My personal opinion is that if you're going to be fucking about with REALLY strong opies, make up an IV bag, and dilute the narcan, and keep it pinched off, with your fingers....
if you get so high you cannot keep it pinched off, the IV will start dripping, and you'll start ingesting narcan, if you stay passed out long enough it'll counteract the effects, if you wake up, pinch that shit off and you're cool. It's like a safety net for being too high.....