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Monitoring depth of anesthesia utilizing precision measures of the coefficient of pulmonary gas exchange


A.Yu. Elizarov Dr. Sc. (Phis.-Math.), Senior Research Ioffe Institute Russian Academy of Science, St. Peter-burg A.G. Kuz’min Ph. D. (Phis.-Math.), Senior Research Scientist, Institute for Analytical Instrumentation Rus-sian Academy of Science, St. Peterburg A.V. Polegaev Dr. Sc. (Med.), Professor, Department of Neurosurgery, Military Medical Academy, St. Pe-terburg Yu. A. Titov Post-graduate student, Institute for Analytical Instrumentation Russian Academy of Science, St. Peterburg V. Yu. Cherebillo Dr. Sc. (Med.), Professor, Department of Neurosurgery, Military Medical Academy, St. Peterburg

Herein, a brief description of the stress-response evaluation method based on the precision measurement of the respiratory coef-ficient is provided. By analogy with the respiratory coefficient we can introduce coefficient N(t) Precision measurements of CO2 and O2 concentrations in the BC of the PGEC were accomplished by a quadrupole mass spectrometer (Prisma Plus, Pfeiffer Vacuum) with the resolution of 0.5M/∆M and the partial pressure sensitivity of 10−12 mbar. The time of simultaneous CO2 and O2 masspeak measurements was 10 ms (the description of the experimental set-up is provided heare. The respiratory coefficient was calculated as a ratio of mass concentrations of CO2 and O2 evolved from the lung at each respiratory cycle using the integration of the concentration-time profiles in the BC of the IAM: N (t) = MCO2 (t)/MO2 (t), where MCO2 and MO2 are mass concentrations of CO2 and O2 correspondingly, evolved from the lung during the respiratory cycle. The boundaries of the respiratory cycle during anesthesia (t) were determined as minimum values on the capnogram (CO2 ) and the oxigram (O2), correspondingly. The minimum values were estimated by numerical differentiation of CO2 and O2 concentration in the BC of the IAM versus time curves. In case of a stress-response to a pain impulse, sharp peaks in the gas concentration in the BC versus time curve were observed. The integration of the peaks leads to the increase in the ratio of the respiratory coefficient, which in the reported case does not reflect an increase in the O2 consumption or CO2 evolution, but only displays stress-response to surgical stimuli in time. In the current study, relative measurements of component concentrations in the gas mixture in the BC of the IAM were performed. For a conventional representation of the results, the relative CO2 and O2 data were normalized in such a way that N (0) ≡ 1 at the first respiratory cycle. Time variation of MCO2 and MO2 concentrations and N (t) during anesthesia awareness under balanced inhalational anesthesia (sevoflurane, nitrous oxide, fentanyl) in a real-time mode . The given method of respiratory coefficient N(t) monitoring has a potential to be used for stress-reaction or pine assessment during anesthesia in a real-time mode. We should mention that by using mass spectrometry to monitor CO2, O2 and propofol in the exhaled air, a control of total intravenous anesthesia adequacy becomes possible inreal-time mode.


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