, 10, 20 min of TCI in both groups ( P 0.05) . But there was no significant difference between the Cm and Cp at 40, 60, 90 and 120 min of TCI in both groups. The median Cm of all blood samples was 5.1 ng·ml-1 in group Ⅰ and 6.9 ng·ml-1 in group Ⅱ respectively and was significantly lower than Cp ( P 0.05 ) . The MDPE, MDAPE and wobble were - 17.2%, 29.6% and 15.1% in group 1 and - 15.5%, 27.8% and 12.5% in group Ⅱ. Conclusion The MDAPE of the new type Ⅰ TCI system incorporating the remifentanil pharmacokinetic set of Minto was clinically acceptable for Chinese people when the target plasma concentration was set at 6 and 8 ng · ml-1. The Cm was significantly lower than the Cp by approximately 15 % at the beginning of TCI.