The threshold of stroke volume variation in deteriuining volume expansion responsiveness during fluid therapy in patients ventilated with different tidal volumes

Objective To determine the threshold of stroke volume variation （SVV） in determining the volume expansion responsiveness during fluid therapy in patients ventilated with different tidal volumes. Methods Fifty ASA I or II patients aged 20-75 yr undergoing elective gastrointestinal surgery under general anesthesia were randomly divided into 2 tidal volume groups （ n = 25 each） ： group I VT 8 ml/kg （ group Vl ） and group II VT 10 ml/kg （group V2 ）. Radial artery was eannulated and connected to Vigelo monitor for continuous monitoring of cardiac index （CI）, stroke volume index （SVI）, systemic vascular resistance index （SVRI） and SVV. Internal jugular vein was cannulated for CVP monitoring. Anesthesia was induced with midazolam, propofol, fentanyl and rocuronium and maintained with intravenous propofol and remifentanil infusion. BIS was maintained at 40-50 during anesthesia. The patients were intubated and mechanically ventilated （VT 8/10 ml/kg, RR 8-12 bpm, oxygen flow 2 L/min）. 6% HES 130/0.4 7 ml/kg was infused iv at a rate of 0.4 ml·kg-1·min-1 after induction of anesthesia. MAP, HR, CVP, CI, SVV, SVI and SVRI were recorded before and at 3 min after fluid therapy. The changing rate of SVV （△SVV） and CI （△CI） were calculated. The criterion for effective volume expansion was ACI 15%. The ROC curve for SVV in determring the volume expansion responsiveness was plotted and the diagnostic threshold was determined. Results ROC curve showed that the diagnostic threshold of SVV was 10.5 % in group V1 and 13.5 % in group V2 . The sensitivity and specificity in determining effective volume expansion were 93.3 % and 75.0 % in group V1 and 87.5 % and 85.7 % in group V2 respectively. The area under the curve for SVV and 95% confidence interval （CI） were 0.946 （0.860-1.031） in group V1 and 0.951 （0.868-1.034） in group V2 . △SVV was negatively correlated with △CI in group V1 （ = 0. 553） and V2 （ = 0. 602）. Conclusion The threshold of SVV in determining the volume expansion responsiveness during fluid therapy is 10.5 % and 13.5 % in mechanically ventilated patients with tidal volmne of 8 and 10 ml/kg respectively. Key words: Stroke volume ;  Respiration, artificial;  Vascular capacitance