Back-to-back shifts with barely a break in between test even people who are used to long hours.
A few things that come up often from nurses managing this: eating small amounts regularly rather than skipping meals during a run of shifts, prioritising sleep on days off over other commitments, and having a plan for caffeine that doesn't rely on whatever's in the break room.
Carrying something portable helps when there's no time to queue for coffee between patients.
Neuchu fits in a pocket and doesn't need a kettle or a queue — 50mg of natural caffeine per piece. You can find it here.