Changes in stroke volume variation and cardiac index during open major bowel surgery

Stroke volume variation (SVV) is a dynamic indicator of preload, which is a determinant of cardiac output. Aims: Aim of this study was to evaluate the relationship between changes in SVV and cardiac index (CI) in patients with normal left ventricular function undergoing major open abdominal surgery.

Patients undergoing major open abdominal surgery were monitored continuously with FloTrac® to measure SVV and CI along with standard monitoring. Both SVV and CI were noted at baseline and every 10 min thereafter till the end of surgery and were observed for concurrence between the measurements.

1800 pairs of measurement of SVV and CI were obtained from 60 patients. Mean SVV and CI (of all patients) measured at different time points of measurement showed that as SVV increased with time, the CI dropped correspondingly. When individual readings of CI and SVV were plotted against each other, the scatter was found to be wide, reiterating the lack of agreement between the two parameters (R² = 0.035). SVV >13% suggesting hypovolemia was found at 207 time points. Of these, 175 had a CI >2.5 L/min/m² and only 32 patients had a CI <2.5 L/min/m².

SVV, a dynamic index of fluid responsiveness can be used to monitor patients expected to have large fluid shifts during major abdominal surgery. It is very specific and has a high negative predictive value. When SVV increases, CI is usually maintained. Since many factors affect SVV and CI, any increase in SVV >13%, must be correlated with other parameters before administration of the fluid challenge.