Method Ethical approval for this study according to the standards set in the Helsinki declaration (Regional Ethics Committee Dnr: 2009/529 and additions to the application with the measurement of cardiac output Dnr 2010/481) will be provided by Regional Ethics Committee, Lund, Sweden on September 2009 and September 2010. The investigation will include 60 patients, ASA physical status 1 or 2, scheduled for elective colon surgery. Patients will be considered for inclusion in the trial if they will be over 18 yr age and have a BMI more than 25 kg/m2. All procedures will be estimated to last more than 60 minutes. Consent to participate in the study will be received from each patient. Patients with known pulmonary or cardiovascular disease will be excluded. Patients will be randomised to one of two groups with 30 patients in each group via randomly mixed sealed envelope assignment at the start of the procedure in the operating theatre. Interim analysis will be performed after 15 + 15 patients.