Stroke volume variation during hemorrhage and after fluid loading: impact of different tidal volumes.

BACKGROUND: Previous studies have shown that stroke volume variation (SVV) may be used to assess preload and fluid responsiveness. It is currently under debate, if SVV reliably displays changes in preload during ventilation with clinically used tidal volumes. This study was designed to evaluate whether the predictive value of SVV depends on the tidal volume applied particularly during acute changes of preload.

METHODS: We studied 14 anesthetized pigs (35 +/- 2 kg) during changing tidal volumes (5, 10 and 15 ml/kg) at normovolemia (BL), after removal of 500 cc of blood (Hypo) and after retransfusion plus additional 500 cc 6% hydroxyethyl starch (Hyper). SVV was recorded continuously, and global end-diastolic volume (GEDV) was obtained by transpulmonary thermodilution at each experimental stage.

RESULTS: GEDV changed significantly comparing the different experimental stages (P < 0.0001). During ventilation with 5 ml/kg, SVV did not change significantly at the different loading conditions. In contrast, during ventilation with both 10 and 15 ml/kg, SVV changed significantly comparing hemorrhage to fluid loading. However, at 15 ml/kg SVV was above the recommended value throughout the experiment.

CONCLUSIONS: In this animal model, SVV was not sensitive to acute changes in preload during ventilation with a tidal volume of 5 ml/kg. Moreover, ventilation with high tidal volume may suggest volume loading even after sufficient volume resuscitation.