Quantitative measurement of blood remifentanil concentration: development of a new method and clinical application

We have developed a new detection method of blood remifentanil concentration using a gas chromatography-mass spectrometry(GC–MS) with fentanyl as the internal standard(IS). The detection was performed at m/z 168 and 245 for remifentanil and fentanyl, respectively. In addition, the retention times of remifentanil and fentanyl were 5 min 45 s and 6 min 51 s, respectively. The standard curve of relationship between remifentanil concentration and the ratio of the peak area of remifentanil to fentanyl was satisfactorily fitted as linear regression (R 2 = 0.998, p < 0.01). Intra- and inter-assay CV was 10.5 and 11.5 %, respectively. In the clinical setting, 21 adult patients undergoing elective surgery under propofol–remifentanil TIVA were enrolled. To determine blood remifentanil concentrations, arterial blood was obtained at 0–30 min after cessation of remifentanil infusion at 0.2 μg/kg/min. Blood samples were given into sample tubes(chilled on ice) containing citric acid 50 % 60 μl which inactivates all esterase, and then stored at −20 °C until assay. Measured blood remifentanil concentration was 3.59 ± 0.74 ng/ml at the end of remifentanil infusion, and the ime for a decrease in blood remifentanil concentration by half was ~2 min. Remifentanil concentration was below the detection limit 30 min after the cessation. Thus, we have confirmed that this new method is clinically applicable.