Purpose of the visit
If the purpose of the visit is for wound vac dressing, and no other issues are addressed, then NO significant, separately identifiable E/M has occurred, so you would not charge for the office visit ... only the wound vac.
If the purpose of the visit is for wound vac dressing, and some completely different issue is raised and addressed (e.g. sinusitis), then you can charge the office visit with mod 25 (and appropriate diagnosis) ... be sure your documentation clearly supports a significant, separately identifiable E/M.
Hope that helps.
F Tessa Bartels, CPC, CEMC