Hemoglobin question

[RxBoy]

If a pt's hemoglobin is 15 g/dL.

1 liter of crystalloid is bolused.

Their new hgb is now 13 g/dL.

Does the patient have a reduced oxygen carrying capacity? (same total quantity of hbg in a larger solution)

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[btbam]

If they have the same quantity of hgb I don't see how the o2 carrying capacity would be reduced as the number you're seeing is falsely low from hemodilution.

If the pt started with a hgb of 15 and then lost 5-600 ccs of blood resulting in a hgb of 13, then yea you have reduced o2 carrying capacity. Right?

 

[RxBoy]

If they have the same quantity of hgb I don't see how the o2 carrying capacity would be reduced as the number you're seeing is falsely low from hemodilution.

If the pt started with a hgb of 15 and then lost 5-600 ccs of blood resulting in a hgb of 13, then yea you have reduced o2 carrying capacity. Right?

I have no idea? Thats what I would assume as well. But according to the oxygen carrying capacity equation, it would be reduced even with dilution.

Carrying capacity = (Hgb x SaO2 x 1.3) + (PaO2 x 0.003)

Either the formula doesn't work in this situation or O2 doesn't bind as avidly when hgb molecules are more spread apart. No clue. Google did not help either.

 

[bostonblaz]

Makes sense it would be less as there is 13g/dl oh hemeglobin in any given volume at any time meaning there is only 13g/dl of hemeglobin carrying oxygen.

 

[Idiopathic]

put simply, yes, but remember carrying capacity is in terms of /dL blood, not as the whole body. Each mL of blood has less hemoglobin so it will carry less O2 but the aggregate oxygen content of the body will remain the same.

 

[Idiopathic]

If the pt started with a hgb of 15 and then lost 5-600 ccs of blood resulting in a hgb of 13, then yea you have reduced o2 carrying capacity. Right?

if a patient started with a hemoglobin of 15 and loss 600 cc of blood, their hemoglobin would still be 15, and no you would not have a reduced O2 carrying capacity, you would be hypovolemic.

 

[RxBoy]

put simply, yes, but remember carrying capacity is in terms of /dL blood, not as the whole body. Each mL of blood has less hemoglobin so it will carry less O2 but the aggregate oxygen content of the body will remain the same.

Thank you! Makes sense.

 

[turkeyjerky]

So in this case there would actually be increased DO2 due to the increased CO with reduced PVR, right?

 

[pgg]

I have no idea? Thats what I would assume as well. But according to the oxygen carrying capacity equation, it would be reduced even with dilution.

Carrying capacity = (Hgb x SaO2 x 1.3) + (PaO2 x 0.003)

Either the formula doesn't work in this situation or O2 doesn't bind as avidly when hgb molecules are more spread apart. No clue. Google did not help either.

Carrying capacity (O2 content) isn't that useful a number by itself.

It's a little more useful if you multiply it by cardiac output and get O2 delivery. If you dilute someone to the point that their Hb is symptomatically low, the symptom you're likely to see first is tachycardia, to maintain O2 delivery.

What's the point of the question though? Test minutia prep? Isovolemic hemodilution?

 

[MTGas2B]

Agree with pgg. Carrying capacity isn't the issue. Oxygen delivery is.

If a fluid bolus moves you to a high cardiac output on your starling curve you've increased oxygen delivery, tissues are happier, they make less lactate, etc.

 

[fakin' the funk]

To take this a step further...

Suppose you have a euvolemic 70kg person with 70ml/kg blood volume (i.e., 5L blood volume), CO = 5L/min, and Hgb = 15g/dL.

You quickly bolus 500ml of colloid (say, FFP or albumin). Blood volume is now 5.5L, Hgb is 13.6g/dL.

What happens to CO and DO2? Does a euvolemic patient respond to a fluid bolus with an increase in SV -> increase in CO -> increase in DO2? Is any increase in CO enough to offset the decrease in Hgb and still increase DO2? Or does this fluid bolus actually decrease DO2?

 

[Hamhock]

To take this a step further...

Suppose you have a euvolemic 70kg person with 70ml/kg blood volume (i.e., 5L blood volume), CO = 5L/min, and Hgb = 15g/dL.

You quickly bolus 500ml of colloid (say, FFP or albumin). Blood volume is now 5.5L, Hgb is 13.6g/dL.

What happens to CO and DO2? Does a euvolemic patient respond to a fluid bolus with an increase in SV -> increase in CO -> increase in DO2? Is any increase in CO enough to offset the decrease in Hgb and still increase DO2? Or does this fluid bolus actually decrease DO2?

I suggest you peri-fleas stop masturbating (mentally).

Or propose a clinically significant question...or start an IM residency .



HH

 

[Idiopathic]

To take this a step further...

Suppose you have a euvolemic 70kg person with 70ml/kg blood volume (i.e., 5L blood volume), CO = 5L/min, and Hgb = 15g/dL.

You quickly bolus 500ml of colloid (say, FFP or albumin). Blood volume is now 5.5L, Hgb is 13.6g/dL.

What happens to CO and DO2? Does a euvolemic patient respond to a fluid bolus with an increase in SV -> increase in CO -> increase in DO2? Is any increase in CO enough to offset the decrease in Hgb and still increase DO2? Or does this fluid bolus actually decrease DO2?

CO goes up (slightly) to maintain DO2. This is multifactorial, but has to do mainly with decreased blood viscosity and increased sympathetic tone.

 

[imfrankie]

Remember also that cardiac output times oxygen content might be the amount delivered, but it doesn't equate with the amount of oxygen that is taken up by the tissues. Good you're thinking about these things. I predict you'll like two site NIRS.

 

[pgg]

I suggest you peri-fleas stop masturbating (mentally).

It's all fair game on the written exam ...