Longer inspiratory time with ongoing flow will increase the tidal volumes. Larger tidal volume at the same rate will lead to higher minute ventilation and peak airway pressure. Ventilation with PEEP may improve oxygenation, but increase peak airway pressure. Hypercapnia is the most common complication in the patients undergoing laparoscopic surgery, and anesthesiologists face challenges in maintaining PETCO2 without increasing obviously the peak airway pressure. In view of the above mentioned, we didn’t use PEEP in this study.
In this study, we discussed the respiratory effects of pressure-controlled IRV (I: E = 2) ventilation in children undergoing laparoscopy, and found that pressure-controlled IRV could significant decreases PETCO2, improve oxygenation and gas exchange in children undergoing laparoscopy compared to conventional ratio ventilation.
IRV is different from the conventional ventilation mode. Prolonging inspiratory time can increase the alveolar ventilation volume and functional residual capacity and expand the collapsed alveolar. Besides, IRV may reduce dead-space, which is contributed to the gas distribution in the lungs. At present, the studies on IRV are fewer in children undergoing laparoscopy. Under the pressure-controlled mode, the Vt and Pmean will be higher in IRV group than those in the control group. As inspiratory time was prolonged and inspiratory flow velocity slowed down, the airway resistance decreased, which brought about an increase in Vt. Moreover, IRV could generate auto-PEEP (endogenous PEEP),  which was beneficial to oxygenation. Besides, it was reported that arterial blood oxygenation is directly related to mean airway pressure, [6, 10] so higher Pmean was also contribute to oxygenation and gas exchange in a certain range. 
As inspiratory time is prolonged, the expiratory time is relatively short under pressure-controlled IRV mode, IRV may generate endogenous PEEP. IRV could lead to an increase in Pmean and reduce venous return. In our study, blood pressure and heart rate had no statistical differences in both groups. It meant that IRV with I: E of 2:1 didn’t affect venous return. IRV might reduce cardiac output only I: E ratio beyond 2:1. [3, 12] Only when inspiratory time was excessive prolonged and Pmean reached a certain high level, IRV would result in a decrease in cardiac output, and have an effect on hemodynamics. [3, 13] IRV could bring about an increase in the Pmean and PaO2, as was agree with the study of Mercat A, et al.  However, Pmean has an important effect on hemodynamics. Although the Pmean was significantly higher in the IRV group than conventional ventilation group, there were no significant differences in hemodynamic parameters between the 2 groups. Hence, Pmean has no effect on hemodynamics in a certain range, it was similar to the results of Movassagi R, et al. 
PaO2 was significantly higher in the IRV group than conventional ventilation group at 30 min after initiation of CO2 pneumoperitoneum. It indicated that IRV could obviously increase the oxygen content, and promote oxygenation. PaCO2 was lower in IRV group than the control group, there was significantly different between the 2 groups. PaCO2 increased obviously in both groups 30 min after initiation of CO2 pneumoperitoneum. The main reason was caused by the CO2 absorption in blood,  IRV did not affect the discharge of CO2. PaCO2 fell down 5.3 mmHg in patient with normal weight during mechanical ventilation when tidal volumes decrease per 100 ml, PaCO2 fell 3.6 mmHg in morbidly obese patients.  So the tidal volume was the main factor that determined CO2 discharge during mechanical ventilation. Moreover, CO2 pneumoperatoneum might affect hemodynamics during laparoscopic surgery. 
The limitations of our study are as following: IRV is different from the conventional ventilation mode, it may have some potential risks: the long-term complications of respiratory system remain to be studied. The large sample sizes are needed to investigate the adverse respiratory and hemodynamic effects.