Is Pleth Variability Index (PVI) a Surrogate for Pulse Pressure Variations (PPV) in Pediatric Spine Fusion (SF) Surgery?

Spine fusion is an involved procedure during which patients are at risk for significant intra-operative blood loss.This study will compare 2 ways of determining fluid status and response to fluid administration. One way is to measure the changes in the arterial wave form from the special IV that is usually placed in an artery (PPV). The second way is to use a non-invasive method of a finger probe that measures changes in the plethysmogram or the pleth variability index (PVI). No actual patient treatments will be based on these values during surgery.