BACKGROUND: The relatively good haemodynamic and respiratory tolerance to abdominal CO(2) insufflation has mostly been observed in healthy patients during short-lasting laparoscopic procedures. End-tidal CO(2) pressure (PetCO(2)) has been shown to be a reliable method to assess arterial CO(2) (PaCO(2)) in the absence of cardio-respiratory disease in this setting. However, no study has investigated whether PetCO(2) is accurately related to PaCO(2) during laparoscopic colon surgery. Indeed, these procedures last longer, prolonging the pneumoperitoneum and requiring a Trendelenburg position. The aim of the present study was to measure the PaCO(2)-PetCO(2) difference over time in patients undergoing laparoscopic colon surgery and to determine whether PaCO(2) is reliably assessed by PetCO(2). METHODS: Forty consecutive patients (ASA I and II) scheduled for laparoscopic colon surgery were anaesthetized and ventilated to obtain a PetCO(2) between 4.0 and 5.5 kPa. After initiation of CO(2) insufflation, PaCO(2) and PetCO(2) were recorded every 30 min during surgery. RESULTS: No complication was observed during anaesthesia. The mean arterial pressure increased significantly after CO(2) insufflation and remained steady up to the end of pneumoperitoneum. The heart rate remained stable over time. The relation between PaCO(2) and PetCO(2) was not constant among patients and increased over time within the same patients. The R(2) values fluctuated and did not show a constant correlation between PaCO(2) and PetCO(2). CONCLUSION: The correlation between PaCO(2) and PetCO(2) during laparoscopic colon surgery is inconsistent mainly due to inter- and intra-individual variability.