Effect Of Tourniquet On Tissue Oxygen Saturation Of Lower Extremity Skeletal Muscle

Objective:The study aimed to observe the changes of tissue oxygen saturation of skeletal muscle during tourniquet-induced lower distal extremity ischemia-reperfusion by near-infrared spectroscopy（NIRS）and to explore the effects of tourniquet on skeletal muscle microcirculation.Methods:Seventy-five patients,aged 18⁶4 years old,ASAⅠorⅡ,BMI18²4 kg/m²,undergoing open reduction and internal fixation of lower distal extremity assisted by a tourniquet were selected.According to the duration of intraoperative application of the tourniquet,the patients were divided into 3groups:group A（30 min）,group B（60 min）and group C（90 min）.Venous pathway was founded after entering the operating room.The patients’vital signs were monitored such as noninvasive blood pressure（NIBP）,heart rate（HR）,electrocardiogram（ECG）and pulse oxygen saturation（SpO₂）.The NIRS probe was attached at the skin（rectus femoris muscle of 10 cm from the upper edge of patella）to obtain monitor continuous StO₂.The room temperature was controlled at 21℃.Combined spinal-epidural anesthesia（CSEA）in all patients was performed by the same anesthesiologist with more than 5 years of experience.Patients were positioned L_3-4 for epidural puncture,given 0.375%bupivacaine 2³ ml to subarachnoid space and cephalad catheterized 4 cm after epidural puncture,lying in lateral position（surgical limb on the upper side）.Patients were instructed to maintain lateral position for 10¹5 minutes aiming at controlling the level of anesthesia at T₁₂.The tourniquet was fixed at the middle and upper 1/3 of the thigh of the surgical limb,its pressure was set at 280 mmHg and released after the operation.All patients received intravenous injection of 2³ mg of midazolam,followed by intravenous injection of 1mg of midazolam every 30min as required,with breathing air independently.MAP,HR and SpO₂ were recorded as the basic reference values after the vital signs were stable.StO₂ changes of the surgical limb were continuously recorded from 10min before anesthesia to 20min after surgery.Professional software（Invos Analytics Tool）was used to record and calculate the following data:before anesthesia（Baseline,%）,after anesthesia（Anesthesia,%）,StO₂ minimum（Min,%）,the hyperemic peak（Peak,%）,StO₂ stable value in the later period of hyperemia（Stable,%）,the difference between before and after（ΔStO₂,%）,the desaturation slope during occlusion（dSlope）,the resaturation rate of the reperfusion phase after the ischemic period（RR）,and duration of the hyperemic period following ischemia（Hyperemic time,s）.Results:1.There was no statistically significant difference in StO₂among the three groups before anesthesia,no significant difference in StO₂after anesthesia,and no significant difference in StO₂ minimum（P>0.05）.There was no significant difference in StO₂ peak between group A and group B（P>0.05）,and the StO₂ peak in group C was significantly lower than that in group A and B（P<0.05）.There was no significant difference in StO₂ stable value among the three groups（P>0.05）.There was no significant difference in dSlope among the three groups（P>0.05）.Compared with group A,RR of group B and group C was lower,and that of group C was lower than group B（P<0.05）.Compared with group A,the hyperemia time of group B and group C was longer,and that of group C was longer than group B（P<0.05）.2.RR showed a linear negative correlation with the ischemic time[P<0.05,r=-0.752],and the hyperemia time showed a linear positive correlation with the ischemic time[P<0.05,r=0.664].There was no correlation between the RR,hyperemia time and the age,BMI,MAP（baseline）and SpO₂（baseline）（P>0.05）.Conclusion:When tourniquet was applied within 90min,StO₂ in skeletal muscles of lower limbs was significantly reduced during ischemia,but its microcirculation function was not irreversibly impaired after reperfusion.