A study out of the University of Kentucky published in November of 2012 in the Southern Medical Journal showed that music therapy can benefit patients pre-operatively, intra-operatively, and post-operatively. They found that patients needed less sedative medication, recovered more quickly, had shorter ICU stays, felt better, and had lower hospital costs. Previous studies have shown that through imagery that patients also had less blood loss during surgery and needed less pain medication post-operatively.
Some great resources for this kind of therapy can be found at Aurelis.org, thehealingmind.org and from music from people like Steven Halpern.