Effects of fraction of inspired oxygen and positive end-expiratory pressure on gradient between arterial and end-tidal carbon dioxide in patients undergoing gynecological laparoscopic surgery

Objective To evaluate the effects of fraction of inspired oxygen (FiO2) and positive end-expiratory pressure (PEEP) on the gradient between arterial and end-tidal carbon dioxide (D(a-ET)CO2).Methods Sixty ASA Ⅰ or Ⅱ patients (body mass index ＜ 30 kg/m2),aged 25-50 yr,weighing 45-75 kg,scheduled for elective gynecological laparoscopic surgery,were randomized into A,B and C groups (n =20 each).The patients were mechanically ventilated with pure oxygen in group A,and with air and O2 (FiO2 =50％) in groups B (PEEP =0) and C (PEEP =5 cm H2O).PETCO2 was monitored during mechanically ventilation.Blood samples were obtained from the radial artery immediately after tracheal intubation (T1) and at 1 h of pneumoperitoneum (T2) for blood gas analysis.D(a-ET) CO2 and Qs/Qt were calculated.Results D(a-ET) CO2 and Qs/Qt were significantly lower at T2 in groups B and C than in group A (P ＜ 0.05).Compared with group B,D(a-ET)CO2 was significantly decreased at T2 (P ＜ 0.05),and no significant change was found in Qs/Qt in group C (P ＞ 0.05).Conclusion Decreased FiO2 and PEEP of 5 cm H2O can decrease D(a-ET)CO2 and increase the accuracy of PErCO2 for reflection of PaCO2,which is due to reduced intrapulmonary shunt. Key words: Oxygen concentration;  Positive end-expiratory pressure;  Carbon dioxide;  Laparoscopic surgery