Abstract: Abstract： Objective To investigate the effects of dexmedetomidine preconditioning on nitric oxide (NO)/endothelin (ET)-1 imbalance and remote lung injury induced by lower limb ischemia-reperfusion (LIR). Methods Sixty patients who scheduled for unilateral lower extremity surgery matched American Society of Anesthesiologists (ASA) Ⅰ-Ⅱ, were random⁃ ized into two groups: control group (R group, n=30) and dexmedetomidine preconditioning group (PD group, n=30). Lumbar plexus combined with sciatic nerve block was performed guided by a nerve stimulator in both groups. In group PD, dexme⁃ detomidine intravenous infusion was started at a dose of 0.125 mL /kg (4 mg/L) for 10 minutes before using tourniquet, where⁃ as group R received an equivalent volume of normal saline. Artery blood gas analysis, respiratory index and oxygenation in⁃ dex were measured, and NO, ET-1, interleukin-8 (IL-8) and malondialdehyde (MDA) concentrations were determined from plasma samples 10 minutes before tourniquet inflation (T0), 15 minutes (T1), 2 h (T2), 6 h (T3) and 24 h (T4) after tourniquet deflation. Results Compared with T0, RI was higher at T3 in group R and OI was lower at T2-4 (P < 0.01). There were no signifi⁃ cant differences in RI and OI of group PD between different time points (P > 0.05). In R and PD groups, ET-1, IL-8 and MDA concentrations were increased, while NO level and NO/ET-1 ratio were significantly decreased after tourniquet defla⁃ tion (P＜0.05). Compared with group R, RI was lower and OI was higher at T3 in group PD (P < 0.01). The levels of ET-1, IL-8, MDA, NO and NO/ET-1 ratio were significantly different after tourniquet deflation between group PD and group R (P＜0.05). In group R, there was positive correlation between ET-1 and IL-8 levels with RI, and negative correlation be⁃ tween ET-1 and IL-8 levels with OI (P < 0.01). There was positive correlation between NO level, NO/ET-1 ratio and RI lev⁃el (P <0.01). Conclusion Lung function impairment induced by tourniquet application could be attenuated by dexmedeto⁃ midine preconditioning based on protecting endothelial cells and inhibiting lipid peroxidation.

Key words: Dexmedetomidine, Limb ischemia-reperfusion, Pulmonary gas exchange, nitric oxide, Endothelin-1