The Effect Of Prone Position On Pulmonary Gas Exchange In Patients For Spine Surgery Under General Anesthesia And Mechanical Ventilation

Background Prone position can improve pulmonary oxygenation of ARDS patients and alleviate hypoxemia, so prone position has beenone of the important methods for the treatment of acute respiratory distress syndrome. Prone position has commonly used for spinal surgery and neurosurgery. However, prone position is not normal position and will lead to a series of pathophysiological changes.The effect of prone position on pulmonary gas exchange in patients for spine surgery under general anesthesia and mechanical ventilation is less.Objective By collecting the blood gas analysisafter prone position and caculating the oxygen index Pa O2/Fi O2 and the shunt rate Qs/Qt,to observe the effects of prone position on pulmonary gas exchange in patients for spine surgery under general anesthesia and mechanical ventilation.Methods Fifty patients for spine surgery in prone position were enrolled and the FIO2 was 60%(n = 25, group P60) or 100%(n = 25, group P100), fifty patients sheduled for elective surgery in supine position were enrolled and he FIO2 was 60%(n = 25, group S60) or 100%(n = 25, group S100). After the patients were induced and intubated, the patients were ventilated mechanically in an IPPV model. The tidal volume was set to 8 ml/Kg and the respiration rate was set to 12 times per minute. The arterial blood gas analysis was performed at three time-points:(1) after the normal anesthesia induction was done under supine position,(2) after the body position was changed to prone position for surgery,(3) after PEEP was set at 10 cm H2 o under prone position. There was a need of 15 minutes for the gas to be balanced before the arterial blood was obtained.Oxygen index Pa O2/Fi O2 and Qs/Qtwas calculated respectively.Results When FIO2 was set at 0.6, oxygen index Pa O2/Fi O2 under supine position was(381.50±134.35 mm Hg), oxygen index Pa O2/Fi O2 under prone position was(452.83±112.55 mm Hg),oxygen index Pa O2/Fi O2 under prone position increased significantly compared to that under supine position(P﹤0.05).The shunt rate Qs/Qt under supine position was(8.30±4.09%), the shunt rate Qs/Qt under prone position was(6.22±3.50%), the shunt rate Qs/Qt under prone position decreased significantly compared to that under supine position(P﹤0.05), When PEEPwas set as 10 cm H2O, oxygen index Pa O2/Fi O2 increased significantly compared to that under prone position(P﹤0.05)and the shunt rate Qs/Qt decreased significantly compared to that under prone position(P﹤0.05);When FIO2 was set as 1.0, oxygen index Pa O2/Fi O2 under supine position was(466.25±117.32 mm Hg), oxygen index Pa O2/Fi O2 under prone position was(532.93±87.79 mm Hg), oxygen index Pa O2/Fi O2 under prone position increased significantly compared to that under that under supine position(P﹤0.05), the shunt rate Qs/Qtunder supine position was(10.68±5.68%), the shunt rate Qs/Qt under prone position was(7.54±4.60%), the shunt rate Qs/Qt under prone position decreased significantly compared to that under supine position(P﹤0.05), When PEEPwas set as 10 cm H2O, oxygen index Pa O2/Fi O2 increased significantly compared to that under prone position(P﹤0.05)and the shunt rate Qs/Qt decreased significantly compared to that under prone position(P﹤0.05). Oxygen index Pa O2/Fi O2 with FIO2 1.0 increased significantly compared to that FIO2 0.6, but Qs/Qt with FIO2 1.0 increased significantly compared to that FIO2 0.6(P﹤0.05).Conclusion The oxygen index Pa O2/Fi O2 under general anesthesia and mechanical ventilation increased and the shunt rate Qs/Qt decreased when the patients were took from supine position to prone position, pulmonary gas exchange was improved in patients for spine surgery under general anesthesia. When PEEPwas set as 10 cm H2O, oxygen index Pa O2/Fi O2 increased significantly compared to that under prone positionand the shunt rate Qs/Qt decreased significantly compared to that under prone position. Mechanical ventilation with 100% oxygen concentration is more profitable in index Pa O2/Fi O2 in patients under spine surgery, but Qs/Qtincreased significantly.