Mulch if ingested could be very bad for him; is there a spot where you could collect some untreated soil? Enough so he can burrow...
Other than that bit, I don't know. Regular neosporin is probably the best bet for his wound, but flushing it seems like a sound idea.
Hope someone chimes in. Kinda worried he already ate a piece of mulch and that's what the swelling is about, but again I don't know how to proceed from there.