Contact Dermatitis after surgical procedures

My husband has had several orthopedic surgeries (4 shoulder, 3 carpal tunnel and a knee) and ever since the 2nd surgery he blisters very badly. He’s had the whole skin patch testing done, but nothing showed a reaction. Nothing for tape, gauze, cleansers, etc. Has anybody ever had this happen? I’m attaching a picture of what happened after surgery this past Wednesday. The blisters always start onday 2. He’s on a double dose of prednisone which calms the blistering and rash down. He had 2 skin biopsies done yesterday but not sure if they will give us any answers. Thank you.