The 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.
Correlations 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.
We 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−1.
The 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.
From the *Key Laboratory for Biomedical Engineering of Ministry of Education, Department of Biomedical Engineering, Zhejiang University, Hangzhou, Zhejiang, China
†Research Institute of Zhejiang University-Taizhou, Taizhou, Zhejiang, China
‡Department of Anesthesiology, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China.
Accepted for publication April 9, 2019.
Funding: This work was supported by the National Natural Science Foundation of China (No. 81571769 to X.C.), the Fundamental Research Funds for the Central Universities (No. 2019QNA5027 to X.C.), and the Public Welfare Technology Application Research Foundation of Zhejiang Province (No. 2017C31096 to F.Z.).
The authors declare no conflicts of interest.
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website (www.anesthesia-analgesia.org).
Trial Registry No: ChiCTR-ONC-13003291. URL: http://www.chictr.org.cn/showproj.aspx?proj=6268.
H. Dong and F. Zhang contributed equally to this study and share first authorship.
Reprints will not be available from the authors.
Address correspondence to Xing Chen, PhD, Key Laboratory for Biomedical Engineering of Ministry of Education, Department of Biomedical Engineering, Zhejiang University, 38 Zheda Rd, Hangzhou, Zhejiang, China, 310027; or Min Yan, MD, Department of Anesthesiology, The Second Affiliated Hospital, Zhejiang University School of Medicine, 88 Jiefang Rd, Hangzhou, Zhejiang, China, 310009. Address e-mail to email@example.com or firstname.lastname@example.org.