The Applied Research On Stroke Volume Variation In Predicting Fluid Responsiveness When Using Tourniquet In Lower-extremity Surgery

Research No.1Effects of tourniquet usage on the accuracy of SVV in predictingthe fluid responsiveness in patients undergoing total knee arthroplasty undergeneral anesthesiaObjective To test whether stroke volume variation(SVV) can predict fluidresponsiveness during the period of tourniquet usage in total knee arthroplasty(TKA),and to investigate the accuracy and threshold of SVV.Methods Sixty patients undergoing TKA under general anaesthesia were prospectivelystudied. Volume expansion comprised the infusion of7ml/kg hydroxyethyl starch130/0.4and sodium chloride injection over15to20minutes after the tourniquetwas inflated. Measure cardiac index (CI),SVV,mean arterial pressure (MAP) before andafter the volume expansion. A positive reponse was defined as a≥15%increase in CI.Results32patients were volume responders and28were non-responders. SVVpredicted fluid responsiveness with an area under the receiver operating characteristiccurve(ROC curve) of0.792(P＜0.01), The optimal cut-off values of SVV were9.5%(sensitivity62.5%, specificity82.1%).Conclusion SVV predicted fluid responsiveness during the period of tourniquet usagein mechanically ventilated patients under general anaesthesia. Research No.2Effects of different levels of SVV on the occurrence of hypotensionafter tourniquet releaseObjective To observe the hemodynamic and metabolic effects of deflation of pneumatictourniquets, and to evaluate the clinical usefulness of SVV before and after tourniquetrelease to forecast and relieve the change of hemodynamic status caused by thereinfusion of the drained blood.Methods60patients undergoing TKA under general anaesthesia were enrolled in thisstudy. All these patients were randomized into four groups(group A, B, C and D) basedon the values of SVV measured at the moment before the tourniquet deflation: A, 1%,2%or3%;B,4%,5%or6%;C,7%,8%or9%;D,SVV≥10%.Appropriate volumeexpansion was performed to control the SVVs to meet the criterion. Two minutes werespent to deflate the tourniquet. The patients undergone deflating-tourniquet-relatedhypotension (the systolic pressure dropped below90mmHg) were given intravenousinjection of ephedrine, and these patients were called cases F, and recorded theintervention time of ephedrine. In other cases, record the happening time of lowestblood pressure. Calculated the percentages of cases F in each of the four groups(defined as F%). Blood samples were taken to measure arterial gas analysis at threedifferent times: before the operation,5minutes before and5minutes after the tourniquetdeflation. Compared the levels of lactic acid (Lac) and base excess (BE) in blood atthese three time points.Results Eight patients were excluded. There were15patients in group A,15patients ingroup B,13patients in group C,9patients in group D. CI increase and SVV decreaseafter tourniquet release(P＜0.01). The percentages of cases F (F%) in group A, B, C andD are40.0%,46.7%,61.5%and100%respectively, the difference have statisticalsense(P＜0.05). The levels of Lac and BE in blood showed significantly increase aftertourniquet release(P＜0.01).Conclusion Keep levels of SVV down before the tourniquet release can contribute tomaintaining a better hemodynamic status, and can help to reduce the incidence ofdeflating-tourniquet-related hypotension.