The purpose of this study is to compare clinical outcomes following use of NAVA versus BiPAP in patients undergoing cardiac surgery, Specifically, comparisons of non-invasive respiratory support, duration of sedation, and length of hospital stay. The investigators hypothesize that the use of NAVA will lead to a shorter duration of non-invasive respiratory support, less sedation requirements, and reduced length of hospital stay compared to the use of BiPAP.