Bestimmung der Propofolkonzentration in der Exspirationsluft während einer intravenösen Allgemeinanästhesie unter Berücksichtigung des Einflusses des Capnoperitoneums

Objectives The intravenous administered hypnotic propofol can be determined in exhaled air. Previous studies have shown a good correlation between the concentration of Propofol in expired air and its concentration in blood plasma. This enables to use the measurement of the concentration in the expiratory air to predict blood plasma concentration. However, it is unclear what influence the capnoperitoneum has on the concentration of exhaled propofol during laparoscopic surgery. In this study, the concentration of propofol in expired air during laparoscopic surgery will be determined in order to compare its concentration during the capnoperitoneum and the surgical parts without capnoperitoneum. Finally, it will be determined whether the determination of the propofol concentration in the expiratory air is reliable under the influence of the capnoperitoneum. Methods Between August 2020 and October 2021, the expiratory propofol concentration was continuously determined in n= 18 patients during laparoscopic surgery. For this purpose, a part of the expiratory air was taken from the end of the ventilation tube close to the patients side via a sampling tube. This air was fed into “Edmon®” for analysis approximately every minute, an MCC IMS measurement method that allows the expiratory propofol concentration to be determined from the bedside. In addition, an arterial blood sample was taken at defined times to determine the propofol concentration in the blood plasma. The vital parameters routinely recorded during surgery as well as the ventilation parameters were documented using the CLINDEMON© Software. 183 blood plasma samples, 61 of which were taken during capnoperitoneum, were analysed from laparoscopic surgery in n= 18 patients. Propofol was determined in the expired air; of a total of 2065 measurement points, the analysis carried out a 738 points during the capnoperitoneum. Statistical analysis was performed with R (version 4.3.0) and Excel (MSO 2021, Version 2302). The ratio of the propofol concentration of the expired air to those of the blood plasma was investigated for the time of the capnoperitoneum and the time of the surgery without capnoperitoneum using regression analysis. In addition, an analysis of the measurements with a time delay of one to ten minutes was performed. The parameters on which the capnoperitoneum showed an influence were put in relation to the expiratory propofol concentration in a further analysis and examined for changes in this. Results A regression analysis was performed to investigate the correlation between the propofol concentration in expired air and blood plasma. This showed a correlation of R²= 0.681 (p= 0.0180) for the entire data and R²= 0.765 (p= 0.0127) for a time offset of three minutes. Analysis of the correlation of propofol concentration in expiratory air to blood plasma during capnoperitoneum (“capnoperitoneum”) and the surgical fraction without capnoperitoneum (“no capnoperitoneum”) showed a good correlation with r= 0.292, p= 0.0128 (no capnoperitoneum) and r= 0.527, p < 0.0001 (capnoperitoneum), respectively. However, a time lag of three minutes showed only a non- significante correlation with r= 0.064, p= 0.6031 (no capnoperitoneum) and r= -0.044, p= 0.7398 (capnoperitoneum). Conclusion With IMS MCC technology the continuous, bedside determination of the propofol concentration in expiratory air is possible. Since there is a good correlation to the concentration in blood plasma, this can be used to predict the blood plasma concentration. The method already validated in general anaesthesia using “Edmon®” was investigated in this study with regard to possible changes during capnoperitoneum. Using data from n= 18 patients, a good correlation between propofol concentration in expiratory air and blood plasma was also shown during capnoperitoneum.