# Oxygen Therapy for Shock: Cardiogenic or otherwise?



## PENNEMT (Oct 20, 2015)

We learned in class that giving 15 lpm oxygen is no longer recommended for cardiac patients as hyperoxia causes decrease in heart rate; hypothetically, if you have a patient who is exhibiting symptoms of shock and is unable to pinpoint the cause of the shock between, say, cardiogenic shock and hemorrhagic (internal) shock, should you still treat the patient with oxygen? 

Also, in general, is giving high-concentration O2 for all shock patients still standard for testing purposes? For real life? 

Thanks.


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## wanderingmedic (Oct 20, 2015)

Do not give O2 unless it is indicated by a SPO2 below 94%. This is regardless of whether shock is cariogenic, hemorrhagic, spinal, or extraterrestrial related. Think about the purpose of giving oxygen. Why in the world would more oxygen help someone who is already sufficiently oxygenated?


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## WolfmanHarris (Oct 20, 2015)

It's not that oxygen therapy is not entirely contraindicated, it's that routine use of oxygen is not recommended in cardiac patients without hypoxia. When a patient is decompensating whether in cardiogenic shock or haemorrhage, they will likely be hypoxic.


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## teedubbyaw (Oct 20, 2015)

azemtb255 said:


> Do not give O2 unless it is indicated by a SPO2 below 94%. This is regardless of whether shock is cariogenic, hemorrhagic, spinal, or extraterrestrial related. Think about the purpose of giving oxygen. Why in the world would more oxygen help someone who is already sufficiently oxygenated?



SpO2 alone is only one piece to a complete clinical picture. You can't base your decisions on that reading alone.


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## Aprz (Oct 22, 2015)

Aw, man. This topic has been beatin' to death on this forum.

Under most circumstances, tests and books are going to encourage you to administer high flow oxygen. Some tests, like if you take an ACLS or ITLS class, will probably encourage you to titrate it to an FiO2 of 94 or higher.

I highly doubt that the problem with oxygen is a decrease heart rate. If the heart rate is decreasing because of the oxygen then that probably meant that they needed the oxygen. Tachycardia can be a sign of hypoxia and you could expect the heart rate to go down if the hypoxia is treated. The problem I have read with oxygen administration is that it increases reperfusion injury due to it being a free radical. I think this is mainly an issue with myocardial infarctions and ischemic strokes. I guess it can be harmful to newborn causing damage to the eyes. I am not sure if this is because of free radicals or because oxygen is a very mild arteriole constrictor and this constriction is blocking blood flow to the eye. For most other types of emergencies, I don't think it is significantly beneficial or harmful to give.

Like Teedubbyaw said, SpO2 is only one piece. The patient could be compensating maintaining a normal SpO2 even though they need oxygen. If you put a pulse oximeter on your finger, hold your breath for as long as you can, you'll see that your heart rate will elevate and you will probably feel the need to take a breath before your SpO2 even drops. Instructors like to bring up carbonmonoxide poisoning too. These patients will probably be at or near 100% SpO2, but their hemoglobins will not be saturated with oxygen. They will require high flow oxygen to displace the carbonmonoxide. These patients should not be denied oxygen even though their SpO2 is normal.

Denying a patient oxygen to a patient that needs oxygen is more rapidly deadly and harmful than giving oxygen to a patient that doesn't need it. If in doubt, give oxygen. Typically low flow with a nasal cannula is good enough.


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## Drewt78 (Oct 22, 2015)

I would say that since your partner is already dead, and the other guy is dying, treat the most critical. That would be your partner. I'm still a student, but that would be my guess.


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## Carlos Danger (Oct 22, 2015)

In the absence of a dyshemoglobinemia or faulty equipment, Sp02 is a very reliable indicator of Ca02 (total arterial oxygen content). In other words, as long as Sp02 is above, say, 95, increasing Fi02 will do very little to improve oxygen delivery.

Your body holds almost no oxygen in reserve, so with the exception of a super-fit person whose body even when stressed consumes relatively little oxygen, compensatory mechanisms are very limited.

Bottom line: if the Sp02 is good, there is probably very minimal benefit in providing supplemental 02, because their 02 tank (the hemoglobin) is aready practically full. On the other hand, in a sick patient it seems like a low-risk maneuver, and any nitrogen exchange could certainly be a good thing if the scenarios progress to invasive airway management.


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## teedubbyaw (Oct 23, 2015)

Keeping in mind that there have been large variations in SpO2 vs Sao2. Someone with a SpO2 WNL in the setting of shock, etc. will probably have an Sao2 on the low end of normal.


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## Carlos Danger (Oct 23, 2015)

teedubbyaw said:


> Keeping in mind that there have been large variations in SpO2 vs Sao2. Someone with a SpO2 WNL in the setting of shock, etc. will probably have an Sao2 on the low end of normal.



Are you sure you aren't thinking of central venous saturation? 

Outside of an equipment failure or sampling error or dyshemoglobinemia, why would Sa02 be different form Sp02?


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## teedubbyaw (Oct 23, 2015)

Studies have shown normal spo2 readings in very ill pt's will actually have an sao2 much lower. 

What I'm getting at is SpO2 is an excellent prehospital tool, but consider all factors before withholding oxygen based on SpO2 alone.


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## Carlos Danger (Oct 23, 2015)

teedubbyaw said:


> Studies have shown normal spo2 readings in very ill pt's will actually have an sao2 much lower.
> 
> What I'm getting at is SpO2 is an excellent prehospital tool, but consider all factors before withholding oxygen based on SpO2 alone.



Interesting. I'd appreciate it if you'd post links to those studies. I've never heard that and a quick Google search turned up a single study (http://www.ncbi.nlm.nih.gov/pubmed/11685301) that was a little old, and the abstract suggests that difference are technical, not physiological.

Sp02 and Sa02 are just different ways of measuring the same thing - the % of hemoglobin with O2 on each of its binding sites. So in theory, they should always be identical. My understanding is that most gas analyzers don't actually_ measure_ Sa02, rather they calculate it based on Pa02 (which is measured chemically) and pH. So I'm not sure it's clear that all things considered, Sa02 is even a more accurate measurement that Sp02.

Technical and practical differences in the way the two are measured usually result in non-identical readings. The clinical ramifications of that are unclear. I've had long and critical OR cases where I've taken a gas every 15 minutes or so, and even though the Sa02 may not have perfectly matched the Sp02, I never saw it as a  clinically significant issue. I always go by Sp02 because it is a constant reading and therefore much easier to trend.


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## Aprz (Oct 23, 2015)

I think he is thinking of SpO2 vs PO2 with the oxygen hemoglobin dissociation curve. It has pointed out to me several times that the patient's PO2 could be low even though the SpO2 is 90.


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## teedubbyaw (Oct 24, 2015)

Aprz said:


> I think he is thinking of SpO2 vs PO2 with the oxygen hemoglobin dissociation curve. It has pointed out to me several times that the patient's PO2 could be low even though the SpO2 is 90.



Wasn't thinking that, but good point, nonetheless. I did a research paper on the subject last year. I'll pull up my references when I get home.

http://www.ncbi.nlm.nih.gov/pubmed/20444248 < This points out that there may be a slight variation in very ill pt's, reiterating my point of looking at all aspects of a sick pt.


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