Effects Of PPV-directed Fluid Therapy On Tourniquet Related Hypotension During Lower Extremity Surgery

Objective To evaluate the effects of Goal-directed Fluid Therapy by different levels of PPV on Tourniquet Related Hypotension during lower extremity surgery under general anesthesia with mechanical ventilation and the effects of lactate on blood pressure changes after tourniquet deflation.Methods eighty patients undergoing unilateral arthroscopic surgery under general anesthesia combined with femoral nerve block were enrolled.All these patients were randomized into two groups based on the values of PPV before anesthesia(group A PPV≤7% and group B 7%< PPV≤12%),Artery puncture and pressure measurement,tourniquet placed were performed before operation,the pressure of tourniquet was set at 50 kpa.PPV was controlled by fluid infusion or medication during operation.PPV,SBP,HR of all patients were recorded before the use of tourniquet and when the lowest blood pressure occurred within 5 minutes after tourniquet deflation.17 cases in group A and 16 cases in group B were detected arterial blood lactate values before and after the application of tourniquet.The relationship between the PPV before tourniquet deflation and related hypotension(systolic blood pressure less than 90 mm Hg)after tourniquet deflation,the decrease of systolic blood pressure after tourniquet deflation and lactate were evaluated by statistical method.Results 80 patients completed the operation,3 cases were excluded because of PPV control failure(1 in group A and 2 in group B)and 1 case was excluded because of hemodynamic instability during the operation(group B).1.There was no significant difference in age,BMI,total time of using tourniquet,fasting time and systolic blood pressure between the two groups(P > 0.05).2.Within 5 minutes after the tourniquet deflated,the blood pressure dropped to varying degrees in all patients.The incidence of tourniquet related hypotension in group A and group B was statistically significant(35.9% vs 75.7%.P < 0.05),and the incidence of hypotension in group B was higher.The intervention rates of hypotension in groups A and B were not statistically significant(57.1% vs82.1%,P> 0.05).3.The decrease of systolic blood pressure after tourniquet deflation had no correlation with BMI,fasting time,total liquid volume,△PPV,PPV before tourniquet deflation,but positive correlation with tourniquet time and age,the correlation coefficients were r =0.404 and r= 0.289(P < 0.05).4.There was no significant difference in the value of lactate and time of tourniquet between the two groups(P > 0.05).The PPV before tourniquet deflation and lactate after tourniquet deflation of group A were higher than group B,the differences were statistically significant(5.53±0.94 vs 8.94±0.93,1.01±0.90 vs1.68±0.74,P <0.05).There was a positive correlation between the lactate and the time of tourniquet,r = 0.716(P < 0.05).There was no correlation between the lactate and the decrease of blood pressure and PPV before tourniquet deflation.Conclusion Controlling PPV below 7% before tourniquet deflation can reduce the occurrence of tourniquet related hypotension.