Ventilation

The exam rarely asks “what is ventilation” — it tests whether air should flow IN or OUT of the room, and the wrong answer is usually a reversed pressure direction. The tell: read the patient, not the diagnosis label. A patient who spreads something (active TB, measles, varicella) needs negative pressure so room air is pulled inward and exhausted outside (or HEPA-filtered before recirculation). A patient who must be protected (post-stem-cell-transplant, severe neutropenia) needs positive pressure pushing clean, HEPA-filtered air outward toward adjacent spaces. Putting a neutropenic client in a negative-pressure room is the classic miss.

The hardest item layers both needs: a neutropenic patient who also develops active TB. Positive pressure protects them but would vent TB into the unit, so the answer isn’t one room type — it’s an anteroom buffer with HEPA-filtered exhaust to the outside, never plain positive pressure. Don’t confuse this engineering control with the personal N95 or with the precaution category itself. Memory hook: positive = protect the patient; negative = protect the world.