ABSTRACT
Objective To study the best combination of respiratory parameters that can maintain good ventilation with a low airway pressure under general anesthesia and CO2 pneumoperitoneum (12 mm Hg) during laparoscopy, which is important for lung protections. Methods Basic respiratory parameters of anesthesia machine, respiratory frequency (f), tidal volume (VT), and respiration ratio (I∶E), were used as three factors A, B, and C. The there levels were set as f=15, 12, and 9 bpm; VT =8, 10, and 12 ml/kg body weight; and I∶E =1∶2.5, 1∶2.0, and 1∶1.5. L9(34) K=3 was adopted for repeated orthogonal experimental design. The effect of different combinations of respiratory parameters on peak inspiratory pressure (PIP), mean airway pressure (Pmean),and end-tidal carbon dioxide partial pressure (PETCO2), were analyzed statistically. Results During the laparoscopy, the vital signs of 27 patients were stable under general anesthesia with 9 combinations of the respiratory parameters, the SpO2 was maintained at 100%, and the PEEP was kept at 1 hPa. The effect of the three levels of VT (factor B) on PIP was not significant (P=0.074). While the effects of f (factor A) on PETCO2 and I∶E on Pmean were significantly different among the three levels (P=0.002 and P=0.017, respectively). Conclusion The best combination of three factors-levels respiratory parameters is not small tidal volume with fast frequency or large tidal volume with slow frequency, but is A2B2C2 (f=12 bpm, VT=10 ml/kg body weight, and I∶E=1∶2.0).