Oxygen

[joe1795]

I was just on a call and had a question about oxygen. The patient had just come back from dinner and was experiencing face tingling/numbness and his arms and legs were shaking. He said he had a lump his throat and had "slight" difficulty breathing. No history of asthma, no food allergies, no meds, no history. No history of anxiety attacks. Lung sounds were clear and patient wasn't short of breath and didn't seem to be in respiratory distress. BP was 128/82, HR 88, Resp 18. SpO2 99%.
Would you have put O2 on this patient?

 

[jkmerrill]

If I had a choice, no.

There was a review article on prehospital oxygen therapy published in Respiratory Care earlier this year, and to quote the authors of that:

"The only evidence-based indication for oxygen therapy is hypoxemia confirmed by oximetry, blood gas analysis, or physical observation. However, oxygen is also often delivered on presumption of need based on disease state (head injury, stroke, myocardial infarction, etc), to alleviate breathlessness, and to prevent hypoxemia in sick patients at risk. These presumptions are not based on evidence that oxygen is useful in these situations, but rather the belief that the oxygen will provide relief of symptoms or prevent untoward effects of hypoxemia. However, oxygen delivery to patents without hypoxemia can lead to worsening outcomes in the presence of hyperoxia."

I don't have the ability to put a link in a post yet apparently, but the URL for the full-text article is: rc.rcjournal.com/content/58/1/86.full

Of course, there are a lot of backwards protocols out there that require EMS providers to strap non-rebreathing mask on every single patient who looks vaguely uncomfortable, and depending on how much leeway your system grants you may be required to do so no matter what. . .


Jason Merrill

 

[joe1795]

That's how I feel. I didn't put him on oxygen. We're a QRS for a college, and I thought it would agitate him more. I got QA'd for not putting him on O2. I wrote in the chart it wasn't indicated. We were only on scene for about 5 minutes before Philly medics arrived too. He was certainly not critical and if anything his symptoms were improving.

 

[Akulahawk]

I was just on a call and had a question about oxygen. The patient had just come back from dinner and was experiencing face tingling/numbness and his arms and legs were shaking. He said he had a lump his throat and had "slight" difficulty breathing. No history of asthma, no food allergies, no meds, no history. No history of anxiety attacks. Lung sounds were clear and patient wasn't short of breath and didn't seem to be in respiratory distress. BP was 128/82, HR 88, Resp 18. SpO2 99%.
Would you have put O2 on this patient?

Probably not, but I'd likely have kept some nearby and a close watch on his lungs. I'd expect him to complain of some constriction before he starts to wheeze. I think whatever he just ate, he's developing a sensitivity to.

 

[2eggs]

It sounds like he may have been hyperventilating, were his hands or feet clenching at all?

 

[2eggs]

It wont let me edit my post for some reason, but I was going to say: It sounds like he may have been hyperventilating, were his hands or feet clenching at all? Did he have any itching in his mouth or throat? Its possible hes having an allergic reaction to something (had he eaten anything new?), but id also try to calm him down a little and see if that helps his symptoms. His Spo2 is good, no apparent difficulty breathing, lungs are clear, more than likely he dooesnt need oxygen, hes managing to saturate his blood with o2 just fine on his own, with an spo2 of 99 (assuming this number is accurate) his blood cant hold much more o2, so he doesnt need supplemental o2.

 

[EMT B]

i might have done nasal prong capnography, i dont think i would have turned the oxygen on though.

 

[joe1795]

I just found out that the patient had an adverse reaction to MSG.

 

[mycrofft]

Ah, "Bushutsuru" (then pres George Bush Sr vomited on the Japanese prime minister after a MSG reaction post tennis match).

 

[Giobobo1]

I just found out that the patient had an adverse reaction to MSG.

Case Closed.

jkmerrill has a neat little theory there too, in most cases it just acts as a placebo

 

[medic6676]

New standards dictate that you don't. AHA recommends anyone 94-99% be kept on room air unless other symptoms dictate the use of oxygen. This is because when you reach 100% you actually end up with more oxygen via treatment resulting in free radicals, and then ozone in the blood, this is bad as ozone at the right levels is toxic.

So in this case the patient was at 99% and other vitals were stable, so no. It sounds like the patient was having an anxiety attack of sorts.

 

[Clipper1]

New standards dictate that you don't. AHA recommends anyone 94-99% be kept on room air unless other symptoms dictate the use of oxygen. This is because when you reach 100% you actually end up with more oxygen via treatment resulting in free radicals, and then ozone in the blood, this is bad as ozone at the right levels is toxic.

An SpO2 of 100% does not always mean hyperoxygenated. Some barely make an adquate PaO2 but still have a high SpO2. Some factors shift the oxyhemoglobin curve which could mean a higher SpO2 but a lower PaO2. Be very careful with assuming especially with sick patients you are seeing for the first time.

 

[medic6676]

An SpO2 of 100% does not always mean hyperoxygenated. Some barely make an adquate PaO2 but still have a high SpO2. Some factors shift the oxyhemoglobin curve which could mean a higher SpO2 but a lower PaO2. Be very careful with assuming especially with sick patients you are seeing for the first time.

Very rarely, if you are presented with good capture, are SPO2 monitors incorrect. Unless there is some other situation to mimic good oxygen, such as CO or a smoker, than generally they are pretty accurate. In the case of this patient, there was no reason to give him oxygen, the presentation, the vitals, and everything about the patient made him appear stable and able to maintain oxygenation without assistance.

As for the oxyhemoglobin curve, if the patient was cold to the touch, or there was some reason to the believe that the patient was acidotic, than the SPO2 should be accurate. Again in this case with the representation of the patient at the time of care, it sounds like the patient may have hyperventilated prior to arrival, resulting in an alkalotic state, which would further mean withholding oxygen therapy so that the patient builds up more CO2 to reverse the effects.

 

[Carlos Danger]

As for the oxyhemoglobin curve, if the patient was cold to the touch, or there was some reason to the believe that the patient was acidotic, than the SPO2 should be accurate. Again in this case with the representation of the patient at the time of care, it sounds like the patient may have hyperventilated prior to arrival, resulting in an alkalotic state, which would further mean withholding oxygen therapy so that the patient builds up more CO2 to reverse the effects.

Even in the presence of a left shift, I can't really see how additional oxygen is helpful when a good saturation is already present. I suppose one could argue that a very high serum partial pressure will always result in more diffusion of oxygen into the tissues than a lower serum partial pressure will, and that is probably true, but it seems that at normal Patm the effect would be far too small to fix any clinically significant tissue hypoxia.

100% is 100%.....you can't get higher than that. It's like trying to pour more water into a glass that is already full.

 

[medic6676]

100% is 100%.....you can't get higher than that. It's like trying to pour more water into a glass that is already full.

The problem with that statement is that the 100% is only measured on the hemoglobin itself. The rest of the blood is not measured, and if there are free radicals, which is oxygen molecules that are not attached to any blood cell, then you create ozone, which is toxic in the blood. And there is more than 100% in that instance.

In the case of a left shift, you can have a higher than correct value on your pulse oximeter. Note the image below. While the shift on this is minimal, if there is a greater change in any of those factors, the inaccurate reading would be more so. SPO2 measures PAO2 when all the factors are normal, otherwise the readings are inaccurate.

 

[Clipper1]

Even in the presence of a left shift, I can't really see how additional oxygen is helpful when a good saturation is already present. I suppose one could argue that a very high serum partial pressure will always result in more diffusion of oxygen into the tissues than a lower serum partial pressure will, and that is probably true, but it seems that at normal Patm the effect would be far too small to fix any clinically significant tissue hypoxia.

100% is 100%.....you can't get higher than that. It's like trying to pour more water into a glass that is already full.

But, what about the tissue perfusion? In the ICUs we are able to see the SaO2, PaO2, ScvO2 or SvO2. We adjust fluids and pressors according with the O2 in place until we know we can improve delivery.

The SpO2 can remain at 100% but the PaO2 can change. Unfortunately all you might have as an EMT or Paramedic is a pulse oximeter. In the ICUs we quickly learn 100% and just a pulse ox tells us very little about the patient especially if the clinical presentation looks bad.

The problem with that statement is that the 100% is only measured on the hemoglobin itself. The rest of the blood is not measured, and if there are free radicals, which is oxygen molecules that are not attached to any blood cell, then you create ozone, which is toxic in the blood. And there is more than 100% in that instance.

In the case of a left shift, you can have a higher than correct value on your pulse oximeter. Note the image below. While the shift on this is minimal, if there is a greater change in any of those factors, the inaccurate reading would be more so. SPO2 measures PAO2 when all the factors are normal, otherwise the readings are inaccurate.

No. SpO2 does not measure PAO2. PAO2 is calculated. Even if you meant to state PaO2, SpO2 still does not measure it. But, with a known PAO2 and the PaO2 we can get the A-a gradient which will give us an idea about how sick the patient. Also, the vertical axis on the oxyhemoglobin curve is SaO2 and not SpO2. If you ever get a chance to see co-oximeter reading for the actual components you would see the difference.

 

[medic6676]

No. SpO2 does not measure PAO2. PAO2 is calculated. Even if you meant to state PaO2, SpO2 still does not measure it. But, with a known PAO2 and the PaO2 we can get the A-a gradient which will give us an idea about how sick the patient. Also, the vertical axis on the oxyhemoglobin curve is SaO2 and not SpO2. If you ever get a chance to see co-oximeter reading for the actual components you would see the difference.

My apologies on the mistake. And thank you for the clarification. I should have stuck with my original statement of 100% isn't always full in the case of SpO2,

 

[Jawdavis]

Just a question that might stray from your original answer (but no no o2 needed with sats that high) do you happen to know what his blood sugar was?

 

[Carlos Danger]

The problem with that statement is that the 100% is only measured on the hemoglobin itself. The rest of the blood is not measured, and if there are free radicals, which is oxygen molecules that are not attached to any blood cell, then you create ozone, which is toxic in the blood. And there is more than 100% in that instance.

In the case of a left shift, you can have a higher than correct value on your pulse oximeter.

Right.....Sp02/Sao2 are measures only of the percentage of bound hemoglobin, not dissolved oxygen. My point was that since dissolved oxygen makes up only about 1% of the total arterial oxygen content, you can increase oxygen delivery very little by continuing to add supplemental oxygen when Sp02 is already adequate.

This is true regardless of whether a right or left shift is present. A left shift represents a greater affinity of hgb for oxygen, but this is not changed by increases or decreases in Pao2 or Sa02.

A left shift will not affect your pulse oximetry readings. It simply describes how readily oxygen leaves the hemoglobin to diffuse into the tissues.


What we really need to think about when considering supplemental oxygen is oxygen delivery:

Oxygen delivery (D02) is Cardiac output (CO) x Arterial oxygen content (Ca02):

• Ca02 is the oxygen carried on hemoglobin + the oxygen dissolved in plasma, or [1.39 x Hb x SaO2 + (0.003 x PaO2)]
• CO, of course, is HR x SV, and SV is affected by preload, contractility, and afterload.
• The complete oxygen delivery equation looks like this: DO2 = Ca02 [1.39 x Hb x SaO2 + (0.003 x PaO2)] x CO [HRxSV]

Being that there are only 2 parts to the equation, there are only 2 things that can be manipulated to improve oxygen delivery: cardiac output and oxygen content.

The primary ways to improve oxygen content are increasing hgb levels (giving PRBC's), and increasing oxygen saturation. If you calculate the equation out using different values, you'll see that increasing Pa02 has a very negligible effect on oxygen delivery, and increasing Sp02 has a small effect as long as it is already above ~95%. Increasing hemoglobin generally has a large effect, however.

The basic first step is to always maximize the Ca02 side of the equation first, which simply means ensuring an adequate hemoglobin level and Sp02.

But, what about the tissue perfusion? In the ICUs we are able to see the SaO2, PaO2, ScvO2 or SvO2. We adjust fluids and pressors according with the O2 in place until we know we can improve delivery.

When you manipulate fluids and pressors in the ICU, you are simply manipulating the other side (the CO side) of the equation. Scv02/Svo2, CVP, SVR, SVV, lactate, etc are simply clues to help you decide whether CO needs to be manipulated, and if so, which component of CO (HR, SV, preload, or SVR) will have the biggest impact.

Changes in Pa02 have very little impact on total oxygen delivery. Assuming, of course, that abnormal forms of hemoglobin or other blood toxicities (methemoglobin or cyanide toxicity) are not present. Also, pulmonary problems that can make it difficult to properly oxygenate the blood (ARDS), or deleterious effects of certain therapies (increased Mv02 or renal or splanchnic hypoperfusion due to vasopressor therapy, etc.) obviously need to be assessed and managed.

It also does not take into account the effects of a serious right or left shift, but that is a problem separate from blood oxygenation. Shifts are avoided primarily by maintaining normal C02 and pH level, not by manipulating Fi02.

 

[Jawdavis]

I realize that some of you are trying to play devils advocate in this situation but in the end if you do not have ABGs you would not give O2 with someone satting at 99% because of the potential of resp alkalosis. If he was having trouble breathing an anti-anxiety med could be considered giving his condition or even vocal reassurance.