February 9, 2022 • 22 mins
Osmosis, osmolality, osmolarity, and fluid balance. How hydrostatic pressure and osmotic pressure drive filtration in our capillaries to deliver nutrients and remove wastes.
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Unknown (00:00):
Okay, and welcome to nursing with Dr. Hobbick. Today
(00:04):
I am thinking about fluidbalance. I know y'all are like,
Oh, fluid balance, we're soexcited, you should be excited
because fluid balances anincredibly important concept to
understand for the nurse. Imean, it's important for
everybody else to understand ittoo. But we need to think about
(00:26):
fluid balance frequently, notjust because our patients could
be at risk for fluid overload,or they could be at risk for
fluid volume deficit, butbecause we're going to give them
fluid directly into theirintravascular space. So let's
talk about fluid. The firstthing we need to remember is
that fluid is not the same thingas water, but rather fluid is
(00:51):
water that has things dissolvedin it, the things that are
dissolved in it representsolutes these are things like
sodium chloride, things likeproteins, or glucose, those are
things that are inside thewater, and those things make up
(01:13):
a concentration of the fluid.
Those are the composition of thefluid. So the number of those is
the osmolality or osmolarity ofthe fluid.
We have a fluid amount, which isvolume, we have fluid
composition, which is what is inthe fluid, what electrolytes or
(01:36):
solutes are in the fluid. Andthen we have concentration, the
amount of solutes to the amountof water. These are important
concepts, because this is howeverything else is driven. As
far as fluid balance, we need totalk about osmosis, we need to
(01:57):
talk about osmotic pole orosmolarity. So first, let's
remember where in the body wekeep our fluid. There are two
main compartments in your bodywhere we keep fluid. One of them
is the intracellular fluid.
Let's guess where that is. Youguessed it inside the cells.
intracellular fluid is insideyourself, and that's two thirds
(02:21):
of your total body water. Twothirds is inside your cells. The
other main compartment is theextracellular compartment, we
have fluid that's inside yourcells and fluid that's not
inside your cells. We actuallybreak that extracellular fluid
into three more divisions. Thoseare the interstitial compartment
(02:46):
which is in between and aroundthe cells. We have the intra
vascular compartment, which isthe fluid that you can find
inside your arteries and veinsin your vascular system. And
then we have the transcellular.
Now most of the time, we'retalking about intravascular. But
(03:09):
we also talk about how theintravascular affects the
interstitial, which then affectsthe intracellular transcellular
we don't talk about as muchtranscellular is fluid that's
secreted by epithelial cells.
This includes pleural fluid,pericardial, fluid, synovial,
fluid, even cerebral spinalfluid. We don't talk about those
(03:31):
as much when we're talking aboutfluid balance as we do the
intravascular. And then how thatcompares or how that impacts our
interstitial and intracellularcompartments. So one more time
we have two main compartmentsintracellular inside the cells,
extracellular outside the cells,and that extracellular is broken
(03:52):
into those three divisions haveinterstitial, which is
surrounding ourselves and inbetween the cells intravascular,
which is inside our vessels, ourvascular compartment, which is
basically our plasma our blood,and then transcellular amount of
fluid. This always blows my mindwhen I talk about this, the
(04:12):
amount of fluid in our bodies isThat's the sound of my brain
exploding. It's so mind blowingevery time I think about it. We
have about 25 liters of fluidinside ourselves. So always want
to think about 12 two literbottles lined up in front of me.
And that's what's inside myself.
(04:36):
Remember that intercellularspace holds about two thirds of
our total body fluid. The otherthird is somewhere around 15 ish
leaders we've got about 10 to 12liters in the interstitial space
which is surrounding the cellsand in between them and
somewhere around three and ahalf to six liters in plasma
(04:59):
volume. The amount that'stranscellular is much smaller,
we don't really address that atleast not here. I think the
orthopedics might disagree, wecan have changes in fluid
volume, we can have changes influid concentration, and these
will affect how the fluidbehaves where the fluid is in
(05:21):
those compartments. Osmosis isthe movement of water through a
semi permeable membrane toachieve equilibrium of
concentration, or osmolarity.
Remember as molarity osmolality,that refers to the concentration
of the fluid fluid is water withsolutes dissolved in it, the
(05:42):
more solutes there are, thehigher the concentration, I have
a semi permeable membrane thatthe solutes can't get through,
but the water can, the waterwants everything to be equal, it
wants to be equal, let's to beBaby Bear just right, not too
high, not too low, the waterwill move across the membrane if
(06:03):
the solutes cannot, in order toachieve equilibrium, you have a
semipermeable membraneseparating two different
concentrations. Let's say on theright hand side, you have 10%
Sodium chloride, and on the lefthand side, you have 5% Sodium
chloride, the water is actuallygoing to move so that there's
(06:24):
more water on the moreconcentrated side so that the
two sides will then have anequal concentration of sodium
chloride and water. Thedifference between these two
osmolarity is about aconcentration per liter
osmolality is a osmoticconcentration per kilogram.
Let's address some other termsthat we use for movement of
(06:49):
solutes and water. Osmosisrefers to the movement of water
across a semi permeablemembrane, water will move from
an area of lesser concentrationto an area of greater
concentration, working to makethat concentration equal on both
sides of that membrane. We dohave some active transport this
(07:12):
requires ATP adenosinetriphosphate to move
electrolytes across the cellmembrane against the
concentration gradient,electrolytes those solutes they
want to diffuse diffusion is apassive motion, where they move
from an area of highconcentration to an area of low
concentration. I always describethis as if I have a candle and I
(07:37):
light my candle and you walkover by where the candle is lit,
it smells really strongly. Butif I walk far away, it smells
less strong. However, when Ifirst lit the candle, it didn't
smell at all farther away. Thoseparticles of scent diffused,
obviously with air movement, butin a passive process, nothing is
(07:58):
really grabbing them and movingthem around. Away from that area
of high concentration, ourelectrolytes try to do the same
thing. And water at the sametime. If the electrolytes are
solutes can't move across themembrane, the water will
everything is working towardsthis equilibrium filtration is
the movement across the membraneunder pressure from higher to
(08:22):
lower pressure. That will becomeimportant when we talk about
filtration, and hydrostaticpressure and osmotic pressure.
The other things we need tothink about are the fact that as
far as a body, a body can have adecrease in volume of fluid. But
that means that there's nochange in concentration, they
(08:45):
can have an increase in volumeof fluid with no change in
concentration, they could havean increase in concentration, or
a decrease in concentration withno change in volume. Or they
could have a decrease in volumewith an increase in
concentration or osmolality.
(09:07):
These terms refer to fluidvolume excess and increase in
volume but no change inconcentration, fluid volume
deficit, a decrease in volumewith no change in concentration.
We can have hypernatremia, whichis an increase in osmolality or
(09:27):
concentration, decrease inosmolality or concentration. And
most of the time when we'retalking about true dehydration,
not always but most of the time.
This is a decrease in volume andan increase in concentration.
Clinically dehydration,according to some textbooks is
the combination of a fluidvolume deficit and
(09:49):
hypernatremia. You might besitting there going well Dr.
Hobbick. Why are you talkingabout sodium? I'm talking about
sodium because so yum is themost abundant cat ion it is the
major player as far as apositively charged ion in our
intravascular compartment whenwe're testing our blood, and
(10:10):
we're testing for electrolytes,that's really one of the big
ones that we're looking at,contributes the most to the
concentration. No, we do alsohave a lot of chloride, that
sodium is our major player. It'sone of the reasons why when we
use sodium chloride normalsaline, we're replacing the
electrolytes that are alreadythe most abundant in the
(10:30):
intravascular compartment. Let'sconsider filtration. You imagine
we have a capillary and thiscapillary, I mean, you know that
our arteries in our veins areattached they come together, but
our capillaries, you have oneside of the capillary is
arterial, one side of thecapillary is venous have four
(10:51):
forces at play here. If youimagine your capillary you are
representing the intra vascularspace inside the capillary,
there's fluid inside there, thatis in the intravascular space.
But on the other side of thecapillary membrane, is the
interstitial space. There'sfluid in the interstitial space
(11:13):
as well. Fluid has pressure,hydrostatic pressure is a
pushing force. Inside thecapillary, the hydrostatic
pressure is pushing against theouter wall of the capillary. On
the outside of the capillaryhydrostatic pressure in the
(11:35):
interstitial space is pushingagainst the wall of the
capillary. Now as you canimagine, with the heart pumping
behind this fluid that's insidethe capillary and the arterial
end, we have more pressure, thehydrostatic pressure is higher
and if you recall, we canactually squeeze our arteries
and what happens if you squeezethe arteries, you know that hose
(11:59):
that you used to play with, youturn the hose on and you stick
your finger over the end whathappens when you made the hose
exit the hole smaller, thepressure increase we constrict
our arteries we increase thatpressure that hydrostatic
pressure on the arterial end,the hydrostatic pressure is
(12:20):
pushing. We also have oursolutes in side of our blood,
which contribute to us Modicpressure as monic pressure is a
pulling force. Osmotic pressureis where the water goes, you may
have heard an instructor say toyou that water follows salt, but
it's not really that simple.
(12:45):
It's that water follows solutes.
Remember we said that Osmosis isthe movement of water across a
semi permeable membrane in orderto reach a equilibrium in
concentration. If there's moresolutes on one side of that
capillary membrane, it will pullwater to the side that has the
most solutes my hydrostaticpressure on the arterial end of
(13:09):
the capillary is pretty high,it's pushing outwards a lot
higher than the asthmaticpressure is pulling in fluid is
pushed out of the capillary.
This moves that fluid betweenthe vascular and the
interstitial space on thearterial and the hydrostatic
(13:30):
pressure overcomes the osmoticpressure inside the vessel and
pushes that fluid out. We havehydrostatic pressure, nice
amount of pressure in theinterstitial space, but it's
nowhere near what it is insidethe vessel. We're losing water
on the arterial end of thevessel. But our albumin, our
solutes, say can't get throughthat membrane, then we've lost
(13:54):
water but not solutes, whichmeans the concentration gets
higher on the venous and becausewe've lost that water on the
arterial end. Now thehydrostatic pressure is lower on
the venous end, but the osmoticpressure is higher because the
concentration increased. Now westart to pull fluid back into
(14:16):
the venous end, and it bringswith it waste products. Those
are then taken on to the liverto the kidneys, where they need
to go and eventually comes backaround to the heart of the lungs
to be reactivated and sent backout to the body. When you're
thinking about what kind offluid we're putting into this
intravascular space. If I add ahypertonic fluid to the
(14:41):
intravascular space hypertonicmeans that the concentration is
higher than that of normal bodyfluid. That means that I've
increased the concentrationinside the vessels and water can
be pulled into the vesselsbecause the concentration the
osmotic pressure has beenincreased. hypotonic fluid would
(15:01):
do the opposite, it would dilutethe blood causing water to move
out into the interstitial space.
When we affect the interstitialspace, it will then affect the
intracellular space, the waterwill move back and forth across
those compartments. The lastthing for us to think about as
far as fluid balance in thisreally short podcast is how the
fluid gets there and how it getsout. Obviously, intake is water
(15:25):
that we drink or other fluids,jello counts as intake. Don't
ask me why. Ice, remember, iceis going to be half because it
doesn't take up the full volumeof the cup or the measuring
tool, ice cream, soups, notchunky soups, though, we would
(15:45):
count all of these things asintake, we also need to count
any IV fluids that you get thepatient, any irrigation that is
done, consider a patient who'son continuous bladder
irrigation. That means that theyhave a large bag of fluid that
is running into a catheter thatgoes through their urethra and
(16:06):
into their bladder. And then allof that fluid plus the urine and
whatever else, maybe blood isdrained out of that another
Lumen or hole in that catheterinto a collection bag. We have
to count that irrigation fluidis intake so that when we
subtract intake and output, weknow how much of the output is
irrigation and how much ispatient's own body fluids. We
(16:30):
would count all of these thingsas intake. How does the fluid
get out? Well, I mean, we allknow that fluid gets out as
urine, right? If you have urine,if you have liquid stool, we
don't count the stool that'sformed or you know, constipated
stools. But we also count vomit.
(16:50):
Sweat is another way for thefluid to get out. Of course,
tears and our breath.
I'm currently live in Florida.
And I joke around that theydon't know that their breath has
water in it because they can'tsee it when it gets really cold
because it doesn't get coldenough here for that. That's
just a joke. I know theFloridians know what that is. We
have that breath vapor that'sconstantly coming out, we have
(17:12):
evaporation off of our skin.
Those things that we can't seewe can't sense are called
insensible losses. Those wecan't measure, I can't measure
how much water you lose throughyour breath. I can't measure how
much comes off your skin. But Ido know that if you're breathing
(17:32):
faster, you're going to losemore water. If you have a fever,
more evaporation will take placeI can expect in a normal course
the patient could lose anywherefrom 500 milliliters to a liter
or more of fluid per day. Inthose insensible losses. We also
have fluid that we take in thatwe can't measure a lot of food
(17:54):
is up to 85% fluid or water. AndI can't measure that you think
about an apple or an orange.
Think about those chunky soups,we can't really measure that
water, but we know it's there.
When we need to measure apatient's fluid balance, we need
to measure intake and output, weneed to make sure that we are
(18:16):
getting an accurate measurementof intake and output. And one of
the most sensitive indicators offluid status is going to be a
daily weight. So important toget that weight on the same
scale at the same time under thesame conditions every day,
making sure that your texts orAIDS or whoever is weighing the
(18:37):
patient knows you have to havethe correct number of blankets
or sheets on the bed, nothingextra. And ideally we want to
get that weight before they'vehad any breakfast. We can
compare that weight and akilogram or 2.2 pounds of weight
equals a liter of fluid. So mypatient has gained three pounds
(18:59):
overnight. That's over a literof fluid. That's pretty bad. We
need to do something we need tolet the provider know. The other
things that we can monitor tohelp us know about our patients
fluid status are the patient'ssodium level, the patient's
hematocrit and their urinespecific gravity. If the patient
(19:21):
has too little body fluid,they've lost water, the
concentration of the blood willgo up. That means the sodium
will go up because when wemeasure it we're measuring how
much is sodium is in this muchof blood. hematocrit is a
measure of the percentage of theblood that is a solid and plasma
(19:44):
if your hematocrit is high. Thenyou have hemo concentration, a
lot of solids and not enoughfluid. If your hematocrit is
low. Then you have hemo dilutionyou have a lot of fluid For a
lesser amount of solids, wemonitor that hematocrit. You'll
(20:04):
also need the hemoglobin to giveyou an idea of what else is
going on there. If thehemoglobin is the same across
three samples, but thehematocrit changes, we know that
it's a fluid balance change.
Rather than say a patient who'sbleeding. We all know that the
kidneys work very hard tomaintain fluid balance. The
kidneys will dilute the urine toget rid of excess fluid or
(20:27):
concentrate the urine to retainfluid and not be putting out as
much this will affect the urinespecific gravity urine specific
gravity will go up. If we don'thave enough fluid in the urine
is being concentrated, and itwill go down if the urine is
being diluted, letting you knowwhat the kidneys are thinking is
happening and how they're tryingto compensate. I hope you
(20:49):
enjoyed this discussion of fluidbalance. And if you're confused
and definitely recommend KhanAcademy has some really good
videos on this concept. And Ihope you have a wonderful day.
Thanks for spending the last 20minutes with me on nursing with
Dr. Hobbick. See you next time.
Okay, and welcome to nursing with Dr. Hobbick. Today
(00:04):
I am thinking about fluidbalance. I know y'all are like,
Oh, fluid balance, we're soexcited, you should be excited
because fluid balances anincredibly important concept to
understand for the nurse. Imean, it's important for
everybody else to understand ittoo. But we need to think about
(00:26):
fluid balance frequently, notjust because our patients could
be at risk for fluid overload,or they could be at risk for
fluid volume deficit, butbecause we're going to give them
fluid directly into theirintravascular space. So let's
talk about fluid. The firstthing we need to remember is
that fluid is not the same thingas water, but rather fluid is
(00:51):
water that has things dissolvedin it, the things that are
dissolved in it representsolutes these are things like
sodium chloride, things likeproteins, or glucose, those are
things that are inside thewater, and those things make up
(01:13):
a concentration of the fluid.
Those are the composition of thefluid. So the number of those is
the osmolality or osmolarity ofthe fluid.
We have a fluid amount, which isvolume, we have fluid
composition, which is what is inthe fluid, what electrolytes or
(01:36):
solutes are in the fluid. Andthen we have concentration, the
amount of solutes to the amountof water. These are important
concepts, because this is howeverything else is driven. As
far as fluid balance, we need totalk about osmosis, we need to
(01:57):
talk about osmotic pole orosmolarity. So first, let's
remember where in the body wekeep our fluid. There are two
main compartments in your bodywhere we keep fluid. One of them
is the intracellular fluid.
Let's guess where that is. Youguessed it inside the cells.
intracellular fluid is insideyourself, and that's two thirds
(02:21):
of your total body water. Twothirds is inside your cells. The
other main compartment is theextracellular compartment, we
have fluid that's inside yourcells and fluid that's not
inside your cells. We actuallybreak that extracellular fluid
into three more divisions. Thoseare the interstitial compartment
(02:46):
which is in between and aroundthe cells. We have the intra
vascular compartment, which isthe fluid that you can find
inside your arteries and veinsin your vascular system. And
then we have the transcellular.
Now most of the time, we'retalking about intravascular. But
(03:09):
we also talk about how theintravascular affects the
interstitial, which then affectsthe intracellular transcellular
we don't talk about as muchtranscellular is fluid that's
secreted by epithelial cells.
This includes pleural fluid,pericardial, fluid, synovial,
fluid, even cerebral spinalfluid. We don't talk about those
(03:31):
as much when we're talking aboutfluid balance as we do the
intravascular. And then how thatcompares or how that impacts our
interstitial and intracellularcompartments. So one more time
we have two main compartmentsintracellular inside the cells,
extracellular outside the cells,and that extracellular is broken
(03:52):
into those three divisions haveinterstitial, which is
surrounding ourselves and inbetween the cells intravascular,
which is inside our vessels, ourvascular compartment, which is
basically our plasma our blood,and then transcellular amount of
fluid. This always blows my mindwhen I talk about this, the
(04:12):
amount of fluid in our bodies isThat's the sound of my brain
exploding. It's so mind blowingevery time I think about it. We
have about 25 liters of fluidinside ourselves. So always want
to think about 12 two literbottles lined up in front of me.
And that's what's inside myself.
(04:36):
Remember that intercellularspace holds about two thirds of
our total body fluid. The otherthird is somewhere around 15 ish
leaders we've got about 10 to 12liters in the interstitial space
which is surrounding the cellsand in between them and
somewhere around three and ahalf to six liters in plasma
(04:59):
volume. The amount that'stranscellular is much smaller,
we don't really address that atleast not here. I think the
orthopedics might disagree, wecan have changes in fluid
volume, we can have changes influid concentration, and these
will affect how the fluidbehaves where the fluid is in
(05:21):
those compartments. Osmosis isthe movement of water through a
semi permeable membrane toachieve equilibrium of
concentration, or osmolarity.
Remember as molarity osmolality,that refers to the concentration
of the fluid fluid is water withsolutes dissolved in it, the
(05:42):
more solutes there are, thehigher the concentration, I have
a semi permeable membrane thatthe solutes can't get through,
but the water can, the waterwants everything to be equal, it
wants to be equal, let's to beBaby Bear just right, not too
high, not too low, the waterwill move across the membrane if
(06:03):
the solutes cannot, in order toachieve equilibrium, you have a
semipermeable membraneseparating two different
concentrations. Let's say on theright hand side, you have 10%
Sodium chloride, and on the lefthand side, you have 5% Sodium
chloride, the water is actuallygoing to move so that there's
(06:24):
more water on the moreconcentrated side so that the
two sides will then have anequal concentration of sodium
chloride and water. Thedifference between these two
osmolarity is about aconcentration per liter
osmolality is a osmoticconcentration per kilogram.
Let's address some other termsthat we use for movement of
(06:49):
solutes and water. Osmosisrefers to the movement of water
across a semi permeablemembrane, water will move from
an area of lesser concentrationto an area of greater
concentration, working to makethat concentration equal on both
sides of that membrane. We dohave some active transport this
(07:12):
requires ATP adenosinetriphosphate to move
electrolytes across the cellmembrane against the
concentration gradient,electrolytes those solutes they
want to diffuse diffusion is apassive motion, where they move
from an area of highconcentration to an area of low
concentration. I always describethis as if I have a candle and I
(07:37):
light my candle and you walkover by where the candle is lit,
it smells really strongly. Butif I walk far away, it smells
less strong. However, when Ifirst lit the candle, it didn't
smell at all farther away. Thoseparticles of scent diffused,
obviously with air movement, butin a passive process, nothing is
(07:58):
really grabbing them and movingthem around. Away from that area
of high concentration, ourelectrolytes try to do the same
thing. And water at the sametime. If the electrolytes are
solutes can't move across themembrane, the water will
everything is working towardsthis equilibrium filtration is
the movement across the membraneunder pressure from higher to
(08:22):
lower pressure. That will becomeimportant when we talk about
filtration, and hydrostaticpressure and osmotic pressure.
The other things we need tothink about are the fact that as
far as a body, a body can have adecrease in volume of fluid. But
that means that there's nochange in concentration, they
(08:45):
can have an increase in volumeof fluid with no change in
concentration, they could havean increase in concentration, or
a decrease in concentration withno change in volume. Or they
could have a decrease in volumewith an increase in
concentration or osmolality.
(09:07):
These terms refer to fluidvolume excess and increase in
volume but no change inconcentration, fluid volume
deficit, a decrease in volumewith no change in concentration.
We can have hypernatremia, whichis an increase in osmolality or
(09:27):
concentration, decrease inosmolality or concentration. And
most of the time when we'retalking about true dehydration,
not always but most of the time.
This is a decrease in volume andan increase in concentration.
Clinically dehydration,according to some textbooks is
the combination of a fluidvolume deficit and
(09:49):
hypernatremia. You might besitting there going well Dr.
Hobbick. Why are you talkingabout sodium? I'm talking about
sodium because so yum is themost abundant cat ion it is the
major player as far as apositively charged ion in our
intravascular compartment whenwe're testing our blood, and
(10:10):
we're testing for electrolytes,that's really one of the big
ones that we're looking at,contributes the most to the
concentration. No, we do alsohave a lot of chloride, that
sodium is our major player. It'sone of the reasons why when we
use sodium chloride normalsaline, we're replacing the
electrolytes that are alreadythe most abundant in the
(10:30):
intravascular compartment. Let'sconsider filtration. You imagine
we have a capillary and thiscapillary, I mean, you know that
our arteries in our veins areattached they come together, but
our capillaries, you have oneside of the capillary is
arterial, one side of thecapillary is venous have four
(10:51):
forces at play here. If youimagine your capillary you are
representing the intra vascularspace inside the capillary,
there's fluid inside there, thatis in the intravascular space.
But on the other side of thecapillary membrane, is the
interstitial space. There'sfluid in the interstitial space
(11:13):
as well. Fluid has pressure,hydrostatic pressure is a
pushing force. Inside thecapillary, the hydrostatic
pressure is pushing against theouter wall of the capillary. On
the outside of the capillaryhydrostatic pressure in the
(11:35):
interstitial space is pushingagainst the wall of the
capillary. Now as you canimagine, with the heart pumping
behind this fluid that's insidethe capillary and the arterial
end, we have more pressure, thehydrostatic pressure is higher
and if you recall, we canactually squeeze our arteries
and what happens if you squeezethe arteries, you know that hose
(11:59):
that you used to play with, youturn the hose on and you stick
your finger over the end whathappens when you made the hose
exit the hole smaller, thepressure increase we constrict
our arteries we increase thatpressure that hydrostatic
pressure on the arterial end,the hydrostatic pressure is
(12:20):
pushing. We also have oursolutes in side of our blood,
which contribute to us Modicpressure as monic pressure is a
pulling force. Osmotic pressureis where the water goes, you may
have heard an instructor say toyou that water follows salt, but
it's not really that simple.
(12:45):
It's that water follows solutes.
Remember we said that Osmosis isthe movement of water across a
semi permeable membrane in orderto reach a equilibrium in
concentration. If there's moresolutes on one side of that
capillary membrane, it will pullwater to the side that has the
most solutes my hydrostaticpressure on the arterial end of
(13:09):
the capillary is pretty high,it's pushing outwards a lot
higher than the asthmaticpressure is pulling in fluid is
pushed out of the capillary.
This moves that fluid betweenthe vascular and the
interstitial space on thearterial and the hydrostatic
(13:30):
pressure overcomes the osmoticpressure inside the vessel and
pushes that fluid out. We havehydrostatic pressure, nice
amount of pressure in theinterstitial space, but it's
nowhere near what it is insidethe vessel. We're losing water
on the arterial end of thevessel. But our albumin, our
solutes, say can't get throughthat membrane, then we've lost
(13:54):
water but not solutes, whichmeans the concentration gets
higher on the venous and becausewe've lost that water on the
arterial end. Now thehydrostatic pressure is lower on
the venous end, but the osmoticpressure is higher because the
concentration increased. Now westart to pull fluid back into
(14:16):
the venous end, and it bringswith it waste products. Those
are then taken on to the liverto the kidneys, where they need
to go and eventually comes backaround to the heart of the lungs
to be reactivated and sent backout to the body. When you're
thinking about what kind offluid we're putting into this
intravascular space. If I add ahypertonic fluid to the
(14:41):
intravascular space hypertonicmeans that the concentration is
higher than that of normal bodyfluid. That means that I've
increased the concentrationinside the vessels and water can
be pulled into the vesselsbecause the concentration the
osmotic pressure has beenincreased. hypotonic fluid would
(15:01):
do the opposite, it would dilutethe blood causing water to move
out into the interstitial space.
When we affect the interstitialspace, it will then affect the
intracellular space, the waterwill move back and forth across
those compartments. The lastthing for us to think about as
far as fluid balance in thisreally short podcast is how the
fluid gets there and how it getsout. Obviously, intake is water
(15:25):
that we drink or other fluids,jello counts as intake. Don't
ask me why. Ice, remember, iceis going to be half because it
doesn't take up the full volumeof the cup or the measuring
tool, ice cream, soups, notchunky soups, though, we would
(15:45):
count all of these things asintake, we also need to count
any IV fluids that you get thepatient, any irrigation that is
done, consider a patient who'son continuous bladder
irrigation. That means that theyhave a large bag of fluid that
is running into a catheter thatgoes through their urethra and
(16:06):
into their bladder. And then allof that fluid plus the urine and
whatever else, maybe blood isdrained out of that another
Lumen or hole in that catheterinto a collection bag. We have
to count that irrigation fluidis intake so that when we
subtract intake and output, weknow how much of the output is
irrigation and how much ispatient's own body fluids. We
(16:30):
would count all of these thingsas intake. How does the fluid
get out? Well, I mean, we allknow that fluid gets out as
urine, right? If you have urine,if you have liquid stool, we
don't count the stool that'sformed or you know, constipated
stools. But we also count vomit.
(16:50):
Sweat is another way for thefluid to get out. Of course,
tears and our breath.
I'm currently live in Florida.
And I joke around that theydon't know that their breath has
water in it because they can'tsee it when it gets really cold
because it doesn't get coldenough here for that. That's
just a joke. I know theFloridians know what that is. We
have that breath vapor that'sconstantly coming out, we have
(17:12):
evaporation off of our skin.
Those things that we can't seewe can't sense are called
insensible losses. Those wecan't measure, I can't measure
how much water you lose throughyour breath. I can't measure how
much comes off your skin. But Ido know that if you're breathing
(17:32):
faster, you're going to losemore water. If you have a fever,
more evaporation will take placeI can expect in a normal course
the patient could lose anywherefrom 500 milliliters to a liter
or more of fluid per day. Inthose insensible losses. We also
have fluid that we take in thatwe can't measure a lot of food
(17:54):
is up to 85% fluid or water. AndI can't measure that you think
about an apple or an orange.
Think about those chunky soups,we can't really measure that
water, but we know it's there.
When we need to measure apatient's fluid balance, we need
to measure intake and output, weneed to make sure that we are
(18:16):
getting an accurate measurementof intake and output. And one of
the most sensitive indicators offluid status is going to be a
daily weight. So important toget that weight on the same
scale at the same time under thesame conditions every day,
making sure that your texts orAIDS or whoever is weighing the
(18:37):
patient knows you have to havethe correct number of blankets
or sheets on the bed, nothingextra. And ideally we want to
get that weight before they'vehad any breakfast. We can
compare that weight and akilogram or 2.2 pounds of weight
equals a liter of fluid. So mypatient has gained three pounds
(18:59):
overnight. That's over a literof fluid. That's pretty bad. We
need to do something we need tolet the provider know. The other
things that we can monitor tohelp us know about our patients
fluid status are the patient'ssodium level, the patient's
hematocrit and their urinespecific gravity. If the patient
(19:21):
has too little body fluid,they've lost water, the
concentration of the blood willgo up. That means the sodium
will go up because when wemeasure it we're measuring how
much is sodium is in this muchof blood. hematocrit is a
measure of the percentage of theblood that is a solid and plasma
(19:44):
if your hematocrit is high. Thenyou have hemo concentration, a
lot of solids and not enoughfluid. If your hematocrit is
low. Then you have hemo dilutionyou have a lot of fluid For a
lesser amount of solids, wemonitor that hematocrit. You'll
(20:04):
also need the hemoglobin to giveyou an idea of what else is
going on there. If thehemoglobin is the same across
three samples, but thehematocrit changes, we know that
it's a fluid balance change.
Rather than say a patient who'sbleeding. We all know that the
kidneys work very hard tomaintain fluid balance. The
kidneys will dilute the urine toget rid of excess fluid or
(20:27):
concentrate the urine to retainfluid and not be putting out as
much this will affect the urinespecific gravity urine specific
gravity will go up. If we don'thave enough fluid in the urine
is being concentrated, and itwill go down if the urine is
being diluted, letting you knowwhat the kidneys are thinking is
happening and how they're tryingto compensate. I hope you
(20:49):
enjoyed this discussion of fluidbalance. And if you're confused
and definitely recommend KhanAcademy has some really good
videos on this concept. And Ihope you have a wonderful day.
Thanks for spending the last 20minutes with me on nursing with
Dr. Hobbick. See you next time.
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