Abstract
Post-operative isoflurane has been observed to be present in the end-tidal breath of patients who have undergone major surgery, for several weeks after the surgical procedures. A major new non-controlled, non-randomized, and open-label approved study will recruit patients undergoing various surgeries under different inhalation anaesthetics, with two key objectives, namely (1) to record the washout characteristics following surgery, and (2) to investigate the influence of a patient’s health and the duration and type of surgery on elimination. In preparation for this breath study using proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), it is important to identify first the analytical product ions that need to be monitored and under what operating conditions. In this first paper of this new research programme, we present extensive PTR-TOF-MS studies of three major anaesthetics used worldwide, desflurane (CF3CHFOCHF2), sevoflurane ((CF3)2CHOCH2F), and isoflurane (CF3CHClOCHF2) and a fourth one, which is used less extensively, enflurane (CHF2OCF2CHFCl), but is of interest because it is an isomer of isoflurane. Product ions are identified as a function of reduced electric field (E/N) over the range of approximately 80 Td to 210 Td, and the effects of operating the drift tube under ‘normal’ or ‘humid’ conditions on the intensities of the product ions are presented. To aid in the analyses, density functional theory (DFT) calculations of the proton affinities and the gas-phase basicities of the anaesthetics have been determined. Calculated energies for the ion-molecule reaction pathways leading to key product ions, identified as ideal for monitoring the inhalation anaesthetics in breath with a high sensitivity and selectivity, are also presented.
Highlights
The monitoring of unlabelled drugs in the body in real-time offers an opportunity to determine their therapeutic effectiveness and washout characteristics in a continuous and non-invasive way
For the first time, we present in this paper density functional theory (DFT) calculations of the proton affinities, gas-phase basicities and changes in the enthalpy and free energy for the key reaction pathways leading to the product ions to be monitored for all four of the halogenated ethers
In the selected ion flow tube study of isoflurane and sevoflurane by Wang et al the reaction rate coefficients for their reactions with H3O+ were determined from the relative decay rates of H3O+ and O2+ reagent ions, and the assumption that O2+ reacts at the collisional rate [22]
Summary
The monitoring of unlabelled drugs in the body in real-time offers an opportunity to determine their therapeutic effectiveness and washout characteristics in a continuous and non-invasive way. Several soft chemical ionisation studies have highlighted the use of breath analysis to detect intravenous anaesthetics, such as propofol during surgery [1,2,3,4,5], or to monitor the concentrations of inhaled anaesthetics post-surgery, either in the breath of patients or within operating and recovery rooms in hospitals [6,7,8,9,10] The former has led to the development of a low cost analytical device to monitor propofol levels in the breath of patients during anaesthesia or under sedation in real-time [11]. This was a very limited study, involving a small number of extremely sick people, and a key aim of our new research programme is to extend this pilot isoflurane study to explore the elimination characteristics for a number of inhalation anaesthetics used in surgical procedures, and to investigate the dependence of the lifetime of an anaesthetic in the body on various factors that could influence the outcome, including the duration and type of surgery, the quantity of an anaesthetic inhaled, ventilation, and the health, body mass index (BMI), gender, and age of patients
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