The study will take place intra-operatively. Monitoring will be instituted as determined necessary by the attending anaesthetists, but as a minimum will consist of pulse oximetry, ECG and non-invasive blood pressure recording. Intravenous cannulae will be sited and general anaesthesia induced by the anaesthetist responsible for the patient, as would be normal for this type of surgery. Once the patient has been transferred to the operating theatre, the research fellow will insert an ODM probe via either the nasal or oral route and the CO and SV will be measured; this constitutes normal care. A sterile Phillips iU22 USS probe will be placed on the patient's abdomen and the research fellow will administer SonoVue contrast agent intravenously via the cannula already sited to facilitate anaesthesia, up to a maximum dose of 2.4ml. Visceral MVBF will be measured using this CEUS technique. Capillary blood samples will be taken from earlobe for measurement of blood lactate levels by the research fellow. At this stage, as would typically occur during an operation of this nature, the research fellow will administer intravenous colloid suspension in boluses of 3ml/kg, up to a maximum of 15ml/kg, until the CO has been maximised, as judged by the ODM. At this stage, the research fellow will perform a further CEUS of the abdominal viscera by administering Sonovue contrast agent (2nd dose of up to 2.4ml) and measuring MVBF with the Phillips iU22. Repeat samples of capillary blood will be drawn to measure the lactate level by the research fellow. At the end of the operation, a 3rd CEUS of the abdominal viscera, along with further SV & CO readings, will be made.