• Hao Dong, Fengjiang Zhang, Jing Chen, Qiwen Yu, Yinbo Zhong, Jun Liu, Min Yan, and Xing Chen.
• From the Key Laboratory for Biomedical Engineering of Ministry of Education, Department of Biomedical Engineering, Zhejiang University, Hangzhou, Zhejiang, China.
• Anesth. Analg. 2020 Apr 1; 130 (4): 958-966.

BackgroundThe anesthetic side effects of propofol still occur in clinical practice because no reliable monitoring techniques are available. In this regard, continuous monitoring of propofol in breath is a promising method, yet it remains infeasible because there is large variation in the blood/exhaled gas partial pressure ratio (RBE) in humans. Further evaluations of the influences of breathing-related factors on RBE would mitigate this variation.MethodsCorrelations were analyzed between breathing-related factors (tidal volume [TV], breath frequency [BF], and minute ventilation [VM]) and RBE in 46 patients. Furthermore, a subset of 10 patients underwent pulmonary function tests (PFTs), and the parameters of the PFTs were then compared with the RBE. We employed a 1-phase exponential decay model to characterize the influence of VM on RBE. We also proposed a modified RBE (RBEM) that was not affected by the different breathing patterns of the patients. The blood concentration of propofol was predicted from breath monitoring using RBEM and RBE.ResultsWe found a significant negative correlation (R = -0.572; P < .001) between VM and RBE (N = 46). No significant correlation was shown between PFTs and RBE in the subset (N = 10). RBEM demonstrated a standard Gaussian distribution (mean, 1.000; standard deviation [SD], 0.308). Moreover, the predicted propofol concentrations based on breath monitoring matched well with the measured blood concentrations. The 90% prediction band was limited to within ±1 μg·mL.ConclusionsThe prediction of propofol concentration in blood was more accurate using RBEM than when using RBE and could provide reference information for anesthesiologists. Moreover, the present study provided a general approach for assessing the influence of relevant physiological factors and will inform noninvasive and accurate breath assessment of volatile drugs or metabolites in blood.

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