Bandage [object-を] do [before-前に] he [topic-は] wound [object-を] cleaned
~前に ('before doing X') takes the plain form of the verb. 洗浄する (せんじょう) = to cleanse/disinfect — a formal medical-register verb compared to casual 洗う. Note the double を: one for 包帯をする, one for 傷を洗浄する.