Evaluation of Low Tidal Volume During General Anesthesia in Prone Position on Respiratory Functions

Background: Surgery is accompanied by postoperative pulmonary functions impairment especially in the prone position. There is evidence suggested that using low tidal volume during general anesthesia may decrease post-operative lung injury. This study aimed to evaluate the effect of low tidal volume on lung functions during mechanical ventilation for general anesthesia while patients lying in the prone position. A prospective clinical trial was performed on 88 patients ASA I&II scheduled for elective surgery while patients lying prone and were randomly assigned to either protective ventilation group A with tidal volume; 5-7 ml/kg, 10 cm H2O positive end expiratory pressure (PEEP) with recruitment maneuver (RM) or conventional group B with Tidal Volume; 10-12 ml/kg, without both PEEP and RM. The primary efficacy variables were assessed by pulmonary function tests, performed before surgery, and 6, 12 and 24 hours postoperatively. Improvement of lung functions were found in the first post-operative 6 and 12 hours in the low tidal volume group and significant difference was found in all parameters P value 0.001 except PaO2/FIO2 ratio P value 0.4. After 24 hours there were significant difference in the FVC, predicted FEV1 and FVC and FEV1/FVC ratio being higher in the low tidal volume group with P value 0.001. Patients in both groups showed similar rates of postoperative chest complications without significant difference. Lung protective ventilation improved lung functions in the first post-operative 24 hours. There was no significant postoperative chest complications difference between the two groups