Optical Detection of Exhaled Intravenous Anaesthetics

Lead Research Organisation: University of Cambridge
Department Name: Chemical Engineering and Biotechnology


In this proposal we respond to a real and acute need for clinical online monitoring of anaesthetic concentrations in patients' blood during surgery. Despite of the routine clinical use of intravenous anaesthetics no viable sensors for online monitoring of their blood plasma concentration exist. The project focuses on the development of next generation sensing technology for propofol, which is used widely as an anaesthetic drug during surgery and as a sedative in critically ill patients on intensive care units. Propofol exerts profound effects on the cardiovascular system, reducing blood pressure, cardiac output, and the perfusion of vital organs such as the brain and kidneys. The consequences of incorrect administering of propofol are therefore grave. Currently the effectiveness of propofol induced anaesthesia is only assessed symptomatically. A viable online capability to monitor exhaled levels of propofol would dramatically improve the level of control over its administration. It would both improve the quality of anaesthetic management by tailoring dosage to individuals' needs and reduce clinical recovery times and patient aftercare with associated cost benefits. We propose to study the feasibility of clinical online monitoring of propofol in patient's blood by optically measuring the concentration of propofol in the patient's exhaled breath. Recent medical studies have shown that mixing ratios of propofol at a level of parts per billion by volume exist in the patients' exhaled breath during surgery. The application is ambitious, high impact, and very topical pushing the frontiers of the field. Challenges for viable optical sensing strategies of exhaled propofol concentration are the low concentrations prevailing; the poor spectroscopic characterization of propofol; the presence of contaminant species that create competitive signals; and, importantly, the requirement for a robust, fast and economical system that stands a chance to be deployed in a clinical context. Currently there are no available technologies that meet all these demands. In this project we propose two state of the art optical detection techniques that have the potential to meet the requirements. We propose to conduct a systematic study on the feasibility of online monitoring of exhaled propofol by, first, quantifying the absorption cross sections of propofol, secondly, determining the attainable detection limits using the selected candidate technologies and, thirdly, studying the effects of spectral intereference caused by the other gases present in the exhaled breath. The project is a pioneering activity and is based on a unique multidisciplinary ensemble of professionals focusing on a high impact research challenge. The high impact application has been established in consultation with medical anaesthesia professionals, Prof. T. Absalom and Dr. D. Wheeler, Division of Anaesthesia, School of Clinical Medicine, University of Cambridge. Only this collaboration can provide the needed expertise and state of the art knowledge on the clinical sample collection and preparation. The Researcher's expertise in the development of novel optical sensors matches the project requirements in an excellent fashion. If successful, this research could lead to a paradigm shift in the way anesthetists are able to operate in the operating theatre.
Description The anaesthetic agent propofol (2,6-diisopropyl-
phenol) is the most widely used intravenously administered
drug in general anaesthesia. However, a viable online capability to monitor metabolised levels of propofol in patients did not exist at the beginning of this project. We showed for the first time that photo-acoustic optical spectroscopy has good potential to detect metabolized propofol from patients' exhaled breath. With this technique the detection limit of propofol in nitrogen was 0.12ppb.
Broadband optical sources generating supercontinuum radiation have been developed to carry out absorption spectroscopy from the UV to the IR. These light sources are characterised by a broad optical spectrum and high intensity which a allow significantly faster acquisition of absorption spectra of gaseous and liquid samples.
Numerical simulations were carried out to improve the cavity design of such supercontinuum radiation sources.
Exploitation Route The detection of the anaesthetic agent propofol in patients' breath could become a standard technique in clinical medicine.
Sectors Chemicals,Environment,Healthcare,Pharmaceuticals and Medical Biotechnology

Description This grant primarily supported a project to develop and apply a fast, sensitive absorption spectroscopy technique to the quantitative, real-time determination of the concentration of the anaesthetic agent propofol by analysis of breath. This required development of a sensing technique with a new level of sensitivity for this agent. In this collaboration we developed and demonstrated technology which is able to quantify the agent at the sub parts per billion level in exhaled breath (10.1021/ac200690f), paving the way for the development of optical monitors. Such sensors offer the possibility of more precise monitoring of anaesthesia, and hence the potential for improved medical outcomes. We studied and developed several approaches to absorption spectroscopy during this project, and it has therefore contributed to our development and review of a number of spectroscopic techniques (e.g. 10.1039/c3an01441j).
First Year Of Impact 2010
Sector Healthcare
Impact Types Policy & public services