The Role of the Lactate Dehydrogenase and the Effect of Prone Position during Ventilator-induced Lung Injury

To examine the impact of lactate dehydrogenase (LDH) as an early marker of ventilator-induced lung injury (VILI) and the effect of prone position during the VILI, we ventilated 28 normal white rabbits (10 supine, 10 prone, 8 controls) for 6 hr or until PaO2/FIO2 ratio was<200 mmHg. We applied an identical injurious ventilatory pattern (peak inspiratory pressure of 35 cmH2O with a PEEP of 3 cmH2O, I:E ratio of 1:2, and FIO2 of 0.40) in the supine and prone group. VILI was assessed by oxygenation, gravimetric analysis and histologic grading. Serum levels of LDH progressively increased significantly during the VILI (supine and prone groups) as compared with controls. There was a significant negative correlation between oxygenation and LDH levels (r=-0.619, p<0.001). Wet weight/dry weight ratios (WW/DW) and histologic scores for dependent regions were significantly higher in the supine than the prone group. There were no differences in WW/DW and histologic scores for nondependent regions between the supine and prone group. These findings suggest that serum LDH levels might be an early marker of severity of lung injury. The prone position resulted in a less severe and more homogenous distribution of VILI.