Well,
sometimes the game is just a bitch. I once had a game where I didn't get any large med-packs (I did see one former captain and one Baron use them :) and very few small ones - fortunately, including all four from the entrance - but that's it. I survived until quite deep on a few Supercharge globes, all guaranteed (Arena, Chained Court, Halls of Carnage) and a few Berserker packs, but then got creamed when a Baron destroyed a wall behind me, opening the way for another Baron and a couple of Cacodemons or Knights, maybe even commandos or Arachs (I don't remember exactly whom).
As for the original question, I did encounter two Arach caves in a row during my only legitimate (not save-scummed) win. I went shottyman route, which is probably the worst for such places (even Double SG doesn't cover 360o), and managed to survive by burning through all of my med-packs and shotgun shells, and then switching to chainsaw to finish off the few remaining ones. This was on medium (hey, not too rough!) difficulty, and by then I had Ironman(3)/TaN(2), which is immensely helpful.
I think this is just the part of the game and you simply learn to deal with it.
FWIW,
Zarin.