1. Is it possible to use a fixed inflation volume instead of a fixed inflation pressure during surgical laparoscopy in obese patients? A group of 33 obese patients with a bmi above 40, ASA class I, II or III between 21 and 75 years old and scheduled for a laparoscopic surgery were included in this study with approval from the hospital ethical committee. Anaesthesia was induced with Propofol 200 mg, Sufentanil 20 ug, Nimbex 20 mg and Sevoflurane 1,5 Mac in a 50 % O2/N2O. Patients were asked to empty the bladder before surgery. The stomach was emptied by suction through a gastric tube. All the CO2 was allowed to escape after insertion of the trocar. An Olympus insufflator UHI-3 was initialised and the abdomen was inflated with a stepwise flow to 7, 10, 13 and 16 cmH20. When the pressure was reached, flow was stopped and the actual pressure and volume measured giving 4 data points. Elastance and pressure at zero volume were calculated by a linear fit. The abdominal pressure at 3 liter volume was calculated and the UHI 3 inflator set to that value. If calculation required a higher pressure the pressure never exceeded 20 cmH2O. The calculated pressures for each patient are recorded and compared to the 15 cmH2O. Is this significant different and what is the average change in pressure? Further muscle relaxation is given as required Jan Paul J Mulier, M.D., Ph.D., 1 Bruno Dillemans, M.D., 2 1 Dep of Anesthesiology,. 2 Dep of General Surgery, AZ st-Jan AV, Brugge, Belgium. The APVR is linear and is described by an elastance E and a pressure at zero volume P V0. (1) Three data points are sufficient to measure this relation. (2) Many surgeons inflate the abdomen to a fixed pressure of 15 cmH2O. Obese patients have two problems Some patients do not have enough working space and might require higher pressures. Some patients are difficult to ventilate during a pneumoperitoneum and would benefit from lower inflation pressures. Using the calculated elastance and pressure at zero volume the needed pressure to reach a working space of 3 liter can be calculated. Background and Goal of Study Materials and Methods 9 patients required a higher inflation pressure of 18 +/- 2 cmH20 and 3 patients reached the maximum value of 20 cmH2O. 24 patients required a lower inflation pressure of 11 +/- 2,5 cmH2O. Results 1. JP Mulier, Eur J Anesth 2006, vol 23 s37, A124 2. JP Mulier, S van Cauwenberge, B Dillemans, Eur J Anesth 2006, vol 23 s37, A127 References Most patients do not need the insufflation pressure of 15 cmH2O. Laparoscopic operation is possible in 70 % with a lower pressure, facilitating ventilation. Only a small group of patients requires higher pressures to reach the desired workspace. Conclusion Goal of this study was to inflate the abdomen to this calculated volume to find out how many patients need a lower abdominal pressure and how many patients need a higher abdominal pressure Anesthesiology 2006; 105: A1278, Annual Meeting ASA October 14-18, 2006 McCormick Place-Chicago, Illinois