oxygen delivery with nasal cannula

  1. According to all the sources it is allowed to give oxygen with nasal cannula from 1 to 6 liters per minute, not more, to avoid damaging of the mucosa, and if you deliver oxygen generally at a rate more than 4 liters per minute you are supposed to humidify to avoid dryness of the mucosa. so my question is why it is not allowed to give oxygen with a nasal canulla at a rate more than 6 liters per minute if it is humidified?
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  2. 6 Comments

  3. by   meanmaryjean
    Because nasal cannulas are hardly precise instruments. In fact, they are the least precise means of oxygen delivery (except blow-by for a newly born infant) They don't account for mouth breathing, and once you get to 6 liters they get damned uncomfortable.
  4. by   amoLucia
    As the rate increases, so does the 'blow' force.

    Like a hurricane blowing into your nose!!! Besides the wind force, the noise would be crazy. And I think the tubing would also prob have water in it that would be sucked up like a nety-pot or spraying into the nose. !

    In all my career, I don't think I ever ran O2 that high. Just NEVER.

    This is a homework question, yes?
  5. by   offlabel
    About 6 lpm is the maximum FiO2 for nasal cannula, which is .44

    1 lpm = .24
    2lpm = .28
    3 lpm= .32
    4lpm =.36
    5lpm = .40
    6 lpm = .44
    7 lpm = .44
    8 lpm= .44
    etc.

    HFNC is a different thing altogether.
  6. by   heinz57
    Cold humidifiers are an inefficient way to provide humidity. Heated humidity at body temperature ,37 degrees, provides comfort and moisture.

    The tubing bore on a standard cannula is not designed to have flows greater than 6 Liters. Simple physics. There are reasons RTs take lots of math and college physics.

    A high flow cannula (not to be confused with heated high flow or HFNC), can go up to 15 liters per minute without the humidifier and 10 with the humidifier. This cannula is used when the patient needs just over 6 liters but not more than 10 L. We use 15 liters without a humidifier during intubation.

    The approximate FiO2 for each liter flow is calculated for a healthy normal RR with normal tidal volumes. This is why we chart liter flow and RR instead of the guess at the FiO2 for a nasal cannula. It is very doubtful the standard cannula will ever give an FiO2 of 0.44 unless there is slow shallow breathing.
    Last edit by heinz57 on Mar 24
  7. by   offlabel
    Quote from heinz57
    The approximate FiO2 for each liter flow is calculated for a healthy normal RR with normal tidal volumes. This is why we chart liter flow and RR instead of the guess at the FiO2 for a nasal cannula. It is very doubtful the standard cannula will ever give an FiO2 of 0.44 unless there is slow shallow breathing.
    Right, and healthy normal people don't need nasal cannulae. The point is that the amount of O2 that can be delivered via NC plateaus at about 6 lpm and if hypoxia that will respond to more 02 is the problem, moving up to a device that can deliver more is indicated. Having a general awareness of ballpark fiO2 when treating hypoxia is fairly important when teasing out fixing a problem. Interpreting an ABG without having an approximate fi02 in mind doesn't have the contextual value of having one.
    Last edit by offlabel on Mar 24
  8. by   heinz57
    Quote from offlabel
    Right, and healthy normal people don't need nasal cannulae. The point is that the amount of O2 that can be delivered via NC plateaus at about 6 lpm and if hypoxia that will respond to more 02 is the problem, moving up to a device that can deliver more is indicated. Having a general awareness of ballpark fiO2 when treating hypoxia is fairly important when teasing out fixing a problem. Interpreting an ABG without having an approximate fi02 in mind doesn't have the contextual value of having one.
    No, it was easier to study the FiO2 in healthy subjects who can control their breathing.

    A person can be breathing with very large slow tidal volumes or very fast small volumes and vary the FiO2 significantly. And, if you put a baby on 1 liter of O2 straight from the wall that infant will be getting greater than an FiO2 of 0.90 but some nurses still document 0.24 for FiO2. Can you see where this is a problem and even dangerous? You can easily give misinformation about the true clinical picture which leads to under or over treatment. For the adult on too little oxygen they must increase work of breathing.

    Until there is an understanding of minute volume along with rate and depth, those cannula estimations are only good for a textbook test. When documenting an ABG, the RR rate and liter flow are the main concern. Only if you are using a Venturi type device (not necessarily a "Venturi mask") or other high flow system or a closed system like a vent or BiPAP would you document actual FiO2.


    BTW, the literature representIng the research for high flow NC, oxymask and even regular NC for smaller adults as well as children discredit those numbers you stated earlier. Not everyone is a 75 kg male breathing a tidal volumes of 500 ml 12 x per minute.

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