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    Hi guys,

    Just needs some help in understanding how certain substances can bring about a change in urine (in terms of pH, Volume, Na+ conc, and specific gravity)


    What is the effect on urine output of an average person drinking 500ml of 0.9% (isotonic) saline?

    (in terms of pH, Vol, Na+ conc and specific gravity)

    I know that isotonic saline is given to patients at risk of dehydration or hypovolaemia. However in this situation a normal person drinks this 500ml of saline so I assume there would be no need to NaCl so it's concentration would increase in blood. Additionally it could increase urine output as we are increasing fluid volume. Presumably specific gravity of urine will increase as there is more solutes.

    I don't know whether if it will have any effect on pH :confused:

    Those were just my thoughts...let me know if I'm going along the right lines. Perhaps some mechanism as to how they work. Will it have any effect on ADH, Aldosterone ect...?

    What is the effect on urine (in terms of pH, Vol, Na+ con, and specific gravity) of an average person drinking 500ml of sodium citrate?

    I assumed it would be an acid....but wiki seems to suggest it is used to control acidity by acting as a buffer. Is it an acid/base?

    In terms of Na+ conc I think it could dissociate into sodium and citrate and therefore increase Na+ in urine? not sure whether it's correct. Completely guessing here. I suppose if it increases urine solute conc it would also increase specific gravity and aslo vol as water follows solutes.

    What do you guys reckon?
    Any help will be appreciated
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    1)

    it would increased urine volume

    sodium concentration in isotonic fluid matches that in the blood - i would have though concentration of sodium in urine would stay the same ?

    2)

    sodium citrate makes is a common treatment for cystitis.

    it makes the urine alkaline and would increase pH

    HTH
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    (Original post by Revenged)
    1)

    it would increased urine volume

    sodium concentration in isotonic fluid matches that in the blood - i would have though concentration of sodium in urine would stay the same ?

    2)

    sodium citrate makes is a common treatment for cystitis.

    it makes the urine alkaline and would increase pH

    HTH
    Thanks a bunch for the response

    1. If the Na+ conc is same in blood then by giving 500ml of saline (0.9%) aren't we adding more Na+ to blood. So wouldn't the excess Na+ just be excreted out?
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    It's a side note, but it might be worth mentioning that drinking 500ml of normal saline is likely to make most people vomit.
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    Am I wrong to think that 0.9% NaCl is slightly hypertonic?
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    (Original post by davey jones)
    Am I wrong to think that 0.9% NaCl is slightly hypertonic?
    I know what you mean..but for purpose of the question just consider it to be isotonic.
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    I would have presumed...

    If you are giving somebody an isotonic solution and not changing the osmotic property of their blood, then you would not significantly change the composition of excreted urine through that method.

    Saline however may have a effect on pH through the abnormal chloride load, in healthy patients the effect in unlikely to be significant.

    As for excreted urine, this is dependent on the individuals fluid status, if I were to give you 1L of fluid that you didn't necessarily need you would pass the majority of it in urine that is very dilute and of low specific gravity (note that specific gravity is a measure of all solutes). However, not absorbing sodium in the nephron, is one of the ways that water is not reabsorbed, so I would presume that the urine would be quite salty (but I wouldn't lay claim to that being absolutely correct because of things like Na+/K+ exchange in the nephron).

    If I were to give 1L of unneeded fluid to an 80 year old CCF patient it would be deposited in lungs, legs etc quite quickly.

    If I were to give 1L to a very dry oliguric patient, it may not have any fantastic effect on urine output. That patient would have high specific gravity urine and probably high serum sodium as nephrons reabsorb sodium and water rather than excrete it. If you give the patient enough fluid, with a bit of luck he will have a normal urine output pretty soon.

    Any help?
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    (Original post by Helenia)
    It's a side note, but it might be worth mentioning that drinking 500ml of normal saline is likely to make most people vomit.
    I said the same but then deleted the comment in case people thought i was being a ****...

    And also because I remembered having diarolyte and think that had lots of salt in.
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    (Original post by Jamie)
    I said the same but then deleted the comment in case people thought i was being a ****...

    And also because I remembered having diarolyte and think that had lots of salt in.
    I have vague memories of a first year lecturer telling us that - same for you?

    Dioralyte does have salt in, though I'm not sure what concentration it would work out to be. Tastes rank anyway. Not sure if better or worse than saline.
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    To understand sodium you need to understand fluid balance and it is difficult to understand. Your question was asking about a healthy patient which is quite straight forward. For your clinical exams you are going to have to know it because it is a medical emergency and fluids prescription is something all FY1s do.

    If you are asked about an unhealthy patient so in a typical exam question you may be shown a blood test result showing hyponatramia. In hypovolamic hyponatramic you will fluid replace, in hypervolaemic hyponatramic you will fluid restrict. You need to remember that the cause and treatment depend on the fluid status of the patient.

    Also sodium is effected by hormones. What you have in the blood is directly effected by two hormones

    1) ADH

    This is a hormone produced by the hypothalamus and it allow the kidney to absorb more water from the urine.

    increase ADH -> decreases water in urine -> increases concentration of urinary salts.

    for your exams:

    euvolaemic + hyponatramia (+ high urinary sodium) -> SIADH

    2) Aldosterone

    This is a hormone produce by the adreanal gland.

    It acts on the kidney to increasing absorption of sodium and to increase loss of potassium.

    Therefore:

    1) Hyperadreanlism (Conn's sydrome)

    - High aldosterone causes hypernatramia and hypokalaemia in the blood.

    2) Adreanal insufficiency (Addison's disease)

    (- Low cortisol)
    - Low aldosterone causes hyponatramia and hyperkalaemia in the blood.

    HTH
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    (Original post by Helenia)
    I have vague memories of a first year lecturer telling us that - same for you?

    Dioralyte does have salt in, though I'm not sure what concentration it would work out to be. Tastes rank anyway. Not sure if better or worse than saline.
    Sage? I seem to remember the same lecture.
 
 
 
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