Rapid and direct measurements of oxygen consumption and CO2 production in patient monitoring.

Oxygen is the gas of life. Without it, we die very quickly. Because of this, groups such as the St John?s Ambulance teach members of the public the basic ?ABC? of resuscitation to ensure that unconscious patients continue to get enough oxygen to their body?s tissues (ABC stands for airway, breathing and circulation). Patients unconscious in hospital, even if stable, would benefit from a simple device to measure how much oxygen their body is using. This includes both patients who are unconscious in intensive care units because of their underlying condition and patients who are deliberately made unconscious by anaesthetists. Such measurements in these patients would allow the right amount of food to be given intravenously, would give an early warning of heart and lung problems, would guide blood transfusion needs, and would provide a range of other benefits. Other patients in hospital may not be stable because of an inadequate supply of oxygen to the body - doctors often refer to such patients as being in shock . These patients need resuscitation in various ways, and without it many would die. However, as with so many other treatments, too much resuscitation can be harmful (as can too little resuscitation). At present, doctors judge their treatment in a variety of ways, but unfortunately they have no good measure of just how much oxygen the patient s body tissues are taking up. The device proposed by Profs Hancock and Robbins would enable accurate monitoring of oxygen uptake in all these patients. The clever part of the invention is to monitor the oxygen concentration continuously within the actual breathing tube of the patient. It does this by using a laser which produces light at a very particular wavelength which is only absorbed by oxygen. As this absorption is weak, to strengthen it Profs Hancock and Robbins use two special mirrors facing one another to bounce the light many times through the gas before measuring how much of the light is absorbed. They have already got this technique to work in the rarefied confines of the university research laboratory. The question now is whether they can make a device that will survive the realities of the hospital environment. If they can, then this device could save lives through better monitoring and better resuscitation of unconscious patients in hospital, just as the St John?s Ambulance saves lives by improving resuscitation within the community.

The metabolic monitoring of oxygen consumption and carbon dioxide production is potentially valuable in a range of clinical settings. Current technology for measuring these variables is limited and is not, for example, generally applicable in ICUs and anaesthesia. These limitations can be overcome by developing instantaneous oxygen and carbon dioxide analysers that operate within the respired gas stream. These would enable much more generally applicable methods for calculating respiratory gas exchange to be adopted. Our approach has been to use laser spectroscopy. To date, with partial funding from an MRC Discipline Hopping Grant, we have assembled a prototype device on an optical bench from which we have recovered (offline) airway concentrations for carbon dioxide and oxygen throughout a number of respiratory cycles from the spectra obtained. This application seeks funds to develop a prototype for oxygen, carbon dioxide and water vapour that can be trialled in a clinical setting (ICU and anaethesiology)and that can provide sufficient pilot data to justify commercial development.