What Causes Swelling In Hand Post Iv Injection Of Heroin?

Hello there. My brother is an IV heroin user. Today he did a shot but believes he missed the whole entire shot. He said he has missed a little bit in the past, but today his WHOLE ENTENTIRE arm and hand is completely swollen.. He is nervous something is seriously wrong.. What could have or could be happening to his arm?? Please help with an answer.. Thank you..