How much oxygen should you give a patient?

From: ATI oxygen therapy
From: ATI oxygen therapy

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: 

  1. 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.
  2. 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?
  3. 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!

Face Mask


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.”

Face tent

Most patients do not look this calm on a face tent. From:
Most patients do not look this calm on a face tent. From: besmed.comHigh-flow O2 up to 60 L/min. Why?!!!

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.

High-flow oxygen

Screen Shot 2015-06-22 at 1.42.43 PM

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.


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