ABSTRACT
Objective Pulmonary dysfunction is common in the obese patients after laparoscopic surgery. To reduce or avoid this complication caused by improper combination of mechanical ventilatory parameters,we conducted the following trial of 3 factors with 3 levels of mechanical ventilation in order to explore the optimal combination with low airway pressure. Methods Patients were randomly allocated into 9 groups (k=3,n=27) according to the "30≤BMI<40" obesity index (ASAⅠ-Ⅱ). Anesthesia machine parameters were set as follows: respiratory frequency (f), tidal volume (VT), respiratory ratio (I:E) as the three factors of A, B, C, with 3 levels of f=15, 12, 9 (bpm), VT=8, 10, 12 (mL/kg), I:E=1:2.5, 1:2.0, 1:1.5. By using L9(3~4)K=3 repeat orthogonal experimental design and analysis table, the variable factors that affect the respiratory index such as the end tidal carbon dioxide pressure (P_(ET)CO_2), peak airway pressure (PIP), mean airway pressure (P_(mean)), and the end of endogenous airway pressure (PEEPi) were analyzed. Results In this study, 27 cases undergoing laparoscopic surgery under general anesthesia were allocated into 9 experimental groups. The hemodynamics of these patients was stable, SPO_2 was kept at 100 percent during the operation. The results of different combinations were described as follows: ①P_(ET)CO_2: f and VT with different level had great impact on P_(ET)CO_2 (P<0.01), I:E had no significant difference in three levels (P>0.05);② PIP: f had great effect on PIP (P<0.05);VT and I:E in three levels also had significant effect on PIP(P<0.01);③ P_(mean): all the ventilation parameters with different combination had significant effect on P_(mean)(P<0.01). Conclusions The best combination of respiratory parameters is A3B1C2, i.e., f=9 bpm, VT=8 mL/kg, and I:E=1:2.0, which indicates that neither small tidal volume and faster frequency, nor slow frequency large tidal volume is a good choice. In order to let obese patients under general anesthesia obtain the best lung protective effect by low airway pressure with good ventilation, it is worth noting that: ①I:E has a great effect on airway pressure (PIP, P_(mean)), which is important for lung protection;②I:E has the opposite effect on PIP and P_(mean).