When you need a precise oxygen level
Read-only coaching — the deeper "why" behind the device you just set.
The FiO₂ from low-flow devices (cannula and simple/non-rebreather masks) is only approximate — it changes with each breath depending on how fast and deep the patient breathes.
For a COPD patient who needs an exact, controlled oxygen level, use a Venturi (air-entrainment) mask — it delivers a preset FiO₂ (24%, 28%, 31%, 35%, 40%, 50%), so you can hold the 88–92% target reliably instead of guessing.
Escalation: if a COPD patient stays hypoxemic, or the CO₂ climbs and they tire, despite controlled oxygen — check an arterial blood gas and escalate to non-invasive ventilation (BiPAP). The classic trigger is respiratory acidosis: pH < 7.35 with a rising PaCO₂ (> 45 mmHg) despite controlled O₂. Give oxygen, never withhold it — but titrate down and get the gas.