Assessment Of Stroke Volume Variations In Monitoring Volume State Undergoing Off-pump Coronary Artery Bypass Grafting Patients During Open Chest Conditions Under General Anesthesia

Objective SVV, derived from the cardiopulmonary interaction in patients under general anesthesia with mechanical ventilation, is used to predict the responsiveness of cardiac preload. In a continuously fixed sliding time window of mechanical ventilation, SVV is calculated as:SVV=(SVmax-SVmin)/SVmean. In recent years, SVV has played an important role in predicting the responsiveness for surgery patients and guiding such patients liquid treatment. From a clinical view, it is important to know how SVV reflects preroad and fluid responsiveness during cardiac surgery. However, conflicting data have published on this subject. This research was to assess the accuracy and reliability of stroke volume variations(SVV) derived from FloTrac/Vigileo system in monitoring the changes in blood volume in patients undergoing off-pump coronary artery bypass grafting(OPCABG) under general anesthesia.Methods After the approval from the ethics committee and get the permmition of the patients, twenty-nine patients, ASA Ⅱ-Ⅲ and NYHA Ⅱ-Ⅲ, aged44-77yr, undergoing elective off-pump coronary artery bypass grafting were randomly divided into2groups:control group (group C, n=8) and volume expansion group(group V, n=21). When patients entered the operating room, ECQ HR, SpO2and PETCO2were continously monitored by multifunctional vital signs monitor. Under local anesthesia, left radial arterial catheter was inserted. The FloTracTM/VigileoTM system was connected to the arterial line and actived after calibration. MAP, CO, CI, SVV, SV, SVI, SVR, SVRI were all continously monitored. Induction of anesthesia was then performed with midazolam3mg, etomidate0.2mg/kg, fentanyl10μg/kg, rocuronium0.6-0.8mg/kg, lidocaine30mg. All the patients were ventilated with intermittent positive-pressure ventilation (IPPV) after routine anesthesia induction. The ventilatory parameters were kept stable during the study:tidal volume (VT)8ml/kg, respiratory rate (RR)12bpm, positive end expiratory pressure (PEEP)0, fractional inspired oxygen (FiO2)80%, oxygen flow2.4L/min, airway pressure<30cmH2O, PETCO235-45mmHg and SpO298%-100%. A three-lumen central venous catheter used for monitoring CVP and transfusion was inserted into the internal jugular vein after induction. Anesthesia was maintained with a continuous infusion of propofol2-3μg/ml TCI, remifentanil0.2-0.45μg·kg-1·min-1and sevoflurane1%-3%(end-tital concentration) and atracurium0.3mg/kg was intermittently infused. BIS was monitored by EEG monitor and was keeped between45and55. Intraoperative arterial blood gas analysis and detection were regularly performed and maintained the Hb>90g/L and the Hct>25%. If the Hb was below90g/L, PRBC was transfused. That6%hydroxyethyl starch130/0.4sodium chloride solution7ml/kg was infused intravenously after completion of sternotomy and pericardiotomy and a period of5min for haemodynamic stabilization(T1) at a rate of0.25ml·kg-1·min-1in group V. MAP, HR, CVP, systemic vascular resistance (SVR), SVV, and stroke volume index (SVI) were determined at T1(before the infusion of hydroxyethyl starch) and T2(10min after the infusion of hydroxyethyl starch), and then the change rate(ΔHR, ΔMAP, ΔCVP, ΔSVR, ΔSVV, ΔSVI) was calculated. In group C, haemodynamic measurements were peformed at T1and T2, and the change rate(ΔHR, ΔMAP, ΔCVP, ΔSVR, ΔSVV, ΔSVI) was calculated as well. During this time interval compound sodium chloride injection3ml/kg was infused. ROC curves of changes in blood volume monitored by hemodynamic parameters were plotted. When patients entered the operating-room(before the chest was opened), compound sodium chloride injection was intravenously infused. Results After volume expansion, it was shown that CVP, SVI,CO and CI increased, SVRI、SVV decreased significantly (P<0.01), while MAP, HR weren’t changed. Variation in HR (r=-0.737,P<0.05), SVR (r=-0.480,P<0.05) were significantly correlated to Variation in SVI; there was no correlation between ΔCVP,ΔMAP,ΔSVV and ΔSVI. SVV (r=0.640,P<0.01) and HR (r=0.591,P<0.01) before volume expansion were correlated to Variation in SVI, but no correlation was found between MAP, SVR, CVP and Variation in SVI. The analysis of receiver operating characteristic (ROC) curve showed that:if the criteria that the change rate of SVI≥25%was used for assessing the changes in blood volume, diagnostic threshold of SVV was8.8%; when SVV≥8.8%, the sensitivity and specificity of blood volume minotoring were52.6%and100%respectively. The size of the area under the ROC curve was used to reflect the value of an indicator on diagnosis of certain diseases. AUC<0.5means that the diagnostic test was no clinical significance.0.5<AUC≤0.7shows that the values of diagnostic was lower.0.7<AUC≤0.9demonstrates that the values of diagnostic was moderate. AUC>0.9illustrates that the values of diagnostic was higher. It is discovered that the best area under the ROC curve for SVV was0.579, more than those of CVP、MAP、SVR (0.053-0.368) statistically, but the accuracy in monitoring blood volume was low.Conclusion SVV derived from FloTrac/Vigileo system can not be used accurately to monitor the changes in blood volume in patients undergoing off-pump coronary artery bypass grafting under general anesthesia.