Km and Vmax of Heme

[Veneficus]

Ok, this is more of a question for vent and the other respiratory types, but figured it could be a good look at the common EMS practice.

Last summer I was in an ACLS EP class, and during some of the discussions EMS providers always liked to say "high flow o2" the hospital based ones were always on the "cannula" I abstained from choosing a side at the time.

These last 2 weeks I have been dealing with the graduate level physio and 3rd semester biochm and the topics have revolved around o2 transport.

Other than displacing CO, or the CPAP patient, what exactly is the purpose on 15 or 10L of NRB? It oesn't seem like it would matter at all for most patients. Even trauma patients would see no measurable benefit. What is the method to the madness?

Was it simply an unfounded practice of: "if a little is good, more is better."

 

[daedalus]

I will not be able to discuss the basic sciences behind oxygen transport, but I can comment on high flow O2. I believe that when the ciricculum for the EMT-Basic was designed, the creators themselves saw the flaw in their design. They added high flow 02 for all patients because they knew that an EMT could not assess a patient properly and determine which needed "high flow" and who could get by on cannula (almost all of our patients). At that point, when an EMT advances to paramedic the idea of high flow o2 is still so ingrained that they never change their ways. I believe you fail EMT class in the practical if a patient does not receive oxygen.

Although, I am seeing in my class at least that cannulas are being promoted for most patients. We will see if that translates into the field. You can count on me not using non-rebreathers unless the patient is in severe respiratory distress and are not at that lets just bag them point.

 

[VentMedic]

First, since you mentioned me, let us get a few definitions out of the way.

High Flow does NOT include the NRBM. It is in true definition low flow but can offer a higher FiO2.

CPAP, in prehospital, must rely more on lower FiO2s in order to maintain a higher flow to actually do any good where preload and afterload is concerned. If a higher FiO2 is used, the flow will be much lower which can compromise work of breathing with essentially the same effects as a NRBM.

Unknowns are reasons why some use higher FiO2s. Unknown carrying capacity, unknown A-a gradients and unknown V/Q mismatching.

In the hospital, we do include an FiO2 of 1.0 in some protocols including Sepsis in adults and PPHN of the neonate, so high FiO2s do have their role. In an ARDS protocol, the FiO2 can only be decreased if the technology and protocols we are using are effective to get the PaO2 to at least 50 mmHg. For sepsis and ARDS we will have CVP and SjvO2 monitors in place with BP MAP being maintained.

If a cardiac patient has increased work of breathing, higher FiO2 will be tried even if it is known the heart muscle is failing. Unfortunately, when a patient is experiencing increased work of breathing, a low flow device such as a NRBM is useless as it does not meet their inspiratory flow demand and what air is entrained makes the FiO2 very variable.

If I want an FiO2 of 1.0 on a patient, the NRBM will not be what I reach for unless it is all I have in a transport situation. However, in the transports I do, I have the luxury of a transport ventilator that will do must anything I want it to.

There is not just one variable involved when it comes to the appropriate O2 delivery method which is why in the hospital, I have about 15 different protocols, each with about 15 different pathways for just a handful of disease processes. When we hit an unknown, we write the recipe as we do it. And that is just for adults. Peds and neo have many more different pathways for ventilation and oxygenation.

 

[triemal04]

CPAP, in prehospital, must rely more on lower FiO2s in order to maintain a higher flow to actually do any good where preload and afterload is concerned. If a higher FiO2 is used, the flow will be much lower which can compromise work of breathing with essentially the same effects as a NRBM.

Alittle of topic, but can you explain that one a bit more? Most of CPAP devices carried prehospital are driven by the O2 tank; wouldn't that lead to a higher FiO2 since the ambient atmosphere is mostly being blocked?

 

[VentMedic]

Alittle of topic, but can you explain that one a bit more? Most of CPAP devices carried prehospital are driven by the O2 tank; wouldn't that lead to a higher FiO2 since the ambient atmosphere is mostly being blocked?

If you ran at an FiO2, your tank would be empty very fast either off the 50 psi or flowmeter. Most will run at a lower FiO2 to save gas which actually is a good thing since more air is entrained to dilute the O2, thus increasing the peak inspiratory flow to the patient.

....Bernoulli and Venturi.

 

[VentMedic]

If you ran at an FiO2 of 1.0, your tank would be empty very fast either off the 50 psi or flowmeter. Most providers will run at a lower FiO2 to save gas which actually is a good thing since more air will be entrained to dilute the O2, thus increasing the peak inspiratory flow to the patient.

....Bernoulli and Venturi.

Corrected version