A Method For Calculating The Blood Concentration Of Isoflurane With The Inspired And Expired Concentrations During Laparoscopic Surgeries

Objective: To record the inspired and expired concentrations of isoflurane and calculate the blood concentration of isoflurane with our formula during laparoscopic surgery in order to operate target-controlled infusion better.Methods: Three sections in this experiment: Section 1, make up the standard curve of isoflurane. Prepare isoflurane standard samples of eight different concentrations by the double dilution method, make the standard samples in the injection port of gas chromatograph, the we could receive the standard curve between concentration and peak area. Section 2:Twenty-nine adult patients, ASA I～II,were recruited to receive abdominal surgeries, twelve patients for non-laparoscopic surgeries, the others for laparoscopic surgeries. The two team circumstances are not different in statistics. When they came in operating room, they all received transfusion,. We monitored electrocardiograph, pulse oximetry and blood pressure., then induce through venous, use the laryngoscope to facilitate insertion of the endotracheal tube into the trachea, place a tube into right internal jugular vein. Patient inspired isoflurane once intubed and we injected fentanyl and atracurium when necessary during surgery. And we record the isoflurane concentration of inspired gas (C_I) and the isoflurane concentration of expired gas (C_ET). Twenty, forty, sixty, eighty minutes after inhalating isoflurane, central venous blood samples were collected. We record C_I and C_ET when collected blood samples. We pumped air through T—piece and then closed it, shake them up and put them into the water tank with 37℃. Wobble them for 15 seconds each 15 minutes. Then put the gas balanced into injection port of gas chromatograph after 150 minutes .We could receive the isoflurane concentration of gas sample balanced through the standard curve of isoflurane between concentration and peak area. Calculate the plasma concentration of isoflurane through a formula. We could receive two different F value (the fraction of uptake of isoflurane) through the formula. Section 3: Other 27 patients were recruited for abdominal surgeries, 13 for laparoscopic surgeries, the others for non-laparoscopic surgeries. All of the processes were the same as the former. Then we confirm the results obtained from section 2.Results: The F was 0.52 in the laparoscopic surgeries and 0.44 in the non-laparoscopic surgeries. In the laparoscopic surgeries, the bias (MDPE) was -17%, accuracy (MDAPE) was 22.88%, the wobble was 11.7%. The correlation coefficient(r) was 0.83. In the non-laparoscopic surgeries, the MDPE was 5.37%, the MDAPE was 16.02%,the wobble was 15.86%.The correlation coefficient was 0.90.Conclusions: (1) The formula could be used in abdominal surgeries to evaluate the concentration of isoflurane according to the clinical standard of MDPE<15%,MDAPE<30. (2) Artificial pneumoperitoneum could affect the uptake of isoflurane.