Oxy Hemoglobin right shift

[tchristifulli]

I have been doing research on the Disassociation curve and I have a question. With a right shift caused by acidosis or increased HGB levels you get a decreased SPO2 value with the same PA02 pressure. According to my research this is very efficient at the tissue level because it has a looser binding to the 02. Soooo how is this ever a problem? I understand how a left shift would be a problem. But a right shift seems very efficient at the tissue level.

 

[Anonymous]

I have been doing research on the Disassociation curve and I have a question. With a right shift caused by acidosis or increased HGB levels you get a decreased SPO2 value with the same PA02 pressure. According to my research this is very efficient at the tissue level because it has a looser binding to the 02. Soooo how is this ever a problem? I understand how a left shift would be a problem. But a right shift seems very efficient at the tissue level.

It is only beneficial for a period of time, you have hemaglobin giving up oxygen to tissues more readily but you have a lower oxygen content in the blood. Eventually you will run out of oxygen for the hemaglobin to give up.

Hope that answers your question.

 

[Carlos Danger]

It is only beneficial for a period of time, you have hemaglobin giving up oxygen to tissues more readily but you have a lower oxygen content in the blood. Eventually you will run out of oxygen for the hemaglobin to give up.

I don't think there is a problem with running out of oxygen. Oxygen will only be released to tissues until the oxygen tension in the tissues matches that of the blood, then it will stop. And as long as you are breathing adequately, you've got an unlimited supply of oxygen from the atmosphere.

Maybe I'm missing something myself but I'm really not aware of any practical implications for a left vs. a right shift. It isn't something that is measured or treated clinically. A shift is a derangement that results from a physiologic process and it goes away when that process is corrected.

I think for our purposes, the primary value in learning the curve is to understand the relationship between Pa02 and Sa02.

 

[tchristifulli]

I don't think there is a problem with running out of oxygen. Oxygen will only be released to tissues until the oxygen tension in the tissues matches that of the blood, then it will stop. And as long as you are breathing adequately, you've got an unlimited supply of oxygen from the atmosphere.

Maybe I'm missing something myself but I'm really not aware of any practical implications for a left vs. a right shift. It isn't something that is measured or treated clinically. A shift is a derangement that results from a physiologic process and it goes away when that process is corrected.

I think for our purposes, the primary value in learning the curve is to understand the relationship between Pa02 and Sa02.

Well if you have a left shift (alkalosis)your proteins have a tighter binding and won't off load easily at the tissue. This seems like a pretty significant finding that we could correct by ventilation control of ETC02.

 

[VFlutter]

Well if you have a left shift (alkalosis)your proteins have a tighter binding and won't off load easily at the tissue. This seems like a pretty significant finding that we could correct by ventilation control of ETC02.

How are you going to decide if you patient has a left shift in the field?

Unless you are doing ABGs on the truck...

 

[Clipper1]

Well if you have a left shift (alkalosis)your proteins have a tighter binding and won't off load easily at the tissue. This seems like a pretty significant finding that we could correct by ventilation control of ETC02.

How is ETCO2 going to show this?

ETCO2 does not show pH. You can have respiratory alkalosis and metabolic alkalosis. You can have compensated and partially compensated or a mixture of just about everything.

You can have a large gradient for the PaCO2 and PetCO2 for several reasons besides alkalosis.

You can have a high SpO2 (even 100%) and a PaO2 which is barely acceptable as adequate oxygenation which is a large A-a gradient.

 

[tchristifulli]

I agree I'm talking more on a critical care transport level with ABGs at hand.

 

[tchristifulli]

Lol or a massive Tums overdose.

 

[Clipper1]

I agree I'm talking more on a critical care transport level with ABGs at hand.

Ventilation alone is still a bad way to correct some metabolic imbalances. For every action there may be a reaction which is not always wanted.

ABGs alone will also tell you very little and that is where a chemistry panel for electrolyte info or the anion gap is needed. Nursing and some other health professionals have been done a great disservice in their education when they were taught "ABGs".

a decreased SPO2 value with the same PA02 pressure.

Be careful with your abbreviations. PAO2 is alveolar and not arterial. A person can have a decreased SpO2 for a variety of reasons while on the same FiO2 as a few minutes earlier.

 

[MSDeltaFlt]

I have been doing research on the Disassociation curve and I have a question. With a right shift caused by acidosis or increased HGB levels you get a decreased SPO2 value with the same PA02 pressure. According to my research this is very efficient at the tissue level because it has a looser binding to the 02. Soooo how is this ever a problem? I understand how a left shift would be a problem. But a right shift seems very efficient at the tissue level.

Um... negative. Right shift means reduced affinity for oxygen (i.e. icreased 2,3 DPG). Yes the hemoglobin will release O2 faster, but that also means the hemoglobin doesn't want to receive oxygen in the first place. Therefore distal tissue hypoxia still occurs. Increased temp (fever). No organ system works properly febrile. Then there's the increased H+ which decreases pH. And nothing, organ systems or any drug, will work in an acid medium.

So no. A right shift AND a left shift are both bad. Period.

 

[Carlos Danger]

Well if you have a left shift (alkalosis)your proteins have a tighter binding and won't off load easily at the tissue. This seems like a pretty significant finding that we could correct by ventilation control of ETC02.

Is a left shift a "finding"? What are the signs of a left shift?

Or is it just something that you keep in the back of your mind as something that can result from respiratory alkalosis, and therefore avoid hyperventilation for that and other reasons?

I'm not saying a shift isn't significant. I'm saying you can't measure it or treat it directly. It is just one of many complicated physiologic consequences of a pH derangement. We generally don't spend too much time thinking about those in the clinical setting, we just do what we can to correct the cause of the pH derangement.

 

[MSDeltaFlt]

Ventilation alone is still a bad way to correct some metabolic imbalances. For every action there may be a reaction which is not always wanted.

ABGs alone will also tell you very little and that is where a chemistry panel for electrolyte info or the anion gap is needed. Nursing and some other health professionals have been done a great disservice in their education when they were taught "ABGs".

ABG's are a great thing. If and only if you know what you're looking at.

"Some metabolic imbalances"??? ALL metabolic imbalances. If your problem is metabolic, attempting to the fix it with ventilation is counterproductive. Remember, CO2 is a potent vasodilator/vasoconstrictor. Dropping the CO2 constricts the vasculature. All of the vasculature.

If they're acidotic with temp corrected ABG's, which is very important because Charles' Law works even in blood, and normal HCO3, looking at the base excess (that small number listed between the HCO3 and the SaO2 that has a range of -2.0 - +2.0). It will read markedly lower than -2.0. And that is when you need to look at the Complete Metabolic Panel with electrolytes.

 

[Clipper1]

I'm not saying a shift isn't significant. I'm saying you can't measure it or treat it directly. It is just one of many complicated physiologic consequences of a pH derangement. We generally don't spend too much time thinking about those in the clinical setting, we just do what we can to correct the cause of the pH derangement.

With hypothermia protocols, fevers from brain injuries and rewarming phases we do think about shifts more in the ICUs and maybe EMS should be more aware of the shifting curve if they do hypothermia or believe in the SpO2 rule of 94% as a definite marker for not giving oxygen.

 

[tchristifulli]

Ventilation alone is still a bad way to correct some metabolic imbalances. For every action there may be a reaction which is not always wanted.

ABGs alone will also tell you very little and that is where a chemistry panel for electrolyte info or the anion gap is needed. Nursing and some other health professionals have been done a great disservice in their education when they were taught "ABGs".



Be careful with your abbreviations. PAO2 is alveolar and not arterial. A person can have a decreased SpO2 for a variety of reasons while on the same FiO2 as a few minutes earlier.

So PA02 is alveolar and pa02 is arterial?

 

[tchristifulli]

ABG's are a great thing. If and only if you know what you're looking at.

"Some metabolic imbalances"??? ALL metabolic imbalances. If your problem is metabolic, attempting to the fix it with ventilation is counterproductive. Remember, CO2 is a potent vasodilator/vasoconstrictor. Dropping the CO2 constricts the vasculature. All of the vasculature.

If they're acidotic with temp corrected ABG's, which is very important because Charles' Law works even in blood, and normal HCO3, looking at the base excess (that small number listed between the HCO3 and the SaO2 that has a range of -2.0 - +2.0). It will read markedly lower than -2.0. And that is when you need to look at the Complete Metabolic Panel with electrolytes.

Then why is slowing down the ventilation a one of the first things the body does to compensate for metabolic acidosis? Not the definitive treatment but seems like a step in the right direction to mimic the body's normal compensatory mechanisms.

 

[tchristifulli]

I'm mean speeding up

 

[Clipper1]

Then why is slowing down the ventilation a one of the first things the body does to compensate for metabolic acidosis? Not the definitive treatment but seems like a step in the right direction to mimic the body's normal compensatory mechanisms.

How long do you think the body can keep that up? Also, what happens when muscles are on overload? What do the muscles produce?

 

[tchristifulli]

Creatinine? And would the muscles be effected as bad if the patient was on a vent? I had a call for a pt in DKA PH 7.20. Tubed and on the vent. Doc said keep his etco2 at 25. Made sence to me.

 

[Clipper1]

Creatinine? And would the muscles be effected as bad if the patient was on a vent? I had a call for a pt in DKA PH 7.20. Tubed and on the vent. Doc said keep his etco2 at 25. Made sence to me.

How about Lactate? Do you run? Most runners will understand muscle fatigue and the by product.

A DKA patient with a pH of 7.20 will fight a ventilator. You would probably need a paralytic. Some DKA patients will take their PaCO2 down to the single digits. ALWAYS verify the ABG yourself or ask the doctor for the other numbers. If the patient already has a PaCO2 of 6, you will need to adjust your thinking with the gradient to meet the needs. Also, what are you doing to correct that pH beside just trying to keep the PaCO2 low? How fast will it correct the DKA and what are you going to do about it on the ventilator? Or what tests will you need? What happens if the pH is being corrected by the other treatment and you are still focused on the ETCO2 of 25?

 

[MSDeltaFlt]

Then why is slowing down the ventilation a one of the first things the body does to compensate for metabolic acidosis? Not the definitive treatment but seems like a step in the right direction to mimic the body's normal compensatory mechanisms.

But it's not the first thing it does. It's the second. And it does what it can to get the pH normal. That's the most important thing. Balance the pH. The body will speed up ventilations naturally, but it can only do so much for so long. And it is by no means whatsoever fixing the problem. So it doesn't work.