If it comes to that, you can also share a conventional ventilator between two people. It's an ugly hack, because you have to use the same settings on both patients, so it doesn't allow for the sort of precise control you want if you're managing ARDS, but probably still a better solution than using a home-made ventilator.

It was successfully used when the ER ran out of ventilators in the wake of the Vegas shooting[1], but is probably better used in the sort of emergency where you just need to win a few hours' time than a sustained crisis.

1: https://epmonthly.com/article/not-heroes-wear-capes-one-las-...