Illustration showing 3 causes of intravenous extravasation, the accidental administration of intravenous drugs into the surrounding tissue. 1) Needle entering vessel, tourniquet causes a small rupture in the vessel and the drug escapes. 2) Needle in the vessel, an old puncture site downstream leaks the drug. 3) With subcutaneous implant - needle misses the receptor or the drug leaks at the implant connection with the catheter.