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Introduction to Fluid Imbalance
Over half our body contains water in the form of fluids. These fluids serve a life-sustaining purpose by acting as a transport mechanism for gases, nutrients, and waste. Fluids also protect organs and bones from external trauma.
To maintain homeostasis, the body moves these fluids between compartments using pressure, electrolytes, and hormones. Understanding these processes helps to better understand fluid imbalances.
After completing this module, you will be able to:
- List pathophysiologic factors that affect fluid imbalance.
- Describe signs and symptoms associated with fluid imbalance.
- Discuss risk factors and prevention strategies for preventing fluid imbalance.
- Review common testing and treatments used to find and treat fluid imbalance.
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What Is Fluid Balance?
Fluids in the body are stored in compartments. Two-thirds of the body’s fluids are intracellular (within the cells in the body). One-third of the fluid in the body is extracellular (outside of the cell). Extracellular fluids include interstitial (outside the cells and the vascular system), intravascular (within blood vessels), and other compartments (cerebrospinal areas). Fluid imbalances occur when these fluids shift from one compartment to another, causing an excess or deficit of fluid needed in each compartment to maintain homeostasis.
Separated by the semipermeable membranes of the cell and blood vessel walls, fluid can move between spaces within the body through two mechanisms, which are hydrostatic pressure and osmotic pressure. This graphic illustrates the separation and amount of fluid contained within each compartment when fluid levels are normal.
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How Does Fluid Move?
Fluid movement occurs when there are changes in hydrostatic pressure and osmotic pressure.
Hydrostatic pressure is the pressure exerted to push fluid from one compartment to another. For example, when pressure in the blood vessels, or blood pressure, is higher, more fluid may be pushed from the intravascular area to the extracellular spaces where the pressure is lower.
Osmotic pressure draws fluid from an area of higher concentration to one of lower concentration. Osmolarity is a value used to describe the concentration (number of particles) within a fluid. Osmolarity determines osmotic pressure.
In the vascular system, osmotic pressure and hydrostatic pressure work opposite of each other to control the movement of fluid between the blood and interstitial areas. Increased hydrostatic pressure causes fluid to move out of the vascular system, and increased osmotic pressure draws fluid back into the blood. Various hormones, protein levels, and pressure changes alter the balance to maintain fluid homeostasis when pathophysiologic conditions occur.
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Homeostatic Response to Fluid Imbalance
When fluid is lost or retained, the body uses homeostatic mechanisms to compensate. Here is an example of how the body responds to two different fluid imbalances. Remember, osmolarity is defined as the concentration of a fluid (in this case, blood).
Assessment of volume status. ECFV is extracellular fluid volume.
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Hyperosmolar state (sodium concentration is high in the ECFV)
- Sodium high
- Water loss
- Dehydration
The body’s mechanisms are activated to:
Conserve water + Increase the secretion of sodium = Lower urine volume with higher urine concentration
The size of ECFV should increase to return the serum osmolality to normal.
Hypoosmolar state (sodium concentration is low in the ECFV)
- Excess water
- Sodium low
- Fluid overload
The body’s mechanisms are activated to:
Increase sodium conservation + Increase water excretion = Higher urine volume with lower urine concentration
The size of ECFV decreases to return the serum osmolality to normal.
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What Causes Fluid Movement
Fluid movement is driven by electrolyte concentrations, blood pressure, proteins, and certain hormones. These are the homeostatic mechanisms used by the body to move fluids from one compartment to another to compensate for a possible fluid imbalance. Abnormalities in any of these mechanisms can also cause fluid imbalances.
Select each tab below for examples of how these mechanisms work.
Electrolytes
Electrolytes are used by the body to adjust fluid levels. For example, the renal system uses sodium to transfer fluid to the urinary system, or to hold fluid in the vascular system when a fluid volume deficit is sensed. Sodium is also used in some instances to pull water from cells or into cells. Intravenous fluids used by healthcare professionals rely on sodium concentrations to treat conditions of fluid imbalance.
Blood Pressure
Blood pressure is regulated by receptors throughout the body that send signals to the autonomic nervous system to constrict or dilate blood vessels depending on the fluid imbalance it may sense.
Proteins
Proteins maintain fluid balance by attracting additional water to increase fluid balance. Low protein levels can cause movement of fluid into interstitial areas, causing edema. For example, someone who has low protein can have water leak from the vascular area into the surrounding tissue, causing edema.
Hormones
Hormones are used to attract fluid or control the pressure of the vascular system. For example, renin, a hormone made by the kidney, is converted to angiotensinogen to cause vasoconstriction. It also stimulates production of aldosterone by the adrenal gland, which helps to keep fluid in the vascular system.
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Hormones That Change Fluid Levels
Three primary hormones used to increase or decrease fluid levels in the body include:
- Antidiuretic hormone (ADH) signals the kidneys to promote reabsorption of water.
- Aldosterone signals the kidneys for reabsorption of sodium ions and water.
- Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are secreted by the heart to assist with fluid level maintenance.
Review the infographic for further explanation of how these hormones work.
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This graphic describes the process of maintaining homeostasis. Blood tonicity includes hypertonic (too much sodium), isotonic (right balance), and hypotonic (too little sodium). In this case, drinking alcohol blocks antidiuretic hormones, leading to an increase in urination and sodium loss. This stimulates the cortex of the adrenal gland to use aldosterone to increase sodium absorption, leading to increased water in the vascular system. Wherever sodium is, water will follow. This is what makes you urinate a lot after drinking alcohol.
Vasopressin (antidiuretic hormone or ADH) is released by the posterior pituitary gland in response to hypertonicity. It increases the amount of water reabsorbed by the kidneys, increasing the amount of water in the blood.
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Fluid Imbalance
Kreimeier (2000) identifies three main ways fluid imbalance occurs:
Hypovolemia through traumatic blood loss is one of the most common causes of fluid imbalance. Another cause is dehydration. While whole blood is lost due to hemorrhage, plasma is what is reduced when someone does not intake enough fluid to replenish fluid lost from sweat and other sources.
Maldistribution of fluid occurs when immune response mediators or other protein or hormone deficits cause a movement of fluid from one compartment to another without a loss of fluid. An example of this is an allergic response where considerable edema may occur.
Hypervolemia happens when too much fluid accumulates and/or organs in the body are unable to manage or excrete this extra fluid. For example, when someone experiences a myocardial infarction, the heart is incapable of pumping the amount of blood in the system, which causes a backup in the venous system and subsequent edema from excessive hydrostatic pressure.
Reference
Kreimeier, U. (2000). Pathophysiology of fluid imbalance. Critical Care, 4(Suppl. 2), S3–S7. https://doi.org/10.1186/cc968
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Causes of Fluid Imbalance
Conditions that lead to fluid imbalance include:
Hypovolemia
- blood loss from external injury
- dehydration
- anemia
- gastrointestinal bleeding
- medications (diuretics, laxatives)
- extensive burns
- severe diarrhea and/or vomiting
Hypervolemia
- heart failure, liver failure (cirrhosis), and renal failure
Maldistribution
- systemic inflammatory response syndrome
- anaphylactic reaction
- transfusion reaction
- neurogenic shock
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Signs and Symptoms of Fluid Imbalance
Signs and symptoms of fluid imbalance depend on the cause. There may be an overlap in signs or symptoms, and not all signs and symptoms may be experienced by all clients. It depends on the underlying reason for the fluid imbalance.
Select each tab to learn about the most common signs and symptoms for each type of fluid imbalance.
Hypovolemia
- dizziness
- lightheadedness
- syncope (passing out)
- low blood pressure
- high heart rate
- weight loss
- oliguria or anuria (scant or no urine output)
- hypernatremia
Maldistribution
- generalized or site-specific edema (swelling)
- shortness of breath
- reduced oxygen saturation
- increased respiratory rate
- low protein or albumin levels
Hypervolemia
- generalized edema
- weight gain
- shortness of breath
- reduced oxygen saturation
- increased respiratory rate
- oliguria or anuria (scant or no urine output)
- hyponatremia
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Diagnostic Testing for Fluid Imbalance
Testing for fluid imbalance focuses on finding the reasons. Here are some tests that are often used to determine fluid imbalances.
Vital Signs
Blood pressure and heart rate are remarkably reliable in identifying some forms of fluid imbalance, particularly hypovolemia.
Laboratory Testing
Blood testing including electrolytes, kidney function, liver enzymes, urinalysis, urine specific gravity, and b-type natriuretic peptide levels can be used to better understand a fluid imbalance.
Monitoring Input and Output
Information on what someone eats and drinks, along with measurements of how much they urinate, is helpful to get information on fluid imbalance. Unfortunately, loss of fluids is not easy to measure when talking about sweat, bowel movements, or even expiratory moisture. This makes input and output measurement a less accurate means of fluid status.
Weight
One of the most accurate and sensitive tests for fluid imbalance is weight compared to previous weights. In people with chronic heart failure, weight is done every day with instructions to notify a healthcare provider with a 3- to 5-pound weight gain within one to two days.
Blood testing including electrolytes, kidney function, liver enzymes, urinalysis, urine specific gravity, and b-type natriuretic peptide levels can be used to better understand a fluid imbalance.
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Treatment of Fluid Imbalance
Basic treatments for fluid imbalance:
For hypovolemia, fluids are given. The type of fluid given is determined by the cause of the imbalance. If hemorrhage is the issue, blood products are the best to give. If dehydration is the issue, a salt solution that is isotonic (same concentration as the blood) can be given. For protein deficiency or malnutrition, something containing albumin may be given.
Maldistribution is more about shifting fluids. Certain sodium preparations may be given, and in some cases the best treatment is steroids or other medication used to reduce inflammatory response and shift fluids to the appropriate compartments.
In instances of hypervolemia, when the kidneys are working, diuretics may be given. When kidneys don’t work, dialysis is often used to remove excess fluid.
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Age and Fluid Imbalance
On average, 60% of our bodies are made up of water. This percentage changes based on age. In addition, weight and height are also factors.
Because of decreased volume of fluid due to body size and weight, children at a young age are much more sensitive to fluid imbalance. A child has much quicker shifts in fluid and an exaggerated response when becoming dehydrated or experiencing excessive vomiting. Therefore, hypovolemia must be found and treated quickly in children.
Older adults are more likely to have conditions that reduce the body’s ability to get rid of fluid. Kidneys become less active, and a less compliant or responsible vascular system makes the older adult less likely to quickly compensate for changes in fluid status.
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Water Distribution by Age
Baby: 80%
Toddler: 70%
Child: 65%
Adult man: 60%
Adult woman: 55%
Senior: 50-55%
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Environment and Fluid Imbalance
Environment can have an effect on fluid balance. Select each tab to learn about some environmental considerations.
Climate
The type of climate someone is exposed to along with the amount of activity within that climate can put someone at a higher risk for hypovolemia due to dehydration. Increased bodily resources including sweat and cellular metabolism may be used and increase the risks of low blood pressure and syncopal episodes.
Resources
Fluid replacement is an important resource for fluid balance. Environments that do not have enough potable (drinkable) water can put people at risk for dehydration.
Chemical Exposure
According to Kataria et al. (2015), chemicals found in the environment can target both the liver and the kidneys, potentially leading to chronic kidney disease or liver failure. Regulators continue to identify potentially harmful chemicals and define safe levels to reduce fluid imbalances caused by kidney or liver failure. For example, bisphenol A (BPA), found in food storage containers, is considered toxic and may contribute to kidney disease.
Reference
Kataria, A., Trasande, L., & Trachtman, H. (2015). The effects of environmental chemicals on renal function. Nature Reviews Nephrology, 11(10), 610–625. https://doi.org/10.1038/nrneph.2015.94
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Fluid Overload and Dehydration
Which hormones will the body use when there is too much fluid (fluid overload) or too little fluid (dehydration)? Select all that apply.
Atrial natriuretic peptide
Antidiuretic hormone
Aldosterone
Oxytocin
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Antidiuretic hormone, aldosterone, atrial natriuretic peptide are triggered for release by the hypothalamus with changes in osmotic or hydrostatic pressure.
Oxytocin is a hormone used in childbirth.
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Case Study: Fluid Imbalance
Chris (preferred pronouns: he, him) is a high school football player who came into the office after practice. He said that he was dizzy and lightheaded. The nurse in the office took his blood pressure and it was low. His pulse rate was elevated. He also had bruising on both arms. The outside temperature during practice was 105 degrees Fahrenheit, and Chris forgot to bring water. He has no medical history, but his father has a history of heart disease and kidney disease.
How Can This Be Prevented?
Which strategies could have prevented this student’s problems? Select all that apply.
Increasing practice time
Making sure to practice using the pads
Having water available at the practice
Taking frequent rest breaks
Offer shaded areas at practice
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Having water at the practice, offering frequent rest breaks and shade could have prevented this student’s symptoms.
Increasing practice time and adding pads would make this student’s situation worse.
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Mechanism of Fluid Imbalance
Select the mechanism that best explains the corresponding example.
Blood pressure Electrolytes Hormones Protein : Intravenous fluids used by healthcare professionals rely on sodium concentrations to treat conditions of fluid imbalance.
Blood pressure Electrolytes Hormones Protein : Receptors throughout the body that send signals to the autonomic nervous system to constrict or dilate blood vessels depending on the fluid imbalance it may sense.
Blood pressure Electrolytes Hormones Protein : Low levels can cause movement of fluid into interstitial areas, causing edema. For example, low levels can cause a water leak from the vascular area into the surrounding tissue, causing edema.
Blood pressure Electrolytes Hormones Protein : Renin is converted to angiotensinogen to cause vasoconstriction. It also stimulates production of aldosterone by the adrenal gland, which helps to keep fluid in the vascular system.
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Electrolytes: Intravenous fluids used by healthcare professionals rely on sodium concentrations to treat conditions of fluid imbalance.
Blood pressure: Receptors throughout the body that send signals to the autonomic nervous system to constrict or dilate blood vessels depending on the fluid imbalance it may sense.
Protein: Low levels can cause movement of fluid into interstitial areas, causing edema. For example, low levels can cause a water leak from the vascular area into the surrounding tissue, causing edema.
Hormones: Renin is converted to angiotensinogen to cause vasoconstriction. It also stimulates production of aldosterone by the adrenal gland, which helps to keep fluid in the vascular system.
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Conditions That Cause Fluid Imbalance
Categorize the following conditions with which type of fluid imbalance.
| Hypovolemia | Maldistribution | Hypervolemia | |
| Conditions | Anaphylactic reaction | Heart failure | Extensive burns |
Blood loss from external injury
Transfusion reaction
Dehydration
Liver failure
Systemic inflammatory response syndrome
Renal failure
Drag and drop the correct answers into the boxes. You can also click the correct answer, then the box where it should go. Reset my answers.
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Categorized conditions based on type of fluid imbalance:
Hypovolemia:
- blood loss from external injury
- dehydration
- extensive burns
Maldistribution:
- systemic inflammatory response syndrome
- anaphylactic reaction
- transfusion reaction
Hypervolemia:
- heart failure
- liver failure (cirrhosis)
- renal failure
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Environment and Fluid Status
Which environmental factors directly affect fluid balance? Select all that apply.
Concentration of bisphenol A in food containers
Lack of potable water in a small town
Regular daily temperature is 120 degrees Fahrenheit
Lack of health literacy in the inner city
Increased missed workdays at a local factory
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The lack of drinkable water in a town, higher concentrations of bisphenol A, and high daily temperatures are all issues that directly impact fluid balance status.
Lack of health literacy and missed workdays are not directly related to fluid balance but are considered factors in social determinants of health.
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Age and Fluid Imbalance
Which risk factors make older adults and children more sensitive to fluid imbalances? Select all that apply.
Blood viscosity
Total body water differences
Liver function
Weight and height
Kidney function
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Older adults are more sensitive to fluid imbalances because of a decrease in kidney function due to increasing age. Children are more sensitive to fluid imbalance due to their weight, height, and differences in total body water.
