Correlation of arterial and end-tidal carbon dioxide in spontaneously breathing patients during ambulatory gynecologic laparoscopy

Laparoscopy can be performed while patients are under total intravenous ane sthesia (TIVA), or sedated and breathing spontaneously through the normal a irway. Respiratory monitoring is difficult when patients are sedated or ane sthetized, however. The purposes of this study were to evaluate the reliabi lity of end-tidal carbon dioxide (ETCO2) measurement for monitoring arteria l carbon dioxide pressure (PaCO2), and to assess the PaCO2/ETCO2 gradient a mong patients receiving TIVA while breathing spontaneously through the norm al airway. Sixty patients were divided into two groups: group 1 patients (n = 30) received general anesthesia with controlled ventilation, while group 2 patients (n = 30) received TIVA with spontaneous breathing through the n ormal airway; ETCO2 was sampled through a 10-French suction catheter insert ed into the nasopharynx via the nasal airway. Arterial blood gas and ETCO2 were recorded at the time of preinduction, induction, CO2 insufflation, and change to Trendelenburg tilt position (20 degrees-30 degrees), and at 10-m inute intervals thereafter. The results showed that ETCO2 was highly correl ated with PaCO2 in group 1 (correlation coefficient r = 0.55), but not in g roup 2 (r = 0.55). In group 2, the PaCO2/ETCO2 gradient increased as time e lapsed, with significant differences (p < 0.05) between the values at induc tion and those at 30 minutes after the change to the Trendelenburg position and thereafter. These results indicate that the ETCO2 and PaCO2 values cor relate well during the first 20 minutes after the change to the Trendelenbu rg position in laparoscopy patients receiving TIVA with spontaneous breathi ng, but that PaCO2 monitoring is still necessary.