Fundamentals - Practice & Skills, part 15: Fluid Balance, Intake/Output, Fluid Volume Deficit and Excess
by Meris Shuwarger August 06, 2021 Updated: March 20, 2022 11 min read
This article covers fluid balance, osmolarity, and calculating fluid intake and output, as well as discussing fluid volume excess and fluid volume deficit. You can follow along with our Fundamentals of Nursing flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.
What is fluid osmolarity
Osmolarity is the concentration of a solution, or its tonicity.
There are three different types of solution osmolarity: hypertonic, isotonic, and hypotonic.
“Hyper” refers to a tonicity of the fluid that is higher than the body’s. This will cause fluid to move out of our cells, shriveling them.
Examples of hypertonic fluid include dextrose 10% in water (D10W), 3% sodium chloride (i.e., more than is in normal saline), and 5% sodium chloride (even more than is in normal saline).
“Iso” means the same; isotonic fluids have the same tonicity as our body’s fluid, that is, the volume of the cell does not change with fluid movement. The most common example is normal saline (0.9% sodium chloride). Lactated Ringer’s (LR, used for replacing fluids and electrolytes in those who have low blood volume or low blood pressure) and dextrose 5% in water (D5W) are two more examples of isotonic fluids.
“Hypo” means low, in other words, lower tonicity than the fluid that's in the body already. This means that fluid is going to move into a cell, causing it to swell and possibly burst or lyse (break down the membrane of the cell). 0.45% sodium chloride (half normal saline) and 0.225% sodium chloride (quarter normal saline) are examples of hypotonic solutions.
Fluid balance is the balance of the input and output of fluids in the body to allow metabolic processes to function correctly. Calculating the intake and output of a patient is an important aspect of nursing.
Intake is any fluid put into the body, and not just fluids a patient drinks (i.e., oral fluids). Intake includes IV fluids, fluids contained within foods, tube feedings, TPN, IV flushes, and bladder irrigation.
It is important to calculate everything that goes into the patient's body as part of their intake.
Output is any fluid that leaves the body, primarily urine. Output also includes fluid in stool, emesis (vomit), blood loss (e.g., hemorrhage or surgery), as well as wound drainage and chest tube drainage.
Sensible losses are excretions that can be measured (e.g., urination, defecation).
Insensible losses are other routes of fluid loss, for example in respiration or the sweat that comes out of the patien’'s skin. This is not necessarily measurable, but fluid is being lost in this way.
Measurement of I&Os
When it comes to calculating I&Os, these should be expressed in milliliters. The most common conversions are:
- 1 cc = 1 mL
- 1 fl oz = 30 mL
- 1 cup = 8 fl oz (which = 240 mL)
- 1 tsp = 5 mL
- 1 Tbsp = 15 mL
- 1 Tbsp = 3 tsp
Of these, the most important one to know is that 1 fluid ounce equals 30 mls. Containers will often be measured in ounces (e.g., juices), so understanding conversions into milliliters is key.
Note that ice chips should be recorded as half their volume (e.g., 8 oz of ice chips is worth 4 fl oz of water, or 120 mL).
Fluid volume deficit
Fluid volume deficit is when fluid output exceeds fluid intake, that is, the patient is not getting enough fluid.
Signs and symptoms of fluid volume deficit
The two main signs and symptoms of fluid volume deficit are hypotension (low blood pressure) and tachycardia. When the body does not have enough fluid, its vascular volume drops, decreasing the resistance against the blood vessels, resulting in a fall in blood pressure. In this situation, the body will compensate with tachycardia (attempting to meet that cardiac output, which is heart rate times stroke volume). So if the stroke volume has gone down because of a dearth of fluid, then the heart rate is going to go up, which is known as “compensatory” tachycardia. The patient’s pulse will be fast but weak and thready, like water trickling through a garden hose, not putting forth very much pressure.
Other signs and symptoms of fluid volume deficit may include tachypnea (abnormally rapid breathing), weakness, thirst, decrease in capillary refill, oliguria (lack of, not a lot of urine), and flattened jugular veins.
Labs and diagnostics for fluid volume deficit
In terms of labs and diagnostics, patients are going to have an elevated hematocrit (the proportion of red blood cells to the fluid component, or plasma, in the blood), an elevated blood osmolality, elevated BUN (blood urea nitrogen), elevated urine-specific gravity, and elevated urine osmolality; that is, concentrated blood and urine. The numbers rise because the fluid volume is decreasing.
You can learn more about these diagnostics with our Lab Values Study Guide & Flashcard Index which is a list of lab values covered in our Lab Values Flashcards for nursing students that can be used as an easy reference guide.
Treatment of fluid volume deficit
Treatment for fluid volume deficit is IV fluid replacement, usually with isotonic fluids.
Nursing care for patients with fluid volume deficit
Notify the provider if urine output drops to less than 30 mL/hr. Urine output has already decreased in this situation, but if it falls below 30 mL per hour, this indicates a serious problem.
Fluid volume excess
Fluid volume excess (or fluid volume overload) is when fluid input exceeds fluid output, that is, the patient is getting too much fluid in their body.
A patient experiencing heart failure, for instance, will have a heart that is big but weak. Their heart is not meeting the cardiac output sufficiently, which causes a “traffic jam,” leading to fluid volume excess somewhere in the body.
Signs and symptoms of fluid volume excess
The signs and symptoms of fluid volume excess include weight gain, edema (swelling), tachycardia (the blood flow is not moving as it should, so the body is experiencing compensatory tachycardia), tachypnea, hypertension (more fluid means more vascular resistance, which means higher blood pressure), dyspnea (shortness of breath), crackles in the lungs, jugular vein distension, fatigue, and bounding pulses. To return to the garden hose metaphor, with fluid volume excess, it’s as if water is gushing through the hose — when you hold the hose, you can feel the water flowing inside, much like you’d feel a patient’s bounding pulse.
Labs and diagnostics for fluid volume excess
Treatment of fluid volume excess
Our Pharmacology Second Edition Flashcards cover many of the most important diuretics that may be administered for fluid volume excess.
Nursing care for patients with fluid volume excess
In terms of nursing care, monitor the patient’s daily weight and I&Os. Sit the patient upright. Limit their fluid and sodium intake. Administer oxygen. And protect skin from breakdown.
It is very important to report a weight gain of 1 to 2 pounds in 24 hours or 3 pounds in a week to the provider, and to educate the patient to do the same at home.
You can also learn about both fluid volume deficit and fluid volume excess with our Medical-Surgical Nursing Flashcards.
Hi, I'm Meris. And in this video, we're going to be talking about fluid balance, osmolarity, calculating intake and output, and also talking about fluid volume excess and fluid volume deficit. Very important stuff to know for nursing school. I'm going to be following along using our Nursing Fundamentals flashcards. These are available on our website, leveluprn.com, if you want to get your own set. And if you already have a set, you want to follow along with me starting on card number 90. Let's get started.
So on card number 90, we are starting by talking about solution osmolarity. And if you see on this card, we've got three different types. We have hypertonic, isotonic, and hypotonic. So hyper means a higher tonicity of the fluid than the body. So that is going to be something that is going to cause fluid to move out of our cells, shriveling them. Then isotonic, iso means the same, so same tonicity as our body's fluid. The big one here is going to be normal saline. Lactated Ringer's is also an isotonic fluid. So that's not going to change the intracellular volume there. Nothing is going to change in that regard. And then hypotonic. Hypo means low, so lower tonicity than the fluid that's in our body already. This means that fluid is going to move from the outside into the cells causing them to swell and possibly burst or lyse.
So I remember this. This is not on the cards, but this is how I remember it. Hypertonic, the E after the P is what I'm looking at. The E looks spiky, hypertonic. It's got points, right? So that means that that's what the cell is going to look like too. Hypotonic, the letter after the P, it's an O. It looks swollen and big, right? Fluid has moved into the cell, and it has swollen. Let's talk really quickly. Some examples of hypertonic fluid would be D10W, dextrose 10% in water, 3% sodium chloride - so that's more than is in normal saline - and 5% sodium chloride, even more. Hypotonic, less than that of our body, we're talking about half-normal saline, 0.45%, or quarter-normal saline, 0.225%, okay? Those are some examples there. Now, I want to show you this illustration. I think this illustration is beautiful. It's available on the cards. And it shows what happens to the cells when fluid moves in and out of them based on what type of solution they are in. Love this illustration, I think it is absolutely beautiful.
Moving on to card number 92. Let's talk about calculating the intake and output for your patients. I have had a lot of questions about this in nursing school and even on the NCLEX. You need to understand what counts for intake and output. Intake is any fluid put into the body. So that's not just like the fluids that they drink. That's IV fluids. That's going to be IV flushes, medications if they're liquid, gastric lavage, right? All of those things, continuous bladder irrigation, all of that counts. So you need to calculate everything that goes into the body as part of your intake. And output is any fluid that comes out of the body. That's going to be urine, primarily. But it could also be emesis, right, vomit. It could be blood if I'm having a hemorrhage or surgery, even wound drainage, chest tube drainage. All of these things count for the output. We have sensible losses, which are those which can be measured, like urine or blood. And insensible losses are things like the water lost through respiration and the sweat that comes out of my skin. I can't really measure it, but I am losing fluid that way. You'll see her that we have some examples of how to calculate I and O's. Remember that everything should be done in milliliters, so we give you the conversions here. The big one here in red is 1 ounce is 30 mls. 1 fluid ounce is 30 mls. You've got to know that. A lot of things will be in ounces on fluid containers, like juices, right? One big key point here, I would really, really know this, is that ice chips are recorded at half of their volume. So if I have 100 mls of ice chips, I have 50 mls of water.
Okay. Up next, we are talking about two crucial concepts to understand for nursing school, fluid volume deficit, not enough fluid, and fluid volume excess, too much fluid. So let's start talking about deficit first. If you see here on card 93, that is a lot of red, bold text. That sure does mean you need to know it. Very, very, very important. So signs and symptoms, the two big ones I want to call your attention to, hypotension, meaning low blood pressure, but tachycardia. Remember, I don't have enough fluid, so my vascular volume has dropped, meaning the resistance against my vessels has dropped, meaning that my blood pressure has fallen. So what does my body do? It tries to compensate for that with tachycardia. It's trying to meet that cardiac output, which is heart rate times stroke volume. So if my stroke volume has gone down because I have less fluid, then my heart rate is going to go up, compensatory tachycardia. Now, when you feel their pulse, right, it's going to be fast but weak and thready. Think of water just trickling through a garden hose. It's not putting forth very much pressure, so you'll feel it going fast, but it's going to be weak. Very important to understand that.
Now, in terms of labs and diagnostics, your patients are going to have an elevated hematocrit, an elevated blood osmolality, elevated BUN, elevated urine-specific gravity, and elevated urine osmolality. So all of these numbers are going up. Why? Because the fluid volume is going down. So if I have five particles in a solution, that's my normal lab, and then as the solution volume drops, it seems like there's more of that, right? Proportionately there's more, so as the volume of the plasma drops, these labs are going to go up. Very important to understand that, as well. So we're going to treat this with IV fluids, usually isotonic, and we're going to notify the provider if the urine output drops to less than 30 mls per hour. We've already reached a decreased urine output if we get to that point, but when we fall below 30 mls per hour, this should be a big red flag in your mind that we have a serious problem. So that is fluid volume deficit.
Okay. Let's move on to fluid volume excess. Now, this one you're going to see a lot because you're going to have patients with fluid volume overload. Big one would be a patient in heart failure, right? This patient's going to have a heart that is big but weak. It is not meeting that cardiac output very well, so it's causing a traffic jam, and now we have fluid volume excess somewhere. So in general, signs and symptoms of fluid volume excess of any ideology, of any cause, we could see weight gain, right? Fluid has weight, so if I have more fluid than usual, weight gain, and edema, swelling, that's a big one. Now remember, I'm going to have tachycardia still, right? I'm going to have tachycardia because my blood flow is not moving appropriately, so I have compensatory tachycardia. But I'm not going to have hypotension. I'm going to have hypertension. More fluid means more vascular resistance means higher BP.
Now, I can have other things like dyspnea, shortness of breath, crackles in the lungs on auscultation, jugular vein distension, fatigue, bounding pulses. So when I feel it, it's going to be very strong. Think of fluid, of water gushing through a garden hose, right? Very strong, I can feel it from the outside very well. Labs, these things are all going to go down, hematocrit, hemoglobin, serum osmolality, urine-specific gravity, right? It's diluting everything. More fluid volume means I'm diluting the particles in solution, so all of those values will fall. We can treat this with diuretics. We can also do procedures to pull off fluid, like a paracentesis. A big, big thing here in bold and red is that we need to report a weight gain of 1 to 2 pounds in 24 hours or 3 pounds in a week. That is a lot. Think of 2.2 pounds is one kilogram. 1 kilogram is 1 liter of fluid. That's a lot of fluid. So if my patient gains 2 pounds in a day, I need to tell the provider, and I need to educate my patient to do the same at home.
Okay. So that is it for osmolality of solutions, talking about fluid volume balance, calculating I's and O's, and fluid volume deficit and excess. I hope that review was helpful. This is very, very, very important content for your nursing exams and for the NCLEX, so really be familiar with these concepts. You've got to know them backwards and forwards. If you have any questions or really cool ways to remember things, I would love it if you would leave me a comment. If you like this video, please like it on YouTube, and be sure you subscribe to our channel. You want to be the first to know. We have new videos coming. We've got electrolytes and electrolyte imbalances up next, plus a whole lot more content headed your way. Thanks so much, and happy studying.
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