A comparison of oesophageal Doppler with arterial pressure waveform derived cardiac output and stroke volume variation for the assessment of haemodynamic state in adult patients undergoing major surgery.

1. This is an observational study comparing three new non-invasive cardiac output monitors. None of these monitors can act as the reference technique as neither are gold standard cardiac output monitors. However, the question is if they are interchangeable? So a comparison study will be able to see if they meausre haemodynamic events in a similar way. In a smaller subgroup of cardiac patients, thermodilution will act as the reference. This control however will only be limited to cardiac surgery. The observation period will start after induction of a general anaesthetic (GA) and be completed at the end of the anaesthetic. Typically a case may last 2 to 4 hours. Haemodynamic measurements will be taken at 10minutely intervals or at the same time as events. In the cardiac subgroup, there will be a further observational period of up to 2 hours in intensive care unit (ICU) whilst the patient remains intubated and sedated. 2. The oesophageal monitor will involve the insertion of a oesophageal probe under GA. It will allow continuous monitoring of cardiac ouput until it is removed before the end of the GA. The arterial pressure derived cardiac ouput (APCO) device/s will measure the cardiac ouput using the signal from a standard arterial line. Two APCO devices will be used; the Vigileo Flotrac by Edwards Lifesciences and the Lidco Rapid by Lidco. The haemodynamic parameters generated by the monitors will be transcibed onto a spreadsheet as will clinical events such as administration of fluid, hypotension, use of vasoactive drugs, etc...