During anaesthesia, cerebral blood flow and MAP may be affected by various factors including release of vasoactive substances. Manipulation of the abdominal organs may induce a so-called mesenteric traction syndrome (MTS) encompassing a triad of flushing, hypotension, and tachycardia in about half of the patients who undergo major abdominal surgery. MTS typically develops 15-20 min after the start of surgery and the haemodynamic manifestations, that appear to be mediated by prostaglandin I2, last for approximately 30 min. The effect of MTS on cerebral blood flow is unknown. Prostaglandin I2 dilates cerebral arteries in vitro but does not affect cerebral blood flow when administered to healthy subjects. In a previous study we found that MTS increases near-infrared spectroscopy determined frontal lobe oxygenation possibly due to an increase in extracranial circulation while there was no effect on middle cerebral artery mean flow velocity as an index of changes in cerebral blood flow.