Modifier 22 for Increased Procedural Services
"When the work required to provide a service is substantially greater than typically required, it may be identified by adding modifier 22 to the usual procedure code. Documentation must support the substantial additional work and the reason for the additional work (ie, increased intensity, time, technical difficulty of procedure, severity of patient's condition, physical and mental effort required). Note: This modifier should not be appended to an E/M service."
Also see this for some good information:
http://www.wpsmedicare.com/j8macpartb/resources/modifiers/modifier-22.shtml