Effect Of Low Tidal Volume Combined With Positive End-expiratory Pressure On Intraoperative Pulmonary Function In Patients Undergoing Urological Retroperitoneal Laparoscopic Surgery

Objective Urologic surgical procedures always adopted admission passage of posterior peritoneum which would reducing the intraperitoneal complications and revealing the operative site better because of its special anatomical position. However, the smaller space of retroperitoneal results in a higher pressure which lead to diaphragma raising, intrathoracic pressure increasing and lung compliance reducing. Due to loosened adipose tissue which widen the absorption area of CO2 and higher pressure in the space of retroperitoneal, the absorptive amount of CO2 has been increasing which result in the high incidence of hypercarbia and pneumoderma. A part of problem, like barotraumas, which was due to the overhigh airway pressure, and CO2 accumulation, which was due to the low ventilatory frequency during traditional ventilation mode, had been eased and improved to a certain degree by high frequency low tidal volume ventilation mode. However, the partial atelectasis would also appeared in this kind of ventilation mode for the low tidal volume, which would weaken the gas exchange function. Positive end expiratory pressure（PEEP） is the positive pressure which is produced by ventilator at the end of inspiratory phase that could keep the airway pressure higher than atmospheric pressure when the air conduct opened. This ventilation pattern would prevent alveolus collapse and improve ventilation function. The previous study shows that the use of PEEP would improve postoperative hyoxemia, reduce the lung complications, and favor the recovery of respiratory function during laparoscopic surgery. However, whether PEEP had the same effect in urological retroperitoneal laparoscopy surgery has not been proved. The purpose of this study is to investigate the efficacy of PEEP on the protective lung ventilation strategy in urological retroperitoneal laparoscopy surgery through different ventilation modes.Methods Forty ASA physical status â… or â…¡patients, aged 30⁶4 yrs, with body mass index 16²9kg/m2, scheduled for urological retroperitoneal laparoscopy surgery, were randomly divided into 2 groups（n=20） using a random number table:control group（Group C） and PEEP group（Group P）. IPPV was performed after finishing trachea cannula but before pneumoperitoneum with f=12,Vt=8ml/kg,I:E=1:2. When began pneumoperitoneum, respiratory parameters of Group P were changed into f=22,Vt=6ml/kg,I:E=1:1.5,PEEP=5cm H2O（0.49kpa）, while these were adjusted to f=22,Vt=6ml/kg,I:E=1:1.5. MAP, HR, Sp O2 were recorded, and arterial blood samples for blood gas analysis were collected before anesthesia induction（T₁） and 5 min before pneumoperitoneum（T₂）, at 10min（T3）, 30min（T4）, 60min（T5）after pneumoperitoneum, stoped the pneumoperitoneum（T6）, 5 min before tube drawing（T7）, 10min（T8） and 30min（T9） after tube drawing, to get the value of PH, Pa CO2 and Pa O2. And Cdyn, A-a DO2, Pa O2/Fi O2, RI and VD/VT were calculated as well. PETCO2, Ppeak and Pmean were recorded from T₂ to T7. 4 ml arterial blood samples were collected at T₁ and T9 for determination of IL-6 and IL-10 concentration.Results Compared with T₂, Pa O2/Fi O2 in Group C was significantly increased in T5, but A-a DO2 was significantly decreased at T5 and T6. RI was significantly decreased at T3, T4, T5 and T6, but increased at T7, and it was significantly decreased in Group P at T4（P<0.05）. Compared with Group C, Pa O2/Fi O2 in Group P was significantly higher at T₂ and T4, but A-a DO2 was significantly lower at T₂, T4 and T7, as well as RI at T4 and T7（P<0.05）. Compared with T₁, the plasma IL-6 and IL-10 concentrations were significantly increased at T9 in both groups, and it was significantly lower in Group P（P<0.05）.Conclusion Low tidal volume combined with PEEP is a safer and effective ventilation strategy which can improve the pulmonary function, increase pulmonary ventilation efficiency and reduce the incidence of lung inflammationin in the patients under urological retroperitoneal laparoscopy surgery when compared with single low tidal volume ventilation strategy.