Frequently you see in patient reports that he/she was “on 2L by nasal cannula” or “20 L on high flow O2.” What does this mean and how the hell are you supposed to know how much O2 to put your patient on?
When deciding how much oxygen a patient needs, consider three things:
- oxygenation %. Are you giving them a gas that is 50% oxygen or 100% oxygen? That will affect how much, quantity-wise, you want to give them.
- liter flow. Are you giving them 2 L just because everyone else is on 2 L, on blasting them with 40 L because you just really don’t want to intubate them?
- Patient comfort. Does the nasal cannula make their nose bleed? Do they keep struggling to take the mask off, but are content with a face tent? If your patient hates whatever contraption you use to administer oxygen, you probably won’t succeed.
Levels of oxygenation:
The nasal cannula
The simplest thing to pop into someone’s nose. If you’re using the oxygen tank on the wall, the FiO2=100%. However, you are thwarted by the always imperfect, mixed O2 content that actually gets up a patient’s nose, mouth breathers, people who wiggle out of them, patients with a low respiratory rate, nasal obstruction, etc. Go up to 6 L before considering another device. If a patient gets cracked or bleeding nares, use vaseline!
Masks can be more comfortable than having two little sticks poking up a patient’s nose.
The simple face mask is pretty self-explanatory.
The Venturi=Venti mask. It provides mixed O2 usually around 50%, and ranges up to 8 LPM. My MICU fellow summarized the Venti mask: “What is this thing really doing, even?” Because it provides reservoir O2, the O2 sat% looks better, but but the patient might as well just be sitting on a half-hanging out nasal cannula.
The partial rebreather is a mask that has a bag attached to it. The bag contains a reservoir of O2 that can be pumped in at 10-15 LPM.One-way valves trap their expired air in the mask and allows about 2/3 of it to escape. Yes, this means that the patient “re-breathes” some of his/her own air. Why??? Because the respiratory drive is stimulated by the rebreathing of CO2.
The non-rebreather (often abbreviated “NRB”) also has a bag attached to it, but it theoretically has 3 valves that prevent ANY expired air from being rebreathed. (You will see that this is often not the case, and a valve is hanging loose, because otherwise the patient would start to breathe in condensate). At a rate of 10-15 LPM, it provides “high concentration O2 at low flow.”
The face tent is for patients who may feel anxious with a mask or uncomfortable on a nasal cannula. As you can see, it’s pretty exposed to the outside air, and so delivers mixed O2, usually at a high flow rate.
This is just another way of administering, as the name suggests, huge amounts of oxygen. It literally sounds like the patient has a hair dryer aimed at their face. If you have a patient on high flow oxygen, really consider if there is an alternative or if intubation is impending.