Background and Aim: It has been demonstrated that pneumoperitoneum and steep Trendelenburg position during laparoscopic surgery increase elastance of the respiratory system and impair gas distribution in the lung, resulting in hypoxia. In this study, we investigated the effect of different PEEP on elastance of respiratory system and regional ventilation distribution using Electrical Impedance Tomography (EIT) during robot-assisted laparoscopic prostatectomy (RALP). 

Materials and methods: Forty-seven patients undergoing RALP were randomly assigned to be ventilated with PEEP 5 cmH2O (PEEP5) or with PEEP 15 cmH2O (PEEP15). After induction of anesthesia (T1), tidal volume was set at between 6 to 8 ml/kg/PBW and each PEEP was applied after lung recruitment maneuvers before the establishment of pneumoperitoneum and the Trendelenburg position (T2). Airway and esophageal pressures were measured and elastances of respiratory system, chest wall, and lung were calculated at T1, T2 and 20 min (T3), 60 min (T4), 120 min (T5) after the patients being placed in the steep Trendelenburg position, and at end of surgery (T6). Differences in elastances and fraction of regional ventilation distribution of the dependent part monitored by EIT were compared at each time point. Data was analyzed by one-way ANOVA with repeated measures and Tukey test as post-hoc analysis for the comparison within group. Independent t-tests or Mann-Whitney U tests were used for the comparisons between the groups.

Results and discussion: 
Elastances of chest wall and respiratory system increased at T3, T4 and T5 compared to T2 (p < 0.05) in both groups, and were significantly higher in PEEP5 compared to PEEP15 (p < 0.05). The fraction of ventilation distribution of the dependent part at T3, T4 and T5 was significantly lower than at T2 in PEEP5, but not in PEEP15. The intergroup comparisons showed significantly higher distribution in PEEP15 than in PEEP5 at T3, T4 and T5. P/F ratio was higher in PEEP15 between T2 to T6, especially there was significant difference at T3 and T6. However, the lung elastane revealed no statistical differences between the two groups at any time point.

Conclusion:
Elastance of chest wall increased during pneumoperitoneum and Trendelenburg position, leading to the impairment of the ventilation distribution at dependent part of the lungs. Higher PEEP could prevent lung collapse and keep the better ventilation distribution, which leads to maintenance of oxygenation. 


01 / The effect of different positive-end expiratory pressures on elastance of respiratory system and ventilation distribution during robot-assisted laparoscopic radical prostatectomy