Background and Goal of Study:
In spite of evolution of lung-protective ventilation strategies during anesthesia, it remains unclear what the most appropriate ventilation for patients under general anesthesia. The purpose of this study is to elucidate temporal trends comparing with trends of 10 years ago, and to better understand change of mechanical ventilation during general anesthesia.
 
Materials and Methods:
All in-patient and day of admission surgical cases performed at a university hostpital under general anesthesia between January 1, 2004 and December 31, 2004 and January 1, 2014 and December 31, 2014 were included in this retrospective analysis. Patients were divided into 2004 group and 2014 group, and 817 cases in each group were included for final analyzing after propensity matching. We also carried out a survey designed to assess the clinician’s knowledge on lung protective ventilation, and actual mechanical ventilation practices including tidal volume, PEEP. Total 82 anesthesiologists in a university hospital participated in the survey. 

Results and Discussion:
The mean tidal volume per IBW were bigger in 2004 group than 2014 group (9.9 ± 1.4 mL vs. 8.4±1.0 mL per kg, p <0.001). Mean tidal volume was decreased (559.6 ± 80.9 mL vs. 475.6 ± 59.5 mL p< 0.000) and usage of PEEP was increased (0.1% vs. 49.5%, p<0.000) for ten years. There was a significant reduction in number of patients receiving VT more than 10mL/IBW (43.6% vs. 5.8%). Especially in obese patients whose body mass index is more than 30, tidal volume per IBW was reduced (10.7 ± 1.5 mL vs. 8.9 ± 0.9 mL /kg, p < 0.001), and the usage of PEEP was increased (0.1% vs. 55.3%, p<0.000). On survey, there was a significant difference in the usage of PEEP in laparoscopic surgery according to whether the anesthesiologists knew about lung protective ventilation or not (62.5% vs. 95.8%, p = 0.012). 

Conclusion(s): 
In general anesthesia, lung protective ventilation strategies have become more widespread in 2014 compared to 10 years ago. We believe this trend is related to the universalization of knowledge of lung protective ventilation. But mean tidal volume in 2014 was still more than 8m L/kg of IBW and more than half of patients was ventilated without PEEP. This highlights the need for continued investigation and education regarding the potential benefits of intraoperative lung protective ventilation.

Change of concepts in protective ventilation during general anesthesia: the concept of intraoperative protective ventilation changes according to the times and the level of knowledge