Accuracy Of Stroke Volume Variability In Evaluate Fluid Responsiveness During Thoracotomy In Cardiac Surgery

Background:Cardiac function decreases in patients undergoing cardiac surgery,volume and fluid therapy were limited.In order to maintain an effective fluid load and the stability of intraoperative hemodynamics,an accurate monitoring indicator is indispensable.Stroke volume variation（SVV）is a dynamic hemodynamic parameter,based on a certain intrathoracic pressure,produced by a periodic cardiopulmonary interaction during mechanical ventilation.It has become a new indicator to judge whether the body has fluid responsiveness and needs fluid therapy,and its clinical value has been widely recognized.However,in the state of thoracotomy during cardiac surgery,the intrathoracic pressure is significantly reduced,the value of SVV will be disturbed,The usual strategy for the assessment of volume responsiveness by SVV does not apply to the state of thoracotomy.The variation range of SVV in different volume and whether SVV can be used to evaluate fluid responsiveness during thoracotomy are still unclear.Objective:Observe and determine the value range of SVV during thoracotomy in cardiac surgery,verify the accuracy of SVV in evaluating volume responsiveness during thoracotomy,in order to expand the clinical application of SVV and provide theoretical basis for reasonable volume therapy during thoracotomy in cardiac surgery.Methods:According to the exclusion and inclusion criteria,37 patients undergoing elective cardiac surgery from June 2022 to December 2022 were selected in this trial.All patients were routinely monitored after entering the room.The radial artery was punctured and catheterized under ultrasound guidance and connect to the Flo Trac/Vigileo monitor,to obtain the parameters of stroke volume variation（SVV）,stroke volume index（SVI）,stroke volume（SV）,cardiac output（CO）and cardiac index（CI）.Anesthesia combined intravenous and inhalational,and monitoring of bispectral index（BIS）at the beginning of anesthesia induction.After tracheal intubation,the tidal volume was set to 6-8ml/kg in PCV-VG mode,the respiratory rate was 10-16/min to maintain P_ETCO₂ at 35-40mm Hg.Positive end-expiratory pressure ventilation（PEEP）was used to maintain airway pressure between 15 and 18cm H₂O.The right internal jugular vein was punctured under ultrasound guidance to monitor central venous pressure（CVP）.SVV and other monitoring indicators were recorded when the sternum was closed（T1）.After 2 minutes of sternal closure,hemodynamic data T2 was recorded,and then liquid impact test was performed with 300ml of hydroxyethyl starch 130/0.4electrolyte injection,which was infused intravenously within 5 minutes.Hemodynamic data T3 were recorded again.ΔSVI≥10%after fluid infusion was defined as fluid responsiveness and response to fluid therapy.The patients were divided into two groups:fluid insufficiency group（effective volume therapy）and adequate volume group（ineffective volume therapy）.According to the recorded data,the ROC curve of each monitoring indicator was drawn to evaluate the accuracy of SVV and other indicators during thoracotomy and after chest closure.SPSS was used for data statistics.The measurement data were tested for normality and homogeneity of variance,and then t-test or nonparametric test was performed according to the type.P<0.05 was considered statistically significant.Results:All 37 patients underwent fluid impulse test.11 patients did not respond significantly to volume therapy（volume sufficient group）,and 26 patients responded（volume insufficient group）.The mean value of SVV was 5.7±0.5 in the insufficient group and 4.8±1.1 in the sufficient group under thoracotomy,and the difference was not significant（P>0.05）.After the chest was closed,the SVV of the insufficient volume group was significantly higher than that of the sufficient volume group（P<0.05）.There were no significant differences in MAP,HR,CO,CI,SV,SVI.WithΔSVI≥10%as the response standard,ROC curve results:during thoracotomy in cardiac surgery,the diagnostic threshold of SVV was 5.0%,with a sensitivity of 42.3%,a specificity of81.8%,and an area under the curve（AUC）of 0.687,95%CI[0.514-0.829].The results indicate that measurement of SVV was affected thoracotomy,leading to the decrease of its accuracy in judging volume,diagnosis role is limited.With sternum closure,the diagnostic threshold of SVV was 10.0%,with a sensitivity of 92.3%,a specificity of63.6%,and an AUC of 0.857,which has certain accuracy and can be used as a reference for guiding postoperative fluid management.Conclusions:The ability of SVV to assess volume during thoracotomy in cardiac surgery is reduced,diagnostic role for fluid response is not high.After thoracic closure,SVV can still be used as a guide and reference for fluid management.