Question: We have a chart with the finding "extravasation of vesicant chemotherapy." What is this, and what is the correct diagnosis? New Mexico Subscriber Answer: Extravasation occurs when a substance passes out of a vessel or organ; vesicant chemotherapy is treatment with a drug that can cause tissue damage and necrosis if the drug extravasates. This can happen for a variety of reasons, from the IV catheter moving or slipping out of the vein, to the IV catheter leaking, to the needle in an implantable port being misplaced or dislodged. ICD-9 includes a new code group for extravasation in 2009: 999.8x (Other infusion and transfusion reaction). Your choice in fifth-digit extensions include 999.81 (Extravasation of vesicant chemotherapy), 999.82 (Extravasation of other vesicant agent), 999.88 (Other infusion reaction), and 999.89 (Other transfusion reaction).