Abstract :
Background: Stroke volume variation (SVV) is a naturally occurring phenomenon, often used by anesthesiologists for hemodynamic response to intra-operative fluid administration. In a mechanically ventilated patient under general anesthesia, the arterial pulse pressure rises during inspiration and falls during expiration due to changes in intra-thoracic pressure secondary to positive pressure ventilation.
Methodology : In this open labelled, parallel group, randomized controlled trial, we investigated the role of using SVV as a marker for optimal intra-operative fluid therapy versus the conventional parameters of hemodynamic monitoring i.e., blood pressure, pulse rate and urine output in patients undergoing major spinal surgery in prone position. It was a single centre study and each group consisted of 35 patients in the age group of 18 – 50 years having ASA grade I status and without any previous comorbidities. SVV was maintained between 10 to 13% and Non-Invasive Blood Pressure (NIBP) and pulse rate maintained within 20% of baseline pre-induction values. Ringer’s lactate solution was chosen as fluid therapy in both groups.
Results : The study showed that the total amount of fluid infused to either group had no statistically significant difference; however, the change in Inferior vena cava maximum diameter (IVCmax) in patients of the SVV monitored group was significantly lower than the conventional arm, for a given amount of fluid in either group. (Levene’s test for equality of variance F = 45.46, test statistics for equality of means t = 3.86; p = 0.001) Moreover, those patients who were maintained on lower margin of SVV range had a remarkable decrease of collapsibility index of IVC compared to pre-operative values. (Spearman’s rank correlation r = 0.533; p = 0.001)
Conclusion: Thus, SVV proves to be a surrogate marker of administering intravenous fluid per-operatively maintaining euvolemic status as reflected by subsequent IVC collapsibility index (CI) values obtained in patients undergoing spinal surgery.
Keyword :
Hemodynamics, Intravenous fluid, Inferior vena cava diameter, Stroke volume variation, Collapsibility index, Spine surgery.