Is Pleth Variability Index (PVI) a Surrogate for Pulse Pressure Variations (PPV) in Pediatric Spine Fusion (SF) Surgery?
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.
Spine fusion is an involved procedure during which patients are at risk for significant
 intra-operative blood loss. The resulting hypovolemia increases the fluctuations in arterial
 pressure associated with positive pressure ventilation. These respiratory induced arterial
 pressure variations (RIAPV) appear as cyclical peaks and troughs on the arterial waveform.

 Different approaches have been used to quantify the RIAPV. One such approach has been to
 measure the pulse pressure variation (PPV), using invasive arterial monitoring. In previous
 studies, PPV has been shown to be a good indicator of fluid responsiveness intra-operatively,
 but this has not been specifically evaluated in patients undergoing spine fusion. This
 patient population is of particular interest because of their underlying scoliosis as well as
 their prone position during the operation. These two variables could potentially alter
 lung-thorax mechanics in a manner which may influence RIAPV, which is specifically determined
 by the interaction between intrathoracic pressure and venous filling of the heart. A second
 approach to quantifying RIAPV relies on non invasive technology initially developed by the
 Masimo Corporation for pulse oximetry. This parameter has been coined pleth variability index
 (PVI), as it specifically quantifies real time changes in the plethysmogram associated with
 respiration. PVI, which is based on arterial blood volume changes, is therefore analogous to
 PPV, which is derived from changes in arterial pressure. To date PVI has only been evaluated
 in adult patients undergoing cardiac surgery and the data suggest that it may be a useful
 indicator of fluid responsiveness.

 Given the non-invasive and continuous nature of PVI, it is appealing for potential use as a
 bedside monitor to guide fluid resuscitation. However, photoplethysmography is known to be
 sensitive to noise due to motion, light and electrical interference. Furthermore, PVI is
 based upon a degree of quantitative evaluation of the photoplethysmogram that is the first of
 its kind. For these reasons, it is important to understand the limits of agreement between
 PVI and PPV before we can accept PVI as a non-invasive surrogate measurement. This study
 intends to evaluate PVI by analyzing it in relation to PPV. More specifically, paired
 measurements of PPV and PVI will be compared to determine the limits of agreement between the
 two parameters in patients undergoing spinal fusion.
Inclusion Criteria:

 -  Males or females age 8 to 18 years inclusive.

 -  History of idiopathic or neuromuscular scoliosis.

 -  Scheduled for posterior spinal fusion.

 -  Parental/guardian permission (informed consent) and if appropriate, child assent.

 Exclusion Criteria:

 -  Inability to understand or read English to provide consent.