Surgeons and patients breathe easy during surgery

30 June 2011

UK scientists have developed a way of continuously analysing the breath of unconscious patients undergoing surgery using mass spectrometry.

Monitoring exhaled gases allows an insight into a patient's metabolic state so that surgeons and anaesthetists can work out how stressed the patient's body is during an operation. Currently, breath analysis can only be done by off-line collection of samples, in which the breath is captured in a bag and taken for analysis elsewhere. The other option is using blood samples, which take a long time to analyse and so are of little use to the medical team.

Breath samples are taken up by the ventilator and sent along a sample line to the mass spectrometer

David Smith from Keele University and colleagues have made a significant advance by taking the measurements and viewing the results in the operating theatre as the surgery is taking place using a selected ion flow tube-mass spectrometer (SIFT-MS). 'Specific breath gases can be monitored that can indicate to the surgeon and anaesthetist the status of the patient, thus allowing more informed decision making and improve the outcome of the surgical procedure,' says Smith.

The team measured the concentrations of acetone, propofol and isoprene in the exhaled breath of patients throughout their operations. Acetone is generated from the metabolism of lipids, propofol is the chemical used to put the patient to sleep and isoprene is related to blood cholesterol levels. They took the breath sample from the ventilator and, using a sampling line, delivered it to the inlet of the SIFT-MS. Paul Monks, an expert in measuring trace gases from the University of Leicester, UK, comments: 'The experimental set-up means that the gases involved in gas-exchange with the lung are directly sampled.'

The technique used is so sensitive it can detect parts-per-billion by volume and it has potential application in 'real-time monitoring in pharmacokinetic - drug effects over time - studies,' says Monks.

'We only monitored two breath metabolites in this initial pilot study, so a major objective of the follow-up research is to include more metabolites, which might be indicative of stress on vital organs such as the lungs, liver, kidneys and heart,' says Smith.

Holly Sheahan
RSC