USMLE Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
4,342 Posts
Discussion Starter #1
Why do we have increased BUN levels in GI hemorrhage even though the patient is not dehydrated?

Can anybody explain this for me :sorry:
 

·
Ex-USMLE Forums Staff
Joined
·
753 Posts
Blood is full of proteins

Why do we have increased BUN levels in GI hemorrhage even though the patient is not dehydrated?

Can anybody explain this for me :sorry:
Blood contains many proteins such as hemoglobin and immunoglobulins. So when you have blood in the GI lumen, it's as if you had a heavy protein meal.

Blood Urea Nitrogen (BUN) is the end metabolic product of protein break down and therefore it will increase after "that protein meal".
 

·
Registered
Joined
·
316 Posts
pre-renal azotemia is the cause

after GI hemorrhage, patient will have hypovolemia, the sympathetic nervous system will cause a decrease in renal blood flow and thus less GFR, causing pre-renal azotemia, the Blood urea nitrogen will raise because of less GFR... the BUN : Creatinine will raise to > 20:1....
 

·
Registered
Joined
·
414 Posts
If you don't know what's BUN, I don't think you can ever answer the question! :rolleyes:
I am not good with short forms
But isn't it obvious no matter where you have hemorrhage there is always a RELATIVE increase in blood solutes?:redcheeks;
 
  • Like
Reactions: rigbbm

·
Registered
Joined
·
316 Posts
I am not good with short forms
but isn't it obvious no matter where you have hemorrhage there is always a RELATIVE increase in blood solutes??????????:redcheeks;
dear brother!! u seem to be very new to med field... 1st yr student i feel...:) neways no problem its good to keep visiting these type of medical forums...

No hemorrhage doesn't cause relative increase in solutes... hemorrhage cause isotonic decrease in fluid volume.... hemorrhage and diarrhea are two conditions that cause an isotonic fluid contraction.... so there is no relative increase in solutes.
 

·
Registered
Joined
·
414 Posts
dear brother!! u seem to be very new to med field... 1st yr student i feel...:) neways no problem its good to keep visiting these type of medical forums...

No hemorrhage doesn't cause relative increase in solutes... hemorrhage cause isotonic decrease in fluid volume.... hemorrhage and diarrhea are two conditions that cause an isotonic fluid contraction.... so there is no relative increase in solutes.
Thx first of all I knew it blunder of mistake in thinking still don't understand why diahria will be isotonic when it's only a excessive loss of water mainly???????
I do not mean directly by relative I mean after any blood loss to maintain normal BP there is absorption of excessive fluid with relative increase in solute coc.
Waiting for your one more good explanation.
 
  • Like
Reactions: rigbbm

·
Registered
Joined
·
625 Posts
Hi there - so is the answer the blood meal idea or the decreased renal function idea? Can anyone clarify?

Theory 1: You hemorrhage into your GIT, the blood is digested, blood has protein - this protein has nitrogen so your BUN increases

Theory 2: You hemorrhage into your GIT, body notices it's losing fluid, shuts down kidneys, now no nitrogen is lost as urea, so your BUN increases

I guess the question also is - if the patient is hemorrhaging into their bowel the blood will still need to be broken down so if the hemorrhage is in the large instestine or later, the decreased renal function theory would be the only possible one.

I'm leaning towards that theory also because the blood meal thing seems a little too "cool" to be true ;) - you're drinking your own blood mwa ha ha ha.. though who knows.. stranger things have happened...
 

·
Registered
Joined
·
741 Posts
Hi there - so is the answer the blood meal idea or the decreased renal function idea? Can anyone clarify?

Theory 1: You hemorrhage into your GIT, the blood is digested, blood has protein - this protein has nitrogen so your BUN increases

Theory 2: You hemorrhage into your GIT, body notices it's losing fluid, shuts down kidneys, now no nitrogen is lost as urea, so your BUN increases

I guess the question also is - if the patient is hemorrhaging into their bowel the blood will still need to be broken down so if the hemorrhage is in the large instestine or later, the decreased renal function theory would be the only possible one.

I'm leaning towards that theory also because the blood meal thing seems a little too "cool" to be true ;) - you're drinking your own blood mwa ha ha ha.. though who knows.. stranger things have happened...
The increased BUN is not seen when you have lower GI hemorrhage because as you said there's no time for the blood proteins to be absorbed.

On the other hand, the kidney does not shut down when it senses decreased ECF, instead it maximizes water and salt retention. Therefore, it's not the cause behind the increased BUN (in cases of GI hemorrhages).

BUN increases in cases of dehydration (not blood loss). When you lose body water all solutes concentration increases including BUN, Creatinine, and all other solutes. Blood loss is not equivalent to dehydration (physiologically speaking) though clinically you may treat both conditions with isotonic saline.
 

·
Registered
Joined
·
414 Posts
The increased BUN is not seen when you have lower GI hemorrhage because as you said there's no time for the blood proteins to be absorbed.

On the other hand, the kidney does not shut down when it senses decreased ECF, instead it maximizes water and salt retention. Therefore, it's not the cause behind the increased BUN (in cases of GI hemorrhages).

BUN increases in cases of dehydration (not blood loss). When you lose body water all solutes concentration increases including BUN, Creatinine, and all other solutes. Blood loss is not equivalent to dehydration (physiologically speaking) though clinically you may treat both conditions with isotonic saline.
So dehydration is not isotonic loss is it????
Why no reply????:eek::notsure:
 
  • Like
Reactions: rigbbm

·
Registered
Joined
·
741 Posts
Dehydration can be isotonic, hypotonic, or hypertonic

So dehydration is not isotonic loss is it????
Why no reply????:eek::notsure:
Dehydration can be isotonic, hypotonic, or hypertonic. It depends on how much proportionate loss of water and/or salt (mainly sodium) you lose.

  • Isonatremic (isotonic) dehydration occurs when the lost fluid is similar in sodium concentration to the blood. Sodium and water losses are of the same relative magnitude in both the intravascular and extravascular fluid compartments.
  • Hyponatremic (hypotonic) dehydration occurs when the lost fluid contains more sodium than the blood (loss of hypertonic fluid). Relatively more sodium than water is lost. Because the serum sodium is low, intravascular water shifts to the extravascular space, exaggerating intravascular volume depletion for a given amount of total body water loss.
  • Hypernatremic (hypertonic) dehydration occurs when the lost fluid contains less sodium than the blood (loss of hypotonic fluid). Relatively less sodium than water is lost. Because the serum sodium is high, extravascular water shifts to the intravascular space, minimizing intravascular volume depletion for a given amount of total body water loss.
In any case of these you may have increased BUN and/or Creatinine. There are two reasons for that:
1- In dehydration (hypovolemia) you have less kidney perfusion and so you build up Nitrogen waste products.
2- In dehydration you have more solutes concentration so your BUN rise as well as other parameters such as the hemoglobin and hematocrit.

The terms isotonic, hypotonic, and hypertonic refer to the concentration of Sodium (not other solutes) that's why they are more appropriately called hyponatremic, hyerpnatremic, or isonatremic.
 

·
Registered
Joined
·
316 Posts
The increased BUN is not seen when you have lower GI hemorrhage because as you said there's no time for the blood proteins to be absorbed.

On the other hand, the kidney does not shut down when it senses decreased ECF, instead it maximizes water and salt retention. Therefore, it's not the cause behind the increased BUN (in cases of GI hemorrhages).

BUN increases in cases of dehydration (not blood loss). When you lose body water all solutes concentration increases including BUN, Creatinine, and all other solutes. Blood loss is not equivalent to dehydration (physiologically speaking) though clinically you may treat both conditions with isotonic saline.
MAN this is confusing!!! so u say that GI hemorrhage doesnot cause pre-renal azotemia???

Iis written in FA.... dec. RBF (e.g. hypotension) -> dec GFR -> Na/ h20 and urea retained by kidney so BUN/creatinine ratio inc.
 
  • Like
Reactions: rigbbm

·
Registered
Joined
·
741 Posts
Sorry ...

MAN this is confusing!!! so u say that GI hemorrhage doesnot cause pre-renal azotemia???

Iis written in FA.... dec. RBF (e.g. hypotension) -> dec GFR -> Na/ h20 and urea retained by kidney so BUN/creatinine ratio inc.
I apologize, my two previous posts seem to be conflicting with each other.
Yes, GI hemorrhage can cause prerenal failure (if it was severe enough to cause hypovolemia and decreased renal perfusion) but that's not the sole reason why you have increased BUN in these cases, the more plausible reason is the increased protein (blood) absorption leading to increased metabolic waste product increasing the BUN.
In dehydration, on the other hand, it's mainly the prerenal azotemia that causes the increased BUN as you pointed out.

Sorry for the confusion :sorry:
 

·
Registered
Joined
·
741 Posts
Intestinal flora

Another theory about the increased BUN in GI hemorrhage is that blood get broken down in the intestinal lumen by the action of bacterial flora which releases urea which then get absorbed.
 

·
Registered
Joined
·
60 Posts
Volume contraction

During any volume contraction , the absorption of solutes in the PCT increases and that should explain increase in BUN and also as posted about BUN : Creatine ratio as Creatine is not reabsorbed.I like the concept of blood containing Proteins but with regard to upper GI versus Lower GI.
 
1 - 17 of 17 Posts
Top