Determination of Best PEEP (Positive End-expiratory Pressure) in Anesthetized Infants in Terms of Prevention of Atelectasis

Purpose of research; to determine the appropriate positive end-expiratory pressure to minimize atelectasis during general anesthesia in infants. Study design : Application of one pressure of PEEP among 3, 6, or 9 cmH2O during mechanical positive ventilation for general anesthesia to randomly assigned infants over 6 months to 13 months of age . Immediately after the start of anesthesia (PEEP=0) and before the end of anesthesia, the score of atelectasis is measured by lung ultrasonography with the standardized method. The scores at PEEP3, PEEP6, and PEEP9 will be compared to identify the appropriate PEEP at which atelectasis is the least likely to occur during anesthesia. Medical Equipment : Ultrasonography with 6 - 13 MHz linear probe, Cardio-Q esophageal Doppler The number of target subjects: According to the results of previous studies, the lung ultrasound score by ultrasonography at the end of anesthesia was 28.5 (IQR 21.8-37) without any recruitment (PEEP 0 cmH2O) (IQR 6-21.3). When PEEP of 5 cmH2O was maintained, the lung ultrasound score is 12.5 (IQR 6-21.3), which is lower than PEEP 0. It is assumed that the score at PEEP3 is 20, the score at optimal PEEP is 10, and the standard deviation is 11. Bonferroni correction is required for statistical analysis. In comparison between the two groups, alpha is used as the Bonferroni corrected alpha level of 0.05 / 3 = 0.017. The significance level alpha is fixed at 0.017 and the number of samples considering the 10% dropout rate when the power (1-β) is 80% is required to be 30 for each group. Data analysis and statistical methods: Atelectasis score, cardiac index, peak inspiratory pressure, and dynamic compliance will be compared by t-test between groups(PEEP3 vs PEEP 6, PEEP 3 vs PEEP 9, PEEP 6 vs PEEP 9). P \< 0.017 is going to be considered statistically significant.