 Methods: a prospective observational study. Thirty five patients undergoing a pulmonary resection lobectomy or pneumonectomy will be included to achieve around one hundred fluid challenges with a 250 milliliters colloid solution in response to hemodynamic instability.Hemodynamic instability is defined as a decrease by 20 of artery pressure from baseline andor an increase by 20 heart rate from baseline. Fluid responsiveness is defined as an increase in stroke volume index SVI10 measured with oesophageal doppler. PPV will be calculated from recorded artery pressure curve PPVref before and after each fluid challenge. An automated measurement of PPV proposed by the monitor Intelview Philips will be recorded simultaneously before and after each fluid challenge. 