volume contraction/expansion help!

[doc29]

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Can someone please explain to me about hypo/hyperosmotic volume contraction/expansion? 😕

 

[PokerDoc]

do you have RR path by goljan? I mean we can try to reiterate it here, but I believe its ch 2 or 3 he discusses it.. I dont think it can be explained any better than how he does.. look at the drawings he includes too.. that show the dashed lines representing the volume changes under different circumstances.

I'm not trying to tell you its an easy concept or anything, just that goljan does a beautiful job explaining it.. I would def try that section of his book out again and then come back with more specific issues you are having with understanding it and then we can certainly help you from there.

 

[doc29]

do you have RR path by goljan? I mean we can try to reiterate it here, but I believe its ch 2 or 3 he discusses it.. I dont think it can be explained any better than how he does.. look at the drawings he includes too.. that show the dashed lines representing the volume changes under different circumstances.

I'm not trying to tell you its an easy concept or anything, just that goljan does a beautiful job explaining it.. I would def try that section of his book out again and then come back with more specific issues you are having with understanding it and then we can certainly help you from there.

thanks for the suggestion pokerdoc. i listened to goljan audio on that topic, but i got confused. May be i should read the chapter from goljan along with audio. I just cant understand the water shift in diff scenarios.

 

[PokerDoc]

thanks for the suggestion pokerdoc. i listened to goljan audio on that topic, but i got confused. May be i should read the chapter from goljan along with audio. I just cant understand the water shift in diff scenarios.

yeah this is one of those topics i think a visual aid will help.. check out the book its drawn out well.. and its not even a chapter, its like 2 pages, wont take u long

 

[kryptik]

the rule to keep in mind is: ECF osmolarity controls ICF volume via an inverse relationship

 

[BenCarson]

scan the RR page then upload here. with this picture we can discuss and help you but otherwise it's hard to explain w/o a diagram.

 

[otacon88]

def read the chapter again! the graphs and blue notes in the margin are good too.

i had a difficult time with the concept, but once you get it and understand it, it's really easy. the way i remember it is if you have any CONTRACTION, that causes volume depletion, and any EXPANSION is an increase in volume. HYPERosmotic means fluid will LEAVE the ICF and ENTER the ECF, since the ECF is hypertonic and draws fluid OUT of the ICF, so the ICF will be contracted and the ECF will be expanded. and hypotonic is the opposite - ICF has a higher osmotic pressure so will draw IN fluid and cause expansion of the ICF and depletion of the ECF.

putting it all together - take for example hypertonic volume expansion, such as in the case of straight infusion of Na. You will expanding the ECF bc of gain of fluid, and decreasing the ICF.

or another example - DI - hypertonic volume contraction. volume contraction because you're losing free water, but hypertonic because, well, you're losing only free water and retain the Na. so your ECF compartment is contracted because of the loss of water, and the ICF is also contracted bc ECF is hypertonic and draws fluid OUT.

hope it helps a litte, it is difficult without diagrams

 

[doc29]

thanks guys...gonna read it tonight 🙂

 

[NRAI2001]

def read the chapter again! the graphs and blue notes in the margin are good too.

i had a difficult time with the concept, but once you get it and understand it, it's really easy. the way i remember it is if you have any CONTRACTION, that causes volume depletion, and any EXPANSION is an increase in volume. HYPERosmotic means fluid will LEAVE the ICF and ENTER the ECF, since the ECF is hypertonic and draws fluid OUT of the ICF, so the ICF will be contracted and the ECF will be expanded. and hypotonic is the opposite - ICF has a higher osmotic pressure so will draw IN fluid and cause expansion of the ICF and depletion of the ECF.

putting it all together - take for example hypertonic volume expansion, such as in the case of straight infusion of Na. You will expanding the ECF bc of gain of fluid, and decreasing the ICF.

or another example - DI - hypertonic volume contraction. volume contraction because you're losing free water, but hypertonic because, well, you're losing only free water and retain the Na. so your ECF compartment is contracted because of the loss of water, and the ICF is also contracted bc ECF is hypertonic and draws fluid OUT.

hope it helps a litte, it is difficult without diagrams

I start to get confused when they breakdown the ECF into interstial vs. Plasma and when an ECF shift occurs which compartment is it going onto or out of??

 

[PokerDoc]

I start to get confused when they breakdown the ECF into interstial vs. Plasma and when an ECF shift occurs which compartment is it going onto or out of??

thats different.. you are referring to the whole capillary pressure, capillary oncotic pressure vs interstitial pressure and interstitial oncotic pressure.

thats not what the OP was talking about


for your case, just simplify it so that you know that hydrostatic pressure pushes stuff out and oncotic pressure pulls stuff in.. and then do the math to get the net flow

random made up example:

a capillary has a hydrostatic pressure of 50 and an oncotic pressure of 12
the adjacent interstitium has a hydrostatic pressure of 5 and an oncotic pressure of 10. what is the direction and net flow?

it would be 43mmHg in the direction toward the interstitium from the capillary... do you follow? or did i misunderstand your issue?

 

[NRAI2001]

thats different.. you are referring to the whole capillary pressure, capillary oncotic pressure vs interstitial pressure and interstitial oncotic pressure.

thats not what the OP was talking about


for your case, just simplify it so that you know that hydrostatic pressure pushes stuff out and oncotic pressure pulls stuff in.. and then do the math to get the net flow

random made up example:

a capillary has a hydrostatic pressure of 50 and an oncotic pressure of 12
the adjacent interstitium has a hydrostatic pressure of 5 and an oncotic pressure of 10. what is the direction and net flow?

it would be 43mmHg in the direction toward the interstitium from the capillary... do you follow? or did i misunderstand your issue?

I understand the whole starlings forces concept... its just when you get to a pharm question and they start talking about Vd (volume of distribution) and into what compartment exactly the drug actually goes into... or when you see one of those physio questions where the patient was infused with 4Liters of X, how much will the plasma volume increase relative to interstial volume relative to ICF...etc.

These type of questions always make me cringe.. I usually end up just moving forward and telling myself I ll go back and learn the concept later. I guess later has become now..haha

 

[PokerDoc]

I understand the whole starlings forces concept... its just when you get to a pharm question and they start talking about Vd (volume of distribution) and into what compartment exactly the drug actually goes into... or when you see one of those physio questions where the patient was infused with 4Liters of X, how much will the plasma volume increase relative to interstial volume relative to ICF...etc.

These type of questions always make me cringe.. I usually end up just moving forward and telling myself I ll go back and learn the concept later. I guess later has become now..haha

oh, well a high volume of distribution means the drug preferentially goes into the tissues meaning theres less of it circulating at an equal dose to another drug with a low Vd (which stays in the vessels).

the equation you need to answer your question is to be found in the beginning of the pharm section of first aid.. ignore the F part of the equation, the bioavailability will always equal 1 for IV.

so loading dose = desired concentration * Vd

so if they say the loading dose was 4L, they must have also given you the concentration theyre trying to achieve or the Vd of the drug, and then you just solve for the missing variable.